数据与计算机通信

mes

Buildings

People

PublicInfrastructure

DataandComputer

Communications

PartIIIWAN

电路交换与分组交换

CircuitSwitchingandPacketSwitching

交换式通信网电路交换网

电路交换的概念控制信令

软交换体系结构分组交换原理

X.25帧中继

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

3

10.1SwitchingNetworks

vLongdistancetransmissionistypically

doneoveranetworkofswitchednodes

/Nodesnotconcernedwithcontentofdata

/Enddevicesarestations

>Computer,terminal,phone,etc.

，Acollectionofnodesandconnectionsisa

communicationsnetwork

'Dataroutedbybeingswitchedfromnodeto

node

4

Nodes

/Nodesmayconnecttoothernodesonly,orto

stationsandothernodes仅与其他节点相连5-7

/Nodetonodelinksusuallymultiplexed

/Networkisusuallypartiallyconnected

>Someredundantconnectionsaredesirablefor

reliability

/Twodifferentswitchingtechnologies

>Circuitswitching

>Packetswitching

5

OVERVIEW

/SwitchingNetworks交换式通信网

,CircuitSwitching电路交换网.

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

7

10.2CircuitSwitching

vDedicatedcommunicationpathbetween

twostations

vThreephases

>Establish

>Transfer

>Disconnect

'Musthaveswitchingcapacityandchannel

capacitytoestablishconnection

'Musthaveintelligencetoworkoutrouting

CircuitSwitching-Applications

vInefficient

>Channelcapacitydedicatedfordurationof

connection连接期间信道的容量是专用的

>Ifnodata,capacitywasted

/Setup(connection)takestime

，Onceconnected,transferistransparent

'Developedforvoicetraffic(phone)

PublicCircuitSwitched

Network

o0

o0Long-distanceLong-distance

o0officeoffice

c^

o0o

o0

EndOffice

EndOffice

。o

。o

*o

SubscriberLoopo

。q

。

ConnectingTrunkIntercityTrunk

ConnectingTrunk

DigitalPBX

10

TelecommsComponents

，Subscriber

>Devicesattachedtonetwork

/Subscriberline用方线路

>LocalLoop

>Subscriberloop

>Connectiontonetwork

>Fewkmuptofewtensofkm

/Exchange交换局

>Switchingcenters

>Endoffice-supportssubscribers

/Trunks中继线

>Branchesbetweenexchanges

CircuitEstablishment

End

office

Trunk

■Intermediate

exchange

Trunk

End

office

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

13

10.3CircuitSwitchElements

ControlUnit

-O……

t

Q……

-O……

\

%

SQ*

8a

W>O

-9

xP

①-o

-p：

d①DigitalSwitch

n、1

O……♦■

p1a

=—■

n

-O,•

・•

LL0♦B

1-O……♦.

