Token bus (802.4) Token ring (802.5) DQDB (802.6)...
39
1 Chapter 2 Data-link layer Problem Statement To transmit data over physical links from one node to another or more nodes effectively and efficiently, there is much more to do than simply modulating bit stream into signal. Transmission impairments, such as crosstalk between two adjacent pairs, can unexpectedly change transmission signal and hence result in errors. The transmitter may transmit faster than the receiver can afford. If there are multiple stations that share common transmission media, an arbitration mechanism is required to determine who can transmit its own data. The transmitter has to somehow indicate the destination, and usually needs to name itself so that the receiver knows where the source is. These problems need to be addressed by a set of functions above the physical layer. In the Open Systems Interconnection (OSI) seven-layer model, a specific layer, named data-link layer, provides the service of controlling data communications over a physical link. This layer provides solutions to the above problems. In addition, upper layers are therefore exempt from the duty of controlling parameters in a physical network. These services greatly alleviate upper-layer protocol design and make it virtually independent of physical transmission characteristics. Throughout this chapter, we intend to equip readers with fundamental background about (1) services and functions provided in the data-link layer, (2) real-world examples of popular data-link protocols, and (3) open source implementation in Linux. Frankly, there are too many real-world examples to choose. Some are legacy or much less popular nowadays. Some are in the mainstream and still some others are under development. It is nearly impossible to enumerate all of them. We subjectively offer a list of well-known data-link protocols in Table 2.1. Among these protocols, we introduce PPP as it is widely used in dial-up services. Network devices, say routers, also run PPP to carry various network layer protocols over point-to-point links among them. Ethernet technology has occupies more than 95 percent of all local area networks. It is also poised to be ubiquitous in the MAN and WAN. It is undoubtedly a technology we have to know. Wireless links allow greater mobility to make life easy. More devices, such as notebooks, Personal Data Assistant (PDA), cellular phones, and so on, are equipped with the 2 capability to access the Internet. In contrast with desktop PCs, which usually use wired links, these devices are mobile, and hence wireless links are preferred. We choose one typical example for wireless local area network, IEEE 802.11, and another for wireless personal local area network, Bluetooth in this chapter. PAN/LAN/MAN WAN Legacy or Minor Token bus (802.4) Token ring (802.5) DQDB (802.6) HIPPI SMDS Fiber Channel Isochronous (802.9) Demand Priority (802.12) ATM FDDI ISDN X.25 Frame Relay ATM Mainstream or Under development Ethernet (802.3) Resilient Packet Ring (802.17) Point-to-Point Protocol (PPP) HDLC DOCSIS Wireless PAN/LAN/MAN (802.15/11/16) Bluetooth HIPERLAN HomeRF Ethernet (802.3) Resilient Packet Ring (802.17) Point-to-Point Protocol (PPP) Table 2.1 data-link protocols Section 2.1 provides a general introduction of the functions in data-link layer. Specifically, they include framing, addressing, error control, flow control, and access control. We primarily explain why and how in this section, and leave technical details in specific protocols to later sections as possible. Section 2.2 introduces the Point-to-Point Protocol (PPP). The PPP is a standard protocol that carries multi-protocol packets in the upper layer over a point-to-point link. We present the open-source implementation so that the readers can know how the protocol operates in a real system. Following it is Section 2.3, which introduces the dominating LAN technology, Ethernet. Having evolved more than twenty years, Ethernet is rich in its physical specifications. However, this section will focus more on its functions in the data-link layer, and leaves the physical details in further reading. We also provide open Verilog code to be familiar with the implementation. Section 2.4 discusses wireless LAN. The nature of wireless media, such as mobility and lack of reliability, brings new impact in design different from wired media. Two typical examples, IEEE 802.11 and the Bluetooth technology, will be introduced in this section. Section 2.5 illustrates general concepts of device drivers in Linux. We will go deeply into Ethernet and PPP driver implementations, and list a map to indicate the source codes of the other drivers for the readers to
Transcript of Token bus (802.4) Token ring (802.5) DQDB (802.6)...
1
Cha
pter
2 D
ata-
link
laye
r Pr
oble
m S
tate
men
t
To tr
ansm
it da
ta o
ver p
hysi
cal l
inks
from
one
nod
e to
ano
ther
or m
ore
node
s ef
fect
ivel
y an
d ef
ficie
ntly,
the
re is
muc
h m
ore
to d
o th
an s
impl
y m
odul
atin
g bi
t st
ream
int
o si
gnal
. Tr
ansm
issi
on i
mpa
irmen
ts,
such
as
cros
stal
k be
twee
n tw
o ad
jace
nt p
airs
, can
une
xpec
tedl
y ch
ange
tran
smis
sion
sig
nal a
nd h
ence
resu
lt in
er
rors
. The
tran
smitt
er m
ay tr
ansm
it fa
ster
than
the
rece
iver
can
affo
rd. I
f the
re
are
mul
tiple
sta
tions
tha
t sh
are
com
mon
tra
nsm
issi
on m
edia
, an
arb
itrat
ion
mec
hani
sm
is
requ
ired
to
dete
rmin
e w
ho
can
trans
mit
its
own
data
. Th
e tra
nsm
itter
has
to s
omeh
ow in
dica
te th
e de
stin
atio
n, a
nd u
sual
ly n
eeds
to n
ame
itsel
f so
that
the
rece
iver
kno
ws
whe
re th
e so
urce
is. T
hese
pro
blem
s ne
ed to
be
addr
esse
d by
a s
et o
f fun
ctio
ns a
bove
the
phys
ical
laye
r. In
the
Ope
n S
yste
ms
Inte
rcon
nect
ion
(OS
I) se
ven-
laye
r m
odel
, a s
peci
fic la
yer,
nam
ed d
ata-
link
laye
r, pr
ovid
es th
e se
rvic
e of
con
trollin
g da
ta c
omm
unic
atio
ns o
ver a
phy
sica
l lin
k. T
his
laye
r pr
ovid
es s
olut
ions
to
the
abov
e pr
oble
ms.
In
addi
tion,
upp
er l
ayer
s ar
e th
eref
ore
exem
pt f
rom
the
dut
y of
con
trollin
g pa
ram
eter
s in
a p
hysi
cal n
etw
ork.
Th
ese
serv
ices
gre
atly
alle
viat
e up
per-l
ayer
pro
toco
l des
ign
and
mak
e it
virtu
ally
in
depe
nden
t of p
hysi
cal t
rans
mis
sion
cha
ract
eris
tics.
Th
roug
hout
thi
s ch
apte
r, w
e in
tend
to
equ
ip r
eade
rs w
ith f
unda
men
tal
back
grou
nd a
bout
(1)
ser
vice
s an
d fu
nctio
ns p
rovi
ded
in t
he d
ata-
link
laye
r, (2
) re
al-w
orld
ex
ampl
es
of
popu
lar
data
-link
pr
otoc
ols,
an
d (3
) op
en
sour
ce
impl
emen
tatio
n in
Lin
ux.
Fran
kly,
ther
e ar
e to
o m
any
real
-wor
ld e
xam
ples
to c
hoos
e. S
ome
are
lega
cy
or m
uch
less
pop
ular
now
aday
s. S
ome
are
in t
he m
ains
tream
and
stil
l so
me
othe
rs a
re u
nder
dev
elop
men
t. It
is n
early
impo
ssib
le to
enu
mer
ate
all o
f the
m.
We
subj
ectiv
ely
offe
r a li
st o
f wel
l-kno
wn
data
-link
pro
toco
ls in
Tab
le 2
.1. A
mon
g th
ese
prot
ocol
s, w
e in
trodu
ce P
PP
as i
t is
wid
ely
used
in
dial
-up
serv
ices
. N
etw
ork
devi
ces,
say
rou
ters
, al
so r
un P
PP
to c
arry
var
ious
net
wor
k la
yer
prot
ocol
s ov
er p
oint
-to-p
oint
link
s am
ong
them
. Eth
erne
t tec
hnol
ogy
has
occu
pies
m
ore
than
95
perc
ent o
f all
loca
l are
a ne
twor
ks. I
t is
also
poi
sed
to b
e ub
iqui
tous
in
the
MA
N a
nd W
AN. I
t is
undo
ubte
dly
a te
chno
logy
we
have
to k
now.
Wire
less
lin
ks a
llow
gre
ater
mob
ility
to m
ake
life
easy
. Mor
e de
vice
s, s
uch
as n
oteb
ooks
, P
erso
nal D
ata
Ass
ista
nt (P
DA
), ce
llula
r pho
nes,
and
so
on, a
re e
quip
ped
with
the
2
capa
bilit
y to
acc
ess
the
Inte
rnet
. In
cont
rast
with
des
ktop
PC
s, w
hich
usu
ally
use
w
ired
links
, the
se d
evic
es a
re m
obile
, and
hen
ce w
irele
ss li
nks
are
pref
erre
d. W
e ch
oose
one
typ
ical
exa
mpl
e fo
r w
irele
ss lo
cal a
rea
netw
ork,
IE
EE
802
.11,
and
an
othe
r for
wire
less
per
sona
l loc
al a
rea
netw
ork,
Blu
etoo
th in
this
cha
pter
.
PA
N/L
AN
/MA
N
WA
N
Lega
cy o
r M
inor
Toke
n bu
s (8
02.4
) To
ken
ring
(802
.5)
DQ
DB
(802
.6)
HIP
PI
SM
DS
Fibe
r Cha
nnel
Is
ochr
onou
s (8
02.9
)
Dem
and
Prio
rity
(802
.12)
AT
M
FD
DI
ISD
N
X.2
5 Fr
ame
Rel
ay
ATM
Mai
nstr
eam
or
U
nder
de
velo
pmen
t
Ethe
rnet
(802
.3)
R
esilie
nt P
acke
t Rin
g (8
02.1
7)
Poi
nt-to
-Poi
nt P
roto
col (
PP
P)
HD
LC
DO
CS
IS
Wire
less
PAN
/LAN
/MAN
(8
02.1
5/11
/16)
B
luet
ooth
HIP
ER
LAN
Hom
eRF
Ethe
rnet
(802
.3)
Res
ilient
Pac
ket R
ing
(802
.17)
P
oint
-to-P
oint
Pro
toco
l (P
PP
)
Tabl
e 2.
1 da
ta-li
nk p
roto
cols
Sec
tion
2.1
prov
ides
a g
ener
al in
trodu
ctio
n of
the
func
tions
in d
ata-
link
laye
r. Sp
ecifi
cally
, th
ey i
nclu
de f
ram
ing,
add
ress
ing,
erro
r co
ntro
l, flo
w c
ontro
l, an
d ac
cess
con
trol.
We
prim
arily
exp
lain
why
and
how
in
this
sec
tion,
and
lea
ve
tech
nica
l de
tails
in s
peci
fic p
roto
cols
to
late
r se
ctio
ns a
s po
ssib
le.
Sec
tion
2.2
intro
duce
s th
e P
oint
-to-P
oint
Pro
toco
l (P
PP
). Th
e P
PP
is a
sta
ndar
d pr
otoc
ol th
at
carri
es m
ulti-
prot
ocol
pac
kets
in
the
uppe
r la
yer
over
a p
oint
-to-p
oint
lin
k. W
e pr
esen
t th
e op
en-s
ourc
e im
plem
enta
tion
so t
hat
the
read
ers
can
know
how
the
pr
otoc
ol o
pera
tes
in a
rea
l sys
tem
. Fol
low
ing
it is
Sec
tion
2.3,
whi
ch in
trodu
ces
the
dom
inat
ing
LAN
tech
nolo
gy, E
ther
net.
Hav
ing
evol
ved
mor
e th
an tw
enty
yea
rs,
Ethe
rnet
is ri
ch in
its
phys
ical
spe
cific
atio
ns. H
owev
er, t
his
sect
ion
will
focu
s m
ore
on it
s fu
nctio
ns in
the
dat
a-lin
k la
yer,
and
leav
es t
he p
hysi
cal d
etai
ls in
fur
ther
re
adin
g. W
e al
so p
rovi
de o
pen
Veril
og c
ode
to b
e fa
milia
r with
the
impl
emen
tatio
n.
Sect
ion
2.4
disc
usse
s w
irele
ss L
AN.
The
natu
re o
f w
irele
ss m
edia
, su
ch a
s m
obilit
y an
d la
ck o
f re
liabi
lity,
brin
gs n
ew im
pact
in d
esig
n di
ffere
nt f
rom
wire
d m
edia
. Tw
o ty
pica
l exa
mpl
es, I
EE
E 8
02.1
1 an
d th
e B
luet
ooth
tech
nolo
gy, w
ill b
e in
trodu
ced
in t
his
sect
ion.
Sec
tion
2.5
illust
rate
s ge
nera
l co
ncep
ts o
f de
vice
dr
iver
s in
Lin
ux. W
e w
ill go
dee
ply
into
Eth
erne
t and
PP
P dr
iver
impl
emen
tatio
ns,
and
list a
map
to in
dica
te th
e so
urce
cod
es o
f the
oth
er d
river
s fo
r the
read
ers
to
3
stud
y fu
rther
. In
Sec
tion
2.6,
we
indi
cate
com
mon
pitf
alls
and
falla
cies
. The
re is
m
uch
mor
e to
lea
rn t
han
the
book
can
cov
er,
we
refe
r th
e re
ader
s to
fur
ther
re
adin
g in
Sec
tion
2.7.
2.1
Gen
eral
Issu
es
W
e ha
ve p
rese
nted
pos
sibl
e pr
oble
ms
over
phy
sica
l com
mun
icat
ion
in t
he
prel
ude.
San
dwic
hed
betw
een
the
phys
ical
lay
er a
nd t
he n
etw
ork
laye
r, th
e da
ta-li
nk la
yer p
rovi
des
cont
rol t
o ph
ysic
al c
omm
unic
atio
ns a
nd s
ervi
ces
to u
pper
ne
twor
k ab
stra
ctio
n. T
he m
ajor
func
tions
to a
ddre
ss th
ese
prob
lem
s in
this
laye
r in
clud
e M
ajor
Fun
ctio
ns
Fram
ing
Con
trol i
nfor
mat
ion
com
es a
long
with
the
bit s
tream
itse
lf to
spe
cify
the
dest
inat
ion
node
, ind
icat
e th
e up
per-l
ayer
pro
toco
l, ch
eck
poss
ible
err
or, a
nd s
o on
. To
be c
onve
nien
t, da
ta a
re s
ent a
nd p
roce
ssed
in u
nits
of f
ram
es.
A ty
pica
l fra
me
usua
lly c
onta
ins
two
mai
n pa
rts: c
ontro
l inf
orm
atio
n an
d th
e da
ta. C
ontro
l in
form
atio
n is
refe
rred
to d
urin
g fra
me
proc
essi
ng b
y th
e da
ta-li
nk p
roto
cols
. The
da
ta
part
com
es
from
up
per
laye
rs
and
is
enca
psul
ated
w
ith
the
cont
rol
info
rmat
ion
into
a w
hole
fra
me.
The
dat
a-lin
k la
yer
serv
ice
shou
ld s
omeh
ow
delim
it bi
t stre
am in
to fr
ames
and
con
vert
fram
es in
to b
it st
ream
. Not
ice
that
the
two
term
s, p
acke
ts a
nd f
ram
es,
are
usua
lly u
sed
inte
rcha
ngea
bly.
To
be m
ore
spec
ific,
her
e w
e re
fer t
o th
e da
ta u
nit i
n th
e da
ta-li
nk la
yer a
s fra
mes
. A
ddre
ssin
g W
e ne
ed a
n ad
dres
s w
hen
writ
ing
a le
tter
to o
ur f
riend
s. W
e al
so
need
a p
hone
num
ber
whe
n di
alin
g up
to
them
. A
ddre
ssin
g is
nee
ded
for
the
sam
e re
ason
in
the
data
-link
lay
er.
The
iden
titie
s of
the
inv
olve
d st
atio
ns a
re
indi
cate
d by
an
addr
ess,
ofte
n pr
esen
ted
in a
num
eric
form
of s
ome
leng
th.
Erro
r co
ntro
l D
ata
trans
mitt
ed o
ver
phys
ical
med
ia a
re s
ubje
ct t
o er
rors
. Th
e er
rors
mus
t be
dete
cted
by
the
rece
iver
. The
rec
eive
r m
ay s
omeh
ow in
form
the
trans
mitt
er t
hat
ther
e ar
e er
rors
so
that
the
tra
nsm
itter
kno
ws
to r
etra
nsm
it th
e da
ta.
Flow
con
trol
The
tra
nsm
itter
may
sen
d at
a r
ate
fast
er t
han
the
rece
iver
can
af
ford
. In
thi
s si
tuat
ion,
the
rec
eive
r ha
s to
dis
card
the
fra
mes
, m
akin
g th
e tra
nsm
itter
ret
rans
mits
the
dro
pped
fra
mes
. H
owev
er,
this
is
inef
ficie
nt.
Flow
co
ntro
l pro
vide
s a
way
to le
t the
rece
iver
slo
w d
own
the
trans
mitt
er.
Med
ium
Acc
ess
cont
rol T
here
mus
t be
an
arbi
tratio
n m
echa
nism
whe
n th
ere
are
mul
tiple
sta
tions
tha
t w
ant
to t
rans
mit
data
ove
r sh
ared
med
ia.
For
a go
od
arbi
tratio
n m
echa
nism
, th
e ac
cess
to
a sh
ared
med
ium
sho
uld
be f
air
and
the
4
utiliz
atio
n of
the
shar
ed m
ediu
m m
ust k
eep
high
if m
any
stat
ions
are
inte
nded
to
trans
mit
sim
ulta
neou
sly.
Th
is s
ectio
n ra
ises
gen
eral
fun
ctio
ns i
n th
e da
ta-li
nk l
ayer
. A
fter
thes
e pr
elim
inar
ies,
we
will
exe
mpl
ify th
e op
erat
ions
in p
opul
ar d
ata-
link
laye
r pro
toco
ls
in la
ter s
ectio
ns.
2.
1.1
Fram
ing
Fram
e D
elim
iting
B
ecau
se d
ata
are
trans
mitt
ed i
n ra
w b
it st
ream
in
the
phys
ical
lay
er,
the
data
-link
laye
r m
ust s
omeh
ow te
ll th
e be
ginn
ing
and
the
end
of a
fram
e. It
mus
t al
so c
onve
rt fra
mes
into
raw
bit
stre
am f
or p
hysi
cal t
rans
mis
sion
. Th
is is
cal
led
fram
ing.
The
re a
re m
any
way
s to
del
imit
fram
es. D
epen
ding
on
the
basi
c un
it of
a
fram
e, w
hich
can
be
byte
(or
oct
et)
or b
it, c
alle
d by
te-o
rient
ed o
r bi
t-orie
nted
fra
mes
, we
may
use
spe
cial
sen
tinel
cha
ract
ers
or b
it pa
ttern
to m
ark
the
fram
e bo
unda
ry.
We
intro
duce
how
fra
min
g is
ach
ieve
d w
ith e
xam
ples
of
bit-o
rient
ed
HD
LC f
ram
es a
nd le
gacy
BIS
YN
C f
ram
es.
Ther
e ar
e st
ill ot
her
way
s to
del
imit
fram
es. F
or e
xam
ples
, som
e E
ther
net s
yste
ms
use
spec
ial p
hysi
cal e
ncod
ing
to
mar
k fra
me
boun
dary
whi
le o
ther
s id
entif
y th
e bo
unda
ry s
impl
y by
the
pres
ence
or
abs
ence
of s
igna
l1 . A
bit-o
rient
ed fr
ame
can
spec
ify a
spe
cial
bit
patte
rn, s
ay 0
1111
110
in H
DLC
, w
hile
a b
yte-
orie
nted
fra
me
can
spec
ify s
peci
al c
hara
cter
s, s
ay S
OH
(st
art
of
head
er)
and
STX
(st
art o
f tex
t) to
mar
k th
e be
ginn
ing
of fr
ame
head
er a
nd d
ata.
Th
ere
may
be
an a
mbi
guity
whe
n no
rmal
dat
a ch
arac
ters
or b
its a
re th
e sa
me
as
the
spec
ial c
hara
cter
s or
pat
tern
. A te
chni
que
calle
d by
te- o
r bit-
stuf
fing
is u
sed
to
solv
e th
e am
bigu
ity, a
s illu
stra
ted
in F
ig. 2
.1. A
spe
cial
esc
ape
char
acte
r, na
mel
y D
LE (
data
lin
k es
cape
), pr
eced
es a
spe
cial
cha
ract
er t
o in
dica
te t
he n
ext
char
acte
r is
nor
mal
dat
a in
a b
yte-
orie
nted
fram
e. O
f cou
rse,
DLE
itse
lf is
als
o a
spec
ial c
hara
cter
. Tw
o co
nsec
utiv
e D
LEs
repr
esen
t a n
orm
al c
hara
cter
the
sam
e as
DLE
. For
bit-
orie
nted
fram
es, t
he b
it pa
ttern
011
1111
0 is
use
d in
HD
LC. W
hen
ther
e ar
e fiv
e co
nsec
utiv
e 1’
s in
the
norm
al d
ata
bits
, a 0
is s
tuffe
d af
ter
the
five
1’s
so th
at th
e pa
ttern
011
1111
0 ne
ver
appe
ars
in th
e no
rmal
dat
a bi
ts. B
oth
the
trans
mitt
er a
nd t
he r
ecei
ver
follo
w t
he s
ame
rule
and
hen
ce t
he a
mbi
guity
is
solv
ed.
A di
ffere
nt a
ppro
ach
is in
the
Eth
erne
t. Fo
r ex
ampl
e, 1
00B
AS
E-X
can
use
sp
ecia
l en
codi
ng t
o m
ark
the
boun
dary
bec
ause
afte
r 4B
/5B
enc
odin
g (S
ee
Sec
tion
1.1.
1),
ther
e ar
e 32
(=
25 ) co
des
that
can
be
trans
mitt
ed o
ver
phys
ical
1 E
ther
net u
ses t
he te
rm ‘s
tream
’ to
refe
r to
phys
ical
enc
apsu
latio
n of
a fr
ame.
Stri
ctly
spea
king
, spe
cial
en
codi
ng o
r pre
senc
e of
sign
al d
elim
it st
ream
, not
fram
e. H
owev
er, w
e do
not
bot
her t
he d
etai
ls h
ere.
5
med
ia w
hile
onl
y 16
out
of t
hem
com
e fro
m a
ctua
l dat
a. O
ther
cod
es c
an b
e us
ed
as c
ontro
l co
des.
The
se c
odes
are
uni
quel
y re
cogn
izab
le b
y th
e re
ceiv
er a
nd
henc
e de
limit
a fra
me
out
of a
seq
uenc
e of
bit
stre
am.
Som
e ot
her
Eth
erne
t sy
stem
s, s
ay 1
0BA
SE
-T,
does
not
hav
e si
gnal
bet
wee
n fra
mes
. Th
ey c
an
reco
gniz
e th
e fra
me
boun
dary
sim
ply
by th
e pr
esen
ce o
r abs
ence
of s
igna
l.
Figu
re 2
.1
(a) b
yte-
stuf
fing
and
(b) b
it-st
uffin
g Fr
ame
Form
at
A fra
me
is d
ivid
ed in
to fi
elds
that
incl
ude
vario
us k
inds
of c
ontro
l inf
orm
atio
n fo
r pr
oces
sing
and
the
data
from
the
netw
ork
laye
r. N
ote
that
the
data
from
the
netw
ork
laye
r co
ver
cont
rol
info
rmat
ion
of h
ighe
r la
yers
and
the
act
ual
data
. C
ontro
l inf
orm
atio
n of
hig
her l
ayer
s is
not
dea
lt w
ith a
nd tr
eate
d as
nor
mal
dat
a in
th
e da
ta-li
nk la
yer.
Typi
cal f
ield
s of
con
trol i
nfor
mat
ion
othe
r th
an th
e da
ta fi
elds
ar
e lis
ted
belo
w:
Add
ress
: us
ually
indi
cate
s th
e so
urce
or
the
dest
inat
ion
addr
ess.
The
rec
eive
r kn
ows
the
fram
e is
for
it if
the
dest
inat
ion
addr
ess
mat
ches
its
own.
It a
lso
can
resp
ond
to th
e so
urce
by
fillin
g in
the
dest
inat
ion
addr
ess
of th
e ou
tgoi
ng fr
ame
with
the
sour
ce a
ddre
ss o
f the
inco
min
g fra
me.
Le
ngth
: may
indi
cate
the
leng
th o
f the
who
le fr
ame
or th
at o
f the
dat
a fie
ld.
Type
: Th
e ty
pe o
f ne
twor
k la
yer
prot
ocol
is e
ncod
ed in
thi
s fie
ld.
The
data
-link
la
yer
prot
ocol
can
rea
d th
e co
de t
o de
term
ine
wha
t ne
twor
k la
yer
mod
ule,
say
In
tern
et P
roto
col (
IP),
to b
e in
voke
d to
dea
l with
the
data
fiel
d fu
rther
. Er
ror
dete
ctio
n co
de: i
s a
func
tion
of th
e co
nten
t in
the
fram
e. T
he tr
ansm
itter
SOH
star
t of a
fram
e he
ader
Hea
der i
nfor
mat
ion
DLE
ST
X
data
-link
esc
ape (a
)
0111
1110
1010
1110
0011
1011
1110
0000
1101
1100
1101
0101
0101
0101
1111
0101
1…
star
t of a
fram
e st
uffin
g bi
t st
uffin
g bi
t
five
cons
ecut
ive
1’s
five
cons
ecut
ive
1’s
(b)
ETX
star
t of t
ext
end
of te
xt
DLE
D
LE
Dat
a po
rtion
6
com
pute
s th
e fu
nctio
n an
d em
beds
the
valu
e in
the
fram
e to
be
trans
mitt
ed. U
pon
rece
ivin
g th
e fra
me,
the
rece
iver
com
pute
s in
the
sam
e w
ay to
see
if b
oth
resu
lts
mat
ch.
If th
ey d
o no
t m
atch
, it
impl
ies
the
cont
ent
is m
ade
chan
ged
durin
g tra
nsm
issi
on.
Two
com
mon
fun
ctio
ns a
re C
heck
sum
and
Cyc
lic R
edun
danc
y C
heck
(CR
C).
2.1.
2 A
ddre
ssin
g G
loba
l or L
ocal
Add
ress
A
n ad
dres
s is
an
id
entif
ier
to
iden
tify
each
st
atio
n fro
m
anot
her
in
com
mun
icat
ions
. Alth
ough
a n
ame
is e
asie
r to
rem
embe
r, it
is c
ompa
ct to
use
a
num
eric
al a
ddre
ss in
low
-leve
l lay
er p
roto
cols
, suc
h as
thos
e in
the
data
-link
laye
r. W
e le
ave
the
conc
ept o
f nam
e as
an
iden
tifie
r to
Cha
pter
5 (
See
Dom
ain
Nam
e S
yste
m).
An
addr
ess
can
be g
loba
lly u
niqu
e or
loc
ally
uni
que.
A g
loba
lly-u
niqu
e ad
dres
s is
uni
que
wor
ldw
ide,
whi
le a
loca
lly-u
niqu
e ad
dres
s is
onl
y un
ique
in a
lo
cal s
ite. I
n ge
nera
l, a
loca
lly-u
niqu
e ad
dres
s co
nsum
es fe
wer
bits
and
req
uire
s th
e ad
min
istra
tor’s
effo
rts t
o m
ake
sure
it
is l
ocal
ly u
niqu
e. S
ince
th
e bi
t ov
erhe
ads
of t
he a
ddre
ss a
re t
rivia
l, gl
obal
ly-u
niqu
e ad
dres
ses
are
pref
erre
d no
wad
ays.
The
adm
inis
trato
r si
mpl
y ad
ds a
sta
tion
at w
ill, a
nd d
oes
not n
eed
to
wor
ry a
bout
the
conf
lict o
f add
ress
es.
Add
ress
Len
gth
H
ow l
ong
shou
ld a
n ad
dres
s be
? A
long
er a
ddre
ss t
akes
mor
e bi
ts t
o be
tra
nsm
itted
, har
der t
o re
fer t
o or
rem
embe
r. O
n th
e co
ntra
ry, a
sho
rt ad
dres
s m
ay
be n
ot e
noug
h fo
r gl
obal
uni
quen
ess.
For
a lo
cally
-uni
que
addr
ess,
8 o
r 16
bits
sh
ould
be
enou
gh. H
owev
er, f
or a
glo
bally
uni
que
addr
ess,
muc
h m
ore
bits
are
ne
cess
ary.
A v
ery
popu
lar
addr
essi
ng f
orm
at a
dopt
ed b
y IE
EE
802
has
48 b
its
long
. W
e le
ave
it as
an
exer
cise
for
the
rea
ders
to
disc
uss
whe
ther
48
bits
are
en
ough
. IE
EE 8
02 M
AC
Add
ress
W
e in
trodu
ce
a po
pula
r da
ta-li
nk
addr
ess
spec
ified
in
th
e IE
EE
80
2 St
anda
rds.
It is
an
exce
llent
exa
mpl
e be
caus
e th
e ad
dres
sing
is w
idel
y ad
opte
d in
m
any
data
-link
pro
toco
ls,
incl
udin
g E
ther
net,
Fibe
r D
istri
butio
n D
ata
Inte
rface
(F
DD
I), T
oken
Rin
g, w
irele
ss L
AN
, etc
. W
hile
the
IEE
E 80
2 sp
ecifi
es t
he u
se o
f ei
ther
2-b
yte
of 6
-byt
e ad
dres
ses,
m
ost
impl
emen
tatio
ns a
dopt
6-b
yte
(or
48-b
it) a
ddre
sses
. To
mak
e su
re t
he
addr
ess
is g
loba
lly u
niqu
e, t
he a
ddre
ss i
s pa
rtitio
ned
into
tw
o m
ain
parts
:
7
Org
aniz
atio
n-U
niqu
e Id
entif
ier
(OU
I) an
d O
rgan
izat
ion-
Ass
igne
d P
ortio
n, e
ach
occu
pyin
g th
ree
byte
s.
The
OU
I pa
rt is
ad
min
istra
ted
by
the
IEE
E.
Eac
h m
anuf
actu
rer
can
cont
act
the
IEE
E
to
appl
y to
ow
n an
O
UI
2 (
See
ht
tp://
stan
dard
s.ie
ee.o
rg) f
or a
fee,
and
then
they
are
in c
harg
e of
the
uniq
uene
ss
of th
e O
rgan
izat
ion-
Ass
igne
d P
ortio
n. In
theo
ry, t
here
are
tota
lly 2
48 (a
roun
d 10
15)
addr
esse
s th
at c
an
be
assi
gned
. Th
is n
umbe
r is
la
rge
enou
gh f
or
glob
al
uniq
uene
ss. T
he fo
rmat
of t
he a
ddre
ss is
illu
stra
ted
in F
ig. 2
.2.
Fi
gure
2.2
IE
EE
802
add
ress
form
at
Th
e fir
st b
it in
tran
smis
sion
ord
er is
rese
rved
to in
dica
te w
heth
er th
e ad
dres
s is
uni
cast
or m
ultic
ast3 . A
uni
cast
add
ress
is d
estin
ed fo
r a s
ingl
e st
atio
n, w
hile
a
mul
ticas
t add
ress
is d
estin
ed fo
r a g
roup
of s
tatio
ns. A
spe
cial
cas
e of
mul
ticas
t is
broa
dcas
t, w
here
all
bits
of t
he a
ddre
ss a
re 1
’s. I
t is
dest
ined
for a
ll st
atio
ns a
s fa
r as
a fr
ame
can
reac
h in
the
data
-link
laye
r. A
lso
note
that
the
trans
mis
sion
ord
er
of b
its i
n ea
ch b
yte
in t
he a
ddre
ss m
ay b
e di
ffere
nt f
rom
the
ord
er s
tore
d in
m
emor
y. In
Eth
erne
t, th
e tra
nsm
issi
on o
rder
is le
ast
sign
ifica
nt b
it (L
SB
) fir
st in
ea
ch b
yte,
cal
led
little
-End
ian.
In o
ther
pro
toco
ls, s
uch
as F
DD
I and
Tok
en R
ing,
th
e tra
nsm
issi
on o
rder
is
mos
t si
gnifi
cant
bit
(MS
B)
first
in
each
byt
e, c
alle
d bi
g-E
ndia
n. T
he a
ddre
ss i
s of
ten
writ
ten
in h
exad
ecim
al f
orm
of
sepa
rate
d by
da
shes
or c
olon
s, e
.g. 0
0-32
-4f-c
c-30
-58.
2.
1.3
Erro
r con
trol
Fram
es a
re s
ubje
ct t
o er
rors
dur
ing
trans
mis
sion
. Th
e er
rors
sho
uld
be
dete
cted
and
the
tra
nsm
itter
may
be
dem
ande
d to
ret
rans
mit
the
fram
e. I
n th
is
subs
ectio
n, w
e in
trodu
ce th
e w
ay to
det
ect e
rrors
and
wha
t act
ion
follo
ws
whe
n er
rors
are
det
ecte
d.
Erro
r de
tect
ion
oper
ates
by
addi
ng a
dditi
onal
bits
as
a fu
nctio
n of
the
fram
e co
nten
t to
the
fram
e by
the
trans
mitt
er. T
he r
ecei
ver
perfo
rms
exac
tly th
e sa
me
calc
ulat
ion
to t
he f
ram
e co
nten
t to
see
if
the
two
resu
lts m
atch
. If
ther
e is
a
2 S
ee h
ttp://
stan
dard
s.iee
e.or
g/re
gaut
h/ou
i/oui
.txt a
bout
how
OU
I has
bee
n as
sign
ed.
3 The
seco
nd b
it ca
n in
dica
te w
heth
er th
e ad
dres
s is g
loba
lly-u
niqu
e or
loca
lly-u
niqu
e. T
he u
se is
seld
om,
so w
e ig
nore
it h
ere.
Firs
t byt
e
Sec
ond
byte
Th
ird b
yte
Fo
urth
byt
e
Fi
fth b
yte
S
ixth
byt
eO
rgan
izat
ion-
Uni
que
Iden
tifie
r (O
UI)
Org
aniz
atio
n-A
ssig
ned
Por
tion
first
bitt
rans
mitt
ed0:
uni
cast
add
ress
1:
mul
ticas
t add
ress
8
mis
mat
ch, t
he fr
ame
is c
onsi
dere
d to
be
subj
ect t
o er
rors
. We
will
illus
trate
two
com
mon
fun
ctio
ns i
n er
ror
dete
ctio
n: c
heck
sum
and
cyc
lic r
edun
danc
y ch
eck
(CR
C).
Erro
r Det
ectio
n C
ode
Th
e ch
ecks
um c
ompu
tatio
n si
mpl
y di
vide
s th
e fra
me
cont
ent i
nto
bloc
ks o
f m
bits
and
tak
es t
he s
um o
f th
ese
bloc
ks.
Anot
her
pow
erfu
l te
chni
que
is c
yclic
re
dund
ancy
che
ck.
Alth
ough
it is
slig
htly
com
plic
ated
tha
n ch
ecks
um,
it is
ver
y ea
sy to
impl
emen
t in
hard
war
e. S
uppo
se t
here
are
m b
its in
the
fram
e co
nten
t. Th
e tra
nsm
itter
can
gen
erat
e a
sequ
ence
of k
bits
as
the
fram
e ch
eck
sequ
ence
(F
CS
) so
that
the
tota
l fra
me,
hav
ing
m+k
bits
, can
be
divi
ded
by a
pre
dete
rmin
ed
bit p
atte
rn, c
alle
d ge
nera
tor.
The
rece
iver
div
ides
in th
e sa
me
way
and
see
s if
the
rem
aind
er
is
zero
. If
the
rem
aind
er
is
not
zero
, th
ere
are
erro
rs
durin
g tra
nsm
issi
on.
We
show
the
CR
C p
roce
dure
to
gene
rate
the
FC
S w
ith t
he f
ollo
win
g ex
ampl
e:
fram
e co
nten
t F=
1101
0001
110
(11
bits
) ge
nera
tor B
= 10
1011
(6 b
its)
FCS
= (5
bits
) Th
e pr
oced
ure
goes
like
the
follo
win
g st
eps:
St
ep 1
Shi
ft F
by 2
5 , and
app
end
it w
ith 5
0’s
, yie
ldin
g 11
0100
0111
0000
00.
Step
2 T
he re
sulti
ng p
atte
rn in
Ste
p 1
is d
ivid
ed b
y B
. The
pro
cess
is a
s fo
llow
s:
(N
otic
e th
at th
e co
mpu
tatio
n is
all
mod
ule-
2 ar
ithm
etic
)
1101
0001
1100
0000
1010
11
1110
0000
111
1010
1111
1110
1010
1110
1011
1010
1111
0000
1010
1111
0110
1010
1111
1010
1010
1110
001
the
rem
aind
er
9
Step
3 T
he re
mai
nder
in th
e ab
ove
com
puta
tion
is a
ppen
ded
in th
e or
igin
al fr
ame
cont
ent,
yiel
ding
110
1000
1110
1000
1. T
he re
sulti
ng fr
ame
is th
en tr
ansm
itted
. The
re
ceiv
er d
ivid
es th
e in
com
ing
fram
e by
the
bit p
atte
rn 1
0101
1 to
ver
ify th
e fra
me.
W
e le
ave
the
verif
icat
ion
on th
e re
ceiv
er s
ide
as a
n ex
erci
se.
