J.Tiberghien - VUB10-05-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 2.1 The Circuit Switched Telephone Network.

J.Tiberghien - VUB10-05-K.Steenhaut & J.Tiberghien - VUB1

TelecommunicationsConcepts

Chapter 2.1

The Circuit Switched

Telephone Network


Contents• Traditional Overall structure

– Access network» Fixed lines» Wireless access

• GSM• UMTS

– Trunk network » Primary multiplexing : E1 / T1 lines» Higher order multiplexing

• Plesiochronous Data Hierarchy• Synchronous Data Hierarchy

– Exchanges and signaling• General purpose SDH networks




• GSM• UMTS





The Telephone NetworkAnalog / Digital

PABX

SW

SW

SW

SW

SW

PABX

SW

SW




• GSM• UMTS





The Fixed Access NetworkAnalog phone on analog switch

Linecircuit

Analogswitch

twisted pair, average length 2.5 Km

Signaling (DTMF or pulse) and voice multiplexed

In Belgium : last one went out of service in 2002


The Fixed Access Network Analog phone on digital switch

Linecircuit

Digitalswitch

DigitalAnalog

twisted pair, average length 2.5 Km

Signaling (DTMF or pulse) and voice multiplexed

In Belgium : the most common situation


The Fixed Access Network The ISDN Basic Access

twisted pair, average length 2.5 Km 144Kb/smodem

Digitalswitch

144Kb/smodem

S bus

2 * 64 Kb/s + 16 Kb/s TDM

In Belgium : e.g. the Belgacom TWIN




• GSM• UMTS





The Mobile Access NetworkMobility Management

NSS

HLR

VLR

PSTN

MSC

NSS

BSS

16 Kb/s13 Kb/s 64 Kb/s

BSS : Base Station SubsystemNSS : Network & Switching Subsystem

HLR : Home Location RegisterVLR : Visitors Location RegisterMSC :Mobile Switching Center


The Mobile Access NetworkMobility Management

• Mobile terminal identification– SIM card with unique id.– Data about SIM stored in HLR of operator who owns SIM– Phone calls directed to HLR of operator

• Mobile terminal localization– BSS regularly makes broadcasts in its cells– Mobile selects best cell and sends its SIM id.– Presence of mobile recorded in local VLR– SIM’s owner HLR updated with applicable VLR

• Handover– When location of mobile changes during conversation– Circuit routing modified “on the fly”– Sound quality briefly degraded– Handover not available between different operators




• GSM• UMTS





The Mobile Access NetworkGSM radio system

time

frequency

15/26 ms

200 KHz

45 M

HzTx

Rx

3 radio slots

• A combination of FDM and TDM• Two separate frequency bands used for Tx and Rx• Slow frequency hopping for propagation diversity• Sender and receiver sequences shifted by 45MHz and 3 slots• Predefined time slot for signaling channel




• GSM• UMTS





The Mobile Access NetworkWireless interference margins

cause considerable loss in transmission capacity

• Considerable room for improvements by controlling interferences : Fast frequency hopping spread spectrum radio with Code Domain Multiple Access

= Third generation mobile networks (UMTS)

Frequency

Space

Time


The Mobile Access Network

• Data combined with known higher frequency pseudo random sequence

• Resulting modulated radio signal has high bandwidth

• Shannon : low data rate combined with high bandwidth = excellent noise margins!

Fast hopping Spread Spectrum

n b/sData

Pseudo-random sequence

m * n b/s

xor

HF carrier

Modulated signalLarge bandwidth ≈ m times bandwidthneeded for data


The Mobile Access NetworkSpread Spectrum and CDMA

D1

S1

xor

HF

Tx1

D2

S2

xor

HF

Tx2

D2

S2

HF

Correl-ator

Rx2

D1

S1

HF

Correl-ator

Rx1

For radio link Tx1-Rx1, emission by Tx2 is just another source of noise


The Mobile Access Network Multi-path Interference

GSM : interference = noiseUMTS : correlator adds similar input signals with appropriate delays so that they reinforce each other

Different paths have different lengths and different delays


The Mobile Access NetworkThird Generation Handover

When a receiver is between two cells, both transmitters send the same signal. These two signals reinforce each other, as multipath propagation does.