■O

9

■

■o-…-

-O……

t

1

■o*

■

K>…

-O

14

Network

Interface

CircuitSwitchingConcepts

/DigitalSwitch

>Providetransparentsignalpathbetweendevices

/NetworkInterface

'ControlUnit

>Establishconnections

•Generallyondemand

•Handleandacknowledgerequests

•Determineifdestinationisfree

•constructpath

>Maintainconnection

>Disconnect15

BlockingorNon-blocking

vBlocking

AAnetworkisunabletoconnectstationsbecause

allpathsareinuse

AAblockingnetworkallowsthis

>Usedonvoicesystems

•Shortdurationcalls

/Non-blocking

>Permitsallstationstoconnect(inpairs)atonce

>Usedforsomedataconnections

10.3.1SpaceDivisionSwitching

空分交换

/Developedforanalogenvironment

VSeparatephysicalpaths

/Crossbarswitch纵横交换机

>Numberofcrosspoints（交叉点）growsas

squareofnumberofstations

>Lossofcrosspointpreventsconnection

>Inefficientuseofcrosspoints

*Allstationsconnected,onlyafewcrosspointsinuse

>Non-blocking

17

SpaceDivisionSwitch

空分交换矩阵

TN_TN~ZN-ZS-ZS-~~~7

3d㈠㈠㈠㈠㈠㈠㈠

8㈠㈠㈠㈠㈠㈠㈠㈠㈠

s

①8㈠㈠㈠U㈠㈠㈠㈠

u

_

_lJ8㈠㈠㈠㈠㈠㈠㈠㈠㈠

dn

_u8㈠㈠㈠㈠㈠㈠㈠㈠㈠

8㈠㈠㈠㈠㈠㈠㈠d

3d㈠㈠㈠㈠㈠㈠㈠

3㈠㈠㈠㈠㈠㈠㊀㈠㈠

"TTTTTTTTTt18

OutputLines

MultistageSwitch多级交换

/Reducednumberofcrosspoints

/Morethanonepaththroughnetwork

>Increasedreliability

，Morecomplexcontrol

“Maybeblocking

ThreeStageSpaceDivision

10.3.2TimeDivisionSwitching

时分交换

/Modemdigitalsystemsrelyonintelligent

controlofspaceandtimedivisionelements

，Usedigitaltimedivisiontechniquestoset

upandmaintainvirtualcircuits

/Partitionlowspeedbitstreamintopieces

thatsharehigherspeedstream

21

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

22

10.4.1ControlSignalingFunctions

信令功能

/Audiblecommunicationwithsubscriber

>Dialtone,ringingtone,busysignal,ColorRingBackTone

/Transmissionofdialednumber

/Callcannotbecompletedindication

/Callendedindication

/Signaltoringphone

/Billinginfo

/Equipmentandtrunkstatusinfo

/Diagnosticinfo

/Controlofspecialistequipment

23

ControlSignalSequence

/Bothphonesonhook(notinuse)

/Subscriberliftsreceiver(offhook)

/Endofficeswitchsignaled

/Switchrespondswithdialtone

/Callerdialsnumber

/Iftargetnotbusy,sendringersignaltotargetsubscriber

/Feedbacktocaller

>Ringingtone,engagedtone(busy),unobtainable

/Targetacceptscallbyliftingreceiver

/Switchterminatesringingsignalandringingtone

/Switchestablishesconnection

/ConnectionreleasewhenSourcesubscriberhang^2j^_

SwitchtoSwitchSignaling

vSubscribersconnectedtodifferentswitches

/Originatingswitchseizesinterswitchtrunk（空

闲的）

/Sendoffhooksignalontrunk,requestingdigit

register（计发器）attargetswitch（foraddress）

/Terminatingswitchsendsoffhookfollowedby

onhook（wink闪挂）toshowregisterready

vOriginatingswitchsendsaddress

25

10.4.2LocationofSignaling

信令的位置

vSubscribertonetwork

>Dependsonsubscriberdeviceandswitch

/Withinnetwork

>Managementofsubscribercallsandnetwork

>Morecomplex

10.4.3InChannelSignaling

随路信令

Usesamechannelforsignalingandcall

>Requiresnoadditionaltransmissionfacilities

/Inband（带内信令）

>Usessamefrequenciesasvoicesignal

>Cangoanywhereavoicesignalcan

>Impossibletosetupacallonafaultyspeechpath

/Outofband

>Voicesignalsdonotusefull4kHzbandwidth

>Narrowsignalbandwithin4kHzusedforcontrol

>Canbesentwhetherornotvoicesignalsarepresent

>Needextraelectronics27

DrawbacksofInChannelSignaling

VLimitedtransferrate

/Delaybetweenenteringaddress(dialing)and

connection

/Overcomebyuseofcommonchannel

signaling(共路信令)

28

CommonChannelSignaling

共路信令

/Controlsignalscarriedoverpathsindependentof

voicechannel

/Onecontrolsignalchannelcancarrysignalsfora

numberofsubscriberchannels

/Commoncontrolchannelforthesesubscriberlines

/AssociatedMode（相关方式）

>Commonchannelcloselytracksinterswitchtrunks

/DisassociatedMode

>Additionalnodes（signaltransferpoints信号传送点）

>Effectivelytwoseparatenetworks

29

CommonvsInChannelSignaling

共路和随路信令

(a)Inchannel

(b)Commonchannel

CCISSIG:Common-channelinterofficesignalingequipment

SIG:Per-trunksianalinaeauioment

Common

Channel

Signaling

Modes

共路信令方式

/\

□,?♦\

，*

O'

