csc 535 communication networks i chapter 4 multiplexing, switching, and telephone systems dr....

CSC 535Communication Networks I

Chapter 4Multiplexing, Switching, and Telephone Systems

Dr. Cheer-Sun yang

2

MultiplexingSeveral slow speed links sharing one high

speed link

3

SwitchingIt is costly to establish a fully-connected

system for which there is a direct connection between any two hosts.

Several transmitters all connecting to a central location, known as central office, in order to save the direction connections among all of the transmitters

Application: telephone system

4

Topics for this chapterMultiplexing techniques including FDM,

TDM, statistical TDM (asynchronous TDM), WDM(4.1, 4.2, 4.3, 5.5.1, and 5.5.2)

Telephone networks: general concepts (data transmission, signaling, traffic engineering), celluar telephone networks.(Sections 4.5, 4.6, 4.7, 4.8)

(Switching will be discussed when network layer concept is introduced in CSC 581. Although switching is a physical layer technique but routing is a network layer concept in which Wide Area Network is involved.)

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks

5

B B

C C

A A

B

C

A

B

C

A

MUXMUX

(a) (b)

Trunkgroup

Figure 4.1

6

Multiplexing TechniquesFrequency Division Multiplexing (FDM)(Synchronous)Time Division Multiplexing

(TDM)(Asynchronous) Statistical Time Division

Multiplexing (Statistical TDM)Wavelength Division Multiplexing (WDM)

7

Frequency Division MultiplexingIntroduced in 1930s into telephone

networkUseful bandwidth of medium exceeds

required bandwidth of channelEach signal is modulated to a different

carrier frequencyCarrier frequencies separated so signals

do not overlap (guard bands)e.g. broadcast radioChannel allocated even if no data

8

Frequency Division MultiplexingDiagram


9

A CBf

Cf

Bf

Af

W

W

W

0

0

0

(a) Individual signals occupy W Hz

(b) Combined signal fits into channel bandwidth

Figure 4.2

10

FDM System

11

FDM of Three Voiceband Signals

12

Analog Carrier SystemsAT&T (USA)Hierarchy of FDM schemesGroup

12 voice channels (4kHz each) = 48kHz Range 60kHz to 108kHz

Supergroup 60 channel FDM of 5 group signals on carriers between

420kHz and 612 kHz

Mastergroup 10 supergroups

13

Asymmetrical Digital Subscriber LineADSLLink between subscriber and network

Local loop

Uses currently installed twisted pair cable Can carry broader spectrum 1 MHz or more

14

ADSL DesignAsymmetric

Greater capacity downstream than upstream

Frequency division multiplexing Lowest 25kHz for voice

Plain old telephone service (POTS)

Use echo cancellation or FDM to give two bands

Use FDM within bands

Range 5.5km

15

Synchronous Time Division Multiplexing Introduced into the telephone network in

1960s.Data rate of medium exceeds data rate of

digital signal to be transmittedMultiple digital signals interleaved in timeMay be at bit level of blocksTime slots preassigned to sources and fixedTime slots allocated even if no dataTime slots do not have to be evenly

distributed amongst sources

16

Time Division Multiplexing

17

T-1 Line (DS-n Signal)The T-1 carrier system carries 24 digital

telephone connections (channels) by sampling a speech waveform 8000 times/second and by representing each sample with eight bits.

The T-1 system uses a frame (a data link layer PDU) that consists of 24 slots of eight bits each.

Each slot carries one PCM sample of a single channel.

Total speed = 1 + 24 * 8 * 8000 = 1.544 Mbps


18

(a) Each signal transmits 1 unit every 3T seconds

(b) Combined signal transmits 1 unit every T seconds

tA1 A2

tB1 B2

tC1 C2

3T0T 6T

3T0T 6T

3T0T 6T

tB1 C1 A2 C2B2A1

0T 1T 2T 3T 4T 5T 6T

Figure 4.3


19

2

24

1

MUXMUX

1

2

24

24 b1 2 . . .b2322

frame

24 . . .

. . .

