Intro Tele

7/28/2019 Intro Tele

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telephony Slide 1

ear

T

R

mouthDTMF

ringer

C

dial switch

SLIC

Telephone

Subscriber

Line

CO

(Local Exchange)

cradle switch

off-hookon-hook

tip (+)

ring (-)

Basic Telephone


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telephony Slide 2

hybrid

TTelephone

current

detector

~

ring switch

ring

generator

(100Vrms

25 Hz)-48 VDC

Subscriber

Line

crossconnectswitch

Subscriber Line Interface Circuit

Processor

control channel

Call Statesidle on hook

dialing dialing in progress

calling after dialing

ringing incoming call

called call in progress

tip (+)

ring (-)

Subscriber Line Interface


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telephony Slide 3

The PSTN circa 1900

pair of copper wires

local loop

manual routing at local exchange office (CO)

Analog voltage travels over copper wire end-to-end Voice signal arrives at destination severely attenuated and distorted

Routing performed manually at exchanges office(s)

Routing is expensive and lengthy operation

Route is maintained for duration of call

PSTN

Review


4/22

telephony Slide 4

Multiplexing

1900: 25% of telephony revenues went to copper mines

standard was 18 gauge, long distance even heavier

two wires per loop to combat cross-talk

needed method to place multiple conversations on a single trunk

1918: Carrier system (FDM)

5 conversations on single trunk

later extended to 12 (group)

still later supergroups, master groups, supermaster groups

1963: T-carrier system (TDM)

T1 = 24 conversations per trunk

later T3 = 28 T1s

still later SDH rates with 1000s of conversations per trunk

PSTN

Review

f

channels

t

timeslots


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telephony Slide 5

Cross-connect switch

Complexity increases rapidly with size

1 2 4 5 6 7 83

1

2

3

45

6

7

Analog Crossbar switch Digital Cross-connect (DXC)

processor

t1 2 3 4 5

t2 1 5 4 3


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telephony Slide 6

SLIC

PCM

MUX

Hybrid

SLIC

TDM

port

TDM

port

TDM

port

TDM

port

Tone

&

Ann

DTMF

decode

Processor

Subscriber

Lines

Hybrid

2w 4w

DXC

E1/T1 E1/T1

Basic TDM CO


7/22telephony Slide 7

PSTN Topology

Many local telephone exchanges had sprung up

Bell Telephone acquired them

and interconnected them for long distance

Local

Exchange LocalExchange

LocalExchange

local loop

Long distance

network

trunkcircuit

subscriber line

PSTN

Review



Old US PSTN

Class 3 Class 3

Class 2 Class 2

Class 1

Class 3

Regional centers

Sectional centers

Primary centers

Toll (tandem) offices

Central (end) offices

Class 4

last milesubscriber lineslocal loop

circuits,trunks

Class 5 switch is the sole interface to the subscriber lines

PSTN

Review

Class 5 Class 5 Class 5 Class 5 Class 5

Class 4 Class 4 Class 4



Numbering Plans

An E.164 International Numberhas the format :

Country-Code Area-Code Exchange-Code Line-Number

EX: 972 2 588 9159

Country-Codes1 : N America (US, CA, Caribbean) 1 digit

2 : Africa 2 or 3 digits 20 Egypt 27 South Africa 235 Chad3 : Europe 2 or 3 digits 31 Netherlands 354 Iceland4 : Europe 2 or 3 digits 44 UK 49 Germany 420 Czech Republic5 : S America 2 or 3 digits 54 Argentina 595 Paraguay6 : Australia & S Pacific 2 or 3 digits 61 Australia 675 Papua7 : Russia 1 digit8 : China & N Pacific 2 or 3 digits 86 PR China 855 Cambodia9 : Middle East 2 or 3 digits 90 Turkey 972 Israel

MAXIMUM 15 DIGITS



Signaling

PSTN with automatic switching requires signaling

The present PSTN has thousands offeatures

and all require signaling support

Examples:

