Kuliah_06 - Transport Layer (TCP)

7/24/2019 Kuliah_06 - Transport Layer (TCP)

1/54

Transport Layer 3-1

Chapter 3

TransportLayer

ComputerNetworking: ATop Down

Approach

6th

editionJim Kurose, KeithRossAddison-WesleyMarch !1

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2/54

TransportLayer 3-

Chapter 3 outline

3"1 transport-layerser#ices

3" multiple$in%

anddemultiple$in%

3"3 connectionlesstransport& '()

3"* principles o+reliale datatrans+er

3.5 connection-oriented

transport: TCP

se%ment structure

reliale datatrans+er

o. control

connection

mana%ement3.6 principles of congestion

control

3.7 TCP congestion control


3/54

TransportLayer 3-3

TC)& /#er#ie. R0Cs& 23,11,133,!1, 41

+ull duple$ data& i-directional data

o. in sameconnection

M55& ma$imumse%ment sie

connection-

oriented& handsha7in%

8e$chan%e o+control ms%s9 inits

sender, recei#erstate e+ore data

point-to-point:

one sender, onerecei#er

:multicastin%; reliable, in-order byte

stream:

no :messa%e

oundaries; pipelined:

TC) con%estion ando. control set

.indo. sie5& the ma$" amount o+ data that can e %raed and place in a se%ment"


4/54

TC) send and recei#eu=ers

TransportLayer 3-*

TC)sendu=er

TC)recei#eu=er

soc7et soc7et

)rocess.rites data

)rocessreads data

se%ment se%ment


5/54

TransportLayer 3-4

TC) se%ment structure

source port 1 dest port 1

2/ bits

applicationdata

(variable length)

se3uence number

ackno!ledgement number

receive !indo!

4rg data pointerchecksum

'5*A4head

len

not

used

options (variable length)

4*6: urgent data(generally not used)

A7: A7 1

valid

58: push data no!

(generally not used)

*5T, 59, '#:

connection estab

(setup, teardo!n

commands)

#nternet

checksum

(as in 4;)

1 bytesrcvr !illing

to accept

counting

by bytes

of data

(not segments$)


6/54

TransportLayer 3-6

TC) se>" numers, ACKs

se>uence numers&yte stream:numer; o+ ?rstyte in se%ment@s

dataac7no.led%ements&

se> o+ ne$t ytee$pected +rom other

sidecumulati#e ACK

B&ho. recei#erhandles out-o+-order

se%mentsA& TC) s ec doesn@t


se3uence number


checksum

r!nd

urg pointer

incomin% se%ment to sender

A

sentACKed

sent, not-yetACKed8:in-i%ht;9

usaleut notyet sent

notusale

.indo. sieN

sender sequence number space


se3uence number


checksum

r!nd

urg pointer

out%oin% se%ment +rom sender


7/54TransportLayer 3-

(i#idin% ?le data into TC) se%ments

! 1 1,!!! 1,222 *22,222

(ata +or 1stse%ment (ata +or ndse%ment

0ile

1stse>" numer ! ndse>" numer 1!!!


8/54TransportLayer 3-

TC) se>" numers, ACKs

'sertypes

DC@

host ACKsreceipt

o+ echoed

DC@

host ACKsreceipt o+DC@, echoesac7 DC@

simple telnet scenario

Eost FEost A

5e>*, ACK2, data DC@

5e3


9/54TransportLayer 3-2

TC) round trip time,timeoutB&ho. to setTC) timeout#alueG

lon%er than RTT ut RTT #aries

too short:premature

timeout,unnecessaryretransmissions

too long:slo.

reaction to

Q:how to estimate TT! SampleRTT:meas"red

time from segment

transmission "ntil #C$

receipt

i%noreretransmissions

SampleRTTwill %ar&,

want estimated TT'smoother(

a#era%e se#eralrecent

measurements, not


10/54

TransportLayer 3-1!

EstimatedRTT = (1- )*EstimatedRTT + *SampleRTT

e$ponential .ei%hted mo#in% a#era%e inuence o+ past sample decreases

e$ponentially +ast typical #alue& =!"14

TC) round trip time,timeout

RTT8milliseconds9

*TT:gaia.cs.umass.edutofantasia.eurecom.fr

sampleRTT

IstimatedRTT

time


11/54

TransportLayer 3-11

timeout inter#al&EstimatedRTTplus :sa+etymar%in; lar%e #ariation in EstimatedRTT ->lar%er sa+ety

mar%in

estimate 5ampleRTT de#iation +romIstimatedRTT&

DevRTT = (1-)*DevRTT +

*|SampleRTT-EstimatedRTT|

TC) round trip time,timeout

(typically, = 0.2)