With
car
eful
des
ign
of th
e ge
nera
tor,
the
CR
C is
pro
ved
mat
hem
atic
ally
to b
e ab
le to
det
ect m
any
kind
s of
erro
rs, i
nclu
ding
: 1.
si
ngle
-bit
erro
r 2.
do
uble
-bit
erro
r 3.
A
ny b
urst
erro
rs w
hose
bur
st le
ngth
is le
ss th
an th
e le
ngth
of t
he F
CS
. Th
e C
RC
co
mpu
tatio
n ca
n be
ea
sily
im
plem
ente
d in
ha
rdw
are
with
ex
clus
ive-
OR
gat
es a
nd s
hift
regi
ster
s. S
uppo
se w
e re
pres
ent
the
gene
rato
r in
th
e fo
rm a
nan-
1an-
2…a 1
a 0.
The
bits
an
and
a 0 a
re d
eman
ded
to b
e 1.
We
plot
a
gene
ral c
ircui
t arc
hite
ctur
e th
at im
plem
ents
the
CR
C c
ompu
tatio
n in
Fig
. 2.3
. The
fra
me
cont
ent i
s sh
ifted
into
this
circ
uit
bit b
y bi
t, an
d th
e fin
al b
it pa
ttern
in th
e sh
ift r
egis
ters
is
the
FCS
, i.e
. C
n-1C
n-2…
C1C
0. N
ote
that
the
ini
tial
valu
es o
f C
n-1C
n-2…
C1C
0 ar
e in
sign
ifica
nt b
ecau
se t
hey
will
be
final
ly s
hifte
d ou
t af
ter
com
puta
tion.
For
ver
y hi
gh-s
peed
net
wor
king
, circ
uits
that
com
pute
CR
C b
its in
pa
ralle
l hav
e be
en d
esig
ned
to s
peed
up
the
com
puta
tion.
Fi
gure
2.3
C
RC
circ
uit d
iagr
am
Er
ror C
ontr
ol A
ppro
ache
s Th
e re
ceiv
er c
an r
espo
nd t
he e
rror
stat
e of
the
inc
omin
g fra
me
in t
he
follo
win
g w
ays:
1.
S
ilent
ly d
isca
rd
2.
Pos
itive
ack
now
ledg
emen
t whe
n th
e in
com
ing
fram
e is
cor
rect
3.
N
egat
ive
ackn
owle
dgem
ent w
hen
the
inco
min
g fra
me
is in
corre
ct
The
trans
mitt
er m
ay r
etra
nsm
it th
e fra
me
that
is in
corre
ctly
rec
eive
d or
just
ig
nore
the
erro
rs. I
n th
e la
tter
case
, hig
her
laye
r pr
otoc
ols,
say
TC
P, c
an h
andl
e th
e re
trans
mis
sion
. 2.
1.4
Flow
con
trol
Fl
ow c
ontro
l add
ress
es th
e pr
oble
m o
f a fa
st tr
ansm
itter
and
a s
low
rece
iver
.
fram
e bi
tsC
0C
1
a 1a 2
Cn-
2C
n-1
a n-1
10
Whe
n th
e re
ceiv
er is
ove
rwhe
lmed
, flo
w c
ontro
l pro
vide
s a
way
to le
t the
rece
iver
te
ll th
e tra
nsm
itter
, “H
ey! Y
ou tr
ansm
it to
o fa
st. P
leas
e w
ait!”
The
sim
ples
t met
hod
is
calle
d st
op-a
nd-w
ait.
The
trans
mitt
er
trans
mits
on
e fra
me,
w
aits
th
e ac
know
ledg
emen
t fro
m th
e re
ceiv
er, a
nd tr
ansm
its th
e ne
xt. T
his
met
hod
resu
lts
in v
ery
low
util
izat
ion
of th
e tra
nsm
issi
on li
nk.
Sl
idin
g W
indo
w P
roto
col
An
impr
ovem
ent i
s th
e sl
idin
g w
indo
w p
roto
col.
The
trans
mitt
er c
an tr
ansm
it a
win
dow
of
fram
es w
ithou
t ac
know
ledg
emen
ts.
Whe
n th
e ac
know
ledg
emen
ts
retu
rn f
rom
the
rec
eive
r, th
e tra
nsm
itter
can
mov
e fo
rwar
d to
tra
nsm
it m
ore
fram
es.
To
track
w
hich
ou
tgoi
ng
fram
e co
rres
pond
s to
a
retu
rned
ac
know
ledg
emen
t, ea
ch fr
ame
is la
bele
d w
ith a
seq
uenc
e nu
mbe
r. Th
e ra
nge
of
sequ
ence
num
ber
shou
ld b
e la
rge
enou
gh s
o th
at a
seq
uenc
e nu
mbe
r w
ill no
t re
appe
ar to
o so
on. I
f so,
am
bigu
ity w
ill ha
ppen
, sin
ce w
e ha
ve n
o m
eans
to te
ll th
e se
quen
ce n
umbe
r rep
rese
nts
an o
ld o
r a n
ew fr
ame.
Fo
r ex
ampl
e, s
uppo
se th
e w
indo
w s
ize
of th
e tra
nsm
itter
is 9
. It m
eans
the
trans
mitt
er c
an tr
ansm
it up
to 9
fram
es w
ithou
t ack
now
ledg
emen
ts. S
uppo
se th
e tra
nsm
itter
has
tra
nsm
itted
4 f
ram
es a
nd r
ecei
ves
an a
ckno
wle
dgem
ent
that
in
dica
tes
the
first
thre
e fra
mes
are
suc
cess
fully
rece
ived
. The
win
dow
will
slid
e 3
mor
e fra
mes
. It
mea
ns
3 m
ore
fram
es
can
be
trans
mitt
ed
with
out
ackn
owle
dgem
ents
. Slid
ing
win
dow
flow
con
trol i
s al
so a
ver
y im
porta
nt te
chni
que
in T
rans
mis
sion
Con
trol P
roto
col (
TCP
). W
e st
rong
ly r
ecom
men
d th
e re
ader
s to
pa
y at
tent
ion
to re
late
d di
scus
sion
in C
hapt
er 4
. O
ther
App
roac
hes
Ther
e ar
e st
ill ot
her
met
hods
to
impl
emen
t flo
w c
ontro
l. Fo
r ex
ampl
e, t
he
mec
hani
sm in
Eth
erne
t inc
lude
s ba
ck p
ress
ure
and
PAU
SE
fra
me.
How
ever
, to
un
ders
tand
thes
e m
etho
ds re
quire
the
know
ledg
e of
how
thes
e pr
otoc
ols
oper
ate.
W
e w
ill le
ave
thes
e flo
w c
ontro
l tec
hniq
ues
to la
ter s
ectio
ns.
2.
1.5
Med
ium
acc
ess
cont
rol
Med
ium
acc
ess
cont
rol,
also
sim
ply
refe
rred
to a
s M
AC
, is
nee
ded
whe
n m
ultip
le s
tatio
ns s
hare
a c
omm
on p
hysi
cal
med
ium
. It
incl
udes
an
arbi
tratio
n m
echa
nism
that
eve
ry s
tatio
n sh
ould
obe
y in
ord
er to
sha
re th
e co
mm
on m
ediu
m
fairl
y an
d ef
ficie
ntly.
The
re a
re p
lent
y of
tech
niqu
es to
do
so. W
e su
mm
ariz
e th
ese
tech
niqu
es in
to th
ree
cate
gorie
s be
low.
C
onte
ntio
n-ba
sed
App
roac
h
11
Mul
tiple
sta
tions
con
tend
for t
he u
se o
f med
ium
in th
is a
ppro
ach.
A c
lass
ical
ex
ampl
e is
ALO
HA
. Sta
tions
tran
smit
data
at w
ill. If
two
or m
ore
stat
ions
tran
smit
at t
he s
ame
time,
cal
led
a co
llisi
on,
thei
r fra
mes
will
be g
arbl
ed,
mak
ing
the
thro
ughp
ut lo
w. A
refin
emen
t is
the
slot
ted
ALO
HA
, in
whi
ch a
sta
tion
is a
llow
ed to
tra
nsm
it on
ly in
the
begi
nnin
g of
a ti
me
slot
. Fur
ther
ref
inem
ents
incl
ude
Car
rier
Sen
se a
nd C
ollis
ion
Det
ectio
n. C
arrie
r sen
se m
eans
the
stat
ion
sens
es if
ther
e is
tra
nsm
issi
on (i
n si
gnal
cal
led
carr
ier)
ove
r the
sha
red
med
ium
. The
tran
smitt
er w
ill w
ait p
olite
ly b
efor
e it
trans
mits
unt
il th
e sh
ared
med
ium
is fr
ee. C
ollis
ion
dete
ctio
n pr
even
ts t
he t
rans
mitt
er f
rom
a g
arbl
ed f
ram
e by
sto
ppin
g tra
nsm
issi
on i
f a
collis
ion
is d
etec
ted.
R
ound
-rob
in A
ppro
ach
Th
e m
ost
typi
cal
exam
ples
are
Tok
en R
ing,
Tok
en B
us,
and
FDD
I. Th
eir
mec
hani
sms
are
sim
ilar
desp
ite t
hat
thei
r st
ruct
ures
are
diff
eren
t. A
toke
n ci
rcul
ates
one
by
one
to a
llow
fair
shar
e of
the
med
ium
am
ong
stat
ions
. A s
tatio
n th
at o
wns
the
toke
n ha
s th
e rig
ht to
tran
smit
its fr
ame.
R
eser
vatio
n-ba
sed
App
roac
h C
ollis
ion-
base
d ap
proa
ch is
inef
ficie
nt if
a c
ollis
ion
cann
ot b
e de
tect
ed in
tim
e.
A fra
me
is c
ompl
exly
gar
bled
bef
ore
the
trans
mitt
er i
s aw
are
of t
he t
rage
dy.
Ano
ther
app
roac
h is
res
ervi
ng b
efor
e tra
nsm
ittin
g. T
he c
hann
el i
s re
serv
ed
som
ehow
bef
ore
the
trans
mitt
er a
ctua
lly tr
ansm
its it
fram
e. A
wel
l-kno
wn
exam
ple
is th
e R
TS/C
TS m
echa
nism
in IE
EE
802
.11
wire
less
LA
N. W
e w
ill ta
lk m
ore
abou
t th
is m
echa
nism
in S
ectio
n 2.
4.
Ther
e is
a tr
adeo
ff as
to th
e us
e of
rese
rvat
ion.
The
rese
rvat
ion
proc
ess
itsel
f is
an
over
head
. If
the
cost
of
a fra
me
loss
is
not
larg
e, e
.g.
a sh
ort
fram
e, a
co
nten
tion-
base
d ap
proa
ch m
ay b
e m
ore
effic
ient
. If
only
two
stat
ions
are
on
a po
int-t
o-po
int l
ink,
the
acce
ss c
ontro
l may
not
be
nece
ssar
y, d
epen
ding
on
the
med
ium
cha
ract
eris
tics.
In
such
a s
ituat
ion,
bot
h st
atio
ns c
an tr
ansm
it at
the
sam
e tim
e, w
hich
we
call
full-
dupl
ex o
pera
tion.
We
will
talk
mor
e ab
out f
ull-d
uple
x op
erat
ion
in S
ectio
n 2.
3.
2.
2 Po
int-t
o-po
int p
roto
col
St
artin
g fro
m th
is s
ectio
n, w
e w
ill lo
ok in
to re
al-w
orld
pro
toco
ls to
see
how
the
prin
cipl
es in
trodu
ced
in S
ectio
n 2.
1 w
ork
in t
hem
. Th
is s
ectio
n fo
cuse
s on
the
P
oint
-to-P
oint
Pro
toco
l (P
PP
), a
wid
ely
used
pro
toco
l we
ofte
n fin
d w
hen
we
dial
12
up a
mod
em o
r us
e A
DS
L to
the
Int
erne
t. W
e w
ould
like
to
emph
asiz
e on
the
ch
arac
teris
tics
in th
e da
ta-li
nk la
yer,
fram
ing,
add
ress
ing,
erro
r co
ntro
l, an
d flo
w
cont
rol,
in o
ur e
xpla
natio
n of
the
prot
ocol
ope
ratio
n. T
he P
PP
was
der
ived
from
an
old,
but
wid
ely
used
pro
toco
l, H
igh-
leve
l D
ata
Link
Con
trol
(HD
LC).
Dur
ing
its
oper
atio
n ar
e tw
o pr
otoc
ols,
Lin
k C
ontro
l P
roto
col (
LCP
), an
d N
etw
ork
Con
trol
Pro
toco
l (N
CP
). A
s E
ther
net
exte
nds
to h
ome
and
orga
niza
tions
, w
ith a
brid
ge
devi
ce s
uch
as A
DS
L m
odem
, con
nect
ed to
the
Inte
rnet
Ser
vice
Pro
vide
r (IS
P),
ther
e is
a r
equi
rem
ent
of P
PP
over
Eth
erne
t (P
PP
oE).
Fig.
2.4
sho
ws
the
rela
tions
hip
betw
een
thes
e co
mpo
nent
s w
e w
ill in
trodu
ce in
this
sec
tion.
Fi
gure
2.4
R
elat
ions
hip
of P
PP
-rela
ted
prot
ocol
s 2.
2.1
Hig
h-le
vel D
ata
Link
Con
trol (
HD
LC)
Th
e H
DLC
pro
toco
l is
old
but i
t is
a ba
sis
of m
any
othe
r pr
otoc
ols.
Der
ived
fro
m a
n ea
rly p
roto
col,
Syn
chro
nous
Dat
a Li
nk C
ontro
l pro
toco
l (S
DLC
), by
IBM
, it
was
late
r sub
mitt
ed to
ISO
and
bec
omes
an
ISO
sta
ndar
d. T
he H
DLC
pro
toco
l is
the
basi
s of
man
y ot
her d
ata-
link
prot
ocol
s. F
or e
xam
ple,
the
PP
P us
es H
DLC
-like
fra
min
g. IE
EE
802
.2 L
ogic
al L
ink
Con
trol (
LLC
) is
a m
odifi
catio
n of
HD
LC. C
CIT
T m
odifi
es H
DLC
as
part
of t
he X
.25
stan
dard
, ca
lled
Link
Acc
ess
Pro
cedu
re,
Bal
ance
d (L
AP-
B).
For
its
varia
tions
, H
DLC
su
ppor
ts
poin
t-to-
poin
t an
d po
int-t
o-m
ultip
oint
link
, and
hal
f-dup
lex
and
full-
dupl
ex li
nk. T
o be
tter
unde
rsta
nd
how
HD
LC w
ork
in te
rms
of th
e da
ta li
nk fu
nctio
ns w
e ha
ve m
entio
ned,
we
first
ta
ke a
look
of t
he H
DLC
ope
ratio
n.
13
HD
LC O
pera
tion:
Med
ium
Acc
ess
Con
trol
In
HD
LC, s
tatio
ns a
re e
ither
prim
ary
or s
econ
dary
sta
tions
. HD
LC s
uppo
rts
the
follo
win
g th
ree
trans
fer
mod
es.
Not
e th
at i
t is
the
way
how
sta
tions
are
co
ntro
lled
to a
cces
s th
e m
ediu
m.
Nor
mal
res
pons
e m
ode
(NR
M):
The
seco
ndar
y st
atio
n ca
n on
ly p
assi
vely
tra
nsm
it da
ta in
res
pons
e to
the
prim
ary’
s po
ll. T
he r
espo
nse
may
hav
e on
e or
m
ore
fram
es.
In
a po
int-t
o-m
ultip
oint
sc
enar
io,
seco
ndar
y st
atio
ns
mus
t co
mm
unic
ate
thro
ugh
the
prim
ary
stat
ion.
A
sync
hron
ous
resp
onse
mod
e (A
RM
): Th
e se
cond
ary
stat
ion
can
initi
ate
the
data
tra
nsfe
r w
ithou
t th
e pr
imar
y’s
poll,
but
the
prim
ary
is s
till
resp
onsi
ble
for
cont
rollin
g th
e co
nnec
tion.
A
sync
hron
ous
bala
nced
mod
e (A
BM
): Bo
th p
artie
s in
com
mun
icat
ion
can
play
th
e ro
le o
f th
e pr
imar
y an
d th
e se
cond
ary.
It
mea
ns b
oth
stat
ions
hav
e eq
ual
stat
us. T
his
type
of s
tatio
n is
cal
led
a co
mbi
ned
stat
ion.
NR
M is
ofte
n us
ed in
a p
oint
-to-m
ultip
oint
link
s, s
uch
as t
hose
bet
wee
n a
com
pute
r an
d its
te
rmin
als.
A
RM
is
ra
rely
us
ed.
It ha
s ad
vant
ages
fo
r po
int-t
o-po
int l
ink,
but
AB
M is
eve
n be
tter.
AB
M h
as le
ss o
verh
ead
such
as
the
prim
ary’
s po
ll an
d bo
th p
artie
s ca
n ha
ve c
ontro
l ove
r th
e lin
k. It
is s
uita
ble
for
a po
int-t
o-po
int l
ink.
Afte
r of
ferin
g an
impr
essi
on o
f the
HD
LC o
pera
tion,
we
go o
n di
scus
sing
the
func
tion
issu
es.
Dat
a lin
k fu
nctio
ns: F
ram
ing,
Add
ress
ing,
and
Err
or C
ontr
ol
W
e lo
ok a
t the
fram
ing,
add
ress
ing,
and
err
or c
ontro
l iss
ues
dire
ctly
from
the
fram
e fo
rmat
. The
n w
e w
ill di
scus
s flo
w c
ontro
l and
med
ium
acc
ess
cont
rol.
The
HD
LC fr
ame
form
at is
dep
icte
d in
Fig
. 2.5
.
Flag
A
ddre
ss
Con
trol
Info
rmat
ion
FCS
Flag
bits
8
8
8
Any
16
8
Figu
re 2
.5
HD
LC fr
ame
form
at
Fl
ag: T
he v
alue
is fi
xed
at 0
1111
110
to d
elim
it th
e be
ginn
ing
and
the
end
of th
e fra
me.
As
illust
rate
d in
Sec
tion
2.1.
1, b
it st
uffin
g is
use
d to
avo
id a
mbi
guity
be
twee
n ac
tual
dat
a an
d th
e fla
g va
lue.
A
ddre
ss: T
he a
ddre
ss in
dica
tes
the
seco
ndar
y st
atio
n in
volv
ed in
tran
smis
sion
, pa
rticu
larly
in p
oint
-to-m
ultip
oint
situ
atio
n. A
sec
onda
ry s
tatio
n w
orks
und
er t
he
14
cont
rol o
f the
prim
ary
stat
ion,
as
we
have
men
tione
d in
the
HD
LC o
pera
tion.
C
ontr
ol: T
his
field
indi
cate
s th
e fra
me
type
as
wel
l as
othe
r co
ntro
l inf
orm
atio
n.
Ther
e ar
e th
ree
type
s of
fra
mes
in
H
DLC
: In
form
atio
n,
Sup
ervi
sory
, an
d U
nnum
bere
d. W
e w
ill lo
ok a
t the
m d
eepe
r lat
er.
Info
rmat
ion:
The
inf
orm
atio
n fie
ld c
an b
e of
arb
itrar
y le
ngth
in
unit
of b
its.
It ca
rries
the
payl
oad
of d
ata
to b
e tra
nsm
itted
. FC
S: A
16-
bit C
RC
-CC
ITT
code
is u
sed.
HD
LC a
llow
s bo
th p
ositi
ve a
nd n
egat
ive
ackn
owle
dgem
ents
. Th
e er
ror
cont
rol
in
HD
LC
is
com
plex
. P
ositi
ve
ackn
owle
dgem
ents
can
indi
cate
a s
ucce
ssfu
l fra
me
or a
ll fra
mes
up
to a
poi
nt,
whi
le n
egat
ive
ackn
owle
dgem
ents
can
rej
ect
a re
ceiv
ed f
ram
e or
a s
peci
fied
fram
e.
We
do
not
go
into
de
tails
ab
out
the
scen
ario
s in
w
hich
th
ese
ackn
owle
dgem
ents
are
em
ploy
ed.
Inte
rest
ed r
eade
rs a
re e
ncou
rage
d to
rea
d fu
rther
from
our
list
in S
ectio
n 2.
7.
D
ata
link
func
tions
: Flo
w C
ontr
ol
Fl
ow c
ontro
l in
HD
LC is
sim
ple.
The
tran
smitt
er k
eeps
a c
ount
er to
reco
rd th
e se
quen
ce n
umbe
r of
the
next
fra
me
to b
e se
nt.
On
the
othe
r si
de,
the
rece
iver
ke
eps
a co
unte
r to
reco
rd th
e ex
pect
ed s
eque
nce
num
ber.
It ch
ecks
whe
ther
the
sequ
ence
num
ber
rece
ived
mat
ches
its
expe
ctat
ion.
If it
is a
nd th
e fra
me
is n
ot
garb
led,
it
incr
ease
s its
cou
nter
by
one
and
ackn
owle
dges
the
sen
der
by
trans
mitt
ing
a m
essa
ge c
onta
inin
g th
e ex
pect
ed s
eque
nce.
If th
e re
ceiv
ed fr
ame
is n
ot a
s ex
pect
ed, o
r an
err
or is
det
ecte
d, th
e fra
me
is d
ropp
ed a
nd a
neg
ativ
e ac
know
ledg
emen
t is
sent
bac
k to
the
send
er.
Fram
e Ty
pe
The
abov
e fu
nctio
ns a
re a
chie
ved
thro
ugh
vario
us k
inds
of
fram
es.
An
info
rmat
ion
fram
e, c
alle
d I-f
ram
e, c
arrie
s da
ta f
rom
the
upp
er l
ayer
and
som
e co
ntro
l inf
orm
atio
n. T
he c
ontro
l inf
orm
atio
n ha
s tw
o se
quen
ce n
umbe
rs o
f thr
ee
bits
to
indi
cate
the
seq
uenc
e nu
mbe
r of
itse
lf an
d th
e ac
know
ledg
ed s
eque
nce
num
ber
from
the
rec
eive
r. Th
ese
sequ
ence
num
bers
are
for
flo
w-c
ontro
l an
d er
ror-c
ontro
l pu
rpos
es.
A po
ll/fin
al (
P/F
) is
als
o in
the
con
trol
info
rmat
ion
to
indi
cate
a p
oll f
rom
the
prim
ary
or th
e la
st re
spon
se fr
om th
e se
cond
ary.
A
supe
rvis
ory
fram
e, c
alle
d S
-fram
e, c
arrie
s co
ntro
l inf
orm
atio
n on
ly. A
s w
e ha
ve
seen
in
th
e illu
stra
tion
of
HD
LC
fram
e,
both
po
sitiv
e an
d ne
gativ
e ac
know
ledg
emen
ts a
re s
uppo
rted
for
erro
r co
ntro
l. O
nce
ther
e is
an
erro
r, th
e tra
nsm
itter
can
eith
er r
etra
nsm
it al
l ou
tsta
ndin
g fra
mes
or
only
the
err
oneo
us
fram
e, a
s sp
ecifi
ed i
n th
e co
ntro
l in
form
atio
n. T
he r
ecei
ver
can
also
ask
for
a
tem
pora
ry s
top
to th
e tra
nsm
itter
with
an
S-fr
ame.
15
An
unnu
mbe
red
fram
e, c
alle
d U
-fram
e, is
als
o us
ed fo
r co
ntro
l pur
pose
, but
no
t ca
rries
an
y se
quen
ce
num
ber,
so
is
the
nam
e de
rived
. Th
ey
incl
ude
mis
cella
neou
s co
mm
ands
for
mod
e se
tting
s, in
form
atio
n tra
nsfe
r, an
d re
cove
ry.
How
ever
, we
do n
ot g
o in
to d
etai
ls h
ere.
2.2.
2 P
oint
-to-P
oint
Pro
toco
l (P
PP
)
The
PP
P is
a s
tand
ard
prot
ocol
def
ined
by
IETF
to
carry
mul
ti-pr
otoc
ol
pack
ets
over
a p
oint
-to-p
oint
link
. It i
s w
idel
y us
ed fo
r dia
l-up
mod
ems
and
leas
ed
lines
. To
carry
mul
ti-pr
otoc
ol p
acke
ts, i
t has
thre
e m
ain
com
pone
nts:
1.
An
enca
psul
atio
n m
etho
d to
cap
pac
kets
from
the
netw
ork
laye
r. 2.
A L
ink
Con
trol
Pro
toco
l (L
CP
) to
han
dle
the
cycl
e of
con
nect
ion
setu
p,
conf
igur
atio
n, a
nd te
ar-d
own.
3.
A N
etw
ork
Con
trol P
roto
col (
NC
P) t
o co
nfig
ure
diffe
rent
net
wor
k-la
yer o
ptio
ns.
We
first
look
at t
he P
PP
oper
atio
n an
d th
en s
tudy
its
func
tions
.
PPP
Ope
ratio
n Th
e sc
enar
io o
f th
e P
PP
oper
atio
n w
orks
lik
e th
is:
Firs
t, P
PP
send
s LC
P pa
cket
s to
est
ablis
h an
d te
st t
he c
onne
ctio
n. A
fter
the
conn
ectio
n is
set
up,
the
peer
may
aut
hent
icat
e its
elf
befo
re a
ny n
etw
ork
laye
r pa
cket
s ar
e ex
chan
ged.
Th
en P
PP
star
ts t
o se
nd N
CP
pack
ets
to c
onfig
ure
one
or m
ore
netw
ork
laye
r pr
otoc
ols.
Onc
e th
e co
nfig
urat
ion
is d
one,
the
netw
ork
laye
r pac
kets
can
be
sent
ov
er t
he li
nk.
The
who
le p
roce
dure
is d
epic
ted
in t
he p
hase
dia
gram
sho
wn
in
Figu
re 2
.6.
Fi
gure
2.6
P
hase
dia
gram
of P
PP
conn
ectio
n se
tup
and
tear
-dow
n
We
expl
ain
each
maj
or tr
ansi
tion
in th
e di
agra
m a
s fo
llow
s:
Dea
d to
Est
ablis
h: T
he t
rans
ition
is
invo
ked
by c
arrie
r de
tect
ion
or n
etw
ork
adm
inis
trato
r con
figur
atio
n to
use
a p
hysi
cal l
ink.
Es
tabl
ish
to
Aut
hent
icat
e:
The
LCP
star
ts
to
set
up
the
conn
ectio
n by
Dea
d U
p Es
tabl
ish
Ope
n A
uthe
ntic
ate
Succ
ess/
Non
e
Net
wor
kC
lose
Te
rmin
ate
Dow
n
Fail
Fail
16
exch
angi
ng c
onfig
urat
ion
pack
ets.
All
optio
ns n
ot n
egot
iate
d ar
e as
sum
ed to
be
defa
ult
valu
es.
Not
e th
at o
nly
optio
ns i
ndep
ende
nt o
f th
e ne
twor
k la
yer
are
nego
tiate
d. T
he o
ptio
ns a
bout
net
wor
k la
yer c
onfig
urat
ion
are
left
to th
e N
CP.
A
uthe
ntic
ate
to N
etw
ork:
Aut
hent
icat
ion
is o
ptio
nal i
n P
PP.
If re
quire
d in
the
link
esta
blis
hmen
t ph
ase,
the
trans
ition
will
com
e to
the
auth
entic
atio
n ph
ase.
If t
he
auth
entic
atio
n fa
ils,
the
conn
ectio
n w
ill b
e te
rmin
ated
. If
it is
suc
cess
ful,
the
prop
er N
CP
star
ts to
neg
otia
te e
ach
netw
ork
laye
r pro
toco
l. N
etw
ork
to T
erm
inat
e: T
he te
rmin
atio
n ha
ppen
s in
man
y si
tuat
ions
. The
y in
clud
e th
e lo
ss o
f ca
rrier
, au
then
ticat
ion
failu
re,
expi
ratio
n of
an
idle
con
nect
ion,
use
r te
rmin
atio
n, e
tc.
The
LCP
is r
espo
nsib
le f
or e
xcha
ngin
g Te
rmin
ate
pack
ets
to
clos
e th
e co
nnec
tion
and
late
r the
PP
P te
lls th
e ne
twor
k la
yer p
roto
col t
o cl
ose.
Th
ere
are
thre
e cl
asse
s of
LC
P fra
mes
: C
onfig
urat
ion,
Ter
min
atio
n an
d M
aint
enan
ce.
A pa
ir of
C
onfig
ure-
requ
est
and
Con
figur
e-ac
k ca
n op
en
a co
nnec
tion.
Opt
ions
, su
ch a
s m
axim
um r
ecei
ve u
nit,
or a
uthe
ntic
atio
n pr
otoc
ol,
are
nego
tiabl
e du
ring
the
conn
ectio
n se
tup.
The
oth
er fu
nctio
ns a
re s
umm
ariz
ed
in F
ig. 2
.7. T
he L
CP
fram
e is
a s
peci
al c
ase
of th
e P
PP
fram
e. T
here
fore
, bef
ore
we
look
at t
he L
CP
fram
e fo
rmat
, we
first
intro
duce
the
PP
P fra
me
form
at b
elow
.
Cla
ss
Type
Fu
nctio
n C
onfig
ure-
requ
est
Ope
n a
conn
ectio
n by
giv
ing
desi
red
chan
ges
to o
ptio
ns
Con
figur
e-ac
k A
ckno
wle
dge
Con
figur
e-re
ques
t
Con
figur
e-na
k D
eny
Con
figur
e-re
ques
t bec
ause
of u
nacc
epta
ble
optio
ns
Con
figur
atio
n
Con
figur
e-re
ject
D
eny
Con
figur
e-re
ques
t be
caus
e of
un
reco
gniz
able
optio
ns
Term
inat
e-re
ques
t R
eque
st to
clo
se th
e co
nnec
tion
Term
inat
ion
Term
inat
e-ac
k Ac
know
ledg
e Te
rmin
ate-
requ
est
Cod
e-re
ject
U
nkno
wn
requ
ests
from
the
peer
Prot
ocol
-reje
ct
Uns
uppo
rted
prot
ocol
from
the
peer
Echo
-requ
est
Echo
bac
k th
e re
ques
t (fo
r deb
uggi
ng)
Echo
-repl
y Th
e ec
ho fo
r Ech
o-re
ques
t (fo
r deb
uggi
ng)
Mai
nten
ance
Dis
card
-req
uest
Ju
st d
isca
rd th
e re
ques
t (fo
r deb
uggi
ng)
Tabl
e 2.
2 Th
e LC
P fra
me
type
s D
ata
link
func
tions
: Fra
min
g, A
ddre
ssin
g, a
nd E
rror
Con
trol
Th
e P
PP
fram
e is
enc
apsu
late
d in
an
HD
LC-li
ke fo
rmat
, as
depi
cted
in F
ig.
2.8.
Not
e th
e fla
g va
lue
is e
xact
ly th
e sa
me
as in
HD
LC. I
t ser
ves
as th
e de
limit
char
acte
rs fo
r fra
min
g.
17
Flag
01
1111
10
Add
ress
11
1111
11
Con
trol
0000
0011
P
roto
col
Info
rmat
ion
FCS
Fl
ag
0111
1110
bits
8
8
8
8
or 1
6
A
ny
16 o
r 32
8
Figu
re 2
.7
PP
P fra
me
form
at
The
diffe
renc
e fro
m a
n H
DLC
fram
e is
sum
mar
ized
bel
ow:
1. T
he a
ddre
ss is
fixe
d at
the
valu
e 11
1111
11, w
hich
is th
e al
l-sta
tions
add
ress
in
the
HD
LC fo
rmat
. Sin
ce th
ere
is o
nly
one
peer
in a
poi
nt-to
-poi
nt li
nk, t
here
is
no n
eed
to in
dica
te a
n in
divi
dual
sta
tion
addr
ess
at a
ll.
2. T
he c
ontro
l co
de i
s fix
ed a
t th
e va
lue
0000
0011
, w
hich
cor
resp
onds
to
an
unnu
mbe
red
fram
e in
the
HD
LC f
orm
at.
This
im
plie
s th
at n
o se
quen
ce
num
bers
and
ack
now
ledg
emen
t ar
e us
ed in
the
PP
P by
def
ault.
RFC
166
3 de
fines
an
exte
nsio
n to
mak
e th
e P
PP
conn
ectio
n re
liabl
e. In
tere
sted
read
ers
are
refe
rred
to th
is d
ocum
ent.
3. A
Pro
toco
l fie
ld is
add
ed to
indi
cate
wha
t kin
d of
net
wor
k la
yer p
roto
col,
say
IP
or IP
X th
e fra
me
is c
arry
ing.
The
fiel
d le
ngth
is 1
6 bi
ts b
y de
faul
t, bu
t it c
an b
e re
duce
d to
8 b
its u
sing
the
LCP
nego
tiatio
n.
4. T
he m
axim
um le
ngth
of
the
Info
rmat
ion
field
is 1
500
byte
s by
def
ault.
Thi
s va
lue
is c
alle
d th
e M
axim
um R
ecei
ve U
nit (
MR
U).
Oth
er v
alue
s fo
r M
RU
are
ne
gotia
ble.
5.
A 1
6-bi
t FC
S i
s us
ed b
y de
faul
t. Th
roug
h th
e LC
P ne
gotia
tion,
it
can
be
exte
nded
to 3
2 bi
ts. T
he re
ceiv
er s
impl
y dr
ops
the
rece
ived
fram
e if
an e
rror i
s de
tect
ed.
The
resp
onsi
bilit
y of
re
trans
mis
sion
fa
lls
on
the
uppe
r-lay
er
prot
ocol
s.
Dat
a lin
k fu
nctio
ns: F
low
Con
trol
and
Med
ium
Acc
ess
Con
trol
PP
P is
full-
dupl
ex a
nd th
ere
are
only
two
stat
ions
in a
poi
nt-to
-poi
nt li
nk. N
o m
ediu
m a
cces
s co
ntro
l is
nece
ssar
y. O
n th
e ot
her
hand
, PP
P do
es n
ot p
rovi
de
flow
con
trol.
Flow
con
trol i
s al
so le
ft to
upp
er-la
yer p
roto
cols
. LC
P an
d N
CP
nego
tiatio
n Th
e LC
P fra
me
is a
PPP
fram
e w
ith th
e P
roto
col f
ield
equ
al to
0xc
021,
whe
re
0x s
tand
s fo
r a h
exad
ecim
al n
umbe
r. Th
e ne
gotia
tion
info
rmat
ion
is e
mbe
dded
in
the
Info
rmat
ion
field
as
four
mai
n fie
lds.
The
y ar
e C
ode
to in
dica
te th
e ty
pe o
f LC
P,
Iden
tifie
r to
mat
ch r
eque
sts
and
repl
ies,
Len
gth
to in
dica
te th
e to
tal l
engt
h of
the
four
fiel
ds, a
nd D
ata
to c
arry
the
nego
tiatio
n op
tions
. S
ince
IP
is t
he d
omin
atin
g ne
twor
k-la
yer
prot
ocol
in
the
Inte
rnet
, w
e ar
e pa
rticu
larly
inte
rest
ed in
IP
over
PP
P. W
e w
ill so
on in
trodu
ce t
he N
CP
for
IP –
18
Inte
rnet
Pro
toco
l Con
trol P
roto
col (
IPC
P) i
n th
e ne
xt s
ubse
ctio
n.
2.
2.3
Inte
rnet
Pro
toco
l Con
trol P
roto
col (
IPC
P)
IP
CP
is a
mem
ber o
f NC
Ps
to c
onfig
ure
IP o
ver P
PP.
As
men
tione
d in
the
last
su
bsec
tion,
PP
P fir
st e
stab
lishe
s a
conn
ectio
n w
ith L
CP
and
then
use
s N
CP
to
conf
igur
e th
e ne
twor
k la
yer p
roto
col i
t car
ries.
Onc
e th
ese
conf
igur
atio
ns a
re d
one,
da
ta p
acke
ts c
an b
e tra
nsm
itted
ove
r the
link
. IP
CP
uses
a s
imila
r fra
me
form
at a
s th
e LC
P. It
s fra
me
is a
lso
a sp
ecia
l cas
e of
the
PP
P fra
me,
with
the
Pro
toco
l fie
ld e
qual
to
0x80
21.
The
exch
ange
m
echa
nism
is th
e sa
me
as th
at o
f the
LC
P. T
hrou
gh IP
CP,
IP m
odul
es o
n bo
th
peer
s ca
n be
ena
bled
, con
figur
ed, a
nd d
isab
led.
IP
CP
prov
ides
th
e co
nfig
urat
ion
optio
ns:
IP-A
ddre
sses
, IP
-Com
pres
sion
-Pro
toco
l, an
d IP
-Add
ress
. The
firs
t is
obso
lete
and
is re
plac
ed b
y th
e th
ird.
The
seco
nd i
ndic
ates
the
use
of
Van
Jaco
bson
’s T
CP
/IP h
eade
r co
mpr
essi
on. T
he th
ird a
llow
s th
e pe
er to
pro
vide
an
IP a
ddre
ss to
be
used
on
the
loca
l end
. Onc
e IP
CP
nego
tiatio
n is
don
e, n
orm
al IP
pac
kets
can
be
trans
mitt
ed
over
the
link
with
the
Pro
toco
l fie
ld e
qual
to 0
x002
1 on
the
PP
P fra
me.
2.