On-hook / off-hook

Pulse / Tone dialing

Receiver off-hook

Call waiting

Caller number identification

Call forwarding

Hook-flash

Fax transmission detect

Inter-CO messaging

Echo cancellation

Voice mail

Conference calls

Coin-drop

Billing

PSTN

Review



Signaling Methods

Signaling can be performed in many ways

Analog voltage signaling loop-start, ground-start, E&M

In-band signaling DTMF, MFR1, MFR2

Channel associated signaling (CAS) AB bits, ABCD bits

Common channel signaling (CCS) SS7, QSIG

Trunk Associated CCS

Separate signaling network CCS

PSTN

Review



Subscriber - ExchangeSignaling*

On/off hook DC current flow

Dial-tone 350+440 continuous

Pulse Dialing

DTMFL1 697 L2 770 L3 852 L4 941

H1 1209 H2 1336 H3 1477 H4 1633

Ring AC with cadence

Ring-back 440+480 with 2:4 cadence

Busy 480+620 with 1/2:1/2 cadence

Trunk busy 480+620 but 0.2:0.3 cadence

Receiver off-hook 1400+2060+2450+2600 with ).1:0.1 cadence

Invalid(nonworking, unobtainable) numberannouncement, SIT-tone

* US cadences - national differences

H1 H2 H3 H4

L11 2 3 A

L24 5 6 B

L37 8 9 C

L4* 0 # D

make

break

>700ms>100ms

(60:40)off-hook



Subscriber - SubscriberSubscriber - Exchange

Signaling Hook-flash on-hook for 0.1 - 1 sec

Echo suppressor disabler2100 continuous

FAX CED2100 2.6 - 4 sec

Modem ANS 2100 with phase reversals every 450 ms for 3.3 s

ANSAM 2100 with phase reversals and 15 Hz AM modulation

CNG

FAX 1100 with 0.5:3 cadence

Modem 1300 with 0.5:2 cadence

Caller Line Identification (CLI/CND) 1200 bps FSK (V.23) data signal 1300 = 1 2100 = 0

Between 1st and 2nd ringsRING RINGCLI>300 ms > 475 ms



Supervision procedures

FXO/FXS Foreign Exchange Office / Foreign Exchange Subscriber

FXS is like exchange - provides voltage, ringing, dialtone

FXO is like a phone - requires voltage, detect ring, etc.

When connecting PBX to CO, PBX is FXO, CO is FXS

Analog loop start

Digital loop start

Analog ground start Digital ground start

E&M (wink)



Interexchange Signaling

CAS - R2

CAS - R1

CCS - SS7

PSTN



Optimized Telephony Routing

Circuit switching (route is maintained for duration of call)

Route set-up is an expensive operation, just as it was for manual switching

Today, complex least cost routingalgorithms are used

Call duration consists ofset-up, voiceand tear-downphases

PSTN

Review

PSTN



The PSTN circa 1960

local loop

subscriber line

automatic routing through universal telephone network

Analog voltages used throughout, but extensive Frequency Division Multiplexing Voice signal arrives at destination after amplification and filtering to 4 KHz

Automatic routing

Universal dial-tone Voltage and tone signaling Circuit switching (route is maintained for duration of call)

trunks

circuits

PSTN

Review

PSTN



The Digitalization of the PSTN

Shannon (Bell Labs) proved

is better than

and the PSTN became digital

Bettermeans

More efficient use of resources (e.g. more channels on trunks)

Higher voice quality (less noise, less distortion)

Added features

Digital

Communications

Analog

Communications

PSTN

Review

PSTN



Timing

In addition to voice, the digital PSTN transports timing

This timing information is essential because of

the universal use of TDM

the requirement of accurate playback (especially for fax/modem)

Receiving switches can recover the clock of the transmitting switch

Every telephony network has an accurate clock called stratum 1

Clocks synchronized to it are called stratum 2

Clocks synchronized to them are called stratum 3

and so on

PSTN

Review

PSTN



The Present PSTN

subscriber line

Analog voltages and copper wire used only in last mile,but core designed to mimic original situation Voice signal filtered to 4 KHz at input to digital network

Time Division Multiplexing of digital signals in the network Extensive use of fiber optic and wireless physical linksT1/E1, PDH and SONET/SDH synchronous protocols

Signaling can be channel/trunk associated or via separate network (SS7)

Automatic routing Circuit switching (route is maintained for duration of call) Complex routing optimization algorithms (LP, Karmarkar, etc)

PSTN Network

core

backbone

PSTN

Review

PSTN



Nonvoice services

The PSTN can even be used to transport non-voice signals

such as FAX or DATA

These services disguise themselves as voice by using a modem

Proper timing is essential

Special signaling is required turn off LEC

turn off call waiting

service recognition

PSTN

VoP course

PSTN

Review

capabilities negotiation

mutual identification

end of page/document

modem recognition

modem training

data compression

PSTN


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Digital Loop Carrier

Pushes the digital PSTN closer to customerAT&T SLC-40, SLC-96, Nortel DMS P-phone, pair-gain

TR-08 multiplex 96 lines on:Mode 1: 4 T1sMode 2: 2 T1s (2:1 concentration)

GR303/V5.1/V5.2 multiplex up to 2048 lines

CLASS

5 StreetcabinetUTP/coax/fiber

UTP

pedestal

TR-08Mode 1pair-gain:Replace 96 pairs with 5 T1s(one spare for span protection)

9610 = 86

TR-08Mode 2pair-gain:Replace 96 pairs with 2 T1s(without span protection)

964 = 92

Access Network

CPEFTTB/FTTC

PSTN

Review

Intro Tele

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