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PCM , PDH AND SDH(DIFFERENCES)T1, E1, E3 AND DS3 (STANDARDS)

By

Abdul Wahab

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OUTLINE

Pulse Code Modulation (PCM)

PCM Based TDM Systems T1,E1 etc.

Plesiochronous Digital Hierarchy (PDH)

Synchronous Digital Hierarchy

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P!SE C"DE M"D!#T$"%

PCM is the most commonly used techni&ue in digital

communications

A'rimarybuilding block for advanced communication systems

sed in many a''lications Telephone systems

Digital audio recording

D laser disks

digital video etc

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P!SE C"DE M"D!#T$"%

Based on the sam'ling theorem

Each analog sam'le is assigned a inary code#nalog sam'les are re*erred to as 'ulse am'litude modulation

(P#M) sam'les

The digital signal consists o* loc+ o* nits, here each n-it numer is the am'litude o* a PCM 'ulse

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!" #$#TE" %LO& DIA'(A"

#ample )*old

omparator

(amp'enerator

%inaryounter

!arallel to#erial

onverter

All pulses have sameheight and +idth,

f(t)

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-

.

/

0

t

12t3

!ulse ode "odulation2!"3

onsider the analog #ignal 12t3,

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-

.

/

0

n

14n5

!ulse ode "odulation2!"3

The signal is first sampled

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#%T$/#T$"%

Is the process of converting thesampled signal to a binary value

Each voltage level +ill correspond to a

different binary numberThe magnitude of the minimum step

si6e is called the resolution,

The error resulting from 7uanti6ing iscalled the 7uanti6ation noise, Its valueis .8/ the resolution

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-

.

/

0

t

192t3

:uanti6ed #ignal

It is 7uite apparent that the 7uanti6ed signal

is not e1actly the same as the originalanalog signal, There is a fair degree of7uanti6ation error here, *o+ever; as thenumber of 7uanti6ation levels is increasedthe 7uanti6ation error is reduced and the7uanti6ed signal gets closer and closer to theoriginal signal

!ulse ode "odulation2!"3

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