2.4
PP
P: O
pen
Sou
rce
Impl
emen
tatio
n In
trod
uctio
n
The
Linu
x P
PP
impl
emen
tatio
n is
prim
arily
com
pose
d of
tw
o pa
rts:
kern
el
(PP
P dr
iver
) an
d us
er-le
vel (
PP
P da
emon
) pa
rts. I
n th
e pa
st, t
he P
PP
pack
ages
ha
ve to
con
tain
upd
ated
ker
nel d
river
s. T
his
is n
o lo
nger
nec
essa
ry, a
s th
e cu
rrent
2.
2 an
d 2.
4 ke
rnel
sou
rces
con
tain
up-
to-d
ate
driv
ers.
Bes
ides
, th
e Li
nux
PP
P im
plem
enta
tion
is c
apab
le o
f bei
ng u
sed
both
for i
nitia
ting
PP
P co
nnec
tions
(as
a `c
lient
') or
for h
andl
ing
inco
min
g P
PP
conn
ectio
ns (a
s a
`ser
ver')
. Not
e th
at th
is is
an
ope
ratio
nal d
istin
ctio
n, b
ased
on
how
the
conn
ectio
n is
cre
ated
, rat
her t
han
a di
stin
ctio
n th
at is
mad
e in
the
PP
P pr
otoc
ols
them
selv
es.
Th
e P
PP
prot
ocol
con
sist
s of
tw
o pa
rts.
One
is
a sc
hem
e fo
r fra
min
g an
d en
caps
ulat
ing
pack
ets,
the
othe
r is
a s
erie
s of
pro
toco
ls c
alle
d LC
P, IP
CP,
PA
P an
d C
HA
P, f
or n
egot
iatin
g lin
k op
tions
and
for
aut
hent
icat
ion.
Sim
ilarly
, P
PP
pack
ages
con
sist
s of
two
parts
: a P
PP
driv
er (
supp
orte
d by
Lin
ux k
erne
l) w
hich
ha
ndle
s P
PP
's lo
w-le
vel f
ram
ing
prot
ocol
, and
a u
ser-l
evel
pro
gram
cal
led
pppd
w
hich
impl
emen
ts P
PP
's n
egot
iatio
n pr
otoc
ols.
Th
e P
PP
driv
er e
stab
lishe
s a
netw
ork
inte
rface
and
pas
ses
pack
ets
betw
een
19
the
seria
l por
t, th
e ke
rnel
net
wor
k co
de a
nd th
e pp
pd. A
lso,
it h
andl
es th
e is
sues
of
dat
a lin
k la
yer (
e.g.
fram
ing,
erro
r det
ectio
n) d
escr
ibed
in p
revi
ous
subs
ectio
ns.
The
pppd
neg
otia
tes
with
the
pee
r to
est
ablis
h th
e lin
k an
d se
ts u
p th
e P
PP
netw
ork
inte
rface
. B
esid
es,
pppd
inc
lude
s su
ppor
t fo
r au
then
ticat
ion,
so
it ca
n co
ntro
l whi
ch o
ther
sys
tem
s m
ay m
ake
a P
PP
conn
ectio
n an
d w
hat I
P ad
dres
ses
they
may
use
. IP
pack
ets
go d
irect
ly to
the
ker
nel n
etw
ork
code
, so
once
ppp
d ha
s ne
gotia
ted
the
link,
it in
pra
ctic
e lie
s co
mpl
etel
y do
rman
t unt
il yo
u w
ant t
o ta
ke
the
link
dow
n, w
hen
it ne
gotia
tes
a gr
acef
ul d
isco
nnec
t. PP
P D
river
A
PP
P dr
iver
is m
ade
of th
e P
PP
gene
ric la
yer
and
the
PP
P ch
anne
l driv
er.
Figu
re 2
.8 p
rese
nts
the
PP
P ar
chite
ctur
e:
Ther
e ar
e as
ynch
rono
us
(/driv
ers/
net/p
pp_a
sync
.c)
and
sync
hron
ous
(/driv
ers/
net/p
pp_s
ynct
ty.c
) P
PP
chan
nel
driv
ers
in
Linu
x ke
rnel
. Th
e as
ynch
rono
us p
pp c
hann
el d
river
is u
sed
for a
sync
hron
ous
seria
l por
ts, w
hile
the
sync
hron
ous
one
is u
sed
for s
ynch
rono
us s
eria
l por
ts. W
e kn
ow th
at s
ynch
rono
us
com
mun
icat
ion
is d
esig
ned
for
bette
r ba
ndw
idth
allo
catio
n th
an a
sync
hron
ous
com
mun
icat
ion,
and
it’s
abo
ut 3
0% f
aste
r ac
tual
ly. F
or t
his
reas
on,
ther
e is
so
met
hing
diff
eren
t be
twee
n as
ync
and
sync
ppp
driv
er.
No
erro
r co
ntro
l is
put
into
pra
ctic
e in
syn
c pp
p dr
iver
, and
it is
left
to b
e do
ne in
the
hard
war
e de
vice
. H
owev
er, t
here
is e
rror
con
trol i
n as
ync
ppp
driv
er. M
ost P
C s
eria
l dev
ices
suc
h as
mic
e, k
eybo
ards
and
mod
ems
are
asyn
chro
nous
, w
here
as t
he h
igh-
spee
d W
AN a
dapt
ors
are
sync
hron
ous.
Hen
ce,
asyn
chro
nous
PP
P en
able
s Li
nux
to
Com
pone
nt F
unct
ion
pppd
ha
ndle
s co
ntro
l-pla
ne p
acke
ts
kern
el
hand
les
data
-pla
ne p
acke
ts
PPP
gene
ric
laye
r
hand
les
PP
P ne
twor
k in
terfa
ce
, /de
v/pp
p de
vice
, VJ
com
pres
sion
, m
ultil
ink
PPP
chan
nel
driv
er
hand
les
enca
psul
atio
n,
fram
ing,
and
erro
r con
trol
pppd
ke
rnel
PP
P ge
neric
laye
r
PP
P ch
anne
l driv
er
tty d
evic
e dr
iver
seria
l lin
e
Figu
re 2
.8
ppp
arch
itect
ure
20
rout
e IP
dat
agra
ms
over
tel
epho
ne n
etw
orks
, an
d sy
nchr
onou
s P
PP
enab
les
Linu
x to
rou
te I
P da
tagr
ams
over
ded
icat
ed le
ased
-line
s. F
ollo
win
g, w
e ex
plai
n th
e pp
p_sy
nctty
.c in
Lin
ux k
erne
l 2.4
. Th
ere
are
two
impo
rtant
dat
a st
ruct
ures
in th
is P
PP
driv
er, o
ne is
PP
P ch
anne
l an
d th
e ot
her i
s P
PP
unit.
A P
PP
chan
nel p
rovi
des
a w
ay fo
r gen
eric
PP
P co
de to
se
nd a
nd r
ecei
ve p
acke
ts.
A P
PP u
nit
corre
spon
ds t
o a
PP
P ne
twor
k in
terfa
ce
devi
ce a
nd it
rep
rese
nts
a m
ultil
ink
bund
le.
Figu
re 2
list
s so
me
usef
ul f
ield
s of
th
ese
two
data
stru
ctur
es :
Fig
2. i
s th
e re
latio
n fo
r th
e ou
tgoi
ng f
low
fun
ctio
ns,
and
Fig
2. i
s th
e de
scrip
tion
of th
em.
PP
P ch
anne
l Fi
eld
Func
tion
file
stuf
f for
read
/writ
e op
s op
erat
ions
for t
his
chan
nel
ppp
ppp
unit
we’
re c
onne
cted
to
clis
t lin
k in
list
of c
hann
els
per u
nit
PPP
Uni
t Fi
eld
Func
tion
file
stuf
f for
read
/writ
e ch
anne
llis
t of a
ttach
ed c
hann
els
xmit_
pe
ndin
g a
pack
et re
ady
to g
o ou
t
dev
netw
ork
inte
rface
dev
ice
Figu
re 2
. f
ield
s of
dat
a st
ruct
ures
Figu
re 2
. f
low
char
t of o
utgo
ing
flow
func
tions
21
Fu
nctio
n D
escr
iptio
n pp
p_st
art_
xmit
put 2
-byt
e P
PP
prot
ocol
num
ber o
n th
e fro
nt o
f skb
pp
p_w
rite
take
out
the
file-
>priv
ate_
data
pp
p_fil
e_w
rite
allo
cate
sk
b,
copy
da
ta
from
us
er
spac
e,
to
PP
Pch
anne
l or P
PP
unit
ppp_
xmit_
proc
ess
to d
o an
y w
ork
queu
ed u
p on
the
trans
mit
side
that
can
be
don
e no
w
ppp_
chan
nel_
push
se
nd d
ata
out o
n a
chan
nel
ppp_
send
_fra
me
VJ
com
pres
sion
pp
p_pu
sh
hand
les
mul
tiple
link
st
art_
xmit
ppp_
sync
_sen
d pp
p_sy
nc_s
end
send
a p
acke
t ove
r an
tty li
ne
ppp_
sync
_tx_
mun
ge e
ncap
sula
tion
and
fram
ing
ppp_
sync
_pus
h pu
sh a
s m
ush
data
as
poss
ible
tty
->dr
iver
.writ
e w
rite
data
to tt
y de
vice
driv
er
Fig
2. is
the
rela
tion
for t
he in
com
ing
flow
func
tions
, and
Fig
2. i
s th
e de
scrip
tion
of
them
.
Figu
re 2
. d
escr
iptio
n of
out
goin
g flo
w fu
nctio
ns
22
Fu
nctio
n D
escr
iptio
n pp
p_sy
nc_r
ecei
ve
take
out
the
tty->
disc
_dat
a pp
p_sy
nc_i
nput
st
uff t
he c
hars
in th
e sk
b pr
oces
s_in
put_
pack
et
strip
add
ress
/con
trol f
ield
pp
p_in
put
take
out
the
pack
ets
that
sho
uld
be in
the
chan
nel
queu
e pp
p_do
_rec
v ch
eck
if th
e in
terfa
ce c
lose
d do
wn
ppp_
rece
ive_
fram
e de
cide
if th
e re
ceiv
ed fr
ame
is a
mul
tilin
k fra
me
ppp_
rece
ive_
nonm
p_fra
me
VJ
deco
mpr
essi
on i
f pr
oto=
=PP
P_V
JC_C
OM
P,
and
deci
de w
heth
er it
’s a
con
trol-p
lane
fram
e or
a
data
-pla
ne fr
ame
ppp_
rece
ive_
mp_
fram
e re
cons
truct
ion
of m
ultil
ink
fram
es
netif
_rx
push
pac
kets
into
the
queu
e fo
r ker
nel
skb_
queu
e_ta
il pu
sh p
acke
ts in
to th
e qu
eue
for p
ppd
Th
e m
ultip
le
chan
nels
av
aila
ble
with
IS
DN
se
rvic
es
mot
ivat
ed
the
deve
lopm
ent
of m
ultil
ink
(bun
dle)
PP
P, a
s do
cum
ente
d in
RFC
-199
0. M
ultil
ink
PP
P ar
rang
es s
ever
al in
depe
nden
t con
nect
ions
bet
wee
n a
fixed
pai
r of e
ndpo
ints
Figu
re 2
. f
low
char
t of i
ncom
ing
flow
func
tions
Figu
re 2
. d
escr
iptio
n of
inco
min
g flo
w fu
nctio
ns
23
to fu
nctio
n lo
gica
lly a
s on
e. F
or e
xam
ple,
if a
rout
er h
as a
n IS
DN
BR
I int
erfa
ce, i
t co
uld
trans
fer d
ata
at 6
4Kbp
s on
one
"B" c
hann
el, b
ut th
en in
tim
es o
f hig
her l
oad
coul
d co
nnec
t a s
econ
d "B
" cha
nnel
and
so
have
an
aggr
egat
e ra
te o
f 128
KB
ps. I
t co
uld
also
be
used
whe
re th
ere
is a
leas
ed li
ne c
onne
ctio
n to
a re
mot
e si
te, b
ut in
tim
es o
f inc
reas
ed lo
ad it
cou
ld a
gain
con
nect
an
ISD
N "B
" cha
nnel
to te
mpo
raril
y in
crea
se t
hrou
ghpu
t. Th
is t
echn
ique
isn
’t lim
ited
to I
SD
N.
Any
num
ber
of P
PP
conn
ectio
ns o
f var
ying
spe
eds
and
diffe
rent
link
type
s m
ay b
e bu
ndle
d to
geth
er.
How
ever
, a
bund
le m
ust
still
conn
ect
betw
een
the
sam
e tw
o en
dpoi
nts.
The
m
ultil
ink
proc
edur
e en
code
s P
PP
fragm
ents
with
in P
PP f
ram
es.
Eac
h lin
k in
a
bund
le b
egin
s as
an
inde
pend
ent a
nd s
tand
alon
e co
nnec
tion.
Lat
er n
egot
iatio
ns
esta
blis
h th
e m
ultil
ink
optio
n an
d un
ique
ly
iden
tify
the
bund
le
a ph
ysic
al
conn
ectio
n pa
rtici
pate
s in
. O
nce
the
bund
le i
s ac
tive,
the
mul
tilin
k pr
oced
ure
fragm
ents
, seq
uenc
es, a
nd re
asse
mbl
es lo
gica
l PP
P fra
mes
. Fig
2 il
lust
rate
s th
is
proc
edur
e. F
ram
es c
onta
inin
g fra
gmen
ts h
ave
the
prot
ocol
fiel
d va
lue
0x00
3d. A
lo
gica
l fra
me
size
is li
mite
d by
a n
egot
iate
d m
axim
um re
ceiv
ed re
cons
truct
ed u
nit
(MR
RU
). Th
is v
alue
may
be
very
lar
ge,
sinc
e ea
ch f
ragm
ent
may
hav
e si
zes
with
in th
e M
RU
est
ablis
hed
for
indi
vidu
al c
onne
ctio
ns. H
owev
er, p
ract
ical
upp
er
limits
do
exis
t du
e to
res
ourc
es n
eces
sary
to
sort
and
asse
mbl
e fra
gmen
ts,
as
wel
l as
dete
ct th
eir l
oss.
pp
pd
2.2.
5 P
PP
over
Eth
erne
t (P
PP
oE)
The
Nee
d of
PPP
oE
As
Eth
erne
t tec
hnol
ogy
beco
mes
che
ap a
nd d
omin
ant,
it is
not
unc
omm
on
that
use
rs h
ave
thei
r ow
n E
ther
net L
AN
in th
eir h
ome
or o
ffice
. On
the
othe
r han
d,
broa
dban
d ac
cess
tec
hnol
ogie
s, s
ay A
DS
L, h
ave
a bo
ostin
g de
velo
pmen
t as
a
Hea
der
Dat
a
Logi
cal P
PP
fram
e
H
D
PPP
PPP
Seria
l con
nect
ion
#1
Ser
ial c
onne
ctio
n #2
H
D
H
D
H
D
24
met
hod
to a
cces
s th
e In
tern
et fr
om h
ome
or o
ffice
. Use
rs o
n an
Eth
erne
t LA
N a
re
likel
y to
acc
ess
the
Inte
rnet
thro
ugh
the
sam
e br
oadb
and
brid
ging
dev
ices
at t
he
sam
e tim
e. F
or s
ervi
ce p
rovi
ders
, th
ey d
esire
a m
etho
d to
hav
e ac
cess
con
trol
and
billin
g on
a p
er-u
ser b
asis
, jus
t sim
ilar t
o co
nven
tiona
l dia
l-up
serv
ices
. P
PP
has
conv
entio
nally
bee
n a
solu
tion
to b
uild
poi
nt-to
-poi
nt r
elat
ions
hip
betw
een
peer
s. H
owev
er,
an E
ther
net
netw
ork
cons
ists
of
mul
tiple
sta
tions
by
natu
re.
The
PP
P ov
er E
ther
net
prot
ocol
(P
PP
oE)
is d
esig
ned
to c
oord
inat
e th
e tw
o co
nflic
ting
philo
soph
ies.
It c
reat
es a
virt
ual i
nter
face
on
an E
ther
net i
nter
face
so
tha
t in
divi
dual
sta
tion
on a
LA
N c
an e
stab
lish
a P
PP s
essi
on w
ith a
rem
ote
PPPo
E se
rver
, kn
own
as A
cces
s C
once
ntra
tor
(AC
) lo
cate
d in
the
IS
P th
roug
h co
mm
on b
ridgi
ng d
evic
es. E
ach
user
on
the
LAN
see
s a
PP
P in
terfa
ce ju
st li
ke
wha
t is
seen
in a
dia
l-up
serv
ice,
but
the
PP
P fra
mes
are
act
ually
enc
apsu
late
d in
th
e E
ther
net f
ram
es. T
hrou
gh P
PP
oE, t
he u
ser’s
com
pute
r obt
ains
an
IP a
ddre
ss,
and
the
ISP
has
an e
asy
way
to tr
ack
the
IP a
ddre
ss to
a s
peci
fic u
ser n
ame
and
pass
wor
d.
PPPo
E O
pera
tion
The
PP
PoE
run
s in
tw
o st
ages
: th
e D
isco
very
sta
ge a
nd t
he P
PP S
essi
on
stag
e. I
n th
e D
isco
very
sta
ge,
the
MA
C a
ddre
ss o
f th
e ac
cess
con
cent
rato
r is
di
scov
ered
. A u
niqu
e P
PPoE
ses
sion
id is
als
o as
sign
ed to
the
sess
ion.
Onc
e a
PP
P se
ssio
n is
est
ablis
hed,
bot
h pe
ers
ente
r the
PP
P S
essi
on s
tage
and
do
wha
t ex
actly
a P
PP s
essi
on d
oes,
say
LC
P ne
gotia
tion.
Th
e D
isco
very
sta
ge p
roce
eds
in th
e fo
llow
ing
four
ste
ps:
1. T
he s
tatio
n th
at w
ould
like
to a
cces
s th
e In
tern
et b
road
cast
s an
Initi
atio
n fra
me
to a
sk fo
r rem
ote
acce
ss c
once
ntra
tors
to re
turn
thei
r MA
C a
ddre
sses
. 2.
The
rem
ote
acce
ss c
once
ntra
tor r
espo
nds
its M
AC
add
ress
es.
3. T
he
orig
inal
st
atio
n se
lect
s on
e ac
cess
co
ncen
trato
r. It
send
s a
Ses
sion
-Req
uest
fram
e to
the
sele
cted
acc
ess
conc
entra
tor.
4. T
he a
cces
s co
ncen
trato
r gen
erat
es a
PP
PoE
ses
sion
id a
nd re
turn
s a
Con
firm
fra
me
with
the
id.
The
PP
P S
essi
on s
tage
run
s in
the
sam
e w
ay a
s a
norm
al P
PP
sess
ion,
as
expl
aine
d in
Sec
tion
2.2.
2, o
nly
bein
g ca
rried
on
the
Eth
erne
t fra
mes
. Whe
n th
e LC
P te
rmin
ates
a P
PP
sess
ion,
the
PP
PoE
ses
sion
is t
orn
dow
n as
wel
l. N
ew
PP
P se
ssio
n re
quire
s a
new
PP
PoE
ses
sion
sta
rting
from
the
Dis
cove
ry s
tage
. To
term
inat
e a
PP
P se
ssio
n, a
nor
mal
PP
P te
rmin
atio
n pr
oces
s is
follo
wed
. P
PP
oE a
llow
s an
exp
licit
Term
inat
e fra
me
to c
lose
a s
essi
on s
ent b
y ei
ther
the
initi
atin
g st
atio
n or
the
acce
ss c
once
ntra
tor.
Onc
e th
e Te
rmin
ate
fram
e is
sen
t or
rece
ived
, no
fu
rther
fra
me
trans
mis
sion
is
al
low
ed,
even
fo
r no
rmal
P
PP
25
term
inat
ion
fram
es.
PPPo
E: O
pen
Sour
ce Im
plem
enta
tion
2.
3 Et
hern
et (I
EEE
802.
3)
O
rigin
ally
pro
pose
d by
Bob
Met
calfe
in 1
973,
Eth
erne
t was
onc
e on
e of
the
com
petit
ors
of t
he L
AN
tec
hnol
ogy,
and
is n
ow t
he w
inne
r. O
ver
mor
e th
an 2
0 ye
ars,
Eth
erne
t ha
s be
en r
einv
ente
d m
any
times
to
acco
mm
odat
e up
-to-d
ate
need
s, re
sulti
ng in
the
1552
-pag
e IE
EE
802
.3 S
tand
ard.
Des
pite
this
, the
sto
ry is
st
ill ro
lling
into
the
futu
re. N
ew s
tand
ards
kee
p co
min
g up
as
time
goes
by.
In th
is
sect
ion,
we
invi
te y
ou t
o ap
prec
iate
the
pic
ture
and
phi
loso
phy
of E
ther
net.
We
also
brin
g th
e ho
t top
ics
in th
e cu
rrent
dev
elop
men
t. E
njoy
it!
2.3.
1 E
ther
net d
evel
opm
ent:
A bi
g pi
ctur
e A
s th
e tit
le o
f th
e st
anda
rd,
“Car
rier
Sen
se m
ultip
le a
cces
s w
ith c
ollis
ion
dete
ctio
n (C
SM
A/C
D)
acce
ss m
etho
d an
d ph
ysic
al la
yer
spec
ifica
tion”
sug
gest
s,
Eth
erne
t is
mos
t dis
tingu
ishe
d fro
m o
ther
LA
N te
chno
logi
es, s
uch
as T
oken
Bus
an
d To
ken
Rin
g, b
y its
med
ium
acc
ess
met
hod.
A la
b at
Xer
ox g
ave
birth
to th
e m
etho
d, w
hich
as
late
r st
anda
rdiz
ed b
y D
EC
, Int
el a
nd X
erox
in 1
981,
kno
wn
as
the
DIX
Eth
erne
t. A
lthou
gh t
his
stan
dard
bor
e lit
tle r
esem
blan
ce t
o th
e or
igin
al
desi
gn a
t X
erox
, th
e es
senc
e of
CS
MA
/CD
was
pre
serv
ed.
In 1
983,
the
IE
EE
80
2.3
Wor
king
Gro
up a
ppro
ved
a st
anda
rd b
ased
on
the
DIX
Eth
erne
t with
onl
y in
sign
ifica
nt
chan
ges.
Th
is
stan
dard
be
com
es
the
wel
l kn
own
IEE
E
802.
3 St
anda
rd.
Sin
ce X
erox
rel
inqu
ishe
d th
e tra
dem
ark
nam
e “E
ther
net”,
the
re is
no
dist
inct
ion
now
aday
s w
hen
we
refe
r to
the
Ethe
rnet
and
the
IEE
E 8
02.3
Sta
ndar
d.
In
fact
, th
e IE
EE
80
2.3
Wor
king
G
roup
ha
s be
en
lead
ing
the
Eth
erne
t de
velo
pmen
t as
of it
s fir
st v
ersi
on o
f the
sta
ndar
d. T
he m
ilest
ones
in th
e E
ther
net
stan
dard
s ar
e illu
stra
ted
in F
ig. 2
.8.
26
Fi
gure
2.8
M
ilest
ones
in th
e E
ther
net S
tand
ards
E
ther
net
has
expe
rienc
ed s
ever
al s
igni
fican
t re
visi
ons
durin
g th
e pa
st 2
0 ye
ars.
We
list t
he m
ajor
tren
ds b
elow
.
From
low
to h
igh
spee
d: S
tarti
ng fr
om a
pro
toty
pe ru
nnin
g at
3 M
b/s,
Eth
erne
t is
on it
s st
eps
to m
ove
tow
ard
10 G
b/s
in th
e ye
ar o
f 200
2 –
a bo
ost o
f mor
e th
an
3000
tim
es i
n sp
eed.
An
asto
nish
ing
deve
lopm
ent
as i
t is
, th
e te
chno
logy
stil
l ke
eps
chea
p, m
akin
g it
wid
ely
acce
pted
aro
und
the
wor
ld.
A gi
gabi
t E
ther
net
adap
ter
has
brok
en t
he c
ost
barri
er t
o be
les
s th
an $
100
in 2
001.
We
wou
ld
alm
ost b
e su
re th
at E
ther
net w
ill be
ubi
quito
us.
From
sha
red
to d
edic
ated
med
ia: T
he o
rigin
al E
ther
net r
uns
on a
bus
topo
logy
of
coa
xial
cab
les.
Mul
tiple
sta
tions
sha
re t
he b
us w
ith t
he C
SM
A/C
D M
AC
al
gorit
hm.
As
of t
he d
evel
opm
ent
of 1
0BA
SE-T
, de
dica
ted
med
ia b
etw
een
two
devi
ces
beco
mes
th
e m
ajor
. A
lthou
gh
not
suffi
cien
t, de
dica
ted
med
ia
are
nece
ssar
y to
the
lat
er d
evel
opm
ent
of f
ull-d
uple
x E
ther
net.
Full-
dupl
ex a
llow
s bo
th s
tatio
ns to
tran
smit
over
the
dedi
cate
d m
edia
sim
ulta
neou
sly,
whi
ch in
effe
ct
doub
les
the
band
wid
th!
Form
LA
N t
o M
AN
and
WA
N:
Eth
erne
t w
as w
ell k
now
n as
a L
AN
tec
hnol
ogy.
Tw
o fa
ctor
s he
lp th
e te
chno
logy
mov
e to
war
d th
e M
AN
and
WAN
mar
ket.
The
first
is
the
cos
t. E
ther
net
has
low
cos
t in
im
plem
enta
tion
beca
use
of i
ts s
impl
icity
. B
esid
es, i
t tak
es le
ss p
ains
and
mon
ey in
inte
rope
rabi
lity
if th
e M
AN a
nd W
AN a
re
also
Eth
erne
t. Th
e se
cond
com
es fr
om fu
ll du
plex
. Ful
l dup
lex
elim
inat
es th
e ne
ed
of C
SM
A/C
D, a
nd h
ence
lifts
the
dist
ance
rest
rictio
n du
e to
this
met
hod.
The
dat
a ca
n be
tran
smitt
ed a
s fa
r as
a ph
ysic
al li
nk c
an re
ach.
We
will
talk
mor
e ab
out f
ull
27
dupl
ex in
the
next
sub
sect
ions
. Th
e m
ediu
m is
get
ting
riche
r: Th
e te
rm “e
ther
” com
es fr
om p
hysi
cs, w
hich
was
on
ce t
houg
ht o
f as
the
med
ium
to
prop
agat
e el
ectro
mag
netic
wav
es t
hrou
gh
spac
e. A
lthou
gh E
ther
net
neve
r us
es e
ther
to
trans
mit
data
, it
does
car
ry
mes
sage
s on
to a
var
iety
of m
edia
: coa
xial
cab
les,
twis
ted
pairs
, and
opt
ical
fibe
rs.
“Eth
erne
t is
Mul
timed
ia!”
-- Th
e am
usin
g w
ords
by
Ric
h S
eife
rt in
his
boo
k G
igab
it E
ther
net b
est d
epic
t the
sce
nario
. We
list a
ll th
e 80
2.3
fam
ily m
embe
rs in
term
s of
sp
eed
and
med
ia in
Tab
le 2
.3.
med
ium
spee
d
Coa
xial
cab
le
Twis
ted
pairs
Fi
ber
1 M
b/s
1B
AS
E5
(198
7)
10 M
b/s
10B
AS
E5
(198
3)
10B
AS
E2
(198
5)
10BR
OAD
36 (1
985)
10BA
SE-
T (1
990)
10
BAS
E-FL
(199
3)
10BA
SE-
FP (1
993)
10
BAS
E-FB
(199
3)
100
Mb/
s
10
0BA
SE
-TX
(199
5)
100B
AS
E-T
4 (1
995)
10
0BA
SE
-T2
(199
7)
100B
ASE-
FX (1
995)
1 G
b/s
10
00B
AS
E-C
X (1
998)
10
00B
AS
E-T
(199
9)
1000
BA
SE
-SX
(199
8)
1000
BA
SE
-LX
(199
8)
10 G
b/s
10G
BAS
E-R
(200
2)
10G
BAS
E-W
(200
2)
10G
BAS
E-X
(200
2)
Tabl
e 2.
3 Th
e 80
2.3
fam
ily
Not
e th
at n
ot a
ll m
embe
rs a
re c
omm
erci
ally
suc
cess
ful.
For
exam
ple,
10
0BA
SE
-T2
has
neve
r be
en a
com
mer
cial
pro
duct
. In
con
trast
, so
me
are
so
succ
essf
ul t
hat
alm
ost
ever
ybod
y ca
n fin
d a
Net
wor
k In
terfa
ce C
ard
(NIC
) of
10
BA
SE
-T o
r 10
0BA
SE
-TX
beh
ind
a co
mpu
ter
on a
LA
N.
The
num
ber
in t
he
pare
nthe
ses
indi
cate
s th
e ye
ar th
e sp
ecifi
catio
n w
as o
r w
ill be
app
rove
d by
the
IEE
E.
The
Ethe
rnet
nom
encl
atur
e E
ther
net i
s ric
h in
its
phys
ical
spe
cific
atio
n, a
s w
e ha
ven
seen
in T
able
2.3
. Th
e no
tatio
n fo
llow
s th
e fo
rmat
{1/
10/1
00/1
000/
10G
}{B
AS
E/B
RO
AD}[-
]phy
. Th
e fir
st i
tem
is
the
spee
d. T
he s
econ
d ite
m d
epen
ds o
n w
heth
er t
he s
igna
ling
is
base
band
or
broa
dban
d. A
lmos
t al
l Eth
erne
t si
gnal
ing
is b
aseb
and,
exc
ept
the
very
unp
opul
ar 1
0BR
OA
D36
. Th
e th
ird i
tem
is
the
max
imum
len
gth
in u
nit
of
100m
in th
e be
ginn
ing.
No
dash
is b
etw
een
the
seco
nd a
nd th
e th
ird it
em. T
he
28
conv
entio
n ha
d la
ter b
een
chan
ged
to in
dica
te th
e ph
ysic
al s
peci
ficat
ions
, suc
h as
m
ediu
m ty
pe, s
igna
l enc
odin
g, e
tc. A
das
h is
loca
ted
betw
een
the
seco
nd a
nd th
e th
ird it
em.
2.
3.2
The
Eth
erne
t MA
C
Ethe
rnet
Fra
min
g, A
ddre
ssin
g, a
nd E
rror
con
trol
Th
e 80
2.3
MA
C s
ubla
yer
is t
he m
ediu
m-in
depe
nden
t pa
rt of
the
Eth
erne
t. A
long
with
the
Log
ic L
ink
Con
trol (
LLC
) su
blay
er s
peci
fied
in I
EE
E 8
02.2
, th
ey
com
pose
the
data
-link
laye
r in
the
OS
I lay
er m
odel
. The
func
tions
ass
ocia
ted
with
th
e M
AC
sub
laye
r in
clud
e da
ta e
ncap
sula
tion
and
med
ia a
cces
s co
ntro
l. Le
t us
take
a lo
ok a
t the
unt
agge
d4 Eth
erne
t fra
me
in F
ig. 2
.9 fi
rst.
Thro
ugh
the
fram
e fo
rmat
, w
e w
ill fir
st i
ntro
duce
fra
min
g, a
ddre
ssin
g an
d er
ror
cont
rol
and
leav
e is
sues
of m
ediu
m a
cces
s co
ntro
l and
flow
con
trol l
ater
.
Prea
mbl
e S
FDD
A SA
T/
LD
ata
FCS
Byt
es
7
1
6
6
2
46-1
500
4
SFD
: Sta
rt of
Fra
me
Del
imit
D
A: D
estin
atio
n A
ddre
ss
SA
: Sou
rce
Add
ress
T
/L: T
ype
leng
th
FCS
: Fra
me
Che
ck S
eque
nce
Figu
re 2
.9
Eth
erne
t fra
me
form
at
Prea
mbl
e: T
his
field
is
used
to
sync
hron
ize
the
phys
ical
sig
nal
timin
g on
the
re
ceiv
er s
ide.
Its
valu
e is
fixe
d at
101
0….1
0 in
tran
smis
sion
ord
er5 , t
otal
ly 5
6 bi
ts
long
. Not
e th
at th
is fi
eld
is n
ot u
sed
to m
ark
the
fram
e bo
unda
ry. T
he b
ound
ary
is
mar
ked
by s
peci
al p
hysi
cal
enco
ding
, or
the
pre
senc
e (a
bsen
ce)
of s
igna
l, de
pend
ing
on th
e P
HY.
For
exa
mpl
e, 1
00B
AS
E-X
Eth
erne
t con
verts
the
first
byt
e of
the
Pre
ambl
e, /
1010
/101
0/,
into
tw
o sp
ecia
l co
de g
roup
s /J
/K/
of t
he v
alue
/1
1000
/100
01/
usin
g 4B
/5B
enc
odin
g. T
he 4
B/5
B e
ncod
ing
conv
erts
101
0 (in
tra
nsm
issi
on o
rder
) to
010
11 f
or n
orm
al d
ata.
No
bit-
or b
yte-
stuf
fing
is n
eede
d be
caus
e th
ere
is n
o am
bigu
ity. S
imila
rly, 1
00B
AS
E-X
app
ends
two
spec
ial c
ode
grou
ps /T
/R/ o
f the
val
ue /0
1101
/100
01/ a
fter a
fram
e to
mar
k th
e en
d.
SFD
: Th
is f
ield
ind
icat
es t
he s
tart
of t
he f
ram
e w
ith t
he v
alue
101
0101
1 in
tra
nsm
issi
on o
rder
. H
isto
rical
ly, t
he D
IX E
ther
net
Stan
dard
spe
cifie
d an
8-b
yte
prea
mbl
e w
ith e
xact
ly t
he s
ame
valu
e as
the
firs
t tw
o fie
lds
in a
n 80
2.3
fram
e.
They
are
onl
y di
ffere
nt in
nom
encl
atur
e.
4 A
n Et
hern
et fr
ame
can
carr
y a
VLA
N ta
g. W
e w
ill se
e th
at fr
ame
form
at w
hen
we
cove
r VLA
N in
Se
ctio
n 2.
3.4.
5 E
ther
net t
rans
mis
sion
is in
Litt
le-E
ndia
n bi
t ord
erin
g. W
e w
ill ta
lk a
bout
tran
smis
sion
ord
erin
g in
Sec
tion
2.6.
29
DA
: Thi
s fie
ld is
the
48-b
it de
stin
atio
n M
AC a
ddre
ss in
the
form
at w
e in
trodu
ced
in
Sec
tion
2.1.
2.
SA: T
his
field
is th
e 48
-bit
sour
ce M
AC a
ddre
ss.
Type
/Len
gth:
Thi
s fie
ld h
as t
wo
mea
ning
s fo
r hi
stor
ical
rea
sons
. Th
e D
IX
Stan
dard
spe
cifie
d th
e fie
ld to
be
a co
de o
f pro
toco
l typ
e, s
ay IP
, whi
le th
e IE
EE
80
2.3
Stan
dard
spe
cifie
d th
e fie
ld to
be
the
leng
th o
f the
dat
a fie
ld6 a
nd le
ft th
e pr
otoc
ol ty
pe to
be
proc
esse
d by
the
LLC
sub
laye
r. Th
e 80
2.3
Stan
dard
late
r (in
19
97)
appr
oved
the
type
fiel
d, r
esul
ting
in th
e du
al r
oles
of t
his
field
toda
y. T
he
way
to
dist
ingu
ish
is s
impl
e. B
ecau
se t
he d
ata
field
is
neve
r la
rger
tha
n 15
00
byte
s, a
val
ue le
ss th
an o
r equ
al to
1500
mea
ns a
leng
th fi
eld.
A v
alue
larg
er th
an
or e
qual
to
1536
(=0
x600
) m
eans
a t
ype
field
. Th
e va
lues
in
betw
een
are
inte
ntio
nally
not
def
ined
. In
fac
t, m
ost
fram
es u
ses
the
type
fie
ld b
ecau
se t
he
dom
inat
ing
netw
ork
laye
r pro
toco
l, IP
, use
s th
e ty
pe fi
eld.
D
ata:
Thi
s fie
ld c
arrie
s th
e da
ta, a
s th
e na
me
says
it. I
t var
ies
from
46
to 1
500
byte
s.
FCS:
Thi
s fie
ld c
arrie
s a
32-b
it C
RC
cod
e as
a f
ram
e ch
eck
sequ
ence
. If
the
rece
iver
fin
ds a
n in
corr
ect
fram
e, it
sile
ntly
dis
card
s th
e fra
me.
The
tra
nsm
itter
kn
ows
noth
ing
abou
t w
heth
er t
he f
ram
e is
dis
card
ed.
The
resp
onsi
bilit
y of
a
retra
nsm
issi
on i
s le
ft to
upp
er-la
yer
prot
ocol
s, s
uch
as T
CP.
Thi
s ap
proa
ch i
s qu
ite e
ffici
ent b
ecau
se th
e tra
nsm
itter
doe
s no
t nee
d to
wai
t an
ackn
owle
dgem
ent
for t
he n
ext t
rans
mis
sion
. The
err
or is
not
a b
ig p
robl
em b
ecau
se th
e bi
t erro
r rat
e is
ass
umed
to b
e ve
ry lo
w in
the
Eth
erne
t phy
sica
l lay
er.