Figure 4.4


20

North American Digital Hierarchy

PrimaryMultiplexEg. DigitalSwitch30 chan PCM

4th orderMultiplex

x4

2nd orderMultiplex

x4

3rd orderMultiplex

x4

34.368 Mbps2.048 Mbps 8.448 Mbps139.264 Mbps

CEPT 1CEPT 4

European Digital Hierarchy

28

M13Multiplex

M23Multiplex

x7

PrimaryMultiplexEg. DigitalSwitch24 chan PCM

M12Multiplex

x4

1

DS3 44.736 Mbps

DS1 1.544 Mbps DS2 6.312 Mbps DS3 44.736 Mbps

Figure 4.5


21

12345 12345

t

Figure 4.6

22

TDM System

23

TDM Link ControlNo headers and tailersData link control protocols not neededFlow control

Data rate of multiplexed line is fixed If one channel receiver can not receive data, the

others must carry on The corresponding source must be quenched This leaves empty slots

Error control Errors are detected and handled by individual

channel systems

24

Data Link Control on TDM

25

FramingNo flag or SYNC characters bracketing

TDM framesMust provide synchronizing mechanismAdded digit framing

One control bit added to each TDM frameLooks like another channel - “control channel”

Identifiable bit pattern used on control channel e.g. alternating 01010101…unlikely on a data

channel Can compare incoming bit patterns on each

channel with sync pattern

26

Pulse StuffingProblem - Synchronizing data sourcesClocks in different sources driftingData rates from different sources not

related by simple rational numberSolution - Pulse Stuffing

Outgoing data rate (excluding framing bits) higher than sum of incoming rates

Stuff extra dummy bits or pulses into each incoming signal until it matches local clock

Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer

27

TDM of Analog and Digital Sources

28

Digital Carrier Systems(1)Hierarchy of TDMUSA/Canada/Japan use one system: T1

Link or DS-1 signalITU-T use a similar (but different) systemUS system based on DS-1 formatMultiplexes 24 channelsEach frame has 8 bits per channel plus

one framing bit193 bits per frame

29

Digital Carrier Systems (2)For voice each channel contains one word of

digitized data (PCM, 8000 samples per sec) Data rate 8000x193 = 1.544Mbps Five out of six frames have 8 bit PCM samples Sixth frame is 7 bit PCM word plus signaling bit Signaling bits form stream for each channel

containing control and routing info

Same format for digital data 23 channels of data

7 bits per frame plus indicator bit for data or systems control

24th channel is sync

30

Synchronous Optical Network(SONET)Using optical fiber as the transmission linkUsed with ISDN or ATMReferred to as Synchronous Digital Hierarchy

(SDH) in EuropeThe signals are called synchronous transport

signal level-n(STS-n) and Synchronous Transfer Module-n(STM-n), respectively, in SONET and SDH.

SONET can transmit STS-1 signals at the speed of 51.84 Mpbs, whereas T-1 can transmit DS-1 signals at the speed of 1.544 Mbps.

31

Design IssuesSONET multiplexing (WDM)Add-drop multiplexingSurvivabilitySONET frame mapping

32

Basic ISDN Interface (1)Digital data exchanged between subscriber

and NTE - Full DuplexSeparate physical line for each directionPseudoternary coding scheme

1=no voltage, 0=positive or negative 750mV +/-10%

Data rate 192kbpsBasic access is two 64kbps B channels and

one 16kbps D channelThis gives 144kbps multiplexed over 192kbpsRemaining capacity used for framing and sync

33

Basic ISDN Interface (2)B channel is basic iser channelDataPCM voiceSeparate logical 64kbps connections o

different destinationsD channel used for control or data

LAPD frames

Each frame 48 bits longOne frame every 250s

34

Frame Structure

35

Primary ISDNPoint to pointTypically supporting PBX1.544Mbps

Based on US DS-1 Used on T1 services 23 B plus one D channel

2.048Mbps Based on European standards 30 B plus one D channel Line coding is AMI usingHDB3

36

Primary ISDN Frame Formats


37

Low-SpeedMappingFunction

MediumSpeed

MappingFunction

High-Speed

MappingFunction

DS3

44.736

DS1

DS2

CEPT-1

CEPT-4

139.264

ATM

150 Mbps

STS-1

STS-1

STS-1STS-1STS-1

STS-1STS-1STS-1

STS-3c

STS-3c

OC-n

Scrambler E/O

51.84 Mbps

High-Speed

MappingFunction

MuxSTS-n

Figure 4.8

38

Sonet/SDHSynchronous Optical Network (ANSI)Synchronous Digital Hierarchy (ITU-T)CompatibleSignal Hierarchy

Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1)

51.84Mbps Carry DS-3 or group of lower rate signals (DS1

DS1C DS2) plus ITU-T rates (e.g. 2.048Mbps) Multiple STS-1 combined into STS-N signal ITU-T lowest rate is 155.52Mbps (STM-1)

