Chapter 4Transmission Systems and

the Telephone Network

School of Info. Sci. & Eng.Shandong Univ.

l Skip in Chapter 3 Articles 3.8.7, 3.8.8 (polynomial math for CRC codes)

l Skip in Chapter 4 4.2.2 (SONET frame structure) 4.6 Signaling in POTS

B B

C C

A A

B

C

A

B

C

A

MUXMUX

(a) (b)Trunkgroup

Figure 4.1

Sharing of an expensive channel by multiplexing (MUX)

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

Frequency Division MUX (FDM)

(a) Each signal transmits 1 unit every 3Tseconds

(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

Time Division MUX (TDM)

2

24

1

MUXMUX

1

2

24

24 b1 2 . . .b2322

frame

24 . . .

. . .

Figure 4.4

Standard T1 Carrier (TDM of 24 PCM voice channels)

(1+24channels*8bits/channel)*8000 frames/sec = 1.544 Mbps

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

lll

Figure 4.5

12345 12345

t

Figure 4.6

Figure 4.7 Optical fiber network for long distance carrier in 1998

Low-SpeedMappingFunction

MediumSpeed

MappingFunction

High-Speed

MappingFunction

DS3

44.736

DS1DS2

CEPT-1

CEPT-4

139.264

ATM150 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

lll

lll

Figure 4.8

MUX DEMUX MUX DEMUX

MUX DEMUX

(a) pre-SONET multiplexing

removetributary

inserttributary

ADM

removetributary

inserttributary

(b) SONET Add-Drop multiplexing

Figure 4.9

a

b

c

3 ADMs

physical loop net

OC-3nOC-3n

OC-3n

Figure 4.10

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

a

b

c

d

a

b

c

d

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

Figure 4.12

Inter-OfficeRings

MetroRing

RegionalRing

Figure 4.13

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

sectionoptical

section

optical

sectionline

optical

sectionline

optical

sectionlinepath

optical

sectionlinepath

(a)

(b)

STSPTE

LTESTE

STS-1 Path

STS LineSection Section

Mux Muxreg reg regSONETTerminal

STE STELTE

STSPTE

SONETTerminal

Figure 4.14

B BB 87B

InformationPayload 9 Rows

125 µsTransportoverhead

90 bytes

SectionOverhead 3 rows

6 rowsLineOverhead

Figure 4.15

Pointer87 columns

9rows

first column is path overhead

SynchronousPayload

Envelope

framek

framek+1

Pointer

first octet

last octet

Figure 4.16

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

λ1

λ2

λm

OpticalMUX

λ1

λ2

λm

OpticaldeMUX

λ1 λ2. λm

Opticalfiber

Figure 4.18

The latest incarnation of FDM: Wavelength Division Multiplexing

To pick good wavelengths, look at Fig. 3.45, p 145.

Figure 4.19 Optical signal in a WDM system

Figure 4.19

(a) WDM chain networka b c d

(b) WDM ring network

a

b

c

3 ADMs

Figure 4.20

Optical ADMs in a Fiber Optic Network

User 1

SwitchLink

User n

User n-1

(a) Network

(b) Switch Control

123

N

123

N

Connectionof inputs to outputsl

ll

lll

Figure 4.21

POTS consists of links and circuit switches

N

1 2

1

N

2lll

l l l N-1

Figure 4.22

Crossbar Switch; Space-Division Switches

Grows as N-squared

nxk

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

lll

lll

lll

1

2

k

2(N/n)nk + k (N/n)2 crosspoints

kxn

kxn

kxn

Figure 4.23

Multistage switch. Grows as N to the 1.5 power

nxk

nxk

nxk

N/n x N/n

N/n x N/n

N/n x N/n

kxn1

N/n

Desiredinput

1

jm

N/n

Desiredoutput

lll l

ll

1

2n-1

kxn

kxn

n-1

N/n x N/nn+1

N/n x N/n2n-2

lll

lll

free path freepath

n-1busy

n-1busy

Figure 4.24

12

24

12

24

FromTDM

DeMUX

ToTDMMUX

24 23 12

2 241 23

l l l

l l l

l l l

l l l

Read slots inpermuted order

Figure 4.25

Time Division Switches

Usually called Time Slot Interchange Switch (TSI)