(b)Disassociated

10.4.4SignalingSystemNumber7

7号信令系统

/SS7

/Commonchannelsignalingscheme

/ISDN

/Optimizedfor64kdigitalchannelnetwork

/Callcontrol,remotecontrol,managementand

maintenance

/Reliablemeansoftransferofinfoinsequence

vWilloperateoveranalogandbelow64k

/Pointtopointterrestrialandsatellitelink^2

SS7SignalingNetwork

Elements信令网络元素

/Signalingpoint（S。信令点）

>AnypointinthenetworkcapableofhandlingSS7

controlmessage

/Signaltransferpoint（STP信号传送点）

AAsignalingpointcapableofroutingcontrol

messages

/Controlplane控制平面

>Responsibleforestablishingandmanaging

connections

，Informationplane信息平面

>Onceaconnectionissetup,infoistransferred填the

informationplane

Transfer

Points

信息传送点

STP=Signalingtransferpoint

SP=Signalingpoint

TC=Transitcenter

LE=LocalExchange

SignalingNetworkStructures

/STPcapacities

>Numberofsignalinglinksthatcanbehandled

>Messagetransfertime

>Throughputcapacity报文吞吐容量

，Networkperformance

>NumberofSPs

>Signalingdelays

vAvailabilityandreliability

>Abilityofnetworktoprovideservicesinthe

faceofSTPfailures■

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

36

10.5SoftswitchArchitecture

软交换体系结构

/Generalpurposecomputerrunningsoftwaretomakeita

smartphoneswitch

/Lowercosts

/Greaterfunctionality

>Packetizingofdigitizedvoicedata

>AllowingvoiceoverIP

/Mostcomplexpartoftelephonenetworkswitchissoftware

controllingcallprocess（控制呼叫过程的软件）

>Callrouting

>Callprocessinglogic

>Typicallyrunningonproprietaryprocessor

vSeparatecallprocessingfromhardwarefunctionofswitch

/Physicalswitchingdonebymediagateway（媒体网关）

/Callprocessingdonebymediagatewaycontroller^2

TraditionalCircuitSwitching

Softswitch

39

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/Softswitch软交换体系结杓

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

40

10.6PacketSwitchingPrinciples

分组交换原理

/Circuitswitchingdesignedfbrvoice

>Resourcesdedicatedtoaparticularcall

>Muchofthetimeadataconnectionisidle

>Datarateisfixed

♦Bothendsmustoperateatthesamerate

/电路交换为话音而设计■■

>资源被-次特定的呼叫所独占

>数据连接的多数时间是空闲的

»数据率固定

♦两端以相同速率工作——对C/S模式数据传输有何影响?

41

BasicOperation分组交换的基本操作

/Datatransmittedinsmallpackets以小的分组传输

数据

>Typically1000octets典型的有1000八比特组

>Longermessagessplitintoseriesofpackets长寸艮文分

成一连串分戒

>Eachpacketcontainsaportionofuserdataplussome

controlinfo每个分组包含部分数据,卜加一些控制彳言

息

/Controlinfd控制信息

>懿9端,ddressing)info路由(寻址)信息或者虚电路

/Packetsarereceived,storedbriefly(buffered)and

pastontothenextnode接收到分组后短暂存储，

然后传递给下一节点42

>Storeandforward存储转发

UseofPackets

43

Advantages

/Lineefficiency

>Singlenodetonodelinkcanbesharedbymanypackets

overtime

>Packetsqueuedandtransmittedasfastaspossible

/Datarateconversion

>Eachstationconnectstothelocalnodeatitsownspeed

>Nodesbufferdataifrequiredtoequalizerates

/Packetsareacceptedevenwhennetworkisbusy

>Deliverymayslowdown

/Prioritiescanbeused

优点

/线路高效率

A单条节点到节点链路可在一段时间内由许多分

组共享

A分组排队并尽可能快地发送..

/实现不同数据率转换■

»每个站点可以自己的速率连接到本地节点H

»需要相等速率时由节点对数据给予缓冲H

，即使网络繁忙也能接受分组

A交付可能慢一些

,可以使用优先级

45

10.6.1SwitchingTechnique交换技术

/Stationbreakslongmessageintopackets

/Packetssentoneatatimetothenetwork

/Packetshandledintwoways

>Datagram

>Virtualcircuit

/站点负责将长报文分割成分组■

/-次送一个分组到网络

，分组以两种方式处理

A数据报Datagram

»虚电路Virtualcircuit46

Datagram数据报

/Eachpackettreatedindependently

/Packetscantakeanypracticalroute

/Packetsmayarriveoutoforder

/Packetsmaygomissing

/Uptoreceivertore-orderpacketsandrecoverfrom

missingpackets

,每个分组独立地处理

,分组可以选择任何存在的路由

/分组到达可能失序

/分组可能丢失

/接收方对分组重新排序，并对丢失分组给予恢复

Datagram

Diagram

数据报方式

(e)