The
fram
e si
ze is
var
iabl
e. W
e of
ten
excl
ude
the
first
tw
o fie
lds
and
say
a m
inim
um E
ther
net f
ram
e ha
s 64
(=6+
6+2+
46+4
) by
tes
and
a m
axim
um E
ther
net
fram
e ha
s 15
18 (
=6+6
+2+1
500+
4) b
ytes
. Peo
ple
may
thin
k th
e m
axim
um le
ngth
is
not
long
eno
ugh
so th
at th
e he
ader
ove
rhea
d is
larg
er, c
ompa
red
with
Tok
en
Rin
g or
FD
DI.
We
will
anal
yze
the
Eth
erne
t effi
cien
cy in
Sec
tion
2.6.
M
ediu
m A
cces
s C
ontr
ol: T
rans
mis
sion
and
Rec
eptio
n Fl
ow
We
now
com
e to
the
show
of h
ow a
fram
e is
tran
smitt
ed a
nd re
ceiv
ed. H
ere
you
will
see
how
the
CS
MA
/CD
mec
hani
sm w
orks
in g
reat
det
ail.
Fig.
2.1
0 sh
ows
wha
t rol
e th
e M
AC
sub
laye
r pla
ys d
urin
g th
e fra
me
trans
mis
sion
and
rece
ptio
n.
6 T
here
is a
wid
e m
isco
ncep
tion
that
the
Leng
th fi
eld
indi
cate
s th
e fr
ame
size
. Thi
s is
not
true
. The
fram
e en
d is
mar
ked
by s
peci
al p
hysi
cal e
ncod
ing
or th
e ab
senc
e of
sig
nal,
depe
ndin
g on
the
PHY.
The
Eth
erne
t M
AC
can
eas
ily c
ount
how
man
y by
tes i
t has
rece
ived
in a
fram
e.
MA
C c
lient
(IP,
LLC
, …)
da
ta e
ncap
sula
tion
da
ta d
ecap
sula
tion
tra
nsm
it m
ediu
m m
anag
emen
t r
ecei
ve m
ediu
m m
anag
emen
t
30
Fi
gure
2.1
0 Fr
ame
trans
mis
sion
and
rece
ptio
n
The
trans
mis
sion
flow
is p
rese
nted
in F
ig. 2
.11.
We
list t
he p
roce
dure
bel
ow:
1. T
he M
AC
clie
nt (I
P, L
LC, …
) ask
s fo
r a fr
ame
trans
mis
sion
. 2.
The
MA
C s
ubla
yer p
repe
nds
and
appe
nds
MA
C in
form
atio
n (P
ream
ble,
SFD
, D
A, S
A, t
ype,
FC
S...
) to
the
data
pro
vide
d by
the
MA
C c
lient
. 3.
In
half-
dupl
ex m
ode,
i.e
., w
ith t
he C
SM
A/C
D m
etho
d, c
arrie
r is
sen
sed
to
dete
rmin
e if
the
trans
mis
sion
cha
nnel
is
busy
. If
yes,
the
tra
nsm
issi
on i
s de
ferre
d un
til th
e ch
anne
l is
clea
r. 4.
Wai
t for
a p
erio
d of
tim
e ca
lled
inte
r-fra
me
gap
(IFG
). Th
e tim
e le
ngth
is 9
6 bi
t tim
es f
or a
ll fla
vors
of
Eth
erne
t. Th
e bi
t tim
e is
the
dur
atio
n of
one
bit
trans
mis
sion
and
thus
the
reci
proc
al o
f the
bit
rate
. Thi
s un
it is
so
conv
enie
nt
that
we
do n
ot n
eed
to s
ay “
In th
e 10
Mb/
s sy
stem
s, th
e IF
G is
9.6
µs;
in th
e 10
0 M
b/s
syst
ems,
the
IFG
is
0.96
µs;
……
”. Th
e IF
G a
llow
s tim
e fo
r th
e re
ceiv
er to
do
poss
ible
pro
cess
ing,
suc
h as
inte
rrup
ts a
nd p
oint
er a
djus
tmen
t, fo
r the
inco
min
g fra
me.
5.
Sta
rt to
tran
smit
the
fram
e.
6. I
n ha
lf-du
plex
mod
e, t
he t
rans
mitt
er s
houl
d ke
ep m
onito
ring
if th
ere
is a
co
llisi
on d
urin
g tra
nsm
issi
on.
The
way
to
dete
ct c
ollis
ions
dep
ends
on
the
atta
ched
med
ium
. M
ultip
le t
rans
mis
sion
s on
a c
oaxi
al c
able
res
ult
in h
ighe
r ab
solu
te v
olta
ge le
vels
than
nor
mal
. For
twis
ted
pairs
, a c
ollis
ion
is a
sser
ted
by p
erce
ivin
g re
ceiv
ed s
igna
l on
the
rece
ive
pair
whi
le tr
ansm
ittin
g.
7. I
f the
re is
no
collis
ion
durin
g tra
nsm
issi
on, t
he fr
ame
is tr
ansm
itted
unt
il do
ne.
tra
nsm
it da
ta e
ncod
ing
rec
eive
dat
a de
codi
ng
lin
e si
gnal
MA
C su
blay
er
Phys
ical
laye
r
31
Fi
gure
2.1
1 Fr
ame
trans
mis
sion
flow
If
ther
e is
a c
ollis
ion
dete
cted
in h
alf d
uple
x m
ode,
the
follo
win
g st
eps
go o
n:
8. T
he t
rans
mitt
er t
rans
mits
a 3
2 bi
ts lo
ng ja
m s
igna
l to
ensu
re t
he c
ollis
ion
is
long
eno
ugh
that
all
invo
lved
sta
tions
are
aw
are
of it
. The
pat
tern
of t
he ja
m
sign
al is
uns
peci
fied.
Com
mon
impl
emen
tatio
ns a
re k
eepi
ng t
rans
mitt
ing
32
mor
e bi
ts o
f dat
a or
tran
smitt
ing
alte
rnat
ing
1’s
and
0’s
by le
vera
ging
the
circ
uit
the
gene
rate
s th
e pr
eam
ble.
9.
Abo
rt th
e cu
rrent
tran
smis
sion
and
atte
mpt
to s
ched
ule
anot
her t
rans
mis
sion
! 10
. Th
e m
axim
um n
umbe
r of
atte
mpt
s to
ret
rans
mit
is 1
6. I
f st
ill no
t ab
le t
o tra
nsm
it, a
bort
the
fram
e.
11.
On
an a
ttem
pt t
o re
trans
mit,
a b
ack-
off
time
is c
hose
n ra
ndom
ly f
rom
the
ra
nge
of 0
to 2
k -1, w
here
k =
min
(n, 1
0) a
nd n
is th
e nu
mbe
r of a
ttem
pts.
Not
e th
at th
e ra
nge
grow
s ex
pone
ntia
lly, s
o th
e al
gorit
hm is
refe
rred
to a
s tru
ncat
ed
bina
ry e
xpon
entia
l bac
k-of
f. Th
e du
ratio
n of
the
slot
tim
e is
512
bit
times
for
10/1
00 M
b/s
Eth
erne
t an
d 40
96 b
it tim
es f
or 1
Gb/
s E
ther
net.
We
will
tal
k ab
out t
he re
ason
whe
n w
e di
scus
s G
igab
it E
ther
net i
n S
ectio
n 2.
3.3.
12
. W
ait f
or th
e ba
ck-o
ff tim
e an
d at
tem
pt to
retra
nsm
it
Tran
smit
star
t
Ass
embl
e fra
me
Hal
f dup
lex
and
Car
rier s
ense
d?
yes no
Wai
t int
erfra
me
gap
Star
t tra
nsm
issi
on
Hal
f dup
lex
and
Col
lisio
n de
tect
ed?
Tran
smis
sion
don
e?
Tran
smis
sion
OK
.
yes
no
Send
jam
Incr
emen
t atte
mpt
s
Too
man
y at
tem
pts?
ye
s
Abo
rt tra
nsm
issi
on
Com
pute
bac
koff
Wai
t bac
koff
time
2. 3.
4.
5. 6. 7.
8. 9. 10.
11.
12.
no
yes
no
1.
32
The
rece
ptio
n flo
w is
illu
stra
ted
in F
ig. 2
.12.
We
list t
he p
roce
dure
bel
ow:
Fi
gure
2.1
2 Fr
ame
rece
ptio
n flo
w
1.
The
arri
val o
f a fr
ame
is d
etec
ted
by th
e ph
ysic
al la
yer o
f the
rece
iver
.
2. T
he r
ecei
ver
deco
des
the
rece
ived
sig
nal,
pass
ing
the
data
exc
ept
the
prea
mbl
e an
d S
FD, u
p to
the
MAC
sub
laye
r. 3.
The
rece
ivin
g pr
oces
s go
es o
n as
long
as
the
rece
ived
sig
nal i
s co
min
g. W
hen
the
sign
al c
ease
s, th
e in
com
ing
fram
e is
trun
cate
d to
an
octe
t bou
ndar
y.
4. I
f the
fram
e si
ze is
too
smal
l (le
ss th
an 5
12 b
its),
it is
thou
ght o
f as
a co
llisio
n fra
gmen
t and
dro
pped
.
Don
e w
ith e
rror
s
Prop
er o
ctet
bou
ndar
y?
yes
no
Fram
e de
caps
ulat
ion
Rec
eptio
n O
K
8.
9.
Rec
eive
star
t
Star
t rec
eivi
ng
Rec
eivi
ng d
one?
no
yes
Fram
e to
o sm
all?
(c
ollis
ion
fragm
ent)
yes
no
Add
ress
reco
gniz
ed?
no
Fram
e to
o lo
ng?
yes
yes
Valid
FC
S?
no
no
1.
2. 3. 4. 5. 6.
7.
33
5. I
f the
des
tinat
ion
addr
ess
is n
ot fo
r the
rece
iver
, the
fram
e is
dro
pped
. 6.
If t
he fr
ame
is to
o lo
ng, i
t is
drop
ped
and
the
erro
r is
reco
rded
for m
anag
emen
t st
atis
tics.
7.
If t
he fr
ame
has
an in
corre
ct F
CS
, it i
s dr
oppe
d an
d th
e er
ror i
s re
cord
ed.
8. I
f the
fram
e si
ze d
oes
not m
eet a
n in
tege
r num
ber o
f oct
ets,
it is
dro
pped
and
th
e er
ror i
s re
cord
ed.
9. I
f eve
ryth
ing
is O
K, t
he fr
ame
is d
ecap
sula
ted
and
the
field
s ar
e pa
ssed
up
to
the
MA
C c
lient
. C
SMA
/CD
: Ope
n So
urce
Impl
emen
tatio
n C
an c
ollis
ion
caus
e ba
d pe
rfor
man
ce?7
Th
e te
rm c
ollis
ion
soun
ds t
errib
le!
How
ever
, co
llisio
n is
par
t of
the
nor
mal
ar
bitra
tion
mec
hani
sm o
f CS
MA
/CD
. It d
oes
not c
ome
from
a s
yste
m m
alfu
nctio
n.
Fran
kly,
col
lisio
n ca
n ca
use
a ga
rble
d fra
me,
but
it
is n
ot a
s ba
d be
caus
e of
co
llisi
on d
etec
tion.
A tr
ansm
issi
on c
an s
top
if a
collis
ion
is d
etec
ted.
Bef
ore
furth
er
anal
ysis
of
was
ted
bit
times
bec
ause
of
a co
llisio
n, w
e fir
st a
nsw
er a
crit
ical
qu
estio
n: w
here
a c
ollis
ion
can
occu
r.
We
mod
el th
e fra
me
trans
mis
sion
in F
ig. 2
.13.
Fi
gure
2.1
3 C
ollis
ion
dete
ctio
n w
ith p
ropa
gatio
n de
lay
S
uppo
se s
tatio
n A
trans
mits
a m
inim
um f
ram
e of
64
byte
s, a
nd t
he
prop
agat
ion
befo
re th
e fra
me
arriv
es a
t sta
tion
B is
t. W
ith c
arrie
r sen
se, s
tatio
n B
is
like
ly t
o tra
nsm
it be
fore
t.
Furth
er s
uppo
se s
tatio
n B
tra
nsm
its ju
st a
t tim
e t,
whi
ch r
esul
ts in
a c
ollis
ion.
The
col
lisio
n ta
kes
anot
her
time
t to
be
prop
agat
ed
back
to s
tatio
n A
. If s
tatio
n A
finis
hes
trans
mitt
ing
the
min
imum
fram
e be
fore
the
roun
d-tri
p tim
e 2t
, it h
as n
o w
ay to
sch
edul
e a
retra
nsm
issi
on, a
nd th
e fra
me
is
7 I
t was
a q
uest
ion
once
ask
ed o
n th
e ne
wsg
roup
com
p.dc
om.la
ns.e
ther
net.
I lik
e th
e hi
lario
us a
nsw
er fr
om
Ric
h Se
ifert,
“Ye
s. M
y ol
d To
yota
nev
er q
uite
per
form
ed th
e sa
me
afte
r I h
it th
at tr
ee.”
34
lost
. For
CS
MA
/CD
to fu
nctio
n no
rmal
ly, th
e ro
und-
trip
time
shou
ld b
e le
ss th
an
the
time
to tr
ansm
it a
min
imum
fram
e. It
mea
ns th
e C
SM
A/C
D m
echa
nism
lim
its
the
exte
nt b
etw
een
two
stat
ions
in
a co
llisio
n do
mai
n. T
his
limita
tion
caus
es
diffi
culty
in h
alf-d
uple
x G
igab
it E
ther
net d
esig
n. W
e w
ill ta
lk m
ore
abou
t thi
s is
sue
whe
n w
e in
trodu
ce G
igab
it E
ther
net.
Bec
ause
the
min
imum
siz
e is
64
byte
s, it
al
so m
eans
a c
ollis
ion
mus
t occ
ur d
urin
g th
e fir
st 6
4 by
tes
for f
ram
es o
f any
siz
e un
der
the
dist
ance
lim
itatio
n. I
f m
ore
than
64
byte
s ha
ve b
een
trans
mitt
ed,
the
collis
ion
is n
ot p
ossi
ble
to o
ccur
und
er n
orm
al o
pera
tion
beca
use
of c
arrie
r sen
se
by o
ther
sta
tions
.
If w
e al
so ta
ke th
e 32
-bit
jam
into
con
side
ratio
n, th
e ac
tual
num
ber o
f bits
in a
fra
me
that
hav
e be
en tr
ansm
itted
plu
s th
e ja
m c
anno
t be
mor
e th
an 5
11 b
its. W
hy?
If m
ore
than
512
bits
, the
rece
iver
will
thin
k of
thes
e bi
ts a
s a
fram
e, ra
ther
than
a
collis
ion
fragm
ent
(See
Ste
p 4
in t
he r
ecep
tion
flow
). Th
eref
ore,
the
max
imum
nu
mbe
r of w
aste
d bi
t tim
es is
511
+ 6
4 (fr
om th
e pr
eam
ble)
+ 9
6 (fr
om th
e IF
G) =
67
1. T
his
is o
nly
a sm
all p
ortio
n fo
r a la
rge
fram
e. In
add
ition
, we
mus
t em
phas
ize
it is
the
wor
st c
ase.
For
mos
t col
lisio
ns, t
hey
occu
r dur
ing
the
prea
mbl
e be
caus
e th
e di
stan
ce b
etw
een
two
trans
mitt
ing
stat
ions
is
not
that
far
. In
thi
s ca
se,
the
num
ber
of w
aste
d bi
t tim
es is
onl
y 64
(fro
m th
e pr
eam
ble)
+ 3
2 (fr
om th
e ja
m)
+ 96
(fro
m t
he I
FG)
= 19
2. W
e w
ill di
scus
s m
ore
on t
he p
erfo
rman
ce i
ssue
on
Sec
tion
2.6.
M
axim
um F
ram
e R
ate
How
man
y fra
mes
can
a t
rans
mitt
er (
rece
iver
) tra
nsm
its (
rece
ives
) in
a
seco
nd?
That
’s a
n in
tere
stin
g qu
estio
n, e
spec
ially
whe
n yo
u de
sign
or a
naly
ze a
pa
cket
pro
cess
ing
devi
ce, s
ay a
sw
itch.
You
are
inte
rest
ed in
kno
win
g ho
w m
any
fram
es a
sec
ond
your
dev
ice
may
nee
d to
pro
cess
. Fr
ame
trans
mis
sion
beg
ins
with
a 7
-byt
e P
ream
ble
and
a 1-
byte
SFD
, as
we
have
see
n in
the
trans
mis
sion
flow
. Int
uitiv
ely,
to r
each
the
max
imum
num
ber
of
fram
es p
er s
econ
d, a
ll fra
mes
sho
uld
be o
f min
imum
siz
e, i.
e. 6
4 by
tes.
Do
not
forg
et th
at th
ere
is a
n IF
G o
f 12
byte
s (=
96
bits
) be
twee
n tw
o su
cces
sive
fram
e tra
nsm
issi
ons.
Tot
ally,
a f
ram
e tra
nsm
issi
on o
ccup
ies
(7+1
+64+
12)*
8 =
672
bit
times
. In
a 1
0 M
b/s
syst
em,
the
max
imum
num
ber
of f
ram
es p
er s
econ
d is
th
eref
ore
10 *
106 /
672
= 14
880.
Thi
s va
lue
is re
ferre
d to
as
max
imum
fram
e ra
te.
Fu
ll-du
plex
MA
C
Ear
ly E
ther
net u
ses
coax
ial c
able
s as
the
trans
mis
sion
med
ia. M
ost o
f the
m
are
late
r rep
lace
d by
twis
ted
pairs
bec
ause
of e
asie
r man
agem
ent.
A tw
iste
d pa
ir ca
ble
conn
ects
a s
tatio
n an
d a
conc
entra
tion
devi
ce, s
uch
as a
hub
or s
witc
h. T
his
35
topo
logy
bec
omes
a v
ery
popu
lar o
ne. F
or p
opul
ar 1
0BA
SE
-T a
nd 1
00B
AS
E-T
X,
a w
ire p
air i
n a
twis
ted
pair
cabl
e is
ded
icat
ed to
eith
er tr
ansm
ittin
g or
rece
ivin
g8 . A
collis
ion
is t
hus
defin
ed b
y pe
rcei
ving
rec
eive
d si
gnal
on
the
rece
ive
pair
whi
le
trans
mitt
ing.
How
ever
, thi
s is
inef
ficie
nt e
noug
h. S
ince
the
med
ium
is d
edic
ated
, w
hy d
oes
it ne
ed “a
rbitr
atio
n” to
be
used
? In
199
7, th
e IE
EE
802
.3x
Task
For
ce a
dded
full-
dupl
ex o
pera
tion
in E
ther
net.
That
is, t
rans
mis
sion
and
rece
ptio
n ca
n pr
ocee
d at
the
sam
e tim
e. N
ote
that
in fu
ll du
plex
mod
e, th
ere
is n
o ca
rrier
sen
se o
r col
lisio
n de
tect
ion
beca
use
they
are
not
ne
eded
. The
re is
no
“mul
tiple
acc
ess”
on
a de
dica
ted
med
ium
. The
refo
re, C
S, M
A,
and
CD
, al
l di
sapp
ear!
This
is
a qu
ite s
igni
fican
t ch
ange
to
Eth
erne
t be
caus
e E
ther
net w
as m
ost k
now
n fo
r its
CS
MA
/CD
. We
sum
mar
ize
thre
e co
nditi
ons
that
sh
ould
be
satis
fied
to ru
n fu
ll-du
plex
Eth
erne
t: 1.
Th
e tra
nsm
issi
on m
ediu
m m
ust b
e ca
pabl
e fo
r tra
nsm
ittin
g an
d re
ceiv
ing
on
both
end
s w
ithou
t int
erfe
renc
e.
2.
The
trans
mis
sion
med
ium
sho
uld
be d
edic
ated
for
exa
ctly
tw
o st
atio
ns,
form
ing
a po
int-t
o-po
int l
ink.
3.
B
oth
stat
ions
sho
uld
be a
ble
to a
nd b
e co
nfig
ured
in fu
ll-du
plex
mod
e.
Not
e th
at t
he I
EE
E 8
02.3
Sta
ndar
d ex
plic
itly
rule
s ou
t th
e po
ssib
ility
of
runn
ing
full-
dupl
ex m
ode
on a
repe
ater
hub
. The
ban
dwid
th in
the
hub
is s
hare
d,
not
dedi
cate
d.
Thre
e ty
pica
l sc
enar
ios
of
full-
dupl
ex
trans
mis
sion
ar
e th
e st
atio
n-to
-sta
tion
link,
the
stat
ion-
to-s
witc
h lin
k, a
nd th
e sw
itch-
to-s
witc
h lin
k.
Full-
dupl
ex E
ther
net i
s an
impa
ct. I
t in
effe
ct d
oubl
es th
e ba
ndw
idth
bet
wee
n tw
o st
atio
ns. I
t als
o lif
ts th
e di
stan
ce li
mita
tion
beca
use
of C
SM
A/C
D. T
his
is v
ery
impo
rtant
fo
r hi
gh-s
peed
E
ther
net,
as
we
will
disc
uss
it in
S
ectio
n 2.
3.3.
N
owad
ays,
virt
ually
all
Eth
erne
t int
erfa
ces
supp
ort f
ull d
uple
x. B
oth
inte
rface
s ca
n pe
rform
aut
o-ne
gotia
tion
to d
eter
min
e w
heth
er f
ull d
uple
x is
sup
porte
d by
bot
h pa
rties
. If y
es, b
oth
will
oper
ate
in fu
ll du
plex
bec
ause
of h
ighe
r effi
cien
cy.
Ethe
rnet
flow
con
trol
Fl
ow c
ontro
l in
the
Eth
erne
t de
pend
s on
the
dup
lex
mod
e. I
n ha
lf-du
plex
m
ode,
if
the
rece
iver
can
not
affo
rd m
ore
inco
min
g fra
mes
, it
coul
d tra
nsm
its
carri
er, s
ay a
ser
ies
of 1
010…
.10,
on
the
shar
ed m
ediu
m u
ntil
it ca
n af
ford
mor
e fra
mes
. Th
e ca
rrie
r w
ill be
se
nsed
by
th
e tra
nsm
itter
, m
akin
g it
defe
r its
su
bseq
uent
tran
smis
sion
. Thi
s te
chni
que
is c
alle
d fa
lse
carr
ier.
The
rece
iver
als
o ca
n fo
rce
a co
llisio
n w
hene
ver a
ny fr
ame
trans
mis
sion
is d
etec
ted.
Thi
s fo
rces
the
trans
mitt
er to
bac
k of
f and
resc
hedu
le it
s tra
nsm
issi
on. T
his
tech
niqu
e is
refe
rred
8 In
100
0BA
SE-T
, tra
nsm
issi
on a
nd r
ecep
tion
can
happ
en s
imul
tane
ousl
y in
a p
air.
Arb
itrat
ion
is s
till n
ot
nece
ssar
y at
the
cost
of s
ophi
stic
ated
DSP
circ
uits
to se
para
te th
e tw
o si
gnal
s.
36
to a
s fo
rce
colli
sion
. The
se tw
o te
chni
ques
are
col
lect
ivel
y ca
lled
back
pre
ssur
e.
How
ever
, ba
ck p
ress
ure
is v
oid
in f
ull d
uple
x m
ode
beca
use
CSM
A/C
D is
ig
nore
d. I
EEE
802.
3 sp
ecifi
es a
PAU
SE
fram
e to
do
flow
con
trol i
n fu
ll du
plex
m
ode.
The
rec
eive
r ex
plic
itly
send
s a
PAU
SE
fra
me
to a
sk f
or a
sto
p. U
pon
rece
ivin
g th
e PA
USE
fra
me,
the
tra
nsm
itter
sto
ps t
rans
mitt
ing
imm
edia
tely.
The
PA
US
E f
ram
e ca
n ca
rry a
fie
ld,
paus
e_tim
e, t
o te
ll th
e tra
nsm
itter
how
lon
g it
shou
ld s
top.
Stil
l, m
ore
ofte
n th
an n
ot, p
ause
_tim
e is
set
to b
e th
e m
axim
um a
nd
anot
her P
AU
SE
fram
e w
ith p
ause
_tim
e =
0 is
sen
t to
the
trans
mitt
er to
tell
it th
at it
ca
n co
ntin
ue w
hen
the
rece
iver
can
acc
ept m
ore
fram
es.
Flow
con
trol
is o
ptio
nal
in t
he E
ther
net.
It ca
n be
ena
bled
by
the
user
or
thro
ugh
auto
-neg
otia
tion.
IE
EE
802
.3 S
tand
ard
prov
ides
an
optio
nal
subl
ayer
be
twee
n M
AC
and
LLC
, na
mel
y M
AC
Con
trol
subl
ayer
. M
AC
Con
trol s
ubla
yer
defin
es M
AC
Con
trol f
ram
es to
pro
vide
rea
l-tim
e m
anip
ulat
ion
of M
AC
sub
laye
r op
erat
ion.
The
PAU
SE
fram
e is
a k
ind
of M
AC
Con
trol f
ram
e. In
fact
, it i
s th
e on
ly
one
kind
def
ined
to d
ate.
Fl
ow C
ontr
ol: O
pen
Sour
ce Im
plem
enta
tion
2.3.
3 N
ew b
lood
in th
e E
ther
net
In
nova
tions
alw
ays
com
e in
the
cyb
ersp
ace.
Eth
erne
t is
no
exce
ptio
n. I
n re
cent
yea
rs,
Eth
erne
t ha
s bo
oste
d its
elf
into
the
line
of
giga
bit
netw
orki
ng.
As
soon
as
the
stan
dard
cam
e ou
t in
1998
and
199
9, a
new
stu
dy g
roup
sta
rted
to
stud
y th
e 10
Gig
abit
tech
nolo
gy, w
hich
turn
ed in
to th
e IE
EE
802
.3ae
Tas
k Fo
rce.
A
t the
tim
e of
writ
ing,
the
10 G
igab
it E
ther
net i
s in
the
Dra
ft st
age
so fa
r an
d is
ex
pect
ed to
be
appr
oved
as
the
Stan
dard
in 2
002.
Ano
ther
new
Tas
k Fo
rce,
the
IEEE
802
.3ah
9 , w
as o
rgan
ized
in
July
200
1. I
t ha
s st
arte
d to
stip
ulat
e a
new
st
anda
rd,
Eth
erne
t Fi
rst
Mile
, in
the
ir fir
st m
eetin
g in
Oct
ober
, 20
01.
This
new
st
anda
rd e
ven
push
es t
he E
ther
net
into
the
sub
scrib
er l
ine
mar
ket.
In t
his
subs
ectio
n, w
e w
ill ta
ke y
ou in
to th
e fu
ture
wor
ld o
f Eth
erne
t. G
igab
it Et
hern
et
The
IEE
E 8
02.3
div
ided
the
stip
ulat
ion
of G
igab
it E
ther
net
into
tw
o Ta
sk
Forc
es, 8
02.3
z an
d 80
3.3a
b. T
heir
phys
ical
spe
cific
atio
ns a
re li
sted
in T
able
2.4
. Ta
sk F
orce
s Sp
ecifi
catio
n na
me
Des
crip
tion
1000
BASE
-CX
25 m
2-p
air S
hiel
ded
Twis
ted
Pai
rs (S
TP) w
ith 8
B/1
0B e
ncod
ing
IEE
E 8
02.3
z (1
998)
1000
BA
SE
-SX
Mul
ti-m
ode
fiber
of s
hort-
wav
e la
ser w
ith 8
B/1
0B e
ncod
ing
9 T
he IE
EE 8
02.3
nam
es it
s new
Tas
k Fo
rce
in a
n al
phab
etic
al o
rder
. Afte
r IEE
E 80
2.3z
, the
subs
eque
nt
new
Tas
k Fo
rces
are
nam
ed 8
02.3
aa, 8
02.3
ab, a
nd so
on.
37
10
00BA
SE-L
X M
ulti-
or s
ingl
e-m
ode
fiber
of l
ong-
wav
e la
ser w
ith 8
B/1
0B
enco
ding
IEE
E 8
02.3
ab (1
999)
10
00BA
SE-T
10
0 m
4-p
air C
ateg
ory
5 ( o
r bet
ter)
Uns
hiel
ded
Twis
ted
Pai
rs
(UTP
) with
8B
1Q4.
Tabl
e 2.
4 P
hysi
cal s
peci
ficat
ions
of G
igab
it E
ther
net
A
diffi
culty
in G
igab
it E
ther
net
desi
gn is
the
dis
tanc
e re
stric
tion
indu
ced
by
CS
MA
/CD
, as
intro
duce
d in
Sec
tion
2.3.
2. F
or 1
0 M
b/s
and
100
Mb/
s E
ther
net,
this
wou
ld n
ot b
e a
prob
lem
. The
lim
itatio
n is
abo
ut 2
00 m
for c
oppe
r con
nect
ion
in 1
00 M
b/s
Eth
erne
t, w
hich
is e
noug
h fo
r m
ost c
onfig
urat
ions
. The
lim
itatio
n is
ev
en h
ighe
r for
10
Mb/
s E
ther
net.
How
ever
, Gig
abit
Eth
erne
t is
ten
times
fast
er to
tra
nsm
it a
fram
e th
an 1
00 M
b/s
Eth
erne
t, m
akin
g th
e di
stan
ce re
stric
tion
ten
times
sh
orte
r. A
rest
rictio
n of
ab
out
20
m
is
unac
cept
able
fo
r m
any
netw
ork
depl
oym
ents
. Th
e IE
EE
802
.3 S
tand
ard
appe
nds
a se
ries
of e
xten
sion
bits
afte
r a
fram
e.
The
exte
nsio
n bi
ts c
an b
e an
y no
n-da
ta s
ymbo
ls i
n th
e ph
ysic
al l
ayer
. Th
is
tech
niqu
e, c
alle
d ca
rrie
r ext
ensi
on, i
n ef
fect
ext
ends
the
leng
th o
f a fr
ame
with
out
chan
ging
the
min
imum
fram
e si
ze. T
heir
leng
th, a
s sp
ecifi
ed in
the
Stan
dard
, is
4096
bits
– fr
ame
size
. The
ext
ensi
on b
its a
re fo
r CS
MA
/CD
pur
pose
onl
y, a
nd w
ill be
dis
card
ed s
ilent
ly b
y th
e re
ceiv
er.
Alth
ough
car
rier
exte
nsio
n ad
dres
ses
the
prob
lem
, the
dat
a th
roug
hput
can
be
low
bec
ause
the
trans
mis
sion
cha
nnel
is m
ostly
occ
upie
d by
the
exte
nsio
n bi
ts
if th
e fra
mes
are
sho
rt. T
he s
olut
ion
is to
allo
w th
e tra
nsm
itter
to tr
ansm
it th
e ne
xt
fram
e, if
any
, w
ithou
t ex
tens
ion
bits
, by
fill
ing
the
IFG
with
car
rier.
Bec
ause
the
IF
G b
etw
een
two
succ
essi
ve f
ram
es i
s oc
cupi
ed w
ith c
arrie
r, th
e tra
nsm
issi
on
chan
nel i
s no
t rel
inqu
ishe
d by
the
trans
mitt
er. T
he tr
ansm
itter
can
tran
smit
one
or
mor
e fra
mes
follo
win
g th
e fir
st fr
ame,
as
long
as
it ha
s m
ore,
up
to a
lim
it. T
his
tech
niqu
e is
cal
led
fram
e bu
rstin
g. T
he s
cena
rio i
s de
pict
ed i
n Fi
g. 2
.14.
The
m
axim
um le
ngth
in th
e bu
rstin
g is
655
36 b
its.
Firs
t fra
me
with
ext
ensi
on b
its
IFG
Fr
ame
2 IF
G
Fram
e 3
IFG
Fram
e n
Fi
gure
2.1
4 Fr
ame
burs
ting
B
oth
carri
er e
xten
sion
and
fra
me
burs
ting
com
plic
ates
the
MA
C d
esig
n.
Bes
ides
, the
thro
ughp
ut is
not
goo
d de
spite
the
solu
tions
. In
cont
rast
, ful
l dup
lex
Eth
erne
t doe
s no
t nee
d C
SM
A/C
D a
t all,
mak
ing
thes
e so
lutio
ns u
nnec
essa
ry. I
ts
impl
emen
tatio
n is
sim
pler
and
the
thro
ughp
ut is
muc
h hi
gher
. Why
do
we
both
er
38
to im
plem
ent h
alf-d
uple
x G
igab
it E
ther
net i
f it i
s no
t nec
essa
ry?
As
the
adva
nce
of
AS
IC t
echn
olog
y, s
witc
hed
netw
orks
are
no
long
er m
uch
mor
e ex
pens
ive
than
sh
ared
net
wor
ks.
For
the
depl
oym
ent
of G
igab
it E
ther
net,
it is
the
per
form
ance
ra
ther
tha
n th
e co
st t
hat
is o
f co
ncer
n. T
he m
arke
t ha
s pr
oved
the
fai
lure
of
half-
dupl
ex E
ther
net.
Onl
y fu
ll du
plex
Eth
erne
t pro
duct
s ex
ist o
n th
e m
arke
t. 10
Gig
abit
Ethe
rnet
Ju
st li
ke M
oore
’s la
w s
tatin
g th
e po
wer
of m
icro
proc
esso
rs d
oubl
es e
very
18
mon
ths,
the
spee
d of
Eth
erne
t has
als
o gr
own
expo
nent
ially
in re
cent
yea
rs. N
ot
long
afte
r 100
Mb/
s E
ther
net S
tand
ard
was
app
rove
d in
199
5 w
ill w
e so
on s
ee th
e 10
Gig
abit
Eth
erne
t Sta
ndar
d co
mes
out
in 2
002.
Fig
. 2.1
5 lis
ts th
e tim
etab
le o
f th
is n
ew s
tand
ard.
N
ote
that
com
mer
cial
pro
duct
s ha
ve e
mer
ged
in th
e m
arke
t in
2001
, bef
ore
the
final
app
rova
l of t
he s
tand
ard.
st
udy
grou
p
IEEE
802
.3ae
802.
3 ba
llot
sp
onso
r bal
lot
s
tand
ard
19
99
20
00
2
001
200
2 Fi
gure
2.1
5 Th
e tim
etab
le o
f the
10
Gb/
s E
ther
net S
tand
ard
Th
e ne
w 1
0 G
igab
it E
ther
net i
s de
velo
ped
by th
e IE
EE
802
.3ae
Tas
k Fo
rce
and
bear
s th
e fo
llow
ing
feat
ures
: Fu
ll du
plex
onl
y: T
he I
EE
E p
eopl
e le
arne
d a
less
on f
rom
the
dev
elop
men
t of
G
igab
it E
ther
net.
Now
, on
ly f
ull d
uple
x m
ode
is in
the
10 G
igab
it E
ther
net.
Hal
f du
plex
mod
e is
no
long
er c
onsi
dere
d.
Opt
ical
fibe
r on
ly: U
nlik
e G
igab
it E
ther
net,
it is
diff
icul
t to
trans
mit
at 1
0 G
igab
it ov
er c
oppe
r wire
s. O
nly
optic
al fi
bers
are
use
d as
the
trans
mis
sion
med
ia.
Com
patib
ility
with
pas
t st
anda
rd:
The
fram
e fo
rmat
and
the
MA
C o
pera
tions
re
mai
n un
chan
ged,
mak
ing
the
inte
rope
rabi
lity
with
exi
stin
g pr
oduc
ts ra
ther
eas
y.
Mov
e to
war
d th
e W
AN
mar
ket:
Sin
ce G
igab
it E
ther
net
has
mov
ed t
owar
d th
e M
AN
mar
ket,
10 G
igab
it E
ther
net
will
go f
urth
er in
to t
he W
AN m
arke
t. O
n on
e ha
nd, t
he lo
nges
t tar
get d
ista
nce
in th
e ne
w s
tand
ard
is a
imed
at 4
0 km
. On
the
othe
r ha
nd,
a W
AN P
HY
is d
efin
ed t
o in
terfa
ce w
ith t
he e
xist
ing
SO
NE
T in
frast
ruct
ure.
We
will
talk
mor
e ab
out t
he W
AN P
HY
belo
w.
Bec
ause
SO
NE
T is
stil
l a
wid
espr
ead
WAN
tec
hnol
ogy
and
the
OC
-192
op
erat
es a
t a
rate
ver
y cl
ose
to 1
0 G
igab
it, t
he I
EEE
802
.3ae
com
es w
ith a
n op
tiona
l WAN
PH
Y be
side
s th
e LA
N P
HY.
Not
e th
at b
oth
PH
Ys
have
the
sam
e tra
nsm
issi
on m
edia
, and
hen
ce th
e sa
me
trans
mis
sion
dis
tanc
e. T
he d
iffer
ence
is
that
the
WAN
PH
Y ha
s a
WA
N In
terfa
ce S
ubla
yer
(WIS
) in
the
Phy
sica
l Cod
ing
39
Sub
laye
r (P
CS
). Th
e W
IS is
a fr
amer
that
map
s an
Eth
erne
t fra
me
into
a S
ON
ET
payl
oad.
Thi
s m
akes
atta
chin
g E
ther
net
to S
ON
ET
devi
ces
easy
. Th
ere
is n
o re
quire
men
t tha
t the
WAN
PH
Y sh
ould
be
depl
oyed
in th
e W
AN. I
n a
WAN
of p
ure
Eth
erne
t, on
ly th
e LA
N P
HY
is n
eede
d.