nxk

nxk

nxk

nxk

N/n x N/n kxn1

2

N/n

Ninputs

1

3lll

1

12

l l l

l l ln

input TDM frame with n slots

output TDM frame with k slots

Figure 4.26

nxk N/n x N/n

N/n x N/n

N/n x N/n

kxn1 1

2

N/n

lll

lll

1

2

k

kxn

kxn

nxk2

nxkN/n

first slot

kth slot

first slot

kth slot

Figure 4.27

nxk

nxk

nxk

nxk

N/n x N/nTime-Shared

SpaceSwitch

kxn1

2

N/n

Ninputs

1

2

3 3

N/n

Noutputs

lll

lll

TDMn slots

n slots

n slots

n slots

kxn

kxn

kxn

TDMk slots TDM

k slots

TSI Stage TSI StageSpace Stage

Figure 4.28

2x3

2x3

3x21

2

1

23x2D1

B1 A1B2 A2

C1D2 C2

B1 A1

C1D1

A1

B1

C1

D1

A1 C1

B1 D1

Figure 4.29

Figure 4.30

4.5 The Telephone Network: POTS or PSTN

Setting up a circuit-switched path for the duration of the call.

Signal

Source

Signal

Release

Signal

Destination

GoAhead Message

Figure 4.31

Telephone call set up. Note the three phase process that propagates through intermediate points

This is an elaboration of the double timing diagram from Test 1.

(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

Routing for local and long-distance connections

Local Access and Transport Areas

Uses LD Carrier nets

local telephone office

Dis

tribu

tion

Fram

e

Serving Area I/f

Serving Area I/f

Pedestal

feeder cable

Switchdistribution cable

Figure 4.33

POTS access transmission facilities

Serving Area Interface

Original signal

Hybrid transformer

Received signal

Echoed signal

Receive pair

Transmit pair

Figure 4.34

2 and 4 wire connections in the telephone network; echos. Hybrid is in the CO or Serving Area Interface

Local Loop

Localanalog

Localdigital

Digitaltrunks

LocalSwitch

Tie lines

Foreign exchange

Channel-switched traffic (digital leased lines)

Circuit-switched traffic

Digitalcross-connect

System

Figure 4.35

Physical SONET

Topology usingADMs and DCCs

Logical Topology

Switches see thistopology

DCC

Figure 4.36

ADM

ADM

ADM

ADM

ADM

ADM

Digital cross connect and SONET

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

End to end digital services (ISDN)

SPC

Control Signaling Message

Figure 4.39

4.6 A little about signaling in the POTS

Stored program control. A computer runs the switching at Cos.

Switch

Processor

Office B

Switch

Office A

ProcessorSignaling

ModemModem

Trunks

Figure 4.39

Common Channel Signaling

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

The signaling network is packet switched!

SSPSSP

Transport Network

ExternalDatabase

SignalingNetwork Intelligent

Peripheral

Figure 4.40

The Latest Incarnation: "The Intelligent Network" allows Caller ID, Conferencing, Etc.

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

FewerTrunks

ManyLines

Figure 4.43

N(t)

t

1

2

3

4

5

6

7

all trunks busytru

nk #

Figure 4.44

# trunks

Blo

ckin

g Pr

obab

ility

offered load

Figure 4.45

Tandem Switch 2

Tandem Switch 1

B CA

(b) Trunkgroup

10 Erlangs between each pair90 Erlangs

E

F

D

B

C

A(a)

E FD

Figure 4.46

Switch SwitchHigh Usage Route

Tandem Switch

Alternate Route

Figure 4.47

High Usage Route B-E

Tandem Switch 1

Alternate Routes for B-E, C-F

High Usage Route C-F

Switch ASwitch B

Switch C

Switch ESwitch D

Switch F

Tandem Switch 2

Figure 4.48

High Usage Route

Alternate Routes

Tandem Switch 3

Tandem Switch 1

Tandem Switch 2

Switch A Switch B

Figure 4.49

Car

ried

Load

Offered Load

Network Capacity

Figure 4.50

6

1

2

5

4

3

7

2

6

1

3

1

7

2

4 5

4

6

37

5

Figure 4.51

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

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

satellitemotion

(a) (b)

Figure 4.54