• GSM• UMTS





Time Domain Multiplexing

Synchronous multiplexing

Unique bit pattern to delimit frames

1 0 0 1

0 1 0 1

1 0 0 10 1 0 1 XX


Primary MultiplexingTrunk Network (E1 = CEPT30)

Digitalswitch

Digitalswitch

n*30*64 Kb/s

n*2048 Kb/s


Primary MultiplexingTrunk Network (T1 = Bell D2)

Digitalswitch

Digitalswitch

n*23*64 Kb/s

n*1544 Kb/s


The ISDN Primary Ratefor connecting Private Branch Exchanges

Digitalswitch

2048 Kb/s (CEPT30)

E1 Optical Fiber or Microwave LinkPABX

pabx

e.g: VUB : 4 E1 lines = 120 simultaneous calls




• GSM• UMTS





Higher Order Multiplexing

Optical Fiber or Microwave Link

Digitalswitch

Digitalswitch


Synchronous Multiplexing

of almost synchronous data

flows

D C B AE

S R Q PT

F

EST D C B AR Q P01F

1 Frame

S C

fout > n * MAX(fin)

Primary rate dataflows to be multiplexed can be derived from independent clocks !




• GSM• UMTS





Plesiochronous Digital Hierarchy–Each multiplexed section has its own clock

–Each level of multiplexing has its own clock

– Frame structure from multiplexed signals is not explicitly present in the multiplexed stream

>Full demultiplexing required at each node !




• GSM• UMTS





Synchronous Digital Hierarchy

STM-1 STM-1

Up to 63 channels at 2 Mb/s

– The entire trunk network has one clock

–Multiplexed stream based on 125 S frames

–Different channels can each have their own asynchronous clock.

–Add-drop multiplexers


Synchronous Digital HierarchySDH - SONETData rate CCITT USA-Elec. USA-Opt.

51.84 STS-1 OC-1

155.52 STM-1 STS-3 OC-3

466.56 STM-3 STS-9 OC-9

622.08 STM-4 STS-12 OC-12

933.12 STM-6 STS-18 OC-18

1244.16 STM-8 STS-24 OC-24

1866.24 STM-12 STS-36 OC-36

2488.32 STM-16 STS-48 OC-48

... ... ... ...


SDH Rings

34 Mb/s 2 Mb/s


SDH Rings


SDH Rings


SDH RingsThe MCI Belgian Network

065

060

064

071

057

069

056

051

058

059 050

068

055054

053

067

02

09 052

03

061

082084

083

085

063

086 080

010

081

016

019

011015

014

04

012

087

089013WCOM POP

WCOM POP

WCOM POP

WCOM POP

WCOM POP

WCOM POP

WCOM POPWCOM POP

WCOM POP

WCOM POPLUXEMBOURG


SDH Rings

CUT !




• GSM• UMTS





Telephone Exchange

(Conceptual Model)

SwitchingMatrix

Line Circuit

Line Circuit

Line Circuit

Line Circuit

Line Circuit

Control Computer

trunk lines +Inter-office

signaling

Register

Register

Register

Register


Signaling system generations

• SS1 - SS5 : Analog call forwarding between exchanges• SS6 : First digital signaling system

– monolithic communications system (no layers)– Full mesh of virtual circuits, based on 2400 b/s links

• SS7 : Signaling system for the intelligent network– uses any digital link, satellites included– layered, OSI inspired, network architecture – supports "intelligent network" applications

» Non-geographic numbers (800)» CLIP, Call forwarding, Conference calls, etc...» Number portability, Carrier selection» Mobility & roaming

• IP ???


The Telephone Network

629

62X

477

538

64X

643

673

Non-geographic Numbering

6234567

62929056433180

0800 12345

4776970

6736476

database0800


The Telephone NetworkNumber portability

Ported numbers




• GSM• UMTS





General Purpose SDH Networks

PABXPABX


BibliographyTo know More about

Telephony

Recommended for this chapter

John C. BELLAMY

Digital Telephony

Third edition

John Wiley, 2000.

ISBN : 0-471-34571-7

J.Tiberghien - VUB10-05-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 2.1 The Circuit Switched Telephone Network.

Documents

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