The
phys
ical
spe
cific
atio
ns o
f the
10
Gig
abit
Eth
erne
t are
list
ed T
able
2.5
.
Phy
sica
l med
ium
Fi
ber t
ype
Targ
et d
ista
nce
(m)
850
nm s
eria
l M
ulti
mod
e 65
13
10 n
m W
WD
M
Mul
ti m
ode
300
1310
nm
WW
DM
S
ingl
e m
ode
10,0
00
1310
nm
ser
ial
Sin
gle
mod
e 10
,000
13
10 n
m s
eria
l S
ingl
e m
ode
40,0
00
Tabl
e 2.
5 P
hysi
cal s
peci
ficat
ions
in th
e 10
Gig
abit
Eth
erne
t Et
hern
et in
the
Firs
t Mile
W
e ha
ve E
ther
net d
omin
ant i
n th
e LA
N. W
e ex
pect
Eth
erne
t will
dom
inat
e in
th
e W
AN. W
e en
joy
broa
d ba
ndw
idth
bot
h in
the
LAN
and
WAN
. How
ever
, wha
t do
you
hav
e w
hen
you
wan
t to
acce
ss to
the
Inte
rnet
at h
ome?
You
’ve
got c
hoic
es
of tr
aditi
onal
mod
ems,
AD
SL,
cab
le m
odem
s, a
nd s
o on
. Stil
l, th
ese
tech
nolo
gies
ar
e sl
ow a
nd e
xpen
sive
. The
seg
men
t of s
ubsc
riber
acc
ess
netw
ork,
ofte
n al
so
calle
d th
e fir
st m
ile o
r la
st m
ile,
beco
mes
the
bot
tlene
ck.
As
the
popu
latio
n of
su
bscr
iber
acc
ess
netw
ork
grow
s ve
ry r
apid
ly, t
he p
oten
tial
mar
ket
beco
mes
hi
ghly
not
icea
ble.
A
new
effo
rt in
the
new
IEE
E 8
02.3
ah E
ther
net i
n th
e Fi
rst M
ile (
EFM
) Ta
sk
Forc
e is
sta
rting
to d
efin
e a
new
sta
ndar
d fo
r thi
s m
arke
t. Th
e ex
pect
ed ti
met
able
is
list
ed in
Fig
. 2.1
6.
stud
y gr
oup
IE
EE
802
.3ah
8
02.3
bal
lot
spon
sor b
allo
t st
anda
rd
2001
2
002
2
003
Figu
re 2
.16
The
timet
able
of E
ther
net i
n th
e Fi
rst M
ile S
tand
ard
Eth
erne
t is
a ve
ry m
atur
e an
d re
liabl
e te
chno
logy
. Hig
h vo
lum
e of
Eth
erne
t de
vice
s ha
s be
en e
xist
ent i
n th
e m
arke
t for
yea
rs, m
akin
g E
ther
net v
ery
chea
p. If
E
ther
net
coul
d be
eve
ryw
here
, no
pro
toco
l co
nver
sion
is
need
ed,
whi
ch a
lso
help
s to
red
uce
the
tota
l cos
t. A
ll in
all,
the
sta
ndar
d is
exp
ecte
d to
pro
vide
a
chea
per
and
fast
er te
chno
logy
in th
e po
tent
ially
bro
ad fi
rst m
ile m
arke
t. E
ther
net
is g
oing
tow
ard
the
goal
to
be u
biqu
itous
. Th
e de
velo
pmen
t go
als
of t
he n
ew
stan
dard
incl
ude
the
follo
win
g:
40
New
topo
logi
es: T
he re
quire
men
ts fo
r sub
scrib
er a
cces
s ne
twor
k in
clud
e po
int t
o po
int
on f
iber
, po
int
to m
ultip
oint
on
fiber
, an
d po
int
to p
oint
on
copp
er.
The
stan
dard
aim
s at
mee
ting
thes
e re
quire
men
ts.
New
PH
Ys: I
nevi
tabl
y, th
is s
tand
ard
need
s to
def
ine
new
PH
Ys.
The
cur
rent
goa
ls
are
ex
tend
ing
tem
pera
ture
rang
e fo
r the
cur
rent
100
0BA
SE
-X
ex
tend
ing
the
dist
ance
lim
itatio
n to
at
leas
t 10
km
long
for
the
cur
rent
10
00B
AS
E-X
of s
ingl
e-m
ode
optic
al fi
ber.
de
finin
g a
new
PH
Y fo
r Pas
sive
Opt
ical
Net
wor
k (P
ON
) to
at le
ast 1
0 km
lo
ng f
or s
ingl
e-m
ode
fiber
at
1 G
b/s
or m
ore.
A P
ON
is
a po
int
to
mul
tipoi
nt o
ptic
al l
ink.
The
ter
m “
pass
ive”
mea
ns n
o co
mpo
nent
s in
a
PO
N n
eeds
ele
ctric
al p
ower
exc
ept a
t the
end
s. A
fan-
out o
f at l
east
16
is
expe
cted
.
defin
ing
a ne
w P
HY
for
non-
load
ed v
oice
gra
de c
oppe
r at
10
Mb/
s or
m
ore
for
at l
east
250
0 ft.
To
achi
eve
this
goa
l, se
vera
l pr
opos
als,
in
clud
ing
VDSL
, 10
0BAS
E-C
U,
10BA
SE-T
4,
are
still
com
petin
g to
be
com
e th
e st
anda
rd. J
ust w
atch
it!
Far-
end
Ope
ratio
ns, A
dmin
istr
atio
n, a
nd M
aint
enan
ce (O
AM
): Th
e re
liabi
lity
is
very
im
porta
nt i
n su
bscr
iber
acc
ess
netw
ork.
For
eas
y O
AM
, th
e st
anda
rd w
ill de
fine
new
met
hods
of
rem
ote
failu
re i
ndic
atio
n, r
emot
e lo
opba
ck,
and
link
mon
itorin
g.
A cr
itica
l po
int
to s
ucce
ss i
s tim
e to
mar
ket.
To s
peed
up
the
stan
dard
izat
ion
proc
ess,
a p
ossi
ble
way
is t
o le
vera
ge e
xist
ing
stan
dard
s fo
r th
e P
HY,
as
wha
t IE
EE 8
02.3
did
for
100
BASE
-X a
nd 1
000B
ASE
-X.
100B
ASE
-X u
ses
a PH
Y m
odifi
ed fr
om th
e FD
DI S
tand
ard,
and
100
0BA
SE
-X h
as it
s P
HY
from
the
Fibe
r C
hann
el S
tand
ard.
For
Eth
erne
t in
the
Firs
t Mile
, som
e ca
ndid
ates
, say
VD
SL,
are
un
der
cons
ider
atio
n. H
owev
er,
sinc
e th
e st
anda
rdiz
atio
n pr
oces
s is
stil
l in
its
be
ginn
ing,
we
do n
ot k
now
wha
t the
cho
ice
will
be in
the
final
sta
ge.
The
stud
y gr
oup
just
clo
sed
its ta
sk a
nd th
e fir
st m
eetin
g of
IEE
E 8
02.3
ah w
ill
be
held
in
O
ctob
er
2001
. Fo
r m
ore
info
rmat
ion,
se
e th
e w
eb
site
at
ht
tp://
ww
w.ie
ee80
2.or
g/3/
efm
/inde
x.ht
ml.
2.
3.4
Eth
erne
t sw
itch
N
etw
ork
adm
inis
trato
rs u
sual
ly h
ave
the
need
to c
onne
ct s
epar
ate
LAN
s in
to
an in
terc
onne
cted
net
wor
k. T
he re
ason
for i
nter
conn
ectio
n m
ay b
e ex
tend
ing
the
exte
nt o
f a L
AN
or
adm
inis
trativ
e pu
rpos
es. A
n in
terc
onne
ctio
n de
vice
ope
ratin
g in
the
dat
a-lin
k la
yer
is c
alle
d a
MA
C
brid
ge,
or
sim
ply
brid
ge.
A br
idge
41
inte
rcon
nect
s LA
Ns
as i
f th
ey w
ere
in t
he s
ame
LAN
. Its
ope
ratio
n ha
s be
en
stan
dard
ized
in t
he I
EE
E 8
02.1
D S
tand
ard.
We
will
intro
duce
the
ins
and
outs
be
low.
A
lmos
t all
brid
ges
are
trans
pare
nt b
ridge
s. A
brid
ge is
tran
spar
ent b
ecau
se
all
stat
ions
on
the
inte
rcon
nect
ed L
AN
s ar
e un
awar
e of
its
exi
sten
ce.
The
trans
mitt
ing
stat
ion
sim
ply
tags
the
dest
inat
ion
MA
C a
ddre
ss a
nd s
ends
it o
ut a
s if
the
dest
inat
ion
wer
e on
the
sam
e LA
N. T
he b
ridge
will
aut
omat
ical
ly fo
rwar
d th
is
fram
e. A
noth
er c
ateg
ory
of b
ridge
s is
sou
rce-
rout
ing
brid
ges,
whi
ch i
s m
ostly
fo
und
in T
oken
Rin
g an
d so
met
imes
in
FDD
I. Th
e st
atio
n sh
ould
dis
cove
r th
e ro
ute
and
tag
forw
ardi
ng in
form
atio
n in
the
fra
me
to in
stru
ct t
he b
ridge
how
to
forw
ard.
As
the
Eth
erne
t dom
inat
es th
e LA
N m
arke
t, th
is c
ateg
ory
is s
eldo
m s
een,
so
we
intro
duce
onl
y tra
nspa
rent
brid
ge in
this
sub
sect
ion.
Th
e br
idge
has
por
ts to
whi
ch e
ach
LAN
is c
onne
cted
. Eac
h po
rt op
erat
es in
pr
omis
cuou
s m
ode,
whi
ch m
eans
it re
ceiv
es e
very
fram
e on
the
LAN
atta
ched
to
it, n
o m
atte
r w
hat t
he d
estin
atio
n ad
dres
s is
. If t
he fr
ame
has
to b
e fo
rwar
ded
to
othe
r por
ts, t
he b
ridge
will
do it
acc
ordi
ngly.
B
ridge
Ope
ratio
n Th
e m
yste
ry is
how
the
brid
ge k
now
s it
shou
ld fo
rwar
d th
e in
com
ing
fram
e an
d to
whi
ch p
ort
it sh
ould
for
war
d. W
e illu
stra
te t
he b
ridge
ope
ratio
n w
ith F
ig.
2.17
bel
ow.
Fi
gure
2.1
7 B
ridge
ope
ratio
n Th
e br
idge
kee
ps a
n ad
dres
s ta
ble,
als
o ca
lled
forw
ardi
ng ta
ble,
to s
tore
the
map
ping
of M
AC
add
ress
to p
ort n
umbe
r. In
itial
ly, th
e ad
dres
s ta
ble
is b
lank
. The
br
idge
kno
ws
noth
ing
abou
t the
loca
tion
of s
tatio
ns. S
uppo
se S
tatio
n 1
with
MA
C
Stat
ion
2
Stat
ion
1
Stat
ion
2 en
try h
ere!
42
addr
ess
00-3
2-12
-12-
6d-a
a tra
nsm
its a
fra
me
to S
tatio
n 2
with
MA
C a
ddre
ss
00-1
c-6f
-12-
dd-3
e. B
ecau
se S
tatio
n 1
is c
onne
cted
to
Por
t 3
of t
he b
ridge
, th
e br
idge
will
rece
ive
the
fram
e fro
m P
ort 3
. By
chec
king
the
sour
ce a
ddre
ss fi
eld
of
the
fram
e, t
he b
ridge
lear
ns t
he M
AC
add
ress
00-
32-1
2-12
-6d-
aa is
loca
ted
on
the
segm
ent
Por
t 3
is c
onne
cted
to.
It
keep
s th
e fa
ct i
n th
e ad
dres
s ta
ble.
H
owev
er, i
t stil
l doe
s no
t kno
w w
here
the
dest
inat
ion
addr
ess
00-1
c-6f
-12-
dd-3
e is
lo
cate
d. T
o m
ake
sure
the
dest
inat
ion
can
rece
ive
the
fram
e, it
sim
ply
broa
dcas
t to
eve
ry p
ort o
ther
than
the
port
from
whi
ch th
e fra
me
com
es. S
uppo
se s
ome
time
late
r, St
atio
n 2
trans
mits
a fr
ame
to s
omew
here
. The
brid
ge w
ill le
arn
its a
ddre
ss
com
es fr
om P
ort 2
and
will
keep
this
fact
in th
e ad
dres
s ta
ble
as w
ell.
Sub
sequ
ent
fram
es d
estin
ed t
o St
atio
n 2
will
be f
orw
arde
d to
Por
t 2
only.
No
broa
dcas
t is
ne
cess
ary.
Thi
s gr
eatly
sav
es th
e ba
ndw
idth
of a
ll ot
her
segm
ents
and
red
uces
th
e pr
obab
ility
of c
ollis
ions
. Of c
ours
e, if
Sta
tion
2 al
way
s ke
eps
sile
nt, t
he b
ridge
w
ill no
t kno
w w
here
it is
and
eve
ry fr
ame
dest
ined
to S
tatio
n 2
will
be b
road
cast
. Th
is s
ituat
ion
is u
nlik
ely
to h
appe
n. A
typi
cal s
cena
rio is
that
Sta
tion
2 re
spon
ds
som
ethi
ng w
hen
afte
r rec
eivi
ng a
fram
e de
stin
ed to
it. T
he b
ridge
can
lear
n w
here
St
atio
n 2
is fr
om th
e re
spon
se.
Som
etim
es, a
sta
tion
may
be
mov
ed to
ano
ther
loca
tion
or re
mov
ed, m
akin
g its
ent
ry in
the
addr
ess
tabl
e st
ale.
To
conq
uer t
his
prob
lem
, an
agin
g m
echa
nism
is
app
lied.
If a
sta
tion
has
not b
een
hear
d fo
r a g
iven
per
iod
of ti
me,
its
entry
will
be e
xpire
d. S
ubse
quen
t fra
mes
des
tined
to
it w
ill be
flo
oded
aga
in u
ntil
its
exis
tenc
e is
rele
arne
d.
In c
ase
that
the
dest
inat
ion
addr
ess
is a
mul
ticas
t or b
road
cast
add
ress
, the
br
idge
will
forw
ard
the
fram
e to
all
ports
exc
ept t
he s
ourc
e. It
is w
aste
ful t
o flo
od
the
fram
e, h
owev
er. T
o ad
dres
s th
e pr
oble
m, t
he IE
EE
802
.1D
Sta
ndar
d sp
ecifi
es
a G
MR
P, s
hort
for G
AR
P M
ultic
ast R
egis
tratio
n P
roto
col.
It is
a s
ubse
t of G
ener
ic
Attr
ibut
e R
egis
tratio
n P
roto
col (
GA
RP
). W
hen
this
pro
toco
l is
enab
led,
the
brid
ge
can
regi
ster
the
requ
irem
ent f
rom
the
inte
nded
rec
eive
rs o
f mul
ticas
t add
ress
es.
The
regi
stra
tion
info
rmat
ion
will
be p
ropa
gate
d am
ong
brid
ges,
and
thu
s al
l in
tend
ed re
ceiv
ers
are
iden
tifie
d. If
ther
e is
no
mul
ticas
t dem
and
on a
giv
en p
ath,
a
mul
ticas
t pr
unin
g is
per
form
ed t
o cu
t of
f th
is p
ath.
Thr
ough
thi
s m
echa
nism
, m
ultic
ast a
ddre
sses
are
forw
arde
d to
onl
y th
ose
path
s in
whi
ch th
ere
are
inte
nded
re
ceiv
ers.
N
ote
that
in F
ig. 2
.17,
ther
e is
a d
evic
e ca
lled
repe
ater
hub
, or
ofte
n si
mpl
y hu
b. T
his
devi
ce i
s a
Laye
r 1
devi
ce,
whi
ch m
eans
it
sim
ply
rest
ores
sig
nal
ampl
itude
and
tim
ing,
pro
paga
tes
sign
al to
all
othe
r po
rts o
ther
than
the
port
the
fram
e co
mes
fro
m,
but
know
s no
thin
g ab
out
the
fram
e. A
fter
all,
fram
es a
re
noth
ing
mor
e th
an a
ser
ies
of e
ncod
ed b
its to
the
phys
ical
laye
r.
43
Cut
-thro
ugh
vs. S
tore
-and
-For
war
d R
ecal
l tha
t th
e de
stin
atio
n ad
dres
s (D
A)
field
is t
he f
irst
field
in t
he f
ram
e ex
cept
the
Pre
ambl
e an
d S
FD fi
elds
. By
look
ing
up th
e D
A in
the
addr
ess
tabl
e,
the
brid
ge c
an d
eter
min
e w
here
to
forw
ard
the
fram
e. T
he b
ridge
can
sta
rt to
fo
rwar
d th
e fra
me
out
of t
he d
estin
atio
n po
rt be
fore
the
fra
me
is r
ecei
ved
com
plet
ely.
Suc
h op
erat
ion
is c
alle
d cu
t-thr
ough
. O
n th
e co
ntra
ry,
if th
e br
idge
on
ly f
orw
ard
afte
r th
e fra
me
is r
ecei
ved
com
plet
ely,
its
ope
ratio
n is
cal
led
stor
e-an
d-fo
rwar
d.
Aha
! The
title
of t
his
subs
ectio
n is
“Eth
erne
t sw
itch,
” but
we
are
talk
ing
abou
t br
idge
so
far.
Wha
t is
goin
g on
? Th
ere
is a
his
toric
al r
easo
n. It
is ti
me
to te
ll th
e an
swer
. Bef
ore
1991
, the
dev
ice
is c
alle
d br
idge
, bot
h in
the
IEE
E S
tand
ard
and
in
the
mar
ket.
Ear
ly b
ridge
s w
ere
all i
mpl
emen
ted
in s
tore
-and
-forw
ard
man
ner.
In
1991
, Kal
pana
Cor
pora
tion
mar
kete
d th
e fir
st c
ut-th
roug
h br
idge
, und
er th
e na
me
“sw
itch”
to
diffe
rent
iate
the
mse
lves
fro
m s
tore
-and
-forw
ard
brid
ges.
It
decl
ared
lo
wer
late
ncy
beca
use
of th
e cu
t-thr
ough
ope
ratio
n. A
rgum
ents
wer
e ra
ised
then
am
ong
prop
onen
ts
of
stor
e-an
d-fo
rwar
d an
d cu
t-thr
ough
ap
proa
ches
. W
e su
mm
ariz
e th
e co
mpa
rison
s of
thes
e tw
o m
echa
nism
s in
Tab
le 2
.6.
St
ore-
and-
forw
ard
Cut
-thro
ugh
Tran
smitt
ing
time
Tran
smit
a fra
me
afte
r re
ceiv
ing
com
plet
ely
May
tran
smit
a fra
me
befo
re re
ceiv
ing
com
plet
ely10
Late
ncy
Slig
htly
larg
er la
tenc
y M
ay h
ave
slig
htly
sm
alle
r lat
ency
Bro
adca
st/M
ultic
ast N
o pr
oble
m fo
r br
oadc
ast o
r m
ultic
ast
fram
es
Gen
eral
ly n
ot p
ossi
ble
for
broa
dcas
tor
mul
ticas
t fra
mes
Erro
r che
ckin
g C
an c
heck
FC
S in
tim
e M
ay b
e to
o la
te to
che
ck F
CS
Pop
ular
ity
Mos
tly fo
und
in th
e m
arke
t Le
ss p
opul
ar in
the
mar
ket
Tabl
e 2.
6 C
ompa
rison
s of
sto
re-a
nd-fo
rwar
d an
d cu
t-thr
ough
B
ridge
vs.
Sw
itch
Follo
win
g K
alpa
na’s
con
vent
ion,
brid
ges
are
mar
kete
d un
der
the
nam
e “s
witc
h,”
no m
atte
r th
eir
oper
atio
n is
sto
re-a
nd-fo
rwar
d or
cut
-thro
ugh.
On
the
othe
r ha
nd,
the
nam
e is
stil
l “b
ridge
” in
the
IE
EE
Sta
ndar
d. T
he I
EE
E 8
02.3
St
anda
rd e
xplic
itly
unde
rline
s th
at th
e tw
o te
rms
are
syno
nym
s. D
espi
te u
nder
the
nam
e “s
witc
h,”
mos
t sw
itche
s pr
ovid
e on
ly s
tore
-and
-forw
ard,
or
both
tha
t ar
e
10
If t
he L
AN
of t
he o
utgo
ing
port
or th
e ou
tput
que
ue is
occ
upie
d by
oth
er fr
ames
, a fr
ame
still
can
not b
e fo
rwar
ded
even
in a
cut
-thro
ugh
switc
h.
44
conf
igur
able
toda
y. T
here
is re
ally
no
sign
ifica
nt b
enef
it in
the
cut-t
hrou
gh d
esig
n,
as c
ompa
red
in F
ig.
2.20
. W
e st
art
to u
se t
he t
erm
“sw
itch”
whe
n co
nven
ient
be
low.
In fa
ct, t
he te
rm “
switc
h” is
so
wid
ely
used
on
devi
ces
mak
ing
forw
ardi
ng
deci
sion
bas
ed o
n th
e in
form
atio
n fro
m u
pper
laye
rs. T
hat’s
why
we
see
L3 s
witc
h,
L4 s
witc
h, a
nd L
7 sw
itch
toda
y.
Span
ning
Tre
e Pr
otoc
ol
As
the
topo
logy
of a
brid
ged
netw
ork
beco
mes
larg
e an
d co
mpl
ex, n
etw
ork
adm
inis
trato
rs m
ay in
adve
rtent
ly c
reat
e a
loop
in t
he t
opol
ogy.
Thi
s si
tuat
ion
is
unde
sira
ble
beca
use
fram
es c
an c
ircul
ate
arou
nd th
e lo
op a
nd th
e ad
dres
s ta
ble
may
bec
ome
unst
able
. For
exa
mpl
e, c
onsi
der t
he fo
llow
ing
disa
ster
. Sup
pose
two
2-po
rt sw
itche
s fo
rm a
loop
and
a s
tatio
n br
oadc
asts
a fr
ame
onto
the
loop
. Eac
h sw
itch
will
for
war
d th
e br
oadc
ast f
ram
e to
the
othe
r up
on r
ecei
ving
it, m
akin
g it
circ
ulat
e ar
ound
the
loop
inde
finite
ly.
The
abov
e si
tuat
ion
is u
ndes
irabl
e. T
o ad
dres
s th
e pr
oble
m,
IEE
E 8
02.1
D
stip
ulat
es a
Spa
nnin
g Tr
ee P
roto
col (
STP
) to
elim
inat
e lo
ops
in a
brid
ged
netw
ork.
Fo
r its
sim
plic
ity i
n im
plem
enta
tion,
alm
ost
all
switc
hes
supp
ort
this
pro
toco
l. D
espi
te th
is, t
he s
peci
ficat
ion
take
s 51
pag
es in
the
stan
dard
doc
umen
t. W
e on
ly
expl
ain
the
prin
cipl
e of
STP
ope
ratio
n w
ith th
e ex
ampl
e in
Fig
. 2.1
8. T
his
exam
ple
is a
littl
e co
mpl
ex. W
e lis
t the
pro
cedu
re b
elow
. For
ser
ious
rea
ders
who
inte
nd
lear
n th
e de
tails
, we
enco
urag
e th
em to
read
the
stan
dard
.
Figu
re 2
.18
A br
idge
d ne
twor
k w
ith lo
ops
1.
Ini
tially
, ea
ch s
witc
h an
d po
rt is
ass
igne
d an
ide
ntifi
er.
The
iden
tifie
r is
co
mpo
sed
of a
man
agea
ble
prio
rity
valu
e an
d sw
itch
addr
ess
(or p
ort n
umbe
r fo
r po
rt id
entif
ier).
For
sim
plic
ity,
we
use
1 to
7 a
s th
e id
entif
iers
in
this
45
illus
tratio
n.
2. E
ach
link
is s
peci
fied
a co
st.
As
a ru
le o
f th
umb,
the
cos
t ca
n be
inve
rsel
y pr
opor
tiona
lly to
the
link
spee
d. F
or s
impl
icity
, we
assu
me
all l
ink
cost
s ar
e 1
here
. 3.
The
sw
itch
with
the
lea
st id
entif
ier
serv
es a
s th
e ro
ot.
It is
ele
cted
thr
ough
ex
chan
ging
fram
es o
f con
figur
atio
n in
form
atio
n am
ong
switc
hes.
4.
Eac
h LA
N is
con
nect
ed to
a p
ort o
f som
e sw
itch
in a
n ac
tive
topo
logy
. The
por
t w
hich
the
LA
N r
ecei
ves
fram
es f
rom
the
dire
ctio
n of
the
roo
t an
d tra
nsm
its
fram
es to
war
d th
e ro
ot is
cal
led
the
Des
igna
ted
Por
t (D
P). T
his
switc
h is
cal
led
the
Des
igna
ted
Brid
ge (T
he s
tand
ard
refe
rs to
a s
witc
h as
a b
ridge
). Th
e po
rt th
at th
e sw
itch
rece
ives
fram
es fr
om th
e ro
ot is
cal
led
the
Roo
t Por
t (R
P).
5. P
erio
dica
lly,
conf
igur
atio
n in
form
atio
n is
pro
paga
ted
dow
n fro
m t
he r
oot
on
Brid
ge P
roto
col
Dat
a U
nit
(BP
DU
). Th
e de
stin
atio
n ad
dres
s of
BP
DU
is
a re
serv
ed m
ultic
ast
addr
ess
for
switc
hes,
01-
80-C
2-00
-00-
00.
The
BP
DU
fra
me
cont
ains
info
rmat
ion
such
as
the
root
iden
tifie
r, th
e tra
nsm
ittin
g sw
itch
iden
tifie
r, th
e tra
nsm
ittin
g po
rt id
entif
ier,
and
the
path
cos
t fro
m th
e ro
ot.
6. E
ach
switc
h m
ay c
onfig
ure
itsel
f by
com
putin
g th
e in
form
atio
n ca
rried
in th
e re
ceiv
ed B
PDU
s. T
he c
onfig
urat
ion
rule
s ar
e If
the
switc
h fin
ds it
self
can
prov
ide
a lo
wer
pat
h co
st b
y co
mpa
ring
with
the
path
cos
t adv
ertis
ed in
BP
DU
s, it
will
atte
mpt
to b
e a
desi
gnat
ed b
ridge
by
trans
mitt
ing
BP
DU
s w
ith lo
wer
pat
h co
st.
In c
ase
of a
mbi
guity
, e.g
., eq
ual p
ath
cost
, the
sw
itch
or p
ort w
ith th
e le
ast
iden
tifie
r is
sele
cted
as
the
desi
gnat
ed b
ridge
(por
t).
If th
e sw
itch
finds
itse
lf ha
s lo
wer
iden
tifie
r th
an th
at o
f the
cur
rent
roo
t, it
will
atte
mpt
to
beco
me
the
new
roo
t by
tra
nsm
ittin
g B
PD
Us
in w
hich
the
ro
ot id
entif
ier i
s th
at o
f its
elf.
Not
e th
at th
e sw
itch
will
not f
orw
ard
inco
min
g B
PD
Us,
but
may
cre
ate
new
B
PD
Us
to c
arry
new
sta
tes
to o
ther
s.
7. A
ll po
rts o
ther
than
DP
s an
d R
Ps
are
bloc
ked.
A b
lock
ed p
ort i
s no
t allo
wed
to
forw
ard
or re
ceiv
e da
ta fr
ames
. How
ever
, it k
eeps
list
enin
g to
BP
DU
s to
see
if
it ca
n be
act
ive
agai
n.
The
resu
lt is
as
indi
cate
d in
Fig
. 2.1
8. T
he r
eade
rs a
re e
ncou
rage
d to
trac
e th
e pr
oced
ure
them
selv
es. T
he p
roto
col i
s so
use
ful t
hat i
t dyn
amic
ally
upd
ates
th
e sp
anni
ng tr
ee a
ccor
ding
to p
ossi
ble
topo
logi
cal c
hang
es.
Virt
ual L
AN
O
nce
a de
vice
is c
onne
cted
to
a LA
N,
it be
long
s to
tha
t LA
N.
That
is,
the
depl
oym
ent o
f LA
Ns
is c
ompl
etel
y de
term
ined
by
phys
ical
con
nect
ivity
. In
som
e
46
appl
icat
ions
, we
need
to b
uild
logi
cal c
onne
ctiv
ity o
n to
p of
phy
sica
l dep
loym
ent.
For e
xam
ple,
we
may
nee
d so
me
ports
in a
sw
itch
belo
ng to
one
LAN
, and
oth
er
ports
bel
ong
to a
noth
er.
Furth
er,
we
may
nee
d po
rts a
cros
s m
ultip
le s
witc
hes
belo
ngin
g to
the
sam
e LA
N, a
ll ot
her
ports
bel
ongi
ng to
ano
ther
LA
N. G
ener
ally,
w
e ne
ed fl
exib
ility
in th
e ne
twor
k de
ploy
men
t. Vi
rtual
LA
N (
VLA
N)
addr
esse
s th
e ab
ove
prob
lem
by
prov
idin
g lo
gica
l gr
oupi
ng o
f LA
Ns.
Adm
inis
trato
rs c
an s
impl
y w
ork
with
man
agem
ent t
ools
with
out
chan
ging
ph
ysic
al
conn
ectiv
ity.
Add
ition
ally,
w
ith
VLA
N
sepa
ratio
n,
we
can
incr
ease
sec
urity
and
sav
e ba
ndw
idth
bec
ause
tra
ffic,
par
ticul
arly
mul
ticas
t an
d br
oadc
ast
traffi
c, is
con
fined
to
the
VLA
N t
he t
raffi
c be
long
s to
. For
exa
mpl
e, a
br
oadc
ast f
ram
e or
a fr
ame
with
an
unkn
own
unic
ast d
estin
atio
n ad
dres
s w
ill be
se
en o
n al
l por
ts o
f a
switc
h w
ithou
t V
LAN
. It
still
may
con
sum
e ba
ndw
idth
on
unin
tend
ed p
orts
and
mal
icio
us u
sers
can
mon
itor
it. B
y di
vidi
ng t
he p
orts
of
a sw
itch
into
sev
eral
VLA
Ns,
the
fra
mes
men
tione
d ab
ove
will
be c
onfin
ed t
o a
VLA
N. We
give
a p
ract
ical
exa
mpl
e be
low
to
mak
e th
e re
ader
s ap
prec
iate
the
us
eful
ness
of
VLA
N.
Con
side
r w
e ha
ve t
wo
IP s
ubne
ts:
140.
113.
88.0
and
14
0.11
3.24
1.0.
Eac
h ha
s se
vera
l st
atio
ns.
If w
e w
ant
to c
onne
ct t
hese
tw
o IP
su
bnet
s w
ith a
rout
er, w
e m
ay d
eplo
y th
e ne
twor
k in
the
man
ner d
epic
ted
in F
ig.
2.19
.
Fi
gure
2.1
9 a
rout
er d
eplo
ymen
t with
out V
LAN
If w
e co
nfig
ure
the
switc
h w
ith tw
o V
LAN
s in
stea
d, o
nly
one
switc
h is
nee
ded.
Th
e ro
uter
is c
onne
cted
to a
por
t tha
t bel
ongs
to tw
o V
LAN
s, a
nd is
con
figur
ed
with
two
IP a
ddre
sses
, one
for
each
sub
net.
The
rout
er in
this
situ
atio
n is
cal
led
the
one-
arm
ed ro
uter
, as
illust
rate
d in
Fig
. 2.2
0.
47
Now
aday
s, m
any
switc
hes
have
the
abilit
y to
ser
ve a
s a
norm
al ro
uter
. The
y ca
n fo
rwar
d fra
mes
bas
ed o
n la
yer
3 in
form
atio
n. S
ome
of th
em a
lso
impl
emen
t ro
utin
g pr
otoc
ols
(See
Cha
pter
3 fo
r rou
ting
prot
ocol
s). W
ith V
LAN
, adm
inis
trato
rs
can
arbi
traril
y gr
oup
ports
int
o se
vera
l IP
sub
nets
. Th
is i
s ve
ry c
onve
nien
t fo
r ne
twor
k ad
min
istra
tion.
Fo
r th
e im
porta
nce
of V
LAN
, th
e IE
EE
802
.1Q
Sta
ndar
d sp
ecifi
es a
set
of
prot
ocol
s an
d al
gorit
hms
to s
uppo
rt th
e V
LAN
ope
ratio
n. T
his
stan
dard
des
crib
es
the
arch
itect
ural
fra
mew
ork
for
VLA
N in
res
pect
of
conf
igur
atio
n, d
istri
butio
n of
co
nfig
urat
ion
info
rmat
ion,
and
rel
ay.
The
first
is s
elf-e
xpla
nato
ry.
The
seco
nd is
co
ncer
ned
with
met
hods
that
allo
w th
e di
strib
utio
n of
VLA
N m
embe
rshi
p am
ong
VLA
N-a
war
e sw
itche
s. T
he th
ird d
eals
with
how
to c
lass
ify a
nd fo
rwar
d in
com
ing
fram
es, a
nd th
e pr
oced
ure
to m
odify
the
fram
es b
y ad
ding
, cha
ngin
g, r
emov
ing
tags
. We
will
soon
dis
cuss
the
conc
ept o
f tag
bel
ow.
Figu
re 2
.20
a on
e-ar
med
rout
er
The
IEE
E 8
02.1
Q S
tand
ard
does
not
enf
orce
the
way
how
fra
mes
are
as
soci
ated
to
VLA
Ns.
The
VLA
N m
embe
rshi
p ca
n be
bas
ed o
n po
rts,
MA
C
addr
esse
s, I
P su
bnet
s, p
roto
cols
, an
d ap
plic
atio
ns.
Eac
h fra
me
can
asso
ciat
e w
ith a
tag
that
bea
rs t
he id
entif
ier
of a
VLA
N s
o th
at t
he s
witc
h ca
n id
entif
y its
V
LAN
ass
ocia
tion
quic
kly
with
out c
ompl
icat
ed fi
eld
clas
sific
atio
n. T
he ta
g sl
ight
ly
chan
ges
the
fram
e fo
rmat
, how
ever
. The
form
at o
f a ta
gged
fram
e is
dep
icte
d in
Fi
g. 2
.2111
. Not
e th
at th
ere
are
12 b
its in
the
VLA
N id
entif
ier.
Giv
ing
one
iden
tifie
r is
rese
rved
unu
sed
and
anot
her o
ne is
use
d to
indi
cate
a p
riorit
y ta
g (s
ee b
elow
),
11
Not
e th
at V
LAN
is n
ot c
onfin
ed to
Eth
erne
t. Th
e st
anda
rd a
lso
appl
ies t
o ot
her L
AN
stan
dard
s, sa
y To
ken
Rin
g. H
owev
er, s
ince
Eth
erne
t is t
he m
ost p
opul
ar, w
e di
scus
s Eth
erne
t fra
me
here
.
48
a m
axim
um n
umbe
r of 4
094
(i.e.
, 212
-2) V
LAN
s ar
e al
low
ed.
Prio
rity
If th
e lo
ad in
a L
AN
is h
igh,
the
user
s w
ill pe
rcei
ve la
rger
late
ncy.
How
ever
, so
me
voic
e or
vi
deo
appl
icat
ions
ar
e tim
e-se
nsiti
ve.
Thei
r qu
ality
w
ill be
de
terio
rate
d w
ith la
rger
late
ncy.
Tra
ditio
nally
, LA
N te
chno
logy
sol
ves
the
prob
lem
w
ith o
ver-p
rovi
sion
ing.
Tha
t is
, pr
ovid
ing
mor
e ba
ndw
idth
tha
n ne
eded
. Th
is
solu
tion
is fe
asib
le b
ecau
se h
igh
band
wid
th is
inex
pens
ive
in L
AN
. But
in c
ase
of
shor
t-ter
m c
onge
stio
n, th
e tra
ffic
may
tem
pora
rily
exce
ed th
e av
aila
ble
band
wid
th.
Hig
her p
riorit
y ca
n be
ass
igne
d to
fram
es o
f crit
ical
app
licat
ions
to g
uara
ntee
they
re
ceiv
e be
tter s
ervi
ce.
Eth
erne
t inh
eren
tly d
oes
not h
ave
the
prio
rity
mec
hani
sm. A
s of
IEE
E 8
02.1
p,
whi
ch w
as la
ter
inte
grat
ed in
to I
EE
E 8
02.1
D,
a pr
iorit
y va
lue
can
be o
ptio
nally
as
sign
ed to
an
Eth
erne
t fra
me.
Thi
s va
lue
is a
lso
carri
ed in
the
tagg
ed fr
ame,
as
illust
rate
d in
Fig
. 2.2
1.
A ta
gged
fram
e ha
s fo
ur m
ore
byte
s ad
ded
into
it. T
hey
are
a ty
pe fi
eld
of tw
o by
tes
that
indi
cate
s a
VLA
N p
roto
col t
ype
(the
valu
e =
0x81
00) a
nd a
tag
cont
rol
info
rmat
ion
field
of a
noth
er tw
o by
tes.
