Medium Access Control
description
Transcript of Medium Access Control
![Page 1: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/1.jpg)
Medium Access Control
![Page 2: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/2.jpg)
Channel Allocation
• Static channel allocation in LANs and MANs
• FDMA, TDMA, CDMA• Dynamic channel allocation in LANs and
MANs• MAC protocols: with collisions, polling, token
![Page 3: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/3.jpg)
Static Channel Allocation
• Delay for one fast channel:
• Delay for multiple FDM slower channels:
][E/1LC
D
NTNLNC
D
/])[E/(
1FDM
![Page 4: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/4.jpg)
Poisson Process
• Probability of k arrivals in time t:
• Probability that packet duration exceeds t:
• Note that λ is the average packet arrival rate, and 1/μ is the average packet duration.
!)(][k
etkAPtk
tetP ]inarrivalno[
![Page 5: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/5.jpg)
M/M/1 Queue
• Queue equations, pj(t) is the probability that the number of packets at time t in a queue is j
• The solution of the previous recursion for stationary probabilities to which pj(t) converge
)()()())(1()()()()1()(
11
100
tdtptdtptpdtdttptdtptpdtdttp
jjjj
jjj pp )/()/1()/(0
![Page 6: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/6.jpg)
Delay
• Little’s formula for average delay E[D]
E[Q] is the average number of packets in a queue
• Delay is:
)/(][E][E
QD
11
/11]packets][[E D
![Page 7: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/7.jpg)
Static Channel Allocation
• Delay for one fast channel:
where C is the channel bit-rate and E[L] is the average packet length.
• Delay for multiple FDM N times slower channels:
][E/1
1)/1(][E
LCD
][E/])[E/(
1][E FDM DNNLNC
D
![Page 8: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/8.jpg)
Multiple Access Protocols
• ALOHA• Carrier Sense Multiple Access (CSMA)
protocols• CSMA/CD• CSMA/CA
• Collision-Free protocols• Reservation based • Token based
![Page 9: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/9.jpg)
Pure ALOHA
Vulnerable period for the shaded frame.
![Page 10: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/10.jpg)
ALOHA Throughput• Throughput is S=GPs, where Ps is the probability of successful transmission.• The k frames per f frame slots is
Ps=e-fG
• For pure ALOHA f=2, for slotted ALOHA f=1, so:
!)(][k
efGkPfGk
![Page 11: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/11.jpg)
Pure and Slotted ALOHA
Throughput versus offered traffic for ALOHA systems.
![Page 12: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/12.jpg)
Carrier Sense Multiple Access
• 1-Persistant CSMA• Nonpersistant CSMA• P-Persistant CSMA
![Page 13: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/13.jpg)
CSMA with Collision Detection
CSMA/CD can be in one of three states: contention, transmission, or idle.
![Page 14: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/14.jpg)
Wireless LAN: CSMA-CA
The MACA protocol. (a) A sending an RTS to B.(b) B responding with a CTS to A.
![Page 15: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/15.jpg)
DOCSIS (Data Over Cable Service Interface Specification)
![Page 16: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/16.jpg)
Collision-Free Protocols:Reservations
The basic bit-map protocol.
![Page 17: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/17.jpg)
Collision-Free Protocols: Bidding
The binary countdown protocol. A dash indicates silence.
![Page 18: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/18.jpg)
Collision Free Protocols: Fiber Distributed Data Interface (FDDI)
• Station transmits only when it has a token• Timers count the time while the token is away• Two timers determine how much data a station
may transmit, so that the token delay is limited
![Page 19: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/19.jpg)
Ethernet
• Ethernet, IEEE 802.3• 10Base (10Mbps)• Fast Ethernet (100Mbps)• Gigabit Ethernet
![Page 20: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/20.jpg)
Ethernet MAC Sublayer Protocol
Frame formats. (a) DIX Ethernet, (b) IEEE 802.3.Preamble-synchronization, Type-upper layer protocol,
Pad-to make the minimum packet size 64B
![Page 21: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/21.jpg)
CSMA with Collision Detection
CSMA/CD can be in one of three states: contention, transmission, or idle.
