8/13/2019 11-ATM.ppt

1/20

Data and ComputerData and Computer

CommunicationsCommunications

Chapter 11 Chapter 11 Asynchronous TransferAsynchronous Transfer

ModeMode

8/13/2019 11-ATM.ppt

2/20

ATMATM

a streamlined packet transfer interfacea streamlined packet transfer interface

similarities to packet switchingsimilarities to packet switching

transfers data intransfers data in discrete chunksdiscrete chunks supports multiple logical connections over asupports multiple logical connections over a

single physical interfacesingle physical interface

ATM usesATM uses fixedfixedsized packets called cellssized packets called cells withwith minimalminimalerror control and flow controlerror control and flow control

data rates of 25.6Mbps to 622.08Mbpsdata rates of 25.6Mbps to 622.08Mbps

8/13/2019 11-ATM.ppt

3/20

Protocol ArchitectureProtocol Architecture

8/13/2019 11-ATM.ppt

4/20

Reference Model PlanesReference Model Planes

user planeuser plane provides for user information transfer,provides for user information transfer,

associated controls (flow control, errorassociated controls (flow control, errorcontrol)control)

control planecontrol plane

call and connection controlcall and connection control

management planemanagement plane plane managementplane management

whole system functionswhole system functions

layer managementlayer management

Resources and parameters in protocol entitiesResources and parameters in protocol entities

8/13/2019 11-ATM.ppt

5/20

ATM Logical ConnectionsATM Logical Connections

virtual channel connections (virtual channel connections (VCCVCC))

analogous to virtual circuit in X.25analogous to virtual circuit in X.25

basic unit of switching between two end usersbasic unit of switching between two end users

full duplexfull duplex

fixed size cellsfixed size cells

also foralso for

user-network exchange (control)user-network exchange (control) network-network exchange (network mgmt & routing)network-network exchange (network mgmt & routing)

8/13/2019 11-ATM.ppt

6/20

8/13/2019 11-ATM.ppt

7/20

Advantages of Virtual PathsAdvantages of Virtual Paths

simplified network architecturesimplified network architecture

increased network performance andincreased network performance and

reliabilityreliability reducedreducedprocessingprocessing

short connection setup time for newshort connection setup time for new

channelchannel

8/13/2019 11-ATM.ppt

8/20

8/13/2019 11-ATM.ppt

9/20

Virtual Channel ConnectionVirtual Channel Connection

UsesUses

betweenbetween end usersend users end to end user dataend to end user data

VPC provides overall capacityVPC provides overall capacity

VCC organization done by users within the capacityVCC organization done by users within the capacity betweenbetween end user and networkend user and network

control signalingcontrol signaling

betweenbetween network entitiesnetwork entities

network traffic managementnetwork traffic management routingrouting

8/13/2019 11-ATM.ppt

10/20

VP/VC CharacteristicsVP/VC Characteristics

quality of servicequality of service -- cell loss ratio, cell delaycell loss ratio, cell delayvariationvariation

switched and semi-permanent channelswitched and semi-permanent channel

connectionsconnections cellcell sequence integritysequence integrity

traffictraffic parameter negotiationparameter negotiation and usageand usagemonitoring -monitoring - average rate, peak rate, burstiness,average rate, peak rate, burstiness,

and peak durationand peak duration VPC onlyVPC only

virtual channel identifier restriction within VPCvirtual channel identifier restriction within VPC

8/13/2019 11-ATM.ppt

11/20

Fixed vs. Variable Length CellFixed vs. Variable Length Cell

##Efficiency Consideration:Efficiency Consideration:

Efficiency N = Information Octets /Efficiency N = Information Octets /

(Information Octets + Header Octets)(Information Octets + Header Octets)

Fixed Length Packets:Fixed Length Packets:

L = Data Field Size (Octets) in a PacketL = Data Field Size (Octets) in a Packet

H = Header Size (Octets)H = Header Size (Octets)

X = Total Message Size (Octets)X = Total Message Size (Octets)

## Expression for N = ? (Needs ceilingExpression for N = ? (Needs ceiling

function), Nopt = ?function), Nopt = ?