The
latte
r is
furth
er d
ivid
ed in
to th
ree
field
s:
prio
rity,
Can
onic
al F
orm
at In
dica
tor (
CFI
), an
d V
LAN
iden
tifie
r. N
ote
that
a ta
gged
fra
me
does
not
nec
essa
rily
carry
VLA
N in
form
atio
n. T
he ta
g ca
n on
ly c
onta
in th
e pr
iorit
y of
the
fram
e, w
hich
was
def
ined
in IE
EE
802
.1p.
The
VLA
N id
entif
ier h
elps
th
e sw
itch
to id
entif
y th
e V
LAN
to w
hich
the
fram
e be
long
s. A
sw
itch
can
easi
ly
iden
tify
the
VLA
N m
embe
rshi
p th
roug
h th
is fi
eld.
The
CFI
fiel
d lo
oks
mys
terio
us. I
t is
a o
ne-b
it fie
ld th
at in
dica
tes
whe
ther
the
poss
ible
MA
C a
ddre
sses
car
ried
in th
e M
AC
dat
a is
in C
anon
ical
form
at. W
e do
not
go
into
the
deta
il of
Can
onic
al fo
rm
here
. Th
e in
tere
sted
rea
ders
are
ref
erre
d to
Cla
use
9.3.
2 in
the
IE
EE
802
.1Q
do
cum
ent.
Pre
ambl
eS
FD
DA
S
A
VLA
N
prot
ocol
ID
Tag
cont
rol
T/L
Dat
a FC
S
byte
s 7
1
6
6
2
2
2
42 –
150
0
4
pr
iorit
yC
FIVL
AN
iden
tifie
r
bits
3
1
12
Fi
gure
2.2
1 Fo
rmat
of a
tagg
ed fr
ame
B
ecau
se th
ere
are
thre
e bi
ts in
the
prio
rity
field
, eig
ht p
riorit
ies
are
allo
wed
in
49
the
prio
rity
mec
hani
sm. T
he s
ugge
sted
map
ping
of p
riorit
y va
lues
to tr
affic
type
s in
the
stan
dard
is li
sted
in T
able
2.7
. By
iden
tifyi
ng th
e ta
g va
lues
, the
sw
itch
is
able
to
clas
sify
the
inco
min
g va
lues
and
arra
nge
appr
opria
te q
ueue
ser
vice
s to
m
eet t
he u
ser’s
dem
and.
P
riorit
y Tr
affic
type
1
Bac
kgro
und
2 Sp
are
0(de
faul
t) B
est e
ffort
3 E
xcel
lent
effo
rt 4
Con
trolle
d lo
ad
5 <
100
ms
late
ncy
and
jitte
r 6
< 10
ms
late
ncy
and
jitte
r 7
Net
wor
k co
ntro
l Ta
ble
2.7
sugg
este
d m
appi
ng o
f prio
rity
valu
es a
nd tr
affic
type
s Li
nk A
ggre
gatio
n Th
e fin
al is
sue
we
wou
ld li
ke to
intro
duce
in th
is s
ectio
n is
link
agg
rega
tion.
M
ultip
le li
nks
can
be a
ggre
gate
d as
if t
hey
wer
e a
pipe
of
larg
er c
apac
ity.
For
exam
ple,
use
rs c
an a
ggre
gate
two
giga
bit l
inks
into
a tw
o gi
gabi
t lin
k if
larg
er li
nk
capa
city
is d
esire
d. T
hey
do n
ot h
ave
to w
ait
for
ten
giga
bit
Eth
erne
t pr
oduc
ts.
Eve
n if
new
pro
duct
s co
me
out,
it m
ay b
e no
t ec
onom
ical
to
buy
them
. Li
nk
aggr
egat
ion
brin
gs fl
exib
ility
in n
etw
ork
depl
oym
ent.
Link
agg
rega
tion
was
orig
inal
ly a
tech
niqu
e of
Cis
co, d
ubbe
d E
ther
Cha
nnel
, or
ofte
n re
ferre
d to
as
Por
t Tr
unki
ng,
and
was
lat
er s
tand
ardi
zed
in t
he I
EE
E
802.
3ad
in 2
000.
The
ope
ratio
n is
not
con
fined
to li
nks
betw
een
switc
hes.
Lin
ks
betw
een
switc
h an
d st
atio
n, a
nd b
etw
een
stat
ion
and
stat
ion
can
also
be
aggr
egat
ed. T
he p
rinci
ple
of o
pera
tion
is s
impl
e: th
e tra
nsm
itter
dis
tribu
tes
fram
es
amon
g ag
greg
ated
link
s, a
nd th
e re
ceiv
er c
olle
cts
thes
e fra
mes
. How
ever
, som
e di
fficu
lties
com
plic
ate
the
desi
gn. F
or e
xam
ple,
con
side
r the
cas
e in
whi
ch a
long
fra
me
is fo
llow
ed b
y se
vera
l sho
rt fra
mes
. If t
he lo
ng fr
ame
is d
istri
bute
d to
one
lin
k, a
nd t
he s
hort
fram
es a
re d
istri
bute
d to
ano
ther
. Th
e re
ceiv
er w
ill re
ceiv
e th
ese
fram
es o
ut o
f or
der.
Alth
ough
an
uppe
r la
yer
prot
ocol
, su
ch a
s TC
P ca
n de
al w
ith o
ut o
f ord
er fr
ames
, it i
s le
ss e
ffici
ent t
o do
so.
The
ord
erin
g of
fram
es in
a
flow
mus
t be
mai
ntai
ned
in th
e da
ta-li
nk la
yer.
A flo
w m
ay n
eed
to m
ove
from
on
e lin
k to
ano
ther
for
wel
l lo
ad-b
alan
cing
or
beca
use
of l
ink
failu
re.
To m
eet
thes
e re
quire
men
ts, a
Lin
k A
ggre
gatio
n C
ontro
l Pro
toco
l (LA
CP
) is
desi
gned
. For
de
tails
, we
refe
r the
read
ers
to C
laus
e 43
in th
e IE
EE
802
.3 S
tand
ard.
2.4
Wire
less
link
s
Wire
less
link
s ar
e ap
peal
ing
to m
any
peop
le. W
ith w
irele
ss li
nks,
peo
ple
are
50
free
from
the
cons
train
ts o
f wire
s he
re a
nd th
ere,
whi
ch m
ay b
e in
conv
enie
nt o
r to
o ex
pens
ive
to d
eplo
y. H
owev
er, w
irele
ss li
nks
feat
ure
diffe
rent
cha
ract
eris
tics
from
wire
d lin
ks,
impo
sing
spe
cial
req
uire
men
ts o
n th
e pr
otoc
ol d
esig
n. W
e lis
t th
ese
char
acte
ristic
s be
low
: Le
ss re
liabi
lity:
Sig
nals
are
pro
paga
ted
with
out p
rote
ctio
n on
the
air,
mak
ing
the
trans
mis
sion
ea
sily
im
paire
d by
ou
tsid
e in
terfe
renc
e,
path
lo
ss,
mul
ti-pa
th
dist
ortio
n, e
tc. O
utsi
de in
terfe
renc
e co
mes
from
nea
rby
wire
less
sig
nal s
ourc
es.
Mic
row
ave
oven
s an
d B
luet
ooth
dev
ices
are
pos
sibl
e so
urce
s be
caus
e th
ey a
ll op
erat
e in
the
unlic
ense
d IS
M (I
ndus
trial
, Sci
entif
ic, a
nd M
edic
al) b
and.
Pat
h lo
ss
is a
ttenu
atio
n th
e si
gnal
und
ergo
es a
s it
prop
agat
es o
n th
e ai
r. Th
e at
tenu
atio
n is
w
orse
bec
ause
the
sig
nal
is i
nher
ently
dis
tribu
ted
over
the
air
rath
er t
han
conc
entra
ted
on a
wire
d lin
k. M
ulti-
path
dis
torti
on re
sults
from
del
ayed
par
ts o
f the
si
gnal
bec
ause
the
y tra
vel
thro
ugh
diffe
rent
pat
hs t
o th
e re
ceiv
er.
Ther
e ar
e po
ssib
ly d
iffer
ent p
aths
in th
e tra
nsm
issi
on b
ecau
se p
arts
of t
he s
igna
l bou
nce
off
phys
ical
obs
tacl
es o
n th
e w
ay.
Mor
e m
obili
ty: B
ecau
se th
ere
is n
o w
ire th
at li
mits
the
mob
ility
of a
sta
tion,
the
netw
ork
topo
logy
may
var
y dy
nam
ical
ly. N
ote
that
mob
ility
and
wire
less
diff
eren
t co
ncep
ts a
lthou
gh th
ey a
re o
ften
refe
rred
to to
geth
er. W
irele
ss is
not
nec
essa
ry
for
mob
ility.
For
exa
mpl
e, a
mob
ile s
tatio
n ca
n be
car
ried
to a
loca
tion
and
then
pl
ugge
d to
a w
ired
netw
ork.
Mob
ility
is a
lso
not
nece
ssar
y fo
r w
irele
ss.
For
exam
ple,
tw
o hi
gh
build
ings
ca
n co
mm
unic
ate
with
w
irele
ss
rela
y de
vice
s be
caus
e a
wire
bet
wee
n th
em is
too
expe
nsiv
e. T
his
is n
ot u
ncom
mon
in n
etw
ork
depl
oym
ent.
Le
ss p
ower
: A m
obile
sta
tion
is o
ften
batte
ry p
ower
ed. S
tatio
ns m
ay s
omet
imes
be
put
int
o sl
eep
to s
ave
pow
er.
Tran
smitt
ers
shal
l bu
ffer
the
data
unt
il th
e re
ceiv
er a
wak
ens
to re
ceiv
e th
em.
Less
sec
urity
: Dat
a pr
opag
ated
on
the
air
are
easi
ly e
aves
drop
ped.
All
stat
ions
w
ithin
the
tra
nsm
issi
on r
ange
can
lis
ten
to t
he d
ata.
Opt
iona
l en
cryp
tion
and
auth
entic
atio
n m
echa
nism
s ar
e pr
ovid
ed t
o ke
ep t
he d
ata
mor
e se
cure
fro
m
outs
ide
thre
ats.
In
this
sec
tion,
we
will
intro
duce
two
notic
eabl
e w
irele
ss li
nk p
roto
cols
: IEE
E 80
2.11
and
Blu
etoo
th. T
he fo
rmer
has
bec
ome
the
stan
dard
of w
irele
ss L
AN
, and
th
e la
tter
is d
esig
ned
for
shor
t-ran
ge c
onne
ctiv
ity.
We
will
conc
lude
thi
s se
ctio
n w
ith t
he c
ompa
rison
of
thes
e tw
o te
chno
logi
es a
nd d
iscu
ss t
heir
coex
iste
nce
issu
es.
2.
4.1
Bas
ics
of IE
EE
802
.11
51
Evol
utio
n Th
e IE
EE
802
.11
Wor
king
Gro
up w
as e
stab
lishe
d in
199
0. I
ts g
oal
is t
o de
velo
p M
ediu
m A
cces
s C
ontro
l (M
AC
) met
hod
and
phys
ical
laye
r spe
cific
atio
ns
to m
eet t
he re
quire
men
ts o
f wire
less
loca
l are
a ne
twor
k. T
he p
roce
ss w
as s
o lo
ng
that
the
first
ver
sion
of s
tand
ards
did
not
app
ear u
ntil
1997
. Ini
tially
, thr
ee k
inds
of
PH
Ys,
in
frare
d,
Dire
ct
Seq
uenc
e S
prea
d S
pect
rum
(D
SS
S),
and
Freq
uenc
y-H
oppi
ng
Spr
ead
Spe
ctru
m
(FH
SS
), ar
e sp
ecifi
ed
to
allo
w
trans
mis
sion
at 1
Mb/
s an
d 2
Mb/
s. S
prea
d sp
ectru
m te
chni
ques
are
inte
nded
to
mak
e si
gnal
rob
ust
to o
utsi
de i
nter
fere
nce.
It
was
lat
er r
evis
ed i
n 19
99.
Two
amen
dmen
ts,
802.
11a
and
802.
11b
are
also
sta
ndar
dize
d in
tha
t ye
ar.
IEE
E
802.
11b
exte
nds
the
DS
SS
syst
em u
p to
a h
ighe
r da
ta r
ate
at 5
.5 M
b/s
and
11
Mb/
s. IE
EE
802
.11a
spe
cifie
s a
new
Orth
ogon
al F
requ
ency
Div
isio
n M
ultip
lexi
ng
(OFD
M)
oper
atin
g at
5 G
Hz
band
, as
opp
osed
to
2.4
GH
z ba
nd i
n pr
evio
us
stan
dard
s. T
he d
ata
rate
is in
crea
sed
sign
ifica
ntly
up
to 5
4 M
b/s.
How
ever
, the
se
two
stan
dard
s ar
e no
t co
mpa
tible
. IE
EE
802
.11b
pro
duct
s op
erat
ing
at 1
1 M
b/s
has
been
pop
ular
in th
e m
arke
t. S
ome
vend
ors,
say
Inte
l, ha
s st
arte
d to
mar
ket
IEE
E 8
02.1
1a p
rodu
cts.
At
the
time
of t
his
writ
ing,
IE
EE
802
.11
proj
ects
und
er
deve
lopm
ent
have
rea
ched
802
.11i
. S
ome
maj
or o
nes
of t
hem
are
802
.11e
for
Q
oS, 8
02.1
1g fo
r hig
her d
ata
rate
at 2
.4 G
Hz
band
, and
802
.11i
for s
ecur
ity. T
he
deve
lopm
ent i
s st
ill ve
ry a
ctiv
e so
far.
B
uild
ing
Blo
cks
The
basi
c bu
ildin
g bl
ock
of a
n 80
2.11
LA
N is
a B
asic
Ser
vice
Set
(B
SS)
. A
BS
S is
com
pose
d of
sta
tions
cap
able
of M
AC
and
PH
Y th
at c
onfo
rm to
the
IEE
E
802.
11 S
tand
ard.
A m
inim
um B
SS
con
tain
s on
ly tw
o st
atio
ns. A
sta
ndal
one
BS
S is
ca
lled
an In
depe
nden
t BS
S (
IBS
S), o
r m
ore
ofte
n th
an n
ot, r
efer
red
to a
s an
Ad
hoc
netw
ork
beca
use
this
typ
e is
ofte
n fo
rmed
with
out
plan
ning
in
adva
nce.
M
ultip
le B
SS
s ca
n be
con
nect
ed th
roug
h a
Dis
tribu
tion
Sys
tem
(D
S).
The
IEE
E
802.
11 S
tand
ard
does
not
man
date
wha
t the
DS
sho
uld
be. E
ther
net n
etw
ork
is
the
DS
we
can
find
mos
t ofte
n. A
DS
and
a B
SS
are
con
nect
ed th
roug
h an
Acc
ess
Poi
nt (A
P).
Suc
h an
ext
ende
d ne
twor
k st
ruct
ure
is c
alle
d an
Infra
stru
ctur
e. T
hese
bu
ildin
g bl
ocks
are
illu
stra
ted
in F
ig. 2
.22.
Th
e la
yerin
g in
the
IE
EE
802
.11
is d
epic
ted
in F
ig.
2.23
. As
we
have
m
entio
ned,
the
IEE
E 8
02.1
1 P
HY
s co
nsis
t of i
nfra
red,
DS
SS
, FH
SS
, and
OFD
M.
Abo
ve th
em is
the
MA
C s
ubla
yer,
whi
ch w
e w
ill in
trodu
ce s
oon.
We
will
focu
s on
th
e IE
EE
802
.11
MA
C in
this
sec
tion.
For
issu
es o
n P
HY,
we
enco
urag
e in
tere
sted
re
ader
s to
ref
er t
o th
e re
sour
ces
liste
d in
Sec
tion
2.7
or s
earc
h m
ore
on t
he
Inte
rnet
.
52
Figu
re 2
.22
IEE
E 8
02.1
1 bu
ildin
g bl
ocks
802.
2 LL
C
802.
11 M
AC
Dat
a-lin
k la
yer
FHS
S D
SS
S
IR
OFD
M
Phys
ical
la
yer
802.
11 M
AC
des
ign
shal
l tak
e ca
re o
f thi
s ca
se.
FH
SS: F
requ
ency
Hop
ping
Spr
ead
Spec
trum
DS
SS
: Dire
ct S
eque
nce
Spre
ad S
pect
rum
OFD
M: O
rthog
onal
Fre
quen
cy D
ivis
ion
Mul
tiple
IR: I
nfra
red
Figu
re 2
.23
Laye
ring
in th
e IE
EE
802
.11
2.
4.2
IEE
E 8
02.1
1 M
AC
An o
bvio
us d
istin
ctio
n be
twee
n th
e IE
EE 8
02.1
1 M
AC a
nd t
he I
EEE
802.
3 M
AC,
a ty
pica
l re
pres
enta
tive
of w
ired
netw
ork,
is
that
col
lisio
n de
tect
ion
is
diffi
cult
to im
plem
ent.
The
cost
of f
ull-d
uple
x R
F is
hig
her a
nd th
ere
are
pote
ntia
lly
hidd
en s
tatio
ns th
at m
ake
collis
ion
dete
ctio
n fa
il. T
he la
tter i
s kn
own
as th
e hi
dden
te
rmin
al p
robl
em,
as w
e illu
stra
ted
in F
ig.
2.24
. Th
eref
ore,
the
rec
eive
r sh
ould
53
resp
ond
with
an
ackn
owle
dgm
ent
if th
e FC
S i
s co
rrec
t. Th
is i
s th
e po
sitiv
e ac
know
ledg
men
t mec
hani
sm a
s w
e ha
d m
entio
ned
in S
ectio
n 2.
1.3.
In F
ig. 2
.24,
Sta
tion
A an
d St
atio
n C
can
not h
ear e
ach
othe
r bec
ause
they
are
lo
cate
d ou
t of
eac
h ot
her’s
tra
nsm
issi
on r
ange
. H
owev
er,
if th
ey b
oth
trans
mit
data
to S
tatio
n B
sim
ulta
neou
sly,
a c
ollis
ion
will
occ
ur a
t Sta
tion
B. T
hus,
the
IEE
E
Fi
gure
2.2
4 Th
e hi
dden
term
inal
pro
blem
The
IEE
E
802.
11
MA
C
allo
cate
s ch
anne
ls
with
tw
o m
ajor
fu
nctio
ns:
Dis
tribu
ted
Coo
rdin
atio
n Fu
nctio
n (D
CF)
and
Poi
nt C
oord
inat
ion
Func
tion
(PC
F).
The
DC
F is
man
dato
ry t
hat
all I
EE
E 8
02.1
1 co
nfor
man
t st
atio
ns s
houl
d fo
llow.
Th
e P
CF
is p
erfo
rmed
in a
n in
frast
ruct
ure
netw
ork.
Bot
h co
ordi
natio
n fu
nctio
ns
can
coex
ist w
ithin
the
sam
e B
SS
. Th
e ph
iloso
phy
behi
nd D
CF
is k
now
n as
Car
rier S
ense
Mul
tiple
Acc
ess
with
C
ollis
ion
Avoi
danc
e (C
SM
A/C
A).
Alth
ough
the
mos
t not
icea
ble
diffe
renc
e fro
m th
e E
ther
net
MA
C i
s th
e co
llisio
n av
oida
nce,
the
CS
MA
/CA
mec
hani
sm h
as m
ore
diffe
renc
es th
an th
at.
The
sam
e as
CS
MA
/CD
, a
stat
ion
mus
t lis
ten
befo
re t
rans
mitt
ing.
If
som
e st
atio
n is
tran
smitt
ing,
the
trans
mis
sion
will
be d
efer
red
until
the
chan
nel i
s fre
e.
Onc
e th
e ch
anne
l is
clea
r, th
e st
atio
n w
ill w
ait f
or a
sho
rt pe
riod
of ti
me,
kno
wn
as
inte
rfram
e sp
ace
(IFS
), be
fore
the
trans
mis
sion
. Not
e th
at d
urin
g th
e tim
e of
last
tra
nsm
issi
on, t
here
are
odd
s th
at m
ultip
le s
tatio
ns a
re w
aitin
g to
tran
smit.
If th
ey
all a
re a
llow
ed to
tran
smit
afte
r IFS
, it i
s ve
ry li
kely
to re
sult
in a
col
lisio
n. T
o av
oid
poss
ible
col
lisio
ns,
the
stat
ions
hav
e to
wai
t a
rand
om b
acko
ff tim
e be
fore
54
trans
mis
sion
. The
per
iod
is d
eter
min
ed w
ith th
e fo
rmul
a:
Bac
koff
time
= R
ando
m v
alue
× s
lot t
ime
In th
e ab
ove
form
ula,
the
rand
om v
alue
is s
elec
ted
rand
omly
from
the
rang
e fro
m 0
to C
W. C
W s
tand
s fo
r Con
tent
ion
Win
dow
, ran
ging
from
CW
min
to C
Wm
ax.
CW
min
, CW
max
, and
the
slot
tim
e, d
epen
d on
the
PH
Y ch
arac
teris
tics.
Initi
ally,
C
W is
set
to C
Wm
in. T
he b
acko
ff tim
e is
dec
reas
ed b
y on
e sl
ot ti
me
if th
e ch
anne
l is
free
for a
n IF
S p
erio
d; o
ther
wis
e, th
e tim
e is
sus
pend
ed. W
hen
it fin
ally
reac
hes
zero
, the
sta
tion
star
ts to
tran
smit.
Thr
ough
the
abov
e pr
oced
ure,
col
lisio
ns c
an
be re
duce
d si
gnifi
cant
ly. W
e su
mm
ariz
e th
e C
SM
A/C
A pr
oced
ure
in F
ig. 2
.25.
Fi
g 2.
25 C
SM
A/C
A flo
w c
hart
Unl
ike
colli
sion
det
ectio
n, w
hich
can
sto
p tra
nsm
issi
on i
mm
edia
tely
if
a co
llisio
n is
det
ecte
d, th
ere
is n
o w
ay fo
r a s
tatio
n to
find
that
the
fram
e it
trans
mits
is
im
paire
d un
til n
o ac
know
ledg
emen
t is
rec
eive
d. T
he c
ost
of c
ollis
ion
is
sign
ifica
nt if
a lo
ng fr
ame
is tr
ansm
itted
. An
optio
nal r
efin
emen
t to
redu
ce th
e co
st
is a
n ex
plic
it R
TS/C
TS m
echa
nism
. B
efor
e tra
nsm
ittin
g a
fram
e, th
e tra
nsm
itter
no
tifie
s al
l sta
tions
with
in it
s tra
nsm
issi
on r
ange
with
a R
eque
st t
o S
end
(RTS
). Th
e re
ceiv
er re
spon
ds w
ith a
Cle
ar to
Sen
d (C
TS) f
ram
e, w
hich
is a
lso
notic
ed b
y al
l sta
tions
with
in it
s tra
nsm
issi
on r
ange
. B
oth
RTS
and
CTS
fra
mes
car
ry th
eir
dura
tion
field
s, te
lling
the
othe
r sta
tions
to w
ait f
or a
ctua
l dat
a fra
me
trans
mis
sion
an
d its
ack
now
ledg
emen
t. Th
is p
roce
dure
is il
lust
rate
d in
Fig
. 2.
31.
Dur
ing
the
rese
rved
per
iod,
the
othe
r sta
tions
inhi
bit t
heir
own
trans
mis
sion
and
do
not n
eed
to p
erfo
rm c
arrie
r se
nse
phys
ical
ly. T
here
fore
, th
is m
echa
nism
is
also
cal
led
55
virtu
al c
arrie
r sen
se. T
his
mec
hani
sm h
as a
noth
er a
dvan
tage
. In
Fig
2.26
, C a
nd
D c
anno
t se
nse
trans
mis
sion
fro
m e
ach
othe
r. If
they
bot
h in
tend
to
trans
mit
sim
ulta
neou
sly,
a c
ollis
ion
will
occu
r. Th
e R
TS/C
TS m
echa
nism
can
avo
id t
his
situ
atio
n. N
ote
that
this
mec
hani
sm is
onl
y ap
plic
able
to u
nica
st fr
ame.
In c
ase
of
mul
ticas
t and
bro
adca
st, m
ultip
le C
TSs
from
the
rece
iver
s w
ill re
sult
in a
col
lisio
n.
Sim
ilarly
, the
ack
now
ledg
emen
t fra
me
will
not b
e re
spon
ded
in c
ase
of m
ultic
ast
or b
road
cast
.
Fi
gure
2.2
6 R
TS/C
TS m
echa
nism
Th
e P
CF
is e
xerc
ised
by
a P
oint
Coo
rdin
ator
(P
C)
that
res
ides
in t
he A
P w
ithin
eac
h B
SS
. P
erio
dica
lly,
the
PC
tra
nsm
its a
bea
con
fram
e to
ann
ounc
e a
Con
tent
ion-
Free
Per
iod
(CFP
). E
very
sta
tion
with
in t
he B
SS
is
awar
e of
the
be
acon
fram
e an
d ke
eps
sile
nt d
urin
g C
FP. T
he o
nly
stat
ion
is a
llow
ed to
tran
smit
whe
n it
is p
olle
d by
the
PC
. Hen
ce, t
he P
C h
as th
e au
thor
ity to
det
erm
ine
who
can
tra
nsm
it. T
he p
ollin
g se
quen
ce is
left
unsp
ecifi
ed in
the
stan
dard
. Th
e D
CF
and
PC
F ca
n co
exis
t in
the
sce
nario
illu
stra
ted
in F
ig.
2.27
. Th
e D
CF
imm
edia
tely
follo
ws
CFP
, ent
erin
g a
perio
d ca
lled
Con
tent
ion
Per
iod
(CP)
. N
orm
ally,
the
PC
tran
smits
a b
eaco
n fra
me
with
a C
FP r
epet
ition
per
iod,
but
the
perio
d m
ay b
e de
laye
d if
the
chan
nel h
appe
ns to
be
busy
at t
he e
nd o
f the
CP.
Figu
re 2
.27
DC
F an
d P
CF
coex
iste
nce
The
IEE
E 8
02.1
1 de
fines
the
MAC
fram
e fo
rmat
as
depi
cted
in F
ig. 2
.28.
56
Fi
gure
2.2
8 IE
EE
802
.11
fram
e fo
rmat
The
fram
e fo
rmat
is
gene
ral.
Cer
tain
fra
me
type
may
con
tain
a s
ubse
t of
th
ese
field
s. W
e ca
tego
rize
the
fram
es in
to th
ree
type
s:
1. C
ontro
l fra
mes
: RTS
, CTS
, AC
K, e
tc.
2. D
ata
fram
es: c
arry
ing
norm
al d
ata
3. M
anag
emen
t fra
mes
: Bea
con,
etc
. To
fully
cov
er th
ese
type
s re
quire
s de
ep u
nder
stan
ding
of e
very
IEE
E 8
02.1
1 op
erat
ion.
The
read
ers
can
refe
r to
the
stan
dard
itse
lf fo
r det
ails
.
2.4.
3 B
luet
ooth
tech
nolo
gy
Lo
ok a
t the
cab
les
behi
nd y
our c
ompu
ter.
Ther
e ar
e pl
enty
of t
hem
. Bes
ides
th
ose
conn
ectin
g co
mpu
ter p
erip
hera
ls, w
e al
so h
ave
cabl
es to
con
nect
diff
eren
t ki
nds
of c
able
s. T
hese
cab
les
are
so c
umbe
rsom
e th
at it
is b
ette
r to
get
rid
of
them
. Blu
etoo
th,
nam
ed a
fter
a D
anis
h ki
ng i
n th
e te
nth
cent
ury,
is
the
very
te
chno
logy
des
igne
d to
rep
lace
cab
les
conn
ectin
g el
ectro
nic
devi
ces.
Bet
wee
n th
e de
vice
s ar
e sh
ort-r
ange
, us
ually
with
in 1
0 m
, ra
dio
links
. To
mak
e su
re t
he
prol
ifera
tion
of t
his
new
tec
hnol
ogy,
the
dev
elop
men
t go
al a
ttem
pts
to in
tegr
ate
man
y fu
nctio
ns in
a s
ingl
e ch
ip a
nd re
duce
s th
e pr
ice
of a
chi
p be
low
five
dol
lars
ev
entu
ally.
Blu
etoo
th is
a r
athe
r ne
w te
chno
logy
. In
1998
, fiv
e m
ajor
com
pani
es,
Eric
sson
, N
okia
, IB
M,
Tosh
iba,
and
Int
el,
coop
erat
e to
cre
ate
it. A
Blu
etoo
th
Spe
cial
Int
eres
t G
roup
(B
luet
ooth
SIG
), co
mpo
sed
of m
any
com
pani
es,
was
fo
rmed
late
r to
prom
ote
and
defin
e th
e ne
w s
tand
ard.
B
luet
ooth
dev
ices
ope
rate
at t
he 2
.4 G
Hz
ISM
ban
d, th
e sa
me
as m
ost I
EE
E 80
2.11
dev
ice
usin
g fre
quen
cy h
oppi
ng. T
he fr
eque
ncy
band
ran
ges
from
2.4
00
GH
z to
2.4
835
GH
z, w
ithin
whi
ch a
re 7
9 ch
anne
ls o
f 1 M
Hz
for f
requ
ency
hop
ping
. B
elow
and
abo
ve t
hese
cha
nnel
s ar
e gu
ard
band
s of
2 M
Hz
and
3.5
MH
z,
resp
ectiv
ely.
An
obse
rvan
t re
ader
may
im
med
iate
ly h
ave
notic
ed t
he p
ossi
ble
inte
rfere
nce
prob
lem
if
devi
ces
of I
EE
E 8
02.1
1 an
d B
luet
ooth
are
clo
se.
The
coex
iste
nce
prob
lem
is a
big
issu
e. W
e w
ill ta
lk m
ore
abou
t thi
s in
the
end
of th
is
57
subs
ectio
n.
The
basi
c Bl
ueto
oth
topo
logy
is il
lust
rate
d in
Fig
. 2.2
9. L
ike
BSS
in th
e IE
EE
802.
11, t
wo
or m
ore
devi
ces
shar
ing
the
sam
e ch
anne
l for
m a
pic
onet
. But
unl
ike
an IB
SS
, in
whi
ch a
ll st
atio
ns a
re c
reat
ed e
qual
, the
re a
re o
ne m
aste
r and
sla
ves
in a
pic
onet
. The
mas
ter h
as th
e au
thor
ity, s
ay d
ecid
ing
the
hopp
ing
sequ
ence
, to
cont
rol c
hann
el a
cces
s in
the
pico
net.
The
slav
es c
an b
e ei
ther
act
ive
or p
arke
d. A
m
aste
r con
trols
up
to s
even
act
ive
slav
es a
t the
sam
e tim
e. P
arke
d sl
aves
do
not
com
mun
icat
e, b
ut th
ey s
till k
eep
sync
hron
ized
with
the
mas
ter
and
can
beco
me
activ
e as
the
mas
ter d
eman
d. If
a m
aste
r des
ired
to c
omm
unic
ate
with
mor
e th
an
seve
n sl
aves
, it t
ells
one
or
mor
e ac
tive
slav
es to
ent
er in
to th
e pa
rk m
ode,
and
th
en i
nvite
s th
e de
sire
d pa
rked
sla
ves
to b
e ac
tive.
For
mor
e de
vice
s to
co
mm
unic
ate
sim
ulta
neou
sly,
mul
tiple
pic
onet
s ca
n ov
erla
p to
for
m a
lar
ger
scat
tern
et. I
n Fi
g. 2
.29
belo
w, w
e se
e tw
o pi
cone
ts fo
rm a
sca
ttern
et w
ith a
brid
ge
node
. The
brid
ge n
ode
can
be a
sla
ve in
bot
h pi
cone
ts o
r be
the
mas
ter
in o
ne
pico
net.
It pa
rtici
pate
s in
bot
h pi
cone
ts in
a m
anne
r of t
ime-
divi
sion
. Som
etim
es, i
t is
par
t of o
ne p
icon
et, a
nd s
omet
imes
, it b
elon
gs to
ano
ther
.
pico
net
scat
tern
et
Figu
re 2
.29
The
Blu
etoo
th to
polo
gy
For
Blu
etoo
th d
evic
es t
o co
mm
unic
ate,
the
y m
ust
be a
war
e of
eac
h ot
her.
Any
inqu
iry p
roce
dure
is d
esig
ned
for
each
dev
ice
to d
isco
ver t
he o
ther
dev
ices
, fo
llow
ed b
y a
page
pro
cedu
re t
o bu
ild u
p a
conn
ectio
n. I
nitia
lly,
all
Blue
toot
h de
vice
s ar
e by
def
ault
in s
tand
by m
ode.
A B
luet
ooth
inte
nd to
com
mun
icat
e w
ill try
to
broa
dcas
t an
inqu
iry w
ithin
its
cove
rage
are
a. T
he d
evic
es a
roun
d it
may
re
spon
d th
e in
quiry
with
info
rmat
ion
abou
t the
mse
lves
, suc
h as
add
ress
es, i
f the
y w
ould
lik
e to
. U
pon
rece
ivin
g th
ese
resp
onse
s, t
he i
nqui
rer
know
s in
form
atio
n ab
out s
urro
undi
ng d
evic
es a
nd b
ecom
e th
e m
aste
r in
the
pico
net.
Oth
er d
evic
es
beco
me
the
slav
es.
Afte
r in
quiry
, th
e m
aste
r se
nds
a un
icas
t m
essa
ge t
o th
e de
stin
atio
n de
vice
. The
des
tinat
ion
resp
onds
with
an
ackn
owle
dgem
ent a
nd th
us
a co
nnec
tion
is e
stab
lishe
d. T
his
is c
alle
d a
page
pro
cedu
re. S
ome
time
late
r, a
slav
e ca
n ru
n th
e sa
me
page
pro
cedu
re, a
nd th
e ro
le o
f the
mas
ter a
nd s
lave
will
58
be
exch
ange
d.
The
proc
ess
is
illust
rate
d in
Fi
g.
2.30
. N
ote
that
m
ultip
le
resp
onse
s fro
m a
n in
quiry
may
resu
lt in
a c
ollis
ion.
The
rece
ivin
g de
vice
s sh
ould
de
fer t
he re
spon
ses
for a
rand
om b
acko
ff tim
e.
Fi
gure
2.3
0 In
quiry
and
Pag
e pr
oced
ure
A pi
cone
t cha
nnel
is d
ivid
ed in
to ti
me
slot
s of
625
µs
each
in w
hich
diff
eren
t ho
ppin
g fre
quen
cy o
ccup
ies.
The
slo
t tim
e is
a re
cipr
ocal
of t
he h
op ra
te, w
hich
is
1600
hop
s/s.
The
se s
lots
are
tim
e m
ultip
lexe
d w
ith th
e sa
me
hopp
ing
sequ
ence
by
the
com
mun
icat
ing
mas
ter a
nd s
lave
. At t
he d
ata
rate
of 1
Mb/
s, e
ach
slot
can
id
eally
car
ry d
ata
of 6
25 b
its. H
owev
er, s
ome
inte
rval
s w
ithin
a s
lot a
re r
eser
ved
for
frequ
ency
hop
ping
and
sta
biliz
atio
n. U
p to
366
bits
can
be
carri
ed in
a s
lot.
Nor
mal
ly, e
ach
slot
car
ries
a B
luet
ooth
fram
e. A
fram
e ha
s fie
lds
of a
cces
s co
de
of 7
2 bi
ts, h
eade
r inf
orm
atio
n of
54
bits
, and
the
payl
oad
of v
aria
ble
leng
th. W
ith
payl
oad
of o
nly
366
– 72
– 5
4 =
240
bits
(30
byt
es)
carri
ed in
a t
ime
slot
tha
t id
eally
car
ries
625
bits
, the
effi
cien
cy is
not
goo
d. T
o im
prov
e ef
ficie
ncy,
a fr
ame
can
occu
py u
p to
five
con
secu
tive
slot
s.
A B
luet
ooth
con
nect
ion
has
two
optio
ns i
n em
ploy
ing
the
time
slot
s to
co
mm
unic
ate.
The
firs
t is
the
Syn
chro
nous
Con
nect
ion-
Orie
nted
link
(S
CO
link
), w
hich
res
erve
s tim
e sl
ots
regu
larly
for
time-
boun
ded
info
rmat
ion,
suc
h as
voi
ce.
For
exam
ple,
a te
leph
one-
grad
e vo
ice
has
a sa
mpl
e ra
te o
f 8 K
Hz,
eac
h sa
mpl
e ge
nera
ting
one
byte
. In
othe
r wor
ds, a
byt
e is
gen
erat
ed e
very
0.1
25 m
s. B
ecau
se
a fra
me
can
carry
30
byte
s in
eac
h sl
ot, o
ne s
lot s
houl
d be
rese
rved
to c
arry
voi
ce
ever
y 3.
75 m
s. E
ach
time
slot
has
a le
ngth
625
µs,
mea
ning
one
out
of s
ix s
lots
is
rese
rved
. Th
e se
cond
opt
ion
is t
he A
sync
hron
ous
Con
nect
ion-
Less
lin
k (A
CL
link)
. Ti
me
slot
s ar
e al
loca
ted
on d
eman
d ra
ther
than
bei
ng re
serv
ed. T
he m
aste
r is
in
59
char
ge o
f th
e al
loca
tion
to o
ne o
r m
ultip
le s
lave
s. I
n th
is w
ay,
collis
ions
fro
m
slav
es a
re a
void
ed a
nd t
he m
aste
r ca
n co
ntro
l th
e Q
ualit
y of
Ser
vice
(Q
oS)
requ
irem
ent i
n th
e lin
k.