Time!"t#$te%val = EstimatedRTT + &*DevRTT

estimated RTT :sa+ety mar%in;


12/54

TransportLayer 3-1

Chapter 3 outline


3" multiple$in%

anddemultiple$in%




transport: TCP

se%ment structure


o. control

connection


control



13/54

TransportLayer 3-13

TC) reliale data trans+er

TC) creates rdtser#ice on top o+)@s unreliale

ser#ice pipelined se%ments cumulati#e ac7s

sin%le

retransmission timer retransmissions

tri%%ered y& timeout e#ents

duplicate ac7s


14/54

TransportLayer 3-1*

TC) sender e#ents&

data rcvd from app: create se%ment

.ith se> se> is yte-

stream numer o+?rst data yte inse%ment

start timer i+ notalready runnin% thin7 o+ timer as

+or oldest unac7edse%ment

e$piration inter#al&

timeout: retransmit segment

that ca"sed timeo"t

restart timer

ack rcvd:

if ac) ac)nowledges

pre%io"sl& "nac)ed

segments update .hat is

7no.n to eACKed

start timer i+ thereare still unac7ed


15/54

TransportLayer 3-14

TC)& retransmissionscenarios

lost ACK scenario

Eost FEost A

5e>2, ytes o+ data

A72, ytes o+ data

Xtimeo

ut

A72, ytes o+ data

A72, ytes o+ data

timeo

ut

A71!!, ! ytes o+ data

A7


16/54

TransportLayer 3-16

TC)& retransmissionscenarios

X

cumulati#e ACK

Eost FEost A

5e>2, ytes o+ data

A71!, 14 ytes o+ data

timeout

5e>1!!, ! ytes o+ data

A7


17/54

TransportLayer 3-1

TC) ACK %enerationR0C 11, R0C41

event at receiver

arrival of inorder segment !ith

epected se3 1. All data up to

epected se3 1 already A7ed

arrival of inorder segment !ith

epected se3 1. Bne other

segment has A7 pending

arrival of outoforder segment

higherthanepect se3. 1 .6ap detected

arrival of segment that

partially or completely fills gap

TCP receiver action

delayed A7. Wait up to C00ms

for net segment. #f no net segment,

send A7

immediately send single cumulative

A7, A7ing both inorder segments

immediately send duplicate ACK,

indicating se3. 1 of net epected byte

immediate send A7, provided that

segment starts at lo!er end of gap


18/54

TransportLayer 3-1

TC) +astretransmit time-out period

o+ten relati#elylon%& lon% delay e+ore

resendin% lostpac7et

detect lostse%ments #iaduplicate ACKs" sender o+ten sends

many se%mentsac7-to-ac7

i+ se%ment is lost,

i+ sender recei#es3 ACKs +or same

data8:triple duplicateACKs;9,resendunac7ed se%ment.ith smallest se> li7ely that unac7ed

se%ment lost, sodon@t .ait +or

timeout

TCP fast retransmit

8:triple duplicateACKs;9,

+


19/54

TransportLayer 3-12

D

+ast retransmit a+ter sender

receipt o+ triple duplicate ACK

Eost FEost A

5e>2, ytes o+ data

A7


20/54

TransportLayer 3-!

Chapter 3 outline


3" multiple$in%

anddemultiple$in%




transport: TCP

se%ment structure


o. control

connection


control



21/54

TransportLayer 3-1

TC) o. controlapplication

process

TC) soc7etrecei#er u=ers

TC)code

)code

application

/5

recei#er protocol stac7

application mayremo#e data +rom

TC) soc7et u=ers "

slo.er than TC)recei#er is

deli#erin%8sender issendin%9

+rom sender

recei#er controls sender,so sender .on@t o#ero.recei#er@s u=er ytransmittin% too much,too +ast