![Page 22: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/22.jpg)
Back-Off Mechanism
• After a collision, user accesses medium with probability 1/W where W is the window size.
• With each collision W doubles.
![Page 23: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/23.jpg)
Ethernet Performance
Collision detection can take as long as 2 .
![Page 24: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/24.jpg)
Throughput of CSMA/CD (Ethernet)• Assume that requests form a Poisson process with rate g, T is time slot duration, and Tp is a packet duration. The throughput equals S=Tp/(Tp+I), where I is the average time between packet transmissions.• The probability of a packet transmission is equal to the probability that there is only one request in some previous time slot which is Ps=gTe-gT.• The average time between transmissions is
ssi
si
PTPPiTI /)1(
![Page 25: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/25.jpg)
Throughput of CSMA/CD• The throughput is
• It tends to 0 when g increases . • Protocol is unstable like ALOHA.
1
1
p
gT
p
p
gTgTe
ITT
S
g
S 1 2
![Page 26: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/26.jpg)
Throughput of CSMA/CD• The throughput is
• If p is the packet generation probability and k is the number of active users Ps=kp(1-p)k-1
• The maximum throughput is achieved for p=1/k and it is tends to e when k tends to infinity
ssp
p
PPTTT
S/)1(
![Page 27: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/27.jpg)
Ethernet Performance
Efficiency of Ethernet at 10 Mbps with 512-bit slot times.
![Page 28: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/28.jpg)
10Mbps Ethernet Cabling
The most common kinds of Ethernet cabling.
![Page 29: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/29.jpg)
10Mbps Ethernet Cabling
Three kinds of Ethernet cabling. (a) 10Base5, (b) 10Base2, (c) 10Base-T.
![Page 30: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/30.jpg)
Ethernet Cabling
Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.
![Page 31: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/31.jpg)
10Mb Ethernet Coding
(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.
![Page 32: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/32.jpg)
10 Mb Ethernet Collision Detection
10Base5 cabling, Kadambi, Crayford and Kalkunte, Gigabit Ethernet, Prentice Hall, 1998
![Page 33: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/33.jpg)
10 Mb Ethernet Collision Detection
10Base2 and 10BaseT cabling,Kadambi, Crayford and Kalkunte, Gigabit Ethernet, Prentice Hall, 1998
![Page 34: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/34.jpg)
Fast Ethernet
The original fast Ethernet cabling.
![Page 35: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/35.jpg)
Fast Ethernet
• Auto negotiation enables communication with 10Mb Ethernet
• Manchester code → 4B/5B code• Full duplex mode is optional with using
PAUSE command
![Page 36: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/36.jpg)
Switched Ethernet
A simple example of switched Ethernet.
![Page 37: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/37.jpg)
Gigabit Ethernet
(a) A two-station Ethernet. (b) A multistation Ethernet.
![Page 38: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/38.jpg)
Gigabit Ethernet
Gigabit Ethernet cabling.
![Page 39: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/39.jpg)
Gigabit Ethernet
• Prioritization of fiber over copper• 4B/5B coding → 8B/10B coding• Full duplex mode is preferred with PAUSE
message• Carrier extension, and frame bursting
introduced in half-duplex mode
![Page 40: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/40.jpg)
IEEE 802.2: Logical Link Control
(a) Position of LLC. (b) Protocol formats.
![Page 41: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/41.jpg)
A Sample HFC System
Secondary Hub
o o o o o oo o
o o o o
o o
HOME
o oo o
5-42 MHz 550 MHz 750 MHz
RF Spectrum on coax:return 80 broadcast channels 30 QAM channels
(~150 video channels)
Downstream: 500 MHz shared by ~50,000 (broadcast) 200 MHz by 1200 (narrowcast)
Upstream: ~37 MHz shared by 300
broadcast narrowcastnarrowcast
Fiber Node
up
b
n (4n/fiber)
Sheryl Woodward, AT&T Labs-Research
![Page 42: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/42.jpg)
Justification for Using Shared Medium
• Equivalent circuit rate (ECR) on a cable with many users is the rate of a dedicated link that would provide the same e.g. average delay (similar results is obtained for 90th percentile page delay). By Shankar, Jiang and Mishra:
where tON is the transmission tim, and tOFF is the think time, r is the channel rate, tON/(tON+tOFF)<<1, on periods have an exponential distribution.
rt
ttMMtt
tr ECR11ECRON
OFFON
OFFON
ON
![Page 43: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/43.jpg)
Justification for Using Shared Medium
• Let’s calculate how many users can be allocated one DOCSIS channel of 32Mbps to get the same experience as DSL user with dedicated rate of 2Mbps. According to traffic statistics page size is 68KB on average, and tOFF is 14.5s on average,
which is much more than 32/2=16 users. Price: high user speed.