39

SONET Frame Format

40

SONET STS-1 Overhead Octets

41

Statistical TDMIn Synchronous TDM many slots are

wastedStatistical TDM allocates time slots

dynamically based on demandMultiplexer scans input lines and collects

data until frame fullData rate on line lower than aggregate

rates of input lines

42

Statistical TDM Frame Formats


43

MUX DEMUX MUX DEMUX

MUX DEMUX

(a) pre-SONET multiplexing

removetributary

inserttributary

ADM

removetributary

inserttributary

(b) SONET Add-Drop multiplexing

Figure 4.9


44

a

b

c

3 ADMs

physical loop net

OC-3nOC-3n

OC-3n

Figure 4.10


45

a

b c

logical fully-connected net

(a)

a

b

c

3 ADMs connected inphysical ring topology

OC-3nOC-3n

OC-3n

(b)

Figure 4.11


46

a

b

c

d

a

b

c

d

(a) Dual ring (b) Loop-around in response to fault

Figure 4.12


47

Inter-OfficeRings

MetroRing

RegionalRing

Figure 4.13


48

STE: Section Terminating Equipment, e.g. a repeaterLTE: Line Terminating Equipment, e.g. a STS-1 to STS-3 multiplexerPTE: Path Terminating Equipment, e.g. an STS-1 multiplexer

optical

section

optical

section

optical

section

optical

section

line

optical

section

line

optical

section

line

path

optical

section

line

path

(a)

(b)

STSPTE

LTESTE

STS-1 Path

STS Line

Section Section

Mux Muxreg reg regSONET

Terminal

STE STELTE

STSPTE

SONET Terminal

Figure 4.14


49

B BB 87B

InformationPayload

9 Rows

125 sTransportoverhead

90 bytes

SectionOverhead 3 rows

6 rowsLineOverhead

Figure 4.15


50

Pointer87 columns

9rows

first column is path overhead

SynchronousPayload

Envelope

framek

framek+1

Pointer

first octet

last octet

Figure 4.16


51

STS-1 STS-1

STS-1 STS-1

STS-1 STS-1

Map

Map

Map

STS-1 STS-1

STS-1 STS-1

STS-1 STS-1B

yteInterleave

STS-3

IncomingSTS-1 Frames

Synchronized NewSTS-1 Frames

Figure 4.17

52

Sonet/SDH WDMWDM can be viewed as an optical-domain

version of FDM in which multiple information signals modulate optical signals at different optical wavelengths (colors).

Prisms and diffraction gratings can be used to combine and split color sigals.

For example, WDM systems are available that use 16 wavelengths at OC-48 to provide aggregate rates up to 16 * 2.5 Gbps = 40 Gbps.


53

1

2

m

OpticalMUX

1

2

m

OpticaldeMUX

1 2.m

Opticalfiber

Figure 4.18


54

(a) WDM chain network

ab c d

(b) WDM ring network

a

b

c

3 ADMs

Figure 4.20

55

Asynchronous TDMAlso known as statistical time division

multiplexing (sections 5.5.1 and 5.5.2)


56

Header Data payload

Buffer

A

B

C

Input lines

Output line

Figure 5.42


57

A1 A2

B1 B2

C2C1

A2B1 B2 C2C1

(a)

(b)A1

Shared Line

Dedicated Lines

Figure 5.43


58

A1 A2

B1 B2

C2C1

A2B1 B2 C2C1

(a)

(b) A1Shared Line

Dedicated Lines

(c) N(t)

Figure 5.44


59

0

0.1

0.2

0.3

0.4

0.5

0.6

0 8000 16000 24000 32000 40000 48000 56000 64000

Ave

rage

Del

ay (

seco

nds)

Goodput (bits/second)