The
prot
ocol
sta
ck in
the
Blu
etoo
th s
peci
ficat
ion
is d
epic
ted
in F
ig. 2
.31.
We
desc
ribe
the
func
tion
of e
ach
mod
ule
shor
tly o
n th
e rig
ht o
f the
figu
re. W
e le
ave
the
deta
il to
the
spe
cific
atio
n. R
eade
rs c
an d
ownl
oad
it fro
m t
he U
RL
give
n in
S
ectio
n 2.
7.
Fi
gure
2.3
1 Th
e B
luet
ooth
pro
toco
l sta
ck
B
luet
ooth
and
the
IEE
E 8
02.1
1 ar
e de
sign
ed fo
r diff
eren
t pur
pose
s. T
he IE
EE
80
2.11
inte
nds
to b
e a
wire
less
LA
N s
tand
ard,
whi
le B
luet
ooth
is d
esig
ned
for t
he
wire
less
per
sona
l are
a ne
twor
k (w
irele
ss P
AN
, or
WPA
N).
A co
mpa
rison
is li
sted
in
Tab
le 2
.8 b
elow
. C
urre
ntly,
the
IEE
E 8
02.1
5 W
PAN
Wor
king
Gro
up a
nd th
e B
luet
ooth
SIG
are
co
oper
atin
g to
impr
ove
the
Blu
etoo
th S
tand
ard.
Mor
eove
r, Ta
sk G
roup
2 in
the
IE
EE
802
.15
focu
ses
on a
ddre
ssin
g th
e co
exis
tenc
e pr
oble
m b
ecau
se o
f pos
sibl
e in
terfe
renc
e. A
lthou
gh t
here
are
arg
umen
ts a
s to
the
suc
cess
of
the
Blu
etoo
th,
man
y pe
ople
exp
ect o
ptim
istic
ally
coe
xist
ence
of t
hese
two
stan
dard
s.
I
EE
E 8
02.1
1 B
luet
ooth
Freq
uenc
y 2.
4 G
Hz
(802
.11,
802
.11b
) 5
GH
z
(80
2.11
a)
2.4G
Hz
Dat
a ra
te
1, 2
Mb/
s (8
02.1
1)
5.5,
11
Mb/
s (8
02.1
1b)
54 M
b/s
(802
.11a
)
1 M
b/s
Ran
ge
roun
d 10
0 m
w
ithin
10
m
Pow
er c
onsu
mpt
ion
high
er
(with
1W
, us
ually
30 –
100
mW
) lo
wer
(1
mW
–10
0 m
W,
usua
lly a
bout
1m
W)
60
PH
Y sp
ecifi
catio
n In
frare
d
OFD
M
FH
SS
D
SSS
FH
SS
MAC
D
CF
PCF
Slo
t allo
catio
n
Pric
e hi
gher
lo
wer
Maj
or a
pplic
atio
n W
irele
ss L
AN
Shor
t-ran
ge c
onne
ctio
n
Tabl
e 2.
8 A
com
paris
on o
f Blu
etoo
th a
nd IE
EE 8
02.1
1
2.5
Dev
ice
driv
ers
2.5.
1 A
n in
trodu
ctio
n to
dev
ice
driv
ers
One
of
the
mai
n fu
nctio
ns o
f an
ope
ratin
g sy
stem
is t
o co
ntro
l I/O
dev
ices
. Th
e I/O
par
t in
the
oper
atin
g sy
stem
can
be
stru
ctur
ed to
four
laye
rs a
s fo
llow
s.
Not
e th
at th
e in
terru
pt h
andl
er c
an a
lso
be th
ough
t as
part
of th
e dr
iver
.
Fi
gure
2.
Stru
ctur
e of
I/O
softw
are
A
ll th
e de
vice
-dep
ende
nt c
odes
are
em
bedd
ed i
n th
e de
vice
driv
ers.
The
de
vice
driv
ers
issu
e co
mm
ands
to
the
devi
ce r
egis
ters
and
che
ck i
f th
ey a
re
carri
ed o
ut p
rope
rly.
Thus
, th
e ne
twor
k de
vice
driv
er i
s th
e on
ly p
art
of t
he
oper
atin
g sy
stem
tha
t kn
ows
how
man
y re
gist
ers
the
netw
ork
adap
tor
has
and
wha
t the
y ar
e us
ed fo
r. In
gen
eral
term
s, th
e jo
b of
a d
evic
e dr
iver
is to
acc
ept a
bstra
ct re
ques
ts fr
om
the
devi
ce-in
depe
nden
t so
ftwar
e ab
ove
it, a
nd t
o ha
ndle
the
se r
eque
sts
by
issu
ing
com
man
ds to
dev
ice
regi
ster
s. A
fter c
omm
ands
hav
e be
en is
sued
, one
of
two
situ
atio
ns w
ill ha
ppen
. O
ne i
s th
at t
he d
evic
e dr
iver
blo
cks
itsel
f un
til t
he
inte
rrupt
co
mes
in
to
un
bloc
k it.
Th
e ot
her
is
that
th
e op
erat
ion
finis
hes
imm
edia
tely,
so
the
driv
er d
oes
not n
eed
to b
lock
.
Use
r pro
cess
es
Dev
ice-
inde
pend
ent O
S so
ftwar
e
Dev
ice
driv
er
Inte
rrup
t han
dler
s
Dev
ice
I/O re
ply
I/O re
ques
t
I/O
func
tions
I/O c
alls
, spo
olin
g
Nam
ing,
pro
tect
ion,
allo
catio
n
Setu
p de
vice
regi
ster
s, ch
eck
stat
us
Wak
eup
driv
er w
hen
I/O c
ompl
eted
Perf
orm
I/O
ope
ratio
ns
61
2.5.
2 H
ow to
writ
e a
devi
ce d
river
in L
inux
Bef
ore
a de
vice
driv
er c
an c
omm
unic
ate
with
a d
evic
e, it
mus
t in
itial
ize
the
envi
ronm
ent
so t
hat
ever
ythi
ng g
ets
read
y. T
he a
ctio
n of
ini
tializ
atio
n in
clud
es
prob
ing
I/O p
orts
for
com
mun
icat
ing
with
dev
ice
regi
ster
s, a
nd p
robi
ng IR
Qs
for
corre
ctly
inst
allin
g th
e in
terru
pt h
andl
er.
Pr
obe
Har
dwar
e Th
e m
etho
d of
pro
bing
har
dwar
e in
a d
river
is d
iffer
ent a
ccor
ding
to th
e ty
pes
of b
us a
rchi
tect
ure.
PC
I de
vice
s ar
e au
tom
atic
ally
con
figur
ed a
t bo
ot t
ime.
The
de
vice
driv
er, t
hen,
mus
t be
able
to a
cces
s co
nfig
urat
ion
info
rmat
ion
in th
e de
vice
in
ord
er to
com
plet
e th
e in
itial
izat
ion.
Thi
s ha
ppen
s w
ithou
t the
nee
d to
per
form
an
y pr
obin
g.
How
ever
, th
e de
vice
dr
iver
s fo
r IS
A de
vice
s ha
ve
to
prob
e th
emse
lves
. Le
t’s s
ee th
e P
CI d
evic
es fi
rst.
In L
inux
ker
nel v
ersi
on 2
.4, t
he I/
O p
orts
of P
CI
devi
ces
have
bee
n in
tegr
ated
in th
e ge
neric
res
ourc
e m
anag
emen
t. W
e ca
n us
e th
e fo
llow
ing
func
tions
to g
et th
e I/O
por
ts o
f a d
evic
e in
the
devi
ce d
river
: un
sign
ed lo
ng p
ci_r
esou
rce_
star
t(str
uct p
ci_d
ev *d
ev, i
nt b
ar);
stru
ct r
esou
rce
*req
uest
_reg
ion
(uns
igne
d lo
ng s
tart
, un
sign
ed l
ong
len,
ch
ar* n
ame)
; vo
id re
leas
e_re
gion
(uns
igne
d lo
ng s
tart
, un
sign
ed lo
ng le
n);
Firs
t, w
e us
e pc
i_re
sour
ce_s
tart(
) to
get
the
bas
e ad
dres
s. T
hen,
we
use
requ
est_
regi
on()
to
re
serv
e th
e I/O
po
rts.
Fina
lly,
the
driv
er
shou
ld
call
rele
ase_
regi
on()
to
rele
ase
the
ports
whe
n it
finis
hes.
As
far
as i
nter
rupt
s ar
e co
ncer
ned,
PC
I is
eas
y to
han
dle.
By
the
time
Linu
x bo
ots,
the
firm
war
e ha
s al
read
y as
sign
ed a
uni
que
inte
rrupt
num
ber
to t
he d
evic
e co
nfig
urat
ion
regi
ster
na
med
PC
I_IN
TER
RU
PT_L
INE,
whi
ch is
one
byt
e w
ide.
We
can
use
the
follo
win
g fu
nctio
n to
get
the
IRQ
num
ber o
f a d
evic
e in
the
devi
ce d
river
: in
t pci
_rea
d_co
nfig
_byt
e(st
ruct
pci
_dev
*dev
, int
whe
re, u
8 *p
tr);
The
whe
re a
rgum
ent s
houl
d be
PC
I_IN
TER
RU
PT_
LIN
E, a
nd th
e pt
r arg
umen
t is
the
poin
ter t
o th
e IR
Q n
umbe
r. N
ow,
let’s
look
at
the
ISA
devi
ces.
If
we
wan
t to
get
the
I/O
por
ts o
f an
IS
A de
vice
in a
dev
ice
driv
er, t
he fo
llow
ing
proc
edur
e m
ust b
e do
ne:
1. in
t che
ck_r
egio
n(un
sign
ed lo
ng s
tart
, uns
igne
d lo
ng le
n); T
his
func
tion
is
used
to s
ee if
a ra
nge
of p
orts
are
ava
ilabl
e fo
r allo
catio
n.
2. T
his
prob
e ro
utin
e pr
obe_
hard
war
e() i
s to
mak
e su
re th
e de
vice
exi
sts.
It is
not
pr
ovid
ed b
y th
e ke
rnel
, but
inst
ead
it m
ust b
e im
plem
ente
d by
driv
er w
riter
s.
62
3. U
se re
ques
t_re
gion
() to
act
ually
allo
cate
the
ports
. 4.
Use
rele
ase_
regi
on()
to re
leas
e th
e po
rts w
hen
it fin
ishe
s.
If w
e w
ant t
o ge
t the
IRQ
num
ber
of a
n IS
A de
vice
in th
e de
vice
driv
er, w
e ca
n us
e th
e fo
llow
ing
func
tions
: un
sign
ed lo
ng p
robe
_irq
_on(
void
); in
t pro
be_i
rq_o
ff(un
sign
ed lo
ng);
The
func
tion
prob
e_irq
_on(
) ret
urns
a b
it m
ask
of u
nass
igne
d in
terr
upts
. The
dr
iver
mus
t pr
eser
ve t
he r
etur
ned
bit
mas
k an
d pa
ss it
to
prob
e_irq
_off(
) la
ter.
Afte
r pr
obe_
irq_o
n(),
the
driv
er s
houl
d ar
rang
e fo
r its
dev
ice
to g
ener
ate
at le
ast
one
inte
rrupt
. A
fter
the
devi
ce h
as r
eque
sted
an
inte
rrupt
, th
e dr
iver
cal
ls
prob
e_irq
_off(
), pa
ssin
g as
ar
gum
ent
the
bit
mas
k pr
evio
usly
re
turn
ed
by
prob
e_irq
_on(
). Th
e fu
nctio
n pr
obe_
irq_o
ff()
retu
rns
the
num
ber
of t
he in
terru
pt
that
was
issu
ed a
fter p
robe
_irq
_on(
). In
terr
upt H
andl
ing
Dat
a tra
nsfe
rred
to o
r fro
m h
ardw
are
devi
ce m
ight
exp
erie
nce
dela
y fo
r som
e re
ason
. The
refo
re, t
he d
evic
e dr
iver
sho
uld
buffe
r th
ese
data
for
a w
hile
. A g
ood
buffe
ring
mec
hani
sm is
inte
rrup
t-driv
en I/
O, w
hich
mea
ns th
e in
put b
uffe
r is
fille
d at
inte
rrupt
tim
e by
an
inte
rrupt
han
dler
and
is c
onsu
med
by
the
proc
ess
late
r. S
imila
rly,
the
outp
ut b
uffe
r is
fille
d by
the
pro
cess
and
is c
onsu
med
at
inte
rrup
t tim
e by
an
inte
rrupt
han
dler
late
r. Fo
r the
mos
t par
t, a
devi
ce d
river
onl
y ne
eds
to
regi
ster
an
inte
rrup
t han
dler
for
its d
evic
e, a
nd h
andl
e th
em p
rope
rly w
hen
they
ar
rive.
We
use
follo
win
g fu
nctio
ns t
o re
gist
er (
inst
all)
and
free
(uni
nsta
ll) a
n in
terru
pt h
andl
er.
#inc
lude
<lin
ux/s
ched
.h>;
in
t re
ques
t_irq
(uns
igne
d in
t, vo
id*
(int,
void
*,
stru
ct p
t_re
gs *
), un
sign
ed
long
, con
st c
har *
,voi
d *)
; vo
id fr
ee_i
rq (u
nsig
ned
int ,
voi
d*);
Whe
n an
inte
rrupt
hap
pens
, a s
erie
s of
eve
nts
liste
d in
Fig
ure
1 m
ay o
ccur
in
the
syst
em.
1. H
ardw
are
stac
ks p
rogr
am c
ount
er, e
tc.
2. H
ardw
are
load
s a
new
pro
gram
cou
nter
from
the
inte
rrupt
vec
tor.
3. A
ssem
bly
lang
uage
pro
cedu
re s
aves
regi
ster
s.
4. A
ssem
bly
lang
uage
pro
cedu
re s
ets
up a
new
sta
ck, a
nd c
alls
a C
pro
cedu
re to
do
the
actu
al w
ork
of p
roce
ssin
g th
e in
terru
pt.
5. C
lang
uage
pro
cedu
re h
andl
es a
ctua
l int
erru
pt r
outin
e, w
akes
up
the
proc
ess,
m
ay c
all s
ched
ule(
), an
d fin
ally
retu
rns
to th
e as
sem
bly
lang
uage
.
63
6. A
ssem
bly
lang
uage
pro
cedu
re s
tarts
up
curre
nt p
roce
ss.
Item
3 to
6 b
elon
g to
the
ISR
pro
cess
, and
Item
5 is
the
inte
rrupt
han
dler
.Old
ve
rsio
ns o
f th
e Li
nux
kern
el t
ook
grea
t pa
ins
to d
istin
guis
h be
twee
n “fa
st”
and
“slo
w” i
nter
rupt
s. F
ast i
nter
rupt
s ar
e th
ose
that
can
be
hand
led
very
fast
, whe
reas
sl
ow o
nes
will
take
muc
h lo
nger
tim
e. I
n fu
nctio
n re
ques
t_irq
(),
the
“flag
s”
argu
men
t can
be
set t
o S
A_I
NTE
RR
UP
T fo
r ins
tallin
g a
fast
han
dler
. How
ever
, in
mod
ern
kern
els,
fas
t an
d sl
ow i
nter
rupt
s ar
e al
mos
t th
e sa
me.
Bel
ow a
re t
he
com
paris
ons
betw
een
fast
and
slo
w in
terru
pts:
Func
tions
Fa
st in
terr
upt
Slo
w in
terr
upt
Dis
able
int
erru
pt r
epor
ting
in
the
mic
ropr
oces
sor
whe
n th
e ha
ndle
r run
s Ye
s N
o
Dis
able
in
terru
pt
bein
g se
rvic
ed
in
the
inte
rrupt
co
ntro
ller
whe
n th
e ha
ndle
r ru
ns
Yes
Yes
Cal
l re
t_fro
m_s
ys_c
all()
afte
r th
e IS
R
finis
hes.
N
o Ye
s
Figu
re 2
. Com
pare
bet
wee
n fa
st a
nd sl
ow in
terr
upts
The
job
of a
n in
terru
pt h
andl
er d
oes
the
follo
win
g im
porta
nt th
ings
:
Con
side
r the
mea
ning
of t
he in
terru
pt
W
ake
up th
e pr
oces
s w
aitin
g th
e in
terru
pt to
be
com
plet
ed
If
part
of t
he s
ervi
ce r
outin
e ta
kes
time,
we
can
use
the
“bot
tom
hal
f” m
echa
nism
to h
andl
e, w
hich
will
be d
iscu
ssed
late
r.
Ther
e ar
e so
me
rest
rictio
ns o
n w
hat
an in
terru
pt h
andl
er c
an d
o be
caus
e it
runs
at t
he in
terru
pt ti
me.
An
inte
rrupt
han
dler
can
not t
rans
fer d
ata
to o
r fro
m th
e us
er s
pace
, be
caus
e it
does
not
exe
cute
in
the
cont
ext
of a
pro
cess
. A
lso,
it
cann
ot d
o an
ythi
ng th
at w
ill m
ake
itsel
f sle
ep, s
uch
as c
allin
g sl
eep_
on()
. The
re
are
thre
e ar
gum
ents
pas
sed
to a
n in
terru
pt h
andl
er:
irq,
dev_
id,
and
regs
. Th
e in
terru
pt n
umbe
r, in
t irq
, can
be
used
as
a lo
g m
essa
ge. T
he s
econ
d ar
gum
ent,
void
*de
v_id
, is
a po
inte
r to
the
devi
ce. W
hen
we
use
shar
ed in
terr
upts
(e.g
., tw
o in
terr
upt h
andl
ers
shar
e an
IRQ
num
ber)
, the
sha
red
hand
ler
can
use
dev_
id to
re
cogn
ize
its o
wn
inte
rrup
t. Th
e la
st a
rgum
ent,
stru
ct p
t_re
gs *r
egs,
is ra
rely
use
d.
It ho
lds
the
proc
esso
r con
text
bef
ore
the
proc
esso
r ent
ers
inte
rrupt
han
dler
, so
it ca
n us
ed fo
r mon
itorin
g an
d de
bugg
ing.
O
ne o
f the
mai
n pr
oble
ms
with
inte
rrupt
han
dlin
g is
how
to p
erfo
rm lo
ng ta
sks
64
with
in a
n in
terru
pt h
andl
er. T
here
is o
ften
muc
h w
ork
to d
o in
resp
onse
to a
dev
ice
inte
rrupt
, but
inte
rrupt
han
dler
s ne
ed to
com
plet
e qu
ickl
y an
d no
t kee
p in
terru
pts
too
long
. O
bvio
usly,
the
se t
wo
will
con
flict
with
eac
h ot
her.
Linu
x re
solv
es t
his
prob
lem
by
split
ting
the
inte
rrupt
han
dler
into
two
halv
es. O
ne is
top
half,
whi
ch is
th
e ro
utin
e th
at a
ctua
lly r
espo
nds
to th
e in
terru
pt. A
nd, i
t is
also
the
one
that
we
use
requ
est_
irq()
to re
gist
er w
ith. T
he o
ther
one
is b
otto
m h
alf.
It ha
ndle
s th
e pa
rt th
at ta
kes
time
of a
task
. And
it is
sch
edul
ed b
y th
e to
p ha
lf to
be
exec
uted
at a
sa
fer
time,
whi
ch m
eans
the
requ
irem
ent o
f exe
cutio
n tim
e is
not
so
criti
cal.
The
Linu
x ke
rnel
has
tw
o di
ffere
nt m
echa
nism
s th
at m
ay b
e us
ed t
o im
plem
ent
botto
m-h
alf p
roce
ssin
g. T
hey
are
BH
(al
so c
alle
d bo
ttom
hal
f) an
d ta
skle
ts. T
he
BH
impl
emen
tatio
n is
the
olde
r on
e, a
nd it
is im
plem
ente
d w
ith ta
skle
ts in
ker
nel
2.4.
Tas
klet
s w
ere
intro
duce
d in
the
2.3
deve
lopm
ent s
erie
s, a
nd th
ey a
re n
ow th
e pr
efer
red
way
to d
o bo
ttom
-hal
f pro
cess
ing.
Des
pite
this
, tas
klet
s ar
e no
t por
tabl
e to
ear
lier k
erne
ls. S
o, if
the
porta
bilit
y is
a c
once
rn, B
H is
pre
fera
ble.
Th
e fo
llow
ing
func
tions
are
use
ful f
or u
sing
task
lets
: D
ECLA
RE_
TASK
LET(
nam
e, fu
nctio
n, d
ata)
; ta
skle
t_sc
hedu
le(s
truc
t tas
klet
_str
uct *
t);
For e
xam
ple,
if y
ou w
rite
a fu
nctio
n fu
nc()
to b
e us
ed a
s a
botto
m-h
alf r
outin
e.
The
first
ste
p is
to d
ecla
re th
e ta
skle
t by
DEC
LAR
E_TA
SKLE
T(ta
sk,fu
nc,0
) whi
ch
task
is th
e na
me
give
n to
the
task
let.
Then
you
hav
e to
sch
edul
e th
e ta
skle
t by
task
let_
sche
dule
(&ta
sk).
The
actu
al ta
skle
t rou
tine,
task
, will
be e
xecu
ted
shor
tly
at th
e sy
stem
’s c
onve
nien
ce. A
s m
entio
ned
earli
er, t
his
rout
ine
perfo
rms
the
bulk
of
the
wor
k of
han
dlin
g th
e in
terru
pt.
In th
e B
H im
plem
enta
tion,
if y
ou w
ant t
o sc
hedu
le a
bot
tom
hal
f for
run
ning
, yo
u ca
n us
e th
e fu
nctio
n be
low
: vo
id m
ark_
bh(in
t nr)
; H
ere,
nr i
s th
e nu
mbe
r of t
he B
H to
be
activ
ated
. In
the
olde
r BH
impl
emen
tatio
n,
mar
k_bh
() w
ould
set
a b
it in
a b
it m
ask,
allo
win
g th
e co
rresp
ondi
ng b
otto
m-h
alf
hand
ler
to
be
foun
d qu
ickl
y at
ru
ntim
e.
In
mod
ern
kern
els,
it
just
ca
lls
task
let_
hi_s
ched
ule(
), lik
e ta
skle
t_sc
hedu
le,
to s
ched
ule
the
botto
m-h
alf
rout
ine
for e
xecu
tion.
N
ow, t
he la
st is
sue
we
wan
t to
disc
uss
in in
terru
pt h
andl
ing
is r
ace
cond
ition
. Th
e in
terru
pt-d
riven
I/O
int
rodu
ces
the
prob
lem
of
sync
hron
izin
g co
ncur
rent
ac
cess
to s
hare
d da
ta it
ems
and
all t
he is
sues
rela
ted
to ra
ce c
ondi
tion.
Sin
ce a
n in
terru
pt c
an h
appe
n at
any
tim
e, it
can
cau
se th
e in
terru
pt h
andl
er to
be
exec
uted
in
the
mid
dle
of a
n ar
bitra
ry p
iece
of d
river
cod
e. T
here
fore
, a d
evic
e dr
iver
that
is
wor
king
with
inte
rrup
ts (
In fa
ct, i
t’s th
e m
ost c
ase)
mus
t be
very
con
cern
ed w
ith
race
con
ditio
ns. I
n Li
nux,
ther
e ar
e m
any
tech
niqu
es to
pre
vent
dat
a co
rrupt
ion,
65
but w
e on
ly in
trodu
ce th
e m
ost c
omm
on o
ne: U
sing
spi
nloc
ks to
enf
orce
mut
ual
excl
usio
n.
Spin
lock
s ar
e re
pres
ente
d by
the
typ
e sp
inlo
ck_t
. Th
ere
are
a nu
mbe
r of
fu
nctio
ns (a
ctua
lly m
acro
s) w
orki
ng w
ith s
pinl
ocks
: vo
id s
pin_
lock
(spi
nloc
k_t *
lock
); vo
id s
pin_
lock
_irq
save
(spi
nloc
k_t *
lock
, uns
igne
d lo
ng fl
ags)
; vo
id s
pin_
lock
_irq
(spi
nloc
k_t *
lock
); vo
id s
pin_
lock
_bh(
spin
lock
_t *l
ock)
; vo
id s
pin_
unlo
ck(s
pinl
ock_
t *lo
ck);
void
spi
n_un
lock
_irq
rest
ore(
spin
lock
_t *l
ock,
uns
igne
d lo
ng fl
ags)
; vo
id s
pin_
unlo
ck_i
rq(s
pinl
ock_
t *lo
ck);
void
spi
n_un
lock
_bh(
spin
lock
_t *l
ock)
; Th
e sp
in_l
ock(
) sp
ins
(bus
y-w
ait)
to a
cqui
re t
he g
iven
lock
. U
pon
retu
rnin
g fro
m s
pin_
lock
(), t
he c
alle
r ow
ns th
e lo
ck. T
he s
pin_
lock
_irq
save
() a
lso
acqu
ires
the
lock
. In
addi
tion,
it d
isab
les
inte
rrupt
s on
the
loca
l pro
cess
or a
nd s
tore
s th
e cu
rren
t in
terr
upt
stat
e in
ar
gum
ent
flags
. Th
e sp
in_l
ock_
irq()
ac
ts
like
spin
_loc
k_irq
save
(), e
xcep
t tha
t it d
oes
not s
ave
the
curre
nt in
terru
pt s
tate
. The
sp
in_l
ock_
bh()
obt
ains
the
give
n lo
ck a
nd p
reve
nts
the
exec
utio
n of
bot
tom
hal
ves.
Th
ose
unlo
ck fu
nctio
ns a
re th
e co
unte
rpar
ts o
f the
var
ious
lock
ing
prim
itive
s. T
he
spin
_unl
ock(
) unl
ocks
the
give
n lo
ck.
The
spin
_unl
ock_
irqre
stor
e()
unlo
cks
the
give
n lo
ck a
nd e
nabl
es i
nter
rupt
s de
pend
ing
on th
e fla
gs v
alue
, whi
ch s
houl
d co
mes
from
spi
n_lo
ck_i
rqsa
ve()
. The
sp
in_u
nloc
k_irq
() u
nloc
ks t
he g
iven
lock
and
ena
bles
inte
rrupt
s un
cond
ition
ally.
Th
e sp
in_u
nloc
k_bh
() u
nloc
ks th
e gi
ven
lock
and
ena
bles
bot
tom
-hal
f pro
cess
ing.
In
eac
h ca
se,
you
shou
ld m
ake
sure
tha
t lo
ck f
unct
ions
to
be e
xecu
ted
befo
re
unlo
ck f
unct
ions
, an
d th
ey a
re a
ll pa
ired.
Oth
erw
ise,
ser
ious
dis
orde
r m
ay
happ
en.
Com
mun
icat
e w
ith H
ardw
are
thro
ugh
I/O P
orts
A
fter
prob
ing
hard
war
e, t
he d
evic
e dr
iver
can
obt
ain
the
I/O p
orts
and
use
th
em in
its
activ
ities
. Mos
t har
dwar
e di
ffere
ntia
tes
betw
een
8-bi
t, 16
-bit,
and
32-
bit
ports
. Th
eref
ore,
a C
pro
gram
mus
t ca
ll di
ffere
nt f
unct
ions
to
acce
ss p
orts
of
diffe
rent
siz
es.
The
Linu
x ke
rnel
def
ines
the
fol
low
ing
func
tions
to
acce
ss I
/O
ports
.
unsi
gned
inb
(uns
igne
d po
rt);
void
out
b (u
nsig
ned
char
bye
, uns
igne
d p
ort);
Th
e in
b() r
eads
byt
e (8
-bit)
por
t, w
hile
the
outb
() w
rites
byt
e po
rt.
66
unsi
gned
inw
(uns
igne
d po
rt);
void
out
w (u
nsig
ned
char
bye
, uns
igne
d p
ort);
Th
e in
w()
read
s 16
-bit
port,
whi
le th
e ou
tw()
writ
es 1
6-bi
t por
t. un
sign
ed in
l (un
sign
ed p
ort);
vo
id o
utl (
unsi
gned
cha
r bye
, uns
igne
d p
ort);
Th
e in
l() re
ads
32-b
it po
rt, w
hile
the
outl(
) writ
es 3
2-bi
t por
t. In
add
ition
to
the
sing
le-s
hot
in a
nd o
ut o
pera
tions
, th
ere
are
strin
g op
erat
ions
su
ppor
ted
in L
inux
: vo
id in
sb (u
nsig
ned
port
, voi
d *a
ddr,
unsi
gned
long
cou
nt);
void
out
sb (u
nsig
ned
port
, voi
d *a
ddr,
unsi
gned
long
cou
nt);
The
insb
() r
eads
cou
nt b
ytes
from
byt
e po
rt, a
nd s
tore
s th
ese
byte
s to
mem
ory
star
ting
at t
he a
ddre
ss a
ddr.
The
outs
b()
writ
es c
ount
byt
es lo
cate
d at
mem
ory
addr
ess
addr
to b
yte
port.
vo
id in
sw (u
nsig
ned
port
, voi
d *a
ddr,
unsi
gned
long
cou
nt);
void
out
sw (u
nsig
ned
por
t, vo
id *a
ddr,
unsi
gned
long
cou
nt);
Thei
r ope
ratio
ns a
re s
imila
r to
the
abov
e fu
nctio
ns, e
xcep
t the
por
t is
a 16
-bit
port.
vo
id in
sl (u
nsig
ned
port
, voi
d *a
ddr,
unsi
gned
long
cou
nt);
void
out
sl (u
nsig
ned
por
t, vo
id *a
ddr,
unsi
gned
long
cou
nt);
Thei
r ope
ratio
ns a
re s
imila
r to
the
abov
e fu
nctio
ns, e
xcep
t the
por
t is
a 32
-bit
port.
2.
5.3
Linu
x O
pen
Sour
ce Im
plem
enta
tion:
A N
etw
ork
Dev
ice
Driv
er
In
this
sec
tion,
we
use
a re
al-w
orld
net
wor
k de
vice
driv
er in
Lin
ux, n
e2k-
pci,
as
an e
xam
ple.
A n
etw
ork
devi
ce d
river
is u
sed
to b
e a
“brid
ge” b
etw
een
the
netw
ork
inte
rface
car
d (N
IC) a
nd th
e pr
otoc
ol d
river
(e.g
., TC
P/IP
pro
toco
l sta
ck).
Als
o, th
e in
terru
pt-d
riven
I/O
is a
pplie
d he
re. W
hen
a N
IC re
ceiv
es p
acke
t, it
notif
ies
the
OS
by
int
erru
ptin
g th
e C
PU
. Th
en,
the
inte
rrupt
han
dler
tra
nsfe
rs t
he i
ncom
ing
pack
ets
from
NIC
mem
ory
to s
yste
m m
emor
y, p
roce
sses
the
pack
et, a
nd fi
nally
pu
shes
it
into
the
ker
nel
queu
e to
be
hand
led
by t
he b
otto
m-h
alf
rout
ine
(e.g
. TC
P/IP
pro
toco
l st
ack)
. W
hen
the
kern
el g
ets
a pa
cket
to
be s
ent
out,
it fir
st
pass
es th
e pa
cket
to th
e N
IC d
river
. The
n th
e dr
iver
will
pro
cess
the
pack
et, s
uch
as fi
lling
the
MA
C a
ddre
ss in
to th
e pa
cket
. Fin
ally,
the
driv
er tr
ansf
ers
the
pack
et
from
sys
tem
mem
ory
to N
IC m
emor
y. A
fter
the
pack
et is
tran
smitt
ed c
ompl
etel
y,
the
NIC
will
inte
rrupt
the
CP
U to
not
ify th
e O
S. E
very
tim
e th
e in
terru
pt h
andl
er
finis
hes
an in
terru
pt, i
t will
ackn
owle
dge
the
NIC
by
writ
ing
som
e m
essa
ges
to th
e N
IC re
gist
ers.
In
Lin
ux 2
.4,
ther
e ar
e tw
o im
porta
nt d
ata
stru
ctur
es w
hich
are
sk_
buff
and
67
net_
devi
ce u
sed
in a
NIC
driv
er. T
he s
k_bu
ff st
ruct
ure
repr
esen
ts a
pac
ket,
whi
le
the
net_
devi
ce s
tand
s fo
r a
netw
ork
devi
ce. W
e sh
ow th
at w
here
thes
e tw
o da
ta
stru
ctur
es lo
cate
in L
inux
in F
ig. 2
.
In F
ig.
2, t
he N
IC d
river
get
s a
fram
e fro
m N
IC,
then
it a
lloca
tes
the
spac
e of
sk
_buf
f to
hold
this
fram
e in
the
field
“dat
a” o
f sk_
buff.
Afte
rwar
d, th
is fr
ame
“live
s”
in th
e ke
rnel
by
the
figur
e of
sk_
buff.
The
sk_
buff
stru
ctur
e is
def
ined
in h
eade
r file
<l
inux
/skb
uff.h
>, a
nd th
e fo
llow
ing
Tabl
e 2.
exp
lain
s m
ajor
fiel
ds o
f sk_
buff.
Fiel
d M
eani
ng
head
po
inte
r to
the
star
t of s
k_bu
ff
data
po
inte
r to
the
star
t of “
actu
al d
ata”
(pac
ket)
tail
poin
ter t
o th
e en
d of
“act
ual d
ata”
(pac
ket)
end
poin
ter t
o th
e en
d of
sk_
buff
dev
devi
ce th
at p
acke
ts a
rrive
on
or le
ave
by.
len
leng
th o
f “ac
tual
dat
a” (p
acke
t)
pkt_
type
pa
cket
cla
ss
h tra
nspo
rt la
yer h
eade
r
nh
netw
ork
laye
r hea
der
mac
lin
k la
yer h
eade
r
Reg
ardi
ng t
he t
rans
latio
n be
twee
n ne
t_de
vice
stru
ctur
e an
d lo
cal
(not
a d
ata
stru
ctur
e) ,
it m
eans
mos
t fie
lds
of n
et_d
evic
e ge
t val
ues
in N
IC d
river
and
thes
e va
lues
are
gen
erat
ed in
NIC
driv
er lo
cally
. The
net
_dev
ice
stru
ctur
e is
def
ined
in
head
er fi
le <
linux
/net
devi
ce.h
>, a
nd T
able
2. l
ists
mai
n fie
lds
of n
et_d
evic
e.
Ker
nel
sk_b
uff
net_
devi
ce
NIC
driv
er
sk_b
uff
fram
e ne
t_de
vice
lo
cal
NIC
Figu
re 2
. Loc
atio
n of
sk_
buff
and
net_
devi
ce
Tabl
e 2.
sk_b
uff s
truct
ure
68
B
efor
e a
driv
er c
an tr
ansm
it an
d re
ceiv
e pa
cket
s, it
mus
t do
the
initi
aliz
atio
n st
uff w
hich
con
tain
s “re
gist
ry o
f an
inte
rrupt
han
dler
” an
d “p
robe
har
dwar
e”. W
e ca
n us
e re
ques
t_irq
( ) to
regi
ster
an
inte
rrupt
han
dler
. How
ever
, thi
s dr
iver
ser
ves
for
PC
I ne
twor
k de
vice
so
it do
n’t
have
to
do t
he r
eal
prob
ing
actio
n. T
he
fund
amen
tal
job
of a
NIC
driv
er i
s to
del
iver
pac
kets
bet
wee
n ke
rnel
and
a
netw
ork
devi
ce.
Hen
ce,
we
illust
rate
pac
ket
trans
mis
sion
and
rec
eptio
n w
ith
ne2k
-pci
NIC
driv
er in
the
Fig.
2 a
nd F
ig. 2
.
Fiel
d M
eani
ng
Nam
e de
vice
nam
e
base
_add
r de
vice
I/O
add
ress
irq
devi
ce IR
Q n
umbe
r
dev_
addr
ha
rdw
are
addr
ess
mtu
in
terfa
ce M
TU v
alue
hard
_sta
rt_xm
it tra
nsm
issi
on s
ervi
ce
Tabl
e 2.
net
_dev
ice
stru
ctur
e
kern
el(in
terr
upt h
andl
er)
ei_i
nter
rupt
(TX
) ei
_sta
rt_xm
it
(RX
) ei
_rec
eive
ei_t
x_in
tr
NIC
1. d
ev->
hard
_sta
rt_xm
it
2. n
e2k_
pci_
bloc
k_ou
tput
3. N
S83
90_t
rigge
r_se
nd
4. a
n in
terru
pt o
ccur
s
5.
6.7.
NS
8390
_trig
ger_
send
8.
net
if_w
ake_
queu
e
Figu
re 2
. pac
ket t
rans
mis
sion
69
In th
e pa
cket
tran
smis
sion
pha
se, w
hen
the
kern
el w
ants
to s
end
a pa
cket
, it c
alls
tra
nsm
issi
on
serv
ice
rout
ine
dev-
>har
d_st
art_
xmit(
)
whi
ch
is
actu
ally
im
plem
ente
d by
ne2
k-pc
i and
nam
ed e
i_st
art_
xmit(
).
ei_s
tart_
xmit(
) f
irst
uses
ne
2k_p
ci_b
lock
_out
put(
) w
hich
mov
es p
acke
ts f
rom
sys
tem
mem
ory
to N
IC
mem
ory,
then
cal
ls N
S83
90_t
rigge
r_se
nd( )
that
trig
gers
the
NIC
to p
ush
pack
ets
out.