800017.0
5.14017.03221
Mbps32/KB68s5.14Mbps32/KB68
M
![Page 44: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/44.jpg)
DOCSIS MAC Protocol
• Traffic that is transmitted downstream to the users is controlled by CMTS (cable modem termination system) in headend. It polices and shapes the traffic, and perform algorithms such are WFQ and RED.• Users requests are resolved at headend, and they are informed about the resolution through the downstream channel. If there is a collision of requests, users repeat their requests according to exponential back-off mechanism, otherwise they send data in specified time slot(s).
![Page 45: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/45.jpg)
QoS in DOCSISService QoS parameters Access Mode Applications
UGS Unsolicited grant size, interval, jitter
Isonchronous Videoconferencing, VoD, VoIP
UGS-AD Unsolicited grant size, interval, jitter;polling interval, jitter
Isonchronous, periodic request polling
VoIP with silence supression
rtPS Polling interval, jitter Periodic request polling, piggybacking reservation
VoIP
![Page 46: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/46.jpg)
QoS in DOCSISService QoS parameters Access Mode Applications
nrtPS Polling interval, min reserved rate, max sustained rate, priority
Periodic request polling, piggybacking reservation, immediate access
Demanding FTP
BE min reserved rate, max sustained rate, priority
Normal, piggybacking reservation, immediate access
Telnet, FTP, WWW
CIR Unspecified Unspecified Unspecified
![Page 47: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/47.jpg)
Performance for BE service in DOCSIS• Assume that requests form a Poisson process with rate g, T is time slot duration, and Tp is a packet duration. The throughput equals S=Tp/(Tp+I), where I is the average time between packet transmissions.• The probability of a packet transmission is equal to the probability that there is only one request in some previous time slot which is gTe-gT.• The average time between transmissions is
ssi
si
PTPPiTI /)1( 1
![Page 48: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/48.jpg)
Performance for BE service in DOCSIS• The throughput is
• It tends to 0 when g increases . • Protocol is unstable like ALOHA.
1
1
p
gT
p
p
gTe
ITT
S
g
S 1 2
![Page 49: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/49.jpg)
Wireless LANs
• Distributed coordination function (DCF)• Point coordination function (PCF)
![Page 50: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/50.jpg)
The 802.11 Protocol Stack
Part of the 802.11 protocol stack.
![Page 51: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/51.jpg)
The 802.11 MAC Sublayer Protocol
(a) The hidden station problem.(b) The exposed station problem.
![Page 52: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/52.jpg)
Wireless LAN: CSMA-CA
The MACA protocol. (a) A sending an RTS to B.(b) B responding with a CTS to A.
![Page 53: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/53.jpg)
The 802.11 MAC Sublayer Protocol
The use of virtual channel sensing using CSMA/CA.
![Page 54: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/54.jpg)
The 802.11 MAC Sublayer Protocol
A fragment burst.
![Page 55: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/55.jpg)
The 802.11 MAC Sublayer Protocol
Interframe spacing in 802.11.
![Page 56: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/56.jpg)
The 802.11 Frame Structure
The 802.11 data frame.Address 3 and 4-for source and dest base stations, Seq-fragment sequence number,
Type-data or control, Subtype-RTS or CTS, MF-more fragments, More-more frames, W-WEP, O-frame sequence maintained
![Page 57: Medium Access Control](https://reader036.fdocuments.in/reader036/viewer/2022062411/56815c2b550346895dca0505/html5/thumbnails/57.jpg)
802.11 Services
• Association• Disassociation• Reassociation• Distribution• Authentication• Integration• Privacy