8/13/2019 11-ATM.ppt

12/20

Fixed vs. Variable Length CellFixed vs. Variable Length Cell

## Variable Length Packets:Variable Length Packets: Needs an additional length field,Needs an additional length field,

Hv = Additional overhead octetsHv = Additional overhead octets

H = Header Size (Octets)H = Header Size (Octets) X = Message Size (Octets)X = Message Size (Octets)

## Expression for N = ? (Assume SingleExpression for N = ? (Assume Single

Cell)Cell)

## Plot of N vs. Message Size (X = 48, 96,Plot of N vs. Message Size (X = 48, 96,

144, 192, 240), for fixed and variable length144, 192, 240), for fixed and variable length

cellscells

8/13/2019 11-ATM.ppt

13/20

What size of Fixed LengthWhat size of Fixed Length

Assume that the cells are completely filledAssume that the cells are completely filled(X / L = integer)(X / L = integer)

Expression for N = ?Expression for N = ?

PacketizationPacketization DelayDelay= buffering bits until= buffering bits until

the entire packet is filled beforethe entire packet is filled before

retransmissionretransmission

Expression for thisExpression for this delay Ddelay D= ? (function of= ? (function ofL and source data rate R)L and source data rate R)

8/13/2019 11-ATM.ppt

14/20

What size of Fixed LengthWhat size of Fixed Length

Plot of D vs. Data Field Size (L = 16, 32,Plot of D vs. Data Field Size (L = 16, 32,64, 128 octets) (64, 128 octets) (RR= 64 kbps for voice= 64 kbps for voice

coding)coding)

Plot of efficiency N vs. Data Field Size (16,Plot of efficiency N vs. Data Field Size (16,

32, 64, 128 octets)32, 64, 128 octets)

=> 48 octet provides a=> 48 octet provides a trade-offtrade-offbetweenbetween

efficiency and delayefficiency and delay

8/13/2019 11-ATM.ppt

15/20

ATM CellsATM Cells

8/13/2019 11-ATM.ppt

16/20

ATM Header FieldsATM Header Fields

generic flow controlgeneric flow control

Virtual path identifier - routingVirtual path identifier - routing

Virtual channel identifier end to end userVirtual channel identifier end to end user payload typepayload type (3-bits, user information,(3-bits, user information,

congestion)congestion)

cellcell loss priorityloss priority header error controlheader error control

8/13/2019 11-ATM.ppt

17/20

ExamplesExamples

##Consider compressed videoConsider compressed videotransmission in ATM network, Cells musttransmission in ATM network, Cells must

pass through 5 switches. The data rate ispass through 5 switches. The data rate is

43 Mbps.43 Mbps. - Transmission time of one cell through- Transmission time of one cell through

one switch?one switch?

- Assume other cells have lower priority- Assume other cells have lower priority(but(but non-premptivenon-premptive) than cell A. What is) than cell A. What is

thethe maximummaximumtime from arrival at the firsttime from arrival at the first

8/13/2019 11-ATM.ppt

18/20

ExamplesExamples

Switch to the completion of transmissionSwitch to the completion of transmissionby the fifth for cell A? (all other delays areby the fifth for cell A? (all other delays are

negligible)negligible)

- if the probability that a switch is busy is- if the probability that a switch is busy is0.6 and the average delay to wait for0.6 and the average delay to wait for

current transmission completion is one halfcurrent transmission completion is one half

a cell transmission time, what is thea cell transmission time, what is theaverage timeaverage timefrom arrival at the first Switchfrom arrival at the first Switch

to the completion of transmission by theto the completion of transmission by the

fifth for cell A?fifth for cell A?

8/13/2019 11-ATM.ppt

19/20

ExamplesExamples

- what is the maximum and average- what is the maximum and averagevariability in encountered delay (variability in encountered delay (the jitterthe jitter)?)?

##IP datagrams are segmented into ATMIP datagrams are segmented into ATMcells and sent over the ATM network. Losscells and sent over the ATM network. Loss

of a cell means loss of entire IP packet.of a cell means loss of entire IP packet.

Pc = cell loss ratePc = cell loss rate n = number of cells for a datagramn = number of cells for a datagram

Expression for Pp = datagram loss rate?Expression for Pp = datagram loss rate?

8/13/2019 11-ATM.ppt

20/20

SummarySummary

Asynchronous Transfer ModeAsynchronous Transfer Mode(ATM)(ATM)

architecture & logical connectionsarchitecture & logical connections

ATM Cell formatATM Cell format transmission of ATM cellstransmission of ATM cells