As
the
pack
et tr
ansm
issi
on is
com
plet
ed, N
IC is
sues
an
inte
rrup
t to
caus
e th
e ke
rnel
’s a
ttent
ion.
Con
sequ
ently
, th
e ke
rnel
cal
ls t
he c
orre
spon
ding
int
erru
pt
hand
ler
whi
ch is
reg
iste
red
usin
g re
ques
t_irq
( )
in in
itial
izat
ion
step
, an
d he
re it
m
eans
ei_
inte
rrup
t( ).
ei_i
nter
rupt
( ) e
xam
ines
wha
t the
inte
rrupt
mea
ns, b
ecau
se
this
is a
n in
terru
pt o
f tra
nsm
issi
on c
ompl
ete,
it c
alls
ei_
tx_i
ntr(
) to
che
ck fo
r err
or
and
then
tri
gger
th
e ne
xt
pack
et
to
be
sent
. Fi
nally
, ei
_tx_
intr(
)
calls
ne
tif_w
ake_
queu
e( )
to te
ll th
e ke
rnel
that
it c
an g
o on
to tr
ansm
it pa
cket
s.
In th
e pa
cket
rece
ptio
n ph
ase,
as
long
as
the
NIC
rece
ive
a pa
cket
, it c
ause
s an
in
terru
pt t
o te
ll th
e ke
rnel
tha
t so
me
pack
et h
as a
rrive
d. T
hen
the
kern
el c
alls
ei
_int
erru
pt(
) to
hand
le th
is in
terru
pt. e
i_in
terru
pt(
) fin
ds o
ut th
at th
is in
terru
pt is
du
e to
a p
acke
t rec
eptio
n, s
o it
calls
ei_
rece
ive(
) to
get
it o
ut o
f the
NIC
’s b
uffe
r. ei
_rec
eive
( ) c
alls
ne2
k_pc
i_bl
ock_
inpu
t( ) t
o m
ove
the
pack
et fr
om N
IC m
emor
y to
sys
tem
mem
ory,
then
it c
alls
net
if_rx
( ) to
enq
ueue
this
pac
ket i
n so
me
kern
el’s
qu
eue
to b
e pr
oces
sed
by n
etw
orki
ng s
yste
m w
hich
is li
ke b
otto
m-h
alf r
outin
e to
do
the
long
ish
task
s.
kern
el
(inte
rrupt
han
dler
)
ei_i
nter
rupt
(TX
) ei
_sta
rt_xm
it
(RX
) ei
_rec
eive
ei_t
x_in
tr
NIC
1. a
n in
terru
pt
occu
rs
2.
3.
4. n
e2k_
pci_
bloc
k_in
put
5. n
etif_
rx
Figu
re 2
. pac
ket r
ecep
tion
70
2.6
Pitfa
lls a
nd fa
llaci
es
Ethe
rnet
per
form
ance
(util
izat
ion
in h
alf-d
uple
x an
d fu
ll-du
plex
mod
e)
R
esea
rche
rs a
re in
tere
sted
in t
he m
axim
um c
hann
el u
tiliz
atio
n of
Eth
erne
t un
der
extre
mel
y he
avy
load
, de
spite
tha
t th
e si
tuat
ion
is u
nlik
ely
to h
appe
n.
Com
pute
r si
mul
atio
n, m
athe
mat
ical
ana
lysi
s, a
nd r
eal-w
orld
mea
sure
men
t, ar
e po
ssib
le a
ppro
ache
s to
obt
ain
the
valu
e. U
nlik
e si
mpl
e m
echa
nism
s su
ch a
s A
LOH
A,
slot
ted
ALO
HA
, an
alyz
ing
full
set
of C
SM
A/C
D m
athe
mat
ical
ly is
ver
y di
fficu
lt. A
s ea
rly a
s th
e in
vent
ion
of th
e ex
perim
enta
l Eth
erne
t at t
he X
erox
lab,
B
ob M
etca
lfe a
nd D
avid
Bog
gs h
ad p
ublis
hed
a pa
per
that
rep
orte
d a
max
imum
of
abo
ut 3
7 pe
rcen
t cha
nnel
util
izat
ion
the
Eth
erne
t can
reac
h w
ith th
eir s
impl
ified
m
odel
. U
nfor
tuna
tely,
the
val
ue h
as b
een
cite
d ov
er y
ears
, ev
en t
houg
h th
e E
ther
net
tech
nolo
gy h
as b
een
alm
ost
diffe
rent
fro
m t
he e
xper
imen
tal o
ne s
ince
th
e D
IX S
tand
ard.
Diff
eren
t FC
S,
diffe
rent
pre
ambl
e, d
iffer
ent
addr
ess
form
at,
diffe
rent
PH
Y, a
nd s
o on
– e
xcep
t tha
t the
spi
rit o
f CS
MA
/CD
was
res
erve
d, le
t al
one
the
sim
plifi
ed m
odel
tha
t is
diff
eren
t fro
m a
rea
l-wor
ld s
ituat
ion.
Bes
ides
, 25
6 st
atio
ns a
re a
ssum
ed i
n th
e sa
me
collis
ion
dom
ain,
whi
ch i
s un
likel
y to
ha
ppen
in th
e re
al w
orld
. A
late
r pa
per
publ
ishe
d by
Dav
id B
oggs
et
al.
in 1
988
tried
to
clar
ify t
he
pitfa
lls. T
hey
perfo
rmed
a re
al-w
orld
test
ing
on a
10
Mb/
s E
ther
net s
yste
m w
ith 2
4 st
atio
ns b
y flo
odin
g fra
mes
con
stan
tly. I
t sho
wed
the
utiliz
atio
n is
mor
e th
an 9
5%
with
the
max
imum
fram
e an
d ab
out 9
0% w
ith th
e m
inim
um fr
ame12
und
er s
tress
te
stin
g. It
sho
wed
Eth
erne
t per
form
ance
is ra
ther
sat
isfa
ctor
y.
As
switc
hes
beco
me
mor
e po
pula
r, m
ulti-
segm
ent n
etw
orks
are
div
ided
into
m
any
indi
vidu
al c
ollis
ion
dom
ains
. Th
e si
tuat
ion
of m
any
stat
ions
in
the
sam
e co
llisio
n do
mai
n is
fur
ther
red
uced
. S
ince
the
adv
ent
of f
ull-d
uple
x op
erat
ion,
th
ere
is n
o re
stric
tion
impo
sed
by C
SM
A/C
D a
t al
l. B
oth
side
s of
a l
ink
can
trans
mit
as fa
st a
s it
can
do. F
or a
sw
itch
that
affo
rds
max
imum
fram
e ra
te a
nd
data
cap
acity
, it i
s ca
lled
a w
ire-s
peed
or n
on-b
lock
ing
switc
h.
Ano
ther
inte
rest
ing
prob
lem
that
mig
ht b
e of
con
cern
is th
at th
e da
ta fi
eld
in
the
Eth
erne
t fra
me
is n
ot “
long
” en
ough
. Com
pare
d w
ith o
ther
tech
nolo
gies
, say
To
ken
Rin
g, w
hich
has
dat
a fie
ld o
f 452
8 by
tes
at 4
Mb/
s an
d 18
173
byte
s at
16
or
100
Mb/
s, t
he d
ata
field
is
only
150
0 by
tes
out
of 1
518
byte
s of
a m
axim
um
12
Bog
g’s
pape
r cou
nts
over
head
s in
hea
der,
traile
r, an
d IF
G, in
to u
tiliz
atio
n. H
ence
, one
hun
dred
per
cent
ut
iliza
tion
is a
ssum
ed if
ther
e is
no
colli
sion
des
pite
thos
e ov
erhe
ads i
n hi
s pap
er.
71
unta
gged
fra
me.
Peo
ple
may
be
susp
icio
us t
hat
the
perc
enta
ge o
f no
n-da
ta
over
head
s, i
nclu
ding
hea
der
info
rmat
ion,
tra
iler,
and
IFG
, is
lar
ger
than
oth
er
tech
nolo
gies
. Th
ere
is a
his
toric
al r
easo
n w
hy th
e E
ther
net f
ram
e is
not
so
long
. Eth
erne
t w
as in
vent
ed m
ore
than
20
year
s ag
o. M
emor
y w
as e
xpen
sive
at t
hat t
ime.
The
bu
ffer
mem
ory
for
fram
es w
as q
uite
lim
ited
in s
ize
on th
ose
days
. It m
ade
sens
e to
des
ign
a fra
me
that
is n
ot to
o lo
ng, a
nd n
or is
the
data
fiel
d.
Thin
gs a
re n
ot t
hat
bad
as t
hey
look
! Fo
r la
rge
data
tra
nsfe
r su
ch a
s FT
P tra
ffic,
whi
ch te
nds
to tr
ansf
er w
ith lo
ng fr
ames
, the
dat
a fie
ld c
an o
ccup
y as
hig
h as
150
0 /
(151
8+8+
12)
= 97
.5%
of
the
chan
nel b
andw
idth
. Th
e ov
erhe
ads
are
quite
low
! It
is h
ardl
y to
im
prov
e th
is v
alue
sig
nific
antly
by
incr
easi
ng t
he
max
imum
fram
e si
ze.
Col
lisio
n do
mai
n, b
road
cast
dom
ain,
and
VLA
N
Th
e fir
st tw
o te
rms
are
ofte
n co
nfus
ed fo
r stu
dent
s w
ho fi
rst l
earn
Eth
erne
t. A
collis
ion
dom
ain
is a
rang
e of
net
wor
k in
whi
ch m
ore
than
one
tran
smis
sion
at t
he
sam
e tim
e re
sults
in a
col
lisio
n. F
or e
xam
ple,
a r
epea
ter
hub
and
the
stat
ions
at
tach
ed t
o it
form
a c
ollis
ion
dom
ain.
In
cont
rast
, a
switc
h ex
plic
itly
sepa
rate
s co
llisio
n do
mai
n fro
m o
ne p
ort t
o an
othe
r. In
oth
er w
ords
, a tr
ansm
issi
on fr
om a
sh
ared
LA
N a
ttach
ed t
o on
e po
rt w
ill no
t re
sult
in a
col
lisio
n w
ith a
noth
er
trans
mis
sion
from
the
LAN
bel
ongi
ng to
ano
ther
por
t. H
owev
er, w
hen
a fra
me
has
a br
oadc
ast a
ddre
ss a
s th
e de
stin
atio
n, a
sw
itch
will
still
forw
ard
to a
ll po
rts b
ut t
he s
ourc
e. T
he r
ange
of
netw
ork
that
the
br
oadc
ast
traffi
c ca
n re
ach
is a
bro
adca
st d
omai
n. S
omet
imes
, w
e ne
ed t
o co
nfin
e th
e br
oadc
ast
traffi
c fo
r se
curit
y re
ason
or
band
wid
th s
avin
g. A
VLA
N
appr
oach
sep
arat
es b
road
cast
dom
ains
from
one
VLA
N to
ano
ther
. It i
s a
logi
cal
sepa
ratio
n fro
m p
hysi
cal c
onne
ctiv
ity. A
dev
ice
prov
idin
g hi
gh-la
yer
conn
ectiv
ity,
such
as
a ro
uter
, is
need
ed to
con
nect
two
or m
ore
sepa
rate
VLA
Ns.
5-4-
3 ru
le a
nd m
ulti-
segm
ent n
etw
orks
It is
sai
d th
at E
ther
net
follo
ws
the
5-4-
3 ru
le.
It so
unds
eas
y to
rem
embe
r. H
owev
er, t
he ru
le is
not
as
sim
ple
as it
sou
nds.
Bes
ides
, the
rule
is a
ctua
lly o
ne o
f th
e co
nser
vativ
e ru
les
that
val
idat
e th
e co
rrect
ness
of
10 M
b/s
mul
ti-se
gmen
t E
ther
net n
etw
orks
. It i
s no
t a la
w th
at e
very
Eth
erne
t dep
loym
ent s
houl
d fo
llow.
Le
t’s g
o to
the
deta
il.
As
we
men
tione
d, t
he r
ound
-trip
pro
paga
tion
time
in a
col
lisio
n do
mai
n
72
shou
ld n
ot b
e to
o lo
ng fo
r pro
per o
pera
tion.
Diff
eren
t tra
nsm
issi
on m
edia
and
the
num
ber
of r
epea
ter
hubs
offe
r di
ffere
nt d
elay
s, h
owev
er.
As
a qu
ick
guid
e fo
r ne
twor
k ad
min
istra
tors
, the
IEE
E 8
02.3
Sta
ndar
d of
fers
two
Tran
smis
sion
Sys
tem
M
odel
s. T
rans
mis
sion
Sys
tem
Mod
el 1
is a
set
of
conf
igur
atio
ns t
hat
mee
t th
e ab
ove
requ
irem
ents
. In
oth
er w
ords
, if
you
follo
w t
hese
con
figur
atio
ns,
your
ne
twor
k w
ill w
ork
prop
erly.
Som
etim
es,
you
may
nee
d to
dep
loy
your
net
wor
k ot
her
than
the
con
figur
atio
ns i
n Tr
ansm
issi
on S
yste
m M
odel
1.
You
have
to
calc
ulat
e yo
urse
lf if
your
net
wor
k is
qua
lifie
d fo
r th
e re
quire
men
ts. T
rans
mis
sion
S
yste
m M
odel
2 o
ffers
a s
et o
f cal
cula
tion
aids
to y
ou. F
or e
xam
ple,
it te
lls y
ou th
e de
lay
valu
e of
a s
egm
ent o
f a c
erta
in m
ediu
m ty
pe.
In C
laus
e 13
“S
yste
m c
onsi
dera
tions
for
mul
ti-se
gmen
t 10
Mb/
s ba
seba
nd
netw
orks
,” th
e S
tand
ard
has
the
follo
win
g ru
le in
the
Tran
smis
sion
Sys
tem
Mod
el
1:
“Whe
n a
trans
mis
sion
pat
h co
nsis
ts o
f fou
r rep
eate
r set
s an
d fiv
e se
gmen
ts,
up t
o th
ree
of t
he s
egm
ents
may
be
mix
ing
and
the
rem
aind
er m
ust
be l
ink
segm
ents
.” –
cite
d fro
m th
e S
tand
ard.
Th
is is
the
face
of t
he w
ell-k
now
n 5-
4-3
rule
. Not
e th
e de
finiti
ons
of m
ixin
g se
gmen
ts a
nd li
nk s
egm
ents
. A m
ixin
g se
gmen
t is
a m
ediu
m o
n w
hich
ther
e ar
e m
ore
than
two
phys
ical
inte
rface
s. A
link
seg
men
t is
a fu
ll-du
plex
-cap
able
med
ium
be
twee
n ex
actly
two
phys
ical
inte
rface
s. P
eopl
e of
ten
refe
r to
a lin
k se
gmen
t as
a se
gmen
t w
ithou
t P
Cs,
but
it is
not
a p
reci
se d
escr
iptio
n. T
he r
ule
mea
ns if
you
co
nfig
ure
your
net
wor
k th
is w
ay, i
t can
wor
k.
As
mor
e an
d m
ore
segm
ents
ope
rate
in fu
ll-du
plex
mod
e, th
e si
gnifi
canc
e of
th
is r
ule
is b
ecom
ing
min
or. H
owev
er, i
t is
ofte
n ov
erem
phas
ized
by
thos
e le
ft in
th
e hi
stor
y.
Big
-End
ian
and
Littl
e-En
dian
Th
ose
who
are
fam
iliar
with
net
wor
k pr
ogra
mm
ing
may
be
conf
used
with
B
ig-E
ndia
n an
d Li
ttle-
End
ian.
The
y kn
ow n
etw
ork
byte
ord
er,
such
as
that
of
Inte
rnet
Pro
toco
l (IP
), us
es B
ig-E
ndia
n by
te o
rder
ing.
How
ever
, ou
r te
xt in
thi
s ch
apte
r de
scrib
es t
he E
ther
net
trans
mits
dat
a in
Litt
le-E
ndia
n or
der.
Is t
here
a
cont
radi
ctio
n?
Con
side
r a
four
-byt
e w
ord
and
let
us d
enot
e ea
ch b
yte
by b
3b2b
1b0
with
de
crea
sing
ord
er o
f sig
nific
ance
. Her
e ar
e tw
o op
tions
in s
torin
g it
in m
emor
y:
1. S
tore
b3 i
n th
e lo
wes
t byt
e ad
dres
s, a
nd b
2 in
the
seco
nd lo
wes
t byt
e ad
dres
s,
and
so o
n.
2. S
tore
b3
in t
he h
ighe
st b
yte
addr
ess,
and
b2
in t
he s
econ
d hi
ghes
t by
te
addr
ess,
and
so
on.
73
The
form
er is
kno
wn
as th
e B
ig-E
ndia
n by
te o
rder
, and
the
latte
r is
know
n as
th
e Li
ttle-
End
ian
byte
ord
er. T
he o
rder
ing
varie
s w
ith th
e C
PU
and
OS
on
a ho
st.
This
resu
lts in
inco
nsis
tenc
y w
hen
trans
mitt
ing
som
e m
ulti-
byte
dat
a, s
ay in
tege
rs,
over
the
netw
ork.
To
keep
the
cons
iste
ncy,
a n
etw
ork
byte
ord
erin
g is
enf
orce
d.
The
mos
t po
pula
r ne
twor
k la
yer
prot
ocol
, In
tern
et P
roto
col,
uses
Big
-End
ian
orde
ring.
Wha
teve
r th
e ho
st b
yte
orde
ring
is, t
he d
ata
shou
ld b
e co
nver
ted
into
ne
twor
k by
te o
rder
ing
befo
re tr
ansm
ittin
g an
d th
en b
e tu
rned
bac
k in
to h
ost b
yte
orde
ring
upon
rece
ipt,
if th
ere
mig
ht b
e an
inco
nsis
tenc
y.
That
’s th
e bu
sine
ss o
f Int
erne
t Pro
toco
l. Th
e da
ta-li
nk la
yer p
roto
col r
ecei
ves
data
to
be t
rans
mitt
ed f
rom
the
upp
er la
yer
prot
ocol
s by
te b
y by
te.
Wha
t by
te
orde
ring
on th
e up
per l
ayer
pro
toco
ls is
of n
o co
nseq
uenc
e to
the
data
-link
laye
r pr
otoc
ol.
The
data
-link
la
yer
prot
ocol
is
co
ncer
ned
with
bi
t or
derin
g in
tra
nsm
issi
on, n
ot b
yte
orde
ring.
E
ther
net
uses
Litt
le-E
ndia
n bi
t or
derin
g. I
t tra
nsm
its t
he le
ast
sign
ifica
nt b
it fir
st a
nd th
e m
ost s
igni
fican
t bit
last
in b
yte
trans
mis
sion
. Con
vers
ely,
Tok
en R
ing
or F
DD
I tra
nsm
its th
e m
ost s
igni
fican
t bit
first
and
the
leas
t sig
nific
ant b
it la
st in
by
te tr
ansm
issi
on. T
hey
are
know
n to
use
Big
-End
ian
bit o
rder
ing.
The
y sh
ould
no
t be
conf
used
with
byt
e or
derin
g.
2.7
Furt
her r
eadi
ngs
Gen
eral
issu
es
A
ndre
w S
. Tan
enba
um, ”
Com
pute
r Net
wor
ks,”
Third
Edi
tion,
Pre
ntic
e H
all,
1996
. Th
is t
extb
ook
intro
duce
s ge
nera
l co
mpu
ter
netw
orki
ng c
once
pts
in a
bo
ttom
-up
appr
oach
, fro
m p
hysi
cal l
ayer
s to
app
licat
ion
netw
orks
.
W
illiam
Sta
lling
s, “
Dat
a an
d C
ompu
ter
Com
mun
icat
ions
,” S
ixth
Edi
tion,
P
rent
ice
Hal
l, 20
00.
This
boo
k fo
cuse
s a
little
mor
e on
com
mun
icat
ions
, be
side
s co
mpu
ter
netw
orks
.
Larry
L.
Pete
rson
and
Bru
ce S
. D
avie
, “C
ompu
ter
Net
wor
ks:
A sy
stem
ap
proa
ch,”
Sec
ond
Edi
tion,
Mor
gan
Kau
fman
n, 2
000.
It
is a
new
er te
xtbo
ok in
com
pute
r ne
twor
ks. I
t cov
ers
new
topi
cs s
uch
as
wire
less
LAN
and
VP
N.
PPP
W
. Sim
pson
, “Th
e Po
int-t
o-P
oint
Pro
toco
l (P
PP
),” R
FC 1
661,
Jul
y 19
94.
The
RFC
doc
umen
t def
ines
PP
P.
L.
Mam
akos
, K
. Li
dl,
J. E
varts
, D
. C
arre
l, D
. S
imon
e, R
. W
heel
er,
”A
met
hod
for t
rans
mitt
ing
PP
P ov
er E
ther
net,”
RFC
251
6, F
ebru
ary
1999
74
The
RFC
doc
umen
t def
ines
PP
PoE
.
G.
McG
rego
r, “T
he
PP
P In
tern
et
Pro
toco
l C
ontro
l P
roto
col
(IPC
P),”
R
FC13
32, M
ay 1
992.
Th
e R
FC d
ocum
ent d
efin
es IP
CP.
And
rew
Sun
, “U
sing
and
Man
agin
g P
PP,
” O’re
illy, 1
999.
Th
e ha
nds-
on b
ook
intro
duce
s pr
actic
al P
PP
oper
atio
n on
Uni
x.
Ethe
rnet
Ric
h S
eife
rt, “G
igab
it E
ther
net,”
Add
ison
Wes
ley,
199
8.
Ric
h S
eife
rt is
coa
utho
r of
the
IEE
E 80
2.1
and
802.
3 St
anda
rd. H
is b
ook
char
acte
rizes
tec
hnic
al a
ccur
acy
and
mar
ket
insi
ght.
It is
a m
ust
if yo
u ho
pe to
get
into
tech
nica
l det
ails
of G
igab
it E
ther
net w
ithou
t bei
ng fe
d up
w
ith th
e de
taile
d bu
t bor
ing
wor
ding
in th
e St
anda
rd.
R
ich
Sei
fert,
“The
Sw
itch
book
,” Jo
hn &
Wile
y, 2
000.
Th
is b
ook
cove
rs a
full
disc
ussi
on o
f sw
itche
s. Y
ou w
ill fin
d gr
eat d
etai
ls in
S
TP, V
LAN
, lin
k ag
greg
atio
n, e
tc. i
n hi
s bo
ok.
C
harle
s E
. Spu
rgeo
n, “E
ther
net:
The
Def
initi
ve G
uide
,” O
’Rei
lly, 2
000.
M
r. Sp
urge
on is
an
expe
rienc
ed n
etw
ork
arch
itect
. Th
is b
ook
intro
duce
s th
e E
ther
net f
rom
an
adm
inis
trativ
e po
int v
iew.
ISO
/IEC
Sta
ndar
d 88
02-3
, “C
arrie
r se
nse
mul
tiple
acc
ess
with
col
lisio
n de
tect
ion
(CS
MA
/CD
) ac
cess
met
hod
and
phys
ical
lay
er s
peci
ficat
ions
,” 20
00 E
ditio
n.
This
is th
e St
anda
rd d
ocum
ent.
As
of A
pril
15, 2
001,
all
of th
e IE
EE
802
St
anda
rds
has
been
fre
ely
avai
labl
e on
ht
tp://
stan
dard
s.ie
ee.o
rg/g
etie
ee80
2/.
10
Gig
abit
Eth
erne
t A
llianc
e, “
10 G
igab
it E
ther
net
Tech
nolo
gy O
verv
iew
: W
hite
pap
er,”
http
://w
ww.
10ge
a.or
g, S
epte
mbe
r 200
1.
This
w
hite
pa
per
is
publ
ishe
d by
10
G
igab
it A
llianc
e,
a te
chni
cal
cons
ortiu
m in
tend
ing
to p
ush
the
next
gen
erat
ion
10 G
igab
it E
ther
net.
H
owar
d Fr
azie
r, “E
ther
net t
akes
on
the
first
mile
,” IT
Pro
fess
iona
l, vo
l. 3,
is
sue
4, J
uly-
Aug
. 200
1.
Mr.
Fraz
ier i
s ch
air o
f IE
EE
802
.3ah
. He
desc
ribes
the
futu
re p
ersp
ectiv
e of
E
ther
net o
n th
e fir
st m
ile in
this
arti
cle.
How
ard
Fraz
ier,
“E
ther
net
in t
he f
irst
mile
tut
oria
l,” I
EE
E 8
02.3
EFM
st
udy
grou
p, h
ttp://
ww
w.ie
ee80
2.or
g/3/
efm
/pub
lic/ju
l01/
tuto
rial/i
ndex
.htm
l, Ju
ly 2
001.
Th
is is
a tu
toria
l pro
vide
s by
the
IEE
E 8
02.3
ah T
ask
Forc
e.
IS
O/IE
C S
tand
ard
1580
2-3,
“M
edia
Acc
ess
Con
trol
(MA
C)
Brid
ges,”
19
98 E
ditio
n.
75
It is
the
MA
C b
ridge
Sta
ndar
d, a
lso
avai
labl
e on
the
web
site
men
tione
d ab
ove.
IEE
E 8
02.1
Q, “
Virtu
al B
ridge
d Lo
cal A
rea
Net
wor
ks,”
1998
Edi
tion.
It
is th
e V
LAN
brid
ge S
tand
ard,
als
o av
aila
ble
on th
e w
eb s
ite m
entio
ned
abov
e.
Dev
ice
Driv
ers
A
. R
ubin
i and
J.
Cor
bet,
“Li
nux
Dev
ice
Driv
ers,”
Sec
ond
Edi
tion,
O’
reilly
, 200
1.
This
is
an e
xcel
lent
boo
k th
at t
each
es y
ou h
ow t
o w
rite
Linu
x de
vice
dr
iver
s.
Wire
less
Pro
toco
ls
A
NS
I/IE
EE
Sta
ndar
d 80
2.11
, “
Wire
less
LA
N M
ediu
m A
cces
s C
ontro
l (M
AC
) and
Phy
sica
l Lay
er (P
HY
) Spe
cific
atio
n,”
1999
Edi
tion.
It
is th
e w
irele
ss L
AN
Sta
ndar
d, a
lso
avai
labl
e on
the
web
site
men
tione
d ab
ove.
P.
Bre
nner
, “A
Te
chni
cal
Tuto
rial
on
the
IEE
E
802.
11
Pro
toco
l,”
http
://w
ww
.sss
-mag
.com
/802
_11t
ut.p
df.
It is
a g
ood
tuto
rial d
ocum
ent o
f IE
EE
802
.11.
Blu
etoo
th
SIG
, “
Spec
ifica
tion
of
the
Blu
etoo
th
Sys
tem
,” V
er.
1.1,
ht
tp://
ww
w.bl
ueto
oth.
com
/dev
elop
er/s
peci
ficat
ion/
spec
ifica
tion.
asp,
Fe
b 20
01
.It is
the
stan
dard
doc
umen
t of t
he B
luet
ooth
.
P. B
hagw
at, “
Blu
etoo
th: T
echn
olog
y fo
r Sho
rt-R
ange
Wire
less
App
s,” I
EE
E
Inte
rnet
Com
putin
g, v
ol. 5
, iss
ue 3
, pp.
96-
103,
May
/Jun
e 20
01.
It is
a g
ood
tuto
rial p
aper
of t
he B
luet
ooth
. 2.
8 Ex
erci
ses
H
ands
-on
exer
cise
s 1.
Rea
d th
e tw
o do
cum
ents
and
see
how
the
IE
EE
Sta
ndar
ds c
omes
out
. W
rite
a su
mm
ary
of th
e st
anda
rdiz
atio
n pr
oces
s.
[1]
10
Gig
abit
Eth
erne
t A
llianc
e,”1
0 G
igab
it E
ther
net
Tech
nolo
gy
Ove
rvie
w: W
hite
pap
er,”
http
://w
ww.
10ge
a.or
g, S
epte
mbe
r 200
1.
[2] h
ttp://
ww
w.ie
ee80
2.or
g/3/
efm
/pub
lic/s
ep01
/age
nda_
1_09
01.p
df.
2. Y
ou m
ay d
ownl
oad
IEE
E 8
02 S
tand
ards
at
http
://st
anda
rds.
ieee
.org
/get
ieee
802/
.
Writ
e do
wn
the
deve
lopm
ent
goal
s of
the
fol
low
ing
proj
ects
: 80
2.1w
, 80
2.3a
c, 8
02.1
5, 8
02.1
6, a
nd 8
02.1
7.
3. F
ind
the
MA
C
addr
ess
of
your
ne
twor
k in
terfa
ce
card
. C
heck
76
http
://st
anda
rds.
ieee
.org
/rega
uth/
oui/o
ui.tx
t to
com
pare
its
OU
I w
ith t
hat
has
been
regi
ster
ed.
4. U
se S
niffe
r or
sim
ilar
softw
are
to f
ind
out
how
man
y ki
nds
of “
prot
ocol
ty
pes”
in
the
“Typ
e” f
ield
of
the
Eth
erne
t fra
mes
you
cap
ture
. W
hat
trans
port/
appl
icat
ion
laye
r pro
toco
ls, i
f any
, do
they
bel
ong
to?
5. F
ind
out w
heth
er y
our n
etw
ork
inte
rface
car
d is
ope
ratin
g in
hal
f-dup
lex
or
full-
dupl
ex m
ode.
6.
Tra
ce th
e so
urce
in o
ne o
f the
follo
win
g pr
otoc
ols:
1.
HD
LC
2. P
PP
oE
3.
wire
less
LA
N
4
. Blu
etoo
th.
Exp
lain
the
purp
ose
of e
ach
maj
or fu
nctio
n of
the
prot
ocol
impl
emen
tatio
n yo
u tra
ce a
nd d
raw
a f
low
cha
rt w
ith t
he f
unct
ion
nam
es t
o sh
ow t
he
exec
utio
n flo
w.
7. A
fter
mak
e ke
rnel
and
cho
ose
som
e dr
iver
s to
be
mod
ular
ized
, ho
w d
o w
e co
mpi
le d
river
, ins
tall
driv
er, a
nd ru
n th
ese
mod
ules
? P
leas
e al
so w
rite
one
smal
l m
odul
e. S
how
wha
t co
mm
ands
are
nee
ded
to c
ompi
le a
nd
inst
all i
t. H
ow d
o yo
u sh
ow y
our m
odul
e ha
s be
en s
ucce
ssfu
lly in
stal
led?
(H
int:
read
insm
od(8
), rm
mod
(8),
and
lsm
od(8
).)
8. A
pac
ket’s
life
: tes
t how
muc
h tim
e a
pack
et s
pend
s on
the
driv
er ,
DM
A ,
and
CS
MA
/CD
ada
pter
. (yo
u ca
n us
e“rd
tscl
l”de
fined
in <
asm
/msr
.h>
to
get t
he p
ast C
PU c
lock
cyc
le. )
9.
Writ
ten
exer
cise
s 1.
We
know
32-
bit
IPv4
add
ress
es m
ay b
e no
t en
ough
. A
re 4
8-bi
t M
AC
ad
dres
ses
enou
gh?
Dis
cuss
it.
2. R
ead
RFC
1071
and
RFC
1624
to
see
how
IP
chec
ksum
is
com
pute
d.
Pra
ctic
e w
ith th
e tri
vial
blo
cks
of w
ords
by
hand
.
0x36
f7
0x
f670
0x21
48
0x8
912
0x
2345
0x
7863
0x
0076
Wha
t if t
he fi
rst w
ord
abov
e is
cha
nged
into
0x3
6f6?
R
FCs
dow
nloa
ded
from
ftp:
//ftp
.csi
e.nc
tu.e
du.tw
/pub
/Doc
umen
ts/R
FC/.
3. C
ompu
te th
e C
RC
cod
e gi
ven
the
mes
sage
110
1010
011
and
the
patte
rn
1001
1. V
erify
the
code
is c
orre
ct.
4. W
hy a
re t
he d
estin
atio
n ad
dres
s fie
ld u
sual
ly l
ocat
ed i
n th
e he
ad o
f a
fram
e, a
nd th
e FC
S fi
eld
loca
ted
in th
e ta
il of
a fr
ame?
5.
Wha
t ar
e th
e ad
vant
ages
and
dis
adva
ntag
es i
f w
e m
ake
the
min
imum
E
ther
net f
ram
e la
rger
? 6.
Sup
pose
dat
a pa
yloa
d is
pre
pend
ed w
ith 4
0 by
tes
of IP
and
TC
P he
ader
s in
a fr
ame.
How
man
y bi
ts o
f dat
a pa
yloa
d ca
n be
car
ried
in th
e 10
0 M
b/s
77
Eth
erne
t if e
ach
fram
e is
a m
axim
um u
ntag
ged
fram
e?
7. S
houl
d a
switc
h re
com
pute
a n
ew F
CS
of a
n in
com
ing
fram
e be
fore
it is
fo
rwar
ded?
8.
The
re is
an
optio
nal p
riorit
y ta
g in
the
Eth
erne
t fra
me,
but
it is
not
ofte
n em
ploy
ed. W
hy?
9.
Why
doe
s no
t Eth
erne
t im
plem
ent a
com
plic
ated
flow
con
trol m
echa
nism
su
ch a
s sl
idin
g-w
indo
w?
10. W
hat h
appe
ns if
you
r net
wor
k in
terfa
ce c
ard
runs
in fu
ll-du
plex
mod
e in
a
shar
ed n
etw
ork?
11
. Sho
uld
each
por
t in
a sw
itch
have
its
own
MA
C a
ddre
ss?
Dis
cuss
it.
12. S
uppo
se e
ach
entry
in th
e ad
dres
s ta
ble
of a
sw
itch
need
s to
rec
ord
the
MA
C a
ddre
ss, 8
-bit
of p
ort n
umbe
r, an
d 2-
bit o
f agi
ng in
form
atio
n. W
hat i
s th
e m
inim
um m
emor
y si
ze if
the
tabl
e ca
n re
cord
409
6 en
tries
? 13
. Sup
pose
bit
stuf
fing
with
0 is
use
d af
ter
5 co
nsec
utiv
e 1’
s. A
ssum
ing
the
prob
abilit
ies
of 0
’s a
nd 1
’s in
the
bit s
tream
are
equ
al a
nd th
e oc
curre
nces
ar
e ra
ndom
, wha
t is
the
trans
mis
sion
ove
rhea
d of
the
bit s
tuffi
ng s
chem
e?
(Hin
t: Fo
rmul
ate
a re
curs
ive
form
ula
f(n)
to fi
nd th
e ex
pect
ed n
umbe
r of
ov
erhe
ad b
its in
an
n-bi
t stri
ng fi
rst.)
14
. Writ
e a
sim
ulat
ion
prog
ram
to
verif
y th
e nu
mer
ical
ans
wer
abo
ve i
s co
rrec
t. 15
. In 1
000B
AS
E-X
, a
fram
e of
64
byte
s is
firs
t bl
ock
code
d w
ith 8
B/1
0B
befo
re tr
ansm
ittin
g. S
uppo
se th
e pr
opag
atio
n sp
eed
is 2
x108 . W
hat i
s th
e fra
me
“leng
th” i
n “m
eter
”? (S
uppo
se th
e ca
ble
is 5
00 m
long
.) 16
. Wha
t is
the
pro
babi
lity
of t
wo
stat
ions
tak
ing
5 m
ore
trial
s to
res
olve
co
llisi
ons
afte
r th
ey h
ave
the
first
col
lisio
n? (
Supp
ose
only
tw
o st
atio
ns
are
in th
e co
llisio
n do
mai
n.)
17. W
hat i
s th
e m
axim
um n
umbe
r of f
ram
es a
sw
itch
of 1
6 Fa
st E
ther
net (
100
Mb/
s) p
orts
may
dea
l with
if e
ach
port
oper
ates
in fu
ll-du
plex
mod
e?
18. A
CP
U e
xecu
tes
inst
ruct
ions
at 8
00 M
IPS
. Dat
a ca
n be
cop
ied
64 b
its a
t a
time,
with
eac
h 64
-bit
wor
d co
pied
cos
ting
six
inst
ruct
ions
. If a
n in
com
ing
fram
e ha
s to
be
copi
ed tw
ice,
how
muc
h bi
t rat
e, a
t mos
t, of
a li
ne c
an th
e sy
stem
han
dle?
(A
ssum
e th
at a
ll in
stru
ctio
ns r
un a
t th
e fu
ll 80
0-M
IPS
ra
te.)
19
. A fr
ame
of 1
500
byte
s tra
vel t
hrou
gh 5
sw
itche
s al
ong
the
path
. Eac
h lin
k ha
s a
band
wid
th o
f 100
Mb/
s, a
leng
th o
f 100
m, a
nd p
ropa
gatio
n sp
eed
of 2
x108 m
/sec
. Ass
umin
g th
e qu
euei
ng a
nd p
roce
ssin
g de
lay
of 5
ms
at
each
sw
itch,
wha
t is
the
appr
oxim
ate
end-
to-e
nd d
elay
for t
his
pack
et.
20. O
ne o
ut o
f n fr
ames
of 1
000
byte
s su
ffers
from
an
erro
r on
aver
age
if th
e
78
bit e
rror r
ate
is 1
0-6.
Wha
t is
n?
21. C
ome
up w
ith a
que
stio
n an
d do
it y
ours
elf.