ow control


22/54

TransportLayer 3-

TC) o. control

u=ered data

+ree u=er space%$d

Rcv"e%

TCP segment paloads

to application process

recei%er 'ad%ertises( free

b"ffer space b& incl"ding

recei%e window *%$d+

%al"e in TCP header of

recei%er-to-sender segments Rcv"e% sie set #ia

soc7et options 8typicalde+ault is *!26 ytes9

many operatin% systems

autoadHust Rcv"e%

sender limits amo"nt of

"nac)ed *'in-flight(+ data to

recei%ers %$d %al"e

g"arantees recei%e b"ffer

receiver!side bu"ering


23/54

TransportLayer 3-3

Chapter 3 outline


3" multiple$in%

anddemultiple$in%




transport: TCP

se%ment structure


o. control

connection


control



24/54

TransportLayer 3-*

Connection Mana%ement

e+ore e$chan%in% data, senderNrecei#er

:handsha7e;& a%ree to estalish connection 8each 7no.in% the

other .illin% to estalish connection9 a%ree on connection parameters

connection state&I5TAFconnection #ariales&

se> client-to-ser#er

ser#er-to-client%cv"e%sie at ser#er,client

application

net.or7

connection state&I5TAFconnection Oariales&

se> client-to-ser#er

ser#er-to-client%cv"e%sie at ser#er,client

application

net.or7

S!cet clie$tS!cet =

$eS!cet(!st$ame,p!%t

$"me%)/

S!cet c!$$ecti!$S!cet =

elc!meS!cet.accept()/

A i t t li h


25/54

TransportLayer 3-4

#:.ill -.ayhandsha7e al.ays.or7 in net.or7G

#ariale delays retransmitted

messa%es 8e"%"re>Pconn8$99 due to

messa%e loss messa%e reorderin% can@t :see; other side

-.ay handsha7e&

Let@s tal7

/K

I5TAF

I5TAF

choose $ re>Pconn8$9

I5TAF

I5TAFaccPconn8$9

A%reein% to estalish aconnection

A i t t li h


26/54

TransportLayer 3-6

A%reein% to estalish aconnection

-.ay handsha7e +ailure scenarios&

retransmitre>Pconn8

$9

I5TAF

re>Pconn8$9

hal+ open connectionQ8no clientQ9

clientterminates

ser#er+or%ets $

connection

$ completes

retransmitre>Pconn8

$9

I5TAF

re>Pconn8$9

data8$19

retransmitdata8$19

acceptdata8$1

9

choose $re>Pconn8$9

I5TAF

I5TAF

accPconn8$9

clientterminat

es

I5TAF

choose $re>Pconn8$9

I5TAF

accPconn8$9

data8$19 acceptdata8$19

connection

$ completes ser#er+or%ets $


27/54

TransportLayer 3-

TC) 3-.ay handsha7e

5Sit1, 5e>$

choose init se> num, $send TC) 5S ms%

I5TAF

5Sit1, 5e>yACKit1U ACKnum$1

choose init se> num, y

send TC) 5SACKms%, ac7in% 5S

ACKit1, ACKnumy1

recei#ed 5SACK8$9indicates ser#er is li#eUsend ACK +or 5SACKU

this se%ment may containclient-to-ser#er data

recei#ed ACK8y9indicates client is li#e

5S5IT

I5TAF

5S RCO(

client state

L5TI

server state

L5TI


28/54

TransportLayer 3-

TC)& closin% a connection

client, ser%er each close their side of connection send TC) se%ment .ith 0 it 1

respond to recei%ed / with #C$

on recei#in% 0, ACK can e comined .ith

o.n 0

sim"ltaneo"s / e0changes can be handled


29/54

TransportLayer 3-2

0PWATP

CL/5IPWAT

0it1, se>y

ACKit1U ACKnumy1

ACKit1U ACKnum$1.ait +or ser#erclose

can stillsend data

can no lon%ersend data

LA5TPACK

CL/5I(

TMI(PWAT

timed .ait+or $can no lon%ersend ut canrecei#e data

clientSocket.close()

client stateserver state

I5TAFI5TAF


30/54

TransportLayer 3-3!

Chapter 3 outline


3" multiple$in%

anddemultiple$in%




transport: TCP

se%ment structure


o. control

connection


control



31/54

TransportLayer 3-31

congestion& in+ormally& :too many sources sendin%

too much data too +ast +or networkto

handle; di=erent +rom o. controlQ mani+estations&

lost pac7ets 8u=er o#ero. atrouters9

lon% delays 8>ueuein% in routeru=ers9

a top-1! prolemQ

)rinciples o+ con%estioncontrol

CausesNcosts o+ con%estion&


32/54

TransportLayer 3-3


scenario 1

t.o senders, t.orecei#ers

one router, in?niteu=ers

output lin7 capacity&

R no retransmission

ma0im"m per-connection

thro"ghp"t: 12

unlimited shared

output link buffers

8ost A

original data: in

8ost E

throughput:out

RN

RN

o

ut

in RN

delay

in

lar%e delays as arri#alrate, in, approaches

capacity



33/54

TransportLayer 3-33

one router, $niteu=ers sender retransmission o+ timed-out

pac7et application-layer input application-layer

output&

in ueue are dropped, luethrou%hput % !