VirtualCircuit

/Preplannedrouteestablishedbeforeany

packetssent

/Callrequestandcallacceptpacketsestablish

connection(handshake)

VEachpacketcontainsavirtualcircuit

identifierinsteadofdestinationaddress

/Noroutingdecisionsrequiredforeachpacket

/Clearrequesttodropcircuit

/Notadedicatedpath

49

虚电路

/建立预定的路由之后再发送所有分组

,由呼叫callrequest分组和callaccept分组建立连接

A握手(handshake)

,每个分组含有一个虚电路标识码，而不是使用目

的地址

,对每个分组不需要路由抉择

,通过一个dearrequest分组终止该电路

,不是-条像电路交换那样的独占通路

A不保留交换和链路容量

＞其它虚电路上的分组也可共享同一链路

»专用路由，而非专用链路

Virtual

Circuit

Diagram

虚电路方式

(e)

智

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VirtualCircuitsvsDatagram

vVirtualcircuits

»网络能够提供按序传输和差错控制

A分组可以更快地转发

集不必作出选路的决策

A可靠性差

率单点故障：一个节点失效将使通过该节点的全部电

—效

'Datagram

A不需呼叫建立阶段

率尤其少量分组时优势明显

»更灵活

(a)1-packetmessage(b)2-packetmessage(c)5-packetmessage(d)10-packetmessage

10.6.2

PacketSize

Message

switching

10.6.3CircuitvsPacketSwitching

电路交换与分组交换的比较

/Performance性能

>Propagationdelay传播时延

>Transmissiontime传输时间

>Nodedelay节点时延

•Processingdelay

EventTiming

laiCircuitswitching<h)Vinuulchvuniwkclswitching(e>Datugrampacketsnitching

56

®®©0

CircuitswitchingDatagrampyckrt«witchin»Virtiuil-circuifpseckrt

switchingTable10.2Other

DedicatedtransmissionpathNodedicatedpathNodedicatedpath

ContinuoustransmissionofTransmissionnipu<kctsTransmissionofpacketsCharacteristics

data

FastenoughQrinteractiveFastenoughforinteractiveFastenouLjliforintdiactive

MessagesarenotstnirdPacketsmaybestoneduntilPacketsstoreduntildchvered

dchvered

ThepathisestablishedfbcRouleestablishedforeachRouteestablishedforentire

entireconversationpacketconversation

Call沁lupdelay;negligiblePackettransmissiondelayCallsetupdelay:packet

transmissiondelaytransmissiondelay

Bus>signalifcalledpartySendermaybenotifiedifSendernuliGedofconnection

busypacketnotdelivereddenial

OverloadinayblockcallOverheadincreasespacketOverloadmayblockcall

setup,no<leluyforestablisheddehssetup;increasespacketdelay

calls

EleutromecluinicalorSmallsuitchinv*nmlcSmallswitchingnode>

computerizeditchingrnnkb

UsertespcnsiblclormessageNetworkmayberesponsibleNetworknuyberespunsibk

lossproteclionforindividualpuck山forpuckelsequence>

Usuallyno*edorcodeSpeedandcodecon\CIM-JIISpeedandcodeconversion

conversion

FixedbunduidthDynamicuuubandwidihDynamicuseorbamiwidth

Nooverheadbitsuitercall।1.'11uchp；K>.<)xerheadbitsineachpackci57

setup

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

7FrameRelay帧中继(Optional)

58

10.7X.25

♦1976

VInterfacebetweenhostandpacketswitched

network

/Almostuniversalonpacketswitched

networksandpacketswitchinginISDN

VDefinesthreelayers

>Physical

>Link

>Packet

59

10.7X.25

♦1976

/主机与分组交换网络间的接口■

,几乎通用于全球的分组交换网络I

,甚至可用于ISDN中的分组交换I

,定义了三个layers

A物理级Physicallevel/Physicallayer

A链路级Linklevel/Framelayer/LAPBlayer

A分组级Packetlevel/Packetlayer

X.25-Physical

vInterfacebetweenattachedstationandlinkto

node

vDataterminalequipmentDTE(userequipment)

/DatacircuitterminatingequipmentDCE(node)