L=200

L=400L=800

L=1200

Figure 5.49


60

FewerTrunks

ManyVoiceCalls

Part of this burst is lost

Figure 5.50


61

Trunks

Spee

ch lo

ss

# connections

0.001

0.01

0.1

1

10 12 14 16 18 20 22 24

24 32 40

48

Figure 5.51


62

Many voice terminalsgenerating voice packets

Buffer

B2

buffer overflow

C1 D1A2 B1C2D2B3 C3 A1

D3 D1D2

B3 B1B2

C3 C1C2

A3 A1A2

Figure 5.52


63

Received t

Sent t1 2 3

1 2 3

Figure 5.53

64

The Telephone NetworkMultiplexingSwitching - details will be discussed in

CSC581Signaling


65

User 1

SwitchLink

User n

User n-1

(a) Network

(b) Switch Control

123

N

123

N

Connectionof inputs to outputs

Figure 4.21


66Figure 4.30


67

Signal

Source

Signal

Release

Signal

Destination

GoAhead Message

Figure 4.31


68

(a) Routing in a typical metropolitan area

(b) Routing between two LATAs

1

2 3

4

5

LATA 1 LATA 2

net 1

net 2

A B

C D

Figure 4.32


69

local telephone office

Dis

trib

utio

n F

ram

e

Serving Area I/f

Serving Area I/f

Pedestal

feeder cable

Switch

distribution cable

Figure 4.33


70

Original signal

Hybrid transformer

Received signal

Echoed signal

Receive pair

Transmit pair

Figure 4.34


71

Localanalog

Localdigital

Digitaltrunks

LocalSwitch

Tie lines

Foreign exchange

Channel-switched traffic (digital leased lines)

Circuit-switched traffic

Digitalcross-connect

System

Figure 4.35


72

Physical SONET

Topology usingADMs and DCCs

Logical Topology

Switches see thistopology

DCC

Figure 4.36

ADM

ADM

ADM

ADM

ADM

ADM


73

Basic Rate Interface (BRI): 2B+D

Primary Rate Interface (PRI): 23B+D

BRI

PRI

BRI

PRI

CircuitSwitched Network

ChannelSwitched NetworkPrivate

SignalingNetwork

PacketSwitched Networks

Figure 4.37


74

SPC

Control Signaling Message

Figure 4.39


75

Switch

Processor

Office B

Switch

Office A

ProcessorSignaling

ModemModem

Trunks

Figure 4.39


76

STP

STP

STP

STP

SSP SSP

Transport Network

Signaling Network

SSP = Service switching point (signal to message)STP = Signal transfer point (message transfer)SCP = Service control point (processing)

SCP

Figure 4.40


77

SSP

SSP

Transport Network

ExternalDatabase

SignalingNetwork Intelligent

Peripheral

Figure 4.40


78

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Presentation Layer

Session Layer

SCCP

MTP Level 3

MTP Level 2

MTP Level 1

ISUPTCAPTUP

Figure 4.42


79

FewerTrunks

ManyLines

Figure 4.43


80

N(t)

t

1

2

3

4

5

6

7

all trunks busytr

unk

#

Figure 4.44


81

TRAFFIC CONTROL

the offered load a = lamda * expected holding time

utilization = a * (1 - blocking probability) / c


82

0.0001

0.001

0.01

0.1

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

# trunks

Blo

ckin

g Pr

obab

ilit

y

1 2 3 4 5 6 7

8

9

10

offered load

Figure 4.45


83

6

1

2

5

4

3

7

2

6

1

3

1

7

2

4 5

4

6

37

5

Figure 4.51


84

AC = authentication centerBSS = base station subsystemEIR = equipment identity registerHLR = home location register

wirelineterminal

MSC

PSTN

BSS BSS

STP SS#7HLRVLR

EIRAC

MSC = mobile switching center PSTN = public switched telephone networkSTP = signal transfer pointVLR = visitor location register

Figure 4.52


85

LAPDm

radio

RRM

MM

CM

radio

LAPDm

RRM

LAPD

64 kbps

SCCP

MTP Level 3

MTP Level 2

CM

MM

RRM

64 kbps

64 kbps

LAPD

RRM

64 kbps

MTP Level 3

MTP Level 2

SCCP

Um Abis A

mobile station base transceiver station

base station controller

MSC

Figure 4.53


86

satellitemotion

(a) (b)

Figure 4.54

87

Mixed DataDS-1 can carry mixed voice and data

signals24 channels usedNo sync byteCan also interleave DS-1 channels

Ds-2 is four DS-1 giving 6.312Mbps

88

ISDN User Network InterfaceISDN allows multiplexing of devices over

single ISDN lineTwo interfaces

Basic ISDN Interface Primary ISDN Interface

89

Reading AssignmentChapter 4

csc 535 communication networks i chapter 4 multiplexing, switching, and telephone systems dr....

Documents

telephone systemtopics

telephone systemsdr

celluar telephone networks

network layer concept

data rate of digital

data rate of medium

bandsuse fdm

group signals