40/54

TransportLayer 3-*!

another :cost; o+ con%estion& .hen pac7et dropped, any :upstream

transmission capacity used +or thatpac7et .as .astedQ


scenario 3

CN

CN

out

in

A h t d ti


41/54

TransportLayer 3-*1

Approaches to.ards con%estioncontrol

t.o road approaches to.ards con%estioncontrol&

end-end

con%estioncontrol& no e$plicit

+eedac7 +romnet.or7

con%estionin+erred +romend-systemoser#ed loss,

delay

networ)-assisted

congestion control: ro"ters pro%ide feedbac)to end s&stems

sin%le itindicatin%con%estion 85A,(ICit, TC)N)IC, ATM9

e$plicit rate +or

sender to send at< ATM& Asynchronous Trans+er Mode

C t d ATM AFR ti


42/54

TransportLayer 3-*

Case study& ATM AFR con%estioncontrol

AFR& a#ailale itrate&

:elastic ser#ice;

i+ sender@s path:underloaded;&

sender shoulduse a#ailaleand.idth

i+ sender@s pathcon%ested&

sender throttledto minimum%uaranteed rate

*reso"rce management+

cells: sent b& sender, interspersed

with data cells bits in cell set b&

switches *'network-assisted+

N% bit:no increase inrate 8mildcon%estion9

C% bit:con%estionindication

cells ret"rned to sender

b& recei%er, with bits intact

Case study& ATM AFR con%estion


43/54

TransportLayer 3-*3

Case study& ATM AFR con%estioncontrol

t.o-yte IR 8e$plicit rate9 ?eld in RM cell con%ested s.itch may lo.er IR #alue in cell

senders@ send rate thus ma$ supportale rateon path

I0C it in data cells& set to 1 incon%ested s.itch i+ data cell recedin RM cell has I0C set,

RM cell data cell


44/54

TransportLayer 3-**

Chapter 3 outline


3" multiple$in%

anddemultiple$in%




transport: TCP

se%ment structure


o. control

connection


control



45/54

TransportLayer 3-*4

TC) con%estion control& additi#eincrease multiplicati#e decrease

approach:senderincreases transmissionrate 8.indo. sie9, proin% +or usaleand.idth, until loss occurs additive increase:increase c$dy 1

M55 e#ery RTT until loss detectedmultiplicative decrease&cut c$d in hal+a+ter loss

c($d0

T7se

nder

congestion!indo!

siGe

A#H; sa! tooth

behavior: probingfor band!idth

additi#ely increase .indo. sie " until loss occurs 8then cut .indo. in hal+9

time

M(& Additi#e ncrease, Multiplicati#e (ecrease

TC) Con%estion Control&


46/54

TransportLayer 3-*6

TC) Con%estion Control&details

sender limitstransmission&

c$dis dynamic,

+unction o+ percei#ed

TCP sending rate: roughly:send cwnd

b&tes, wait TT for

#C$4, then sendmore b&tes

last yteACKed sent, not-

yetACKed8:in-i%ht;9

last yte

sent

c$d

astyteSe$t-

astyteced

< c$d

sender sequence number space

rateVVc.nd

RTTytesNsec


47/54

TransportLayer 3-*

TC) 5lo. 5tart

.hen connectione%ins, increaserate e$ponentiallyuntil ?rst loss e#ent&

initially c$d 1 M55 doule c$de#ery

RTT

done y incrementin%c$d+or e#ery ACKrecei#ed

summar: initial rateis slo. ut ramps upe$ onentiall +ast

8ost A

onesegment

*TT

8ost E

time

t!osegments

foursegments

TC) detectin% reactin% to


48/54

TransportLayer 3-*

TC)& detectin%, reactin% toloss loss indicated y timeout& c$dset to 1 M55U

.indo. then %ro.s e$ponentially 8as in

slo. start9 to threshold, then %ro.slinearly

loss indicated y 3 duplicate ACKs&TC)

RI/dup ACKs indicate net.or7 capale o+deli#erin% some se%ments

c$dis cut in hal+ .indo. then %ro.s

linearly


49/54

TransportLayer 3-*2

TC) throu%hput

a#%" TC) throu%hput as +unction o+ .indo.sie, RTTG i%nore slo. start, assume al.ays data to send

W& .indo. sie 8measured in ytes9.here loss

occurs a#%" .indo. sie 8 in-i%ht ytes9 is W

a#%" throu%hput is 3N*W per RTTW

WN

a#% TC) throu%hput 3*

WRTT

ytesNsec

TC) 0 t TC) :l + t


50/54

TransportLayer 3-4!

TC) 0utures& TC) o#er :lon%, +atpipes;

e$ample& 14!! yte se%ments, 1!!msRTT, .ant 1! Xps throu%hput

re>uires W 3,333 in-i%ht se%ments

throu%hput in terms o+ se%ment lossproaility, L Mathis 122&

to achie#e 1! Xps throu%hput, need a lossrate o+ L Y1!-1! ( a ver small loss rate)

ne. #ersions o+ TC) +or hi%h-speed

T7 throughput

Kuliah_06 - Transport Layer (TCP)

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Transcript of Kuliah_06 - Transport Layer (TCP)