/UsesphysicallayerspecificationX.21

/Reliabletransferacrossphysicallink

/Sequenceofframes

61

X.25的物理层

/接入的站点与通往端节点链路的接口■

＞建立DTE-DCE物理连接

'DataterminalequipmentDTE(userequipment)

'DatacircuitterminatingequipmentDCE(node)

/使用X.21物理层规约

,有时也用EIA-232替代

62

X.25-LinkX.25的链路层

/在DTE-DCE物理连接上的可靠数据传送

,以帧序列的形式传送数据

/链路层标准协议―

ALinkAccessProtocol,Balanced(LAPB)

琳HDLC子集SubsetofHDLC(见教材第7章)

，点到点链路差错与流量的控制

FormatofaLAPBFrame

FlagAddressControlInformationFCSFlag

I-frame:userdata

S-frame:empty

U-frame:controldata

SpecialAddressinginLAPB

□

Address:00000001Address:00000011

CommandCommand

Address:00000001Address:00000011

ResponseResponse

Three

Phases

ofthe

FrameDTE

LayerSABM_____________a

LinkU-frames

setup

/_________UA

Sendingandreceivingnetworklayer

packets(encapsulatedinI-frames)I-framesand

DataandcontrolandusingS-framestocontrolS-frames

transfer

theflowanderrorofthoseI-frames

DISC_____________K,

Link

disconnectU-frames

/_________UA

X.25-PacketX.25的分组层

/Externalvirtualcircuits外部虚电路

VLogicalconnections(virtualcircuits)

betweensubscribersDTE设备之间端到端

的逻辑连接(virtualcircuits)

X>25UseofVirtualCircuits

Solidline=physicallink68

Dashedline=virtualcircuit

FrameLayerandPacketLayerDomains

Packetlayerdomain

FramelayerdomainFramelayerdomain

X.25network

DTEDCEDCEDTE

VirtualCircuitService

vLogicalconnectionbetweentwostations

>Externalvirtualcircuit

'Specificpreplannedroutethroughnetwork

>Internalvirtualcircuit

/Typicallyonetoonerelationshipbetween

externalandinternalvirtualcircuits

/CanemployX.25withdatagramstylenetwork

有可能在数据报类型的网路上采用X.25

vExternalvirtualcircuitsrequirelogicalchannel

>Alldataconsiderednartofstream

X.25Levels层

/UserdatapassestoX.25level3

VX.25appendscontrolinformation

>Header

>Identifiesvirtualcircuit

>Providessequencenumbersfbrflowanderror

control

/X.25packetpasseddowntoLAPBentity

vLAPBappendsfurthercontrolinformation

UserDataandX.25Protocol

ControlInformation

X.25packe

LAPBframe

72

EncapsulationofPLPPacket

PLPPacketNetwor

Data

FlagAddr.ControlInformationlink

I-Frame

Physical

OVERVIEW

/SwitchingNetworks交换式通信网

/CircuitSwitching电路交换网

/CircuitSwitchingConcepts电路交换的概念

/ControlSignaling控制信令难点！

/SoftswitchArchitecture软交换体系结构

/PacketSwitchingPrinciples分组交换原理

/X.25(Optional)

/FrameRelay帧中继(Optional)

74

10.8FrameRelay帧中继

/DesignedtobemoreefficientthanX.25

/DevelopedbeforeATM

/LargerinstalledbasethanATM安装的基础比

ATM大

/ATMnowofmoreinterestonhighspeed

networks

75

FrameRelayBackground帧中

继背景・X.25

/Callcontrolpackets,inbandsignaling带内信令

警呼叫控制分组与数据分组在相同信道和虚电路上运载

/Multiplexingofvirtualcircuitsatlayer3

vLayer2and3includeflowanderrorcontrol

/Considerableoverhead相当可观的额外开销

/Notappropriatefbrmodemdigitalsystemswith

highreliability与高可靠性的现代募字系统不

相适应

76

FrameRelay-Differences

/Callcontrolcarriedinseparatelogicalconnection

/Multiplexingandswitchingatlayer2

>Eliminatesonelayerofprocessing

/Nohopbyhoperrororflowcontrol不采用逐跳的差

错控制与流量控制

>Endtoendflowanderrorcontrol(ifused)aredonebyhigher

layer

>Singleuserdataframesentfromsourcetodestinationand

ACK(fromhigherlayer)sentback一个用户数据帧从源站

发往目的站，来自高层的确认帧则由反向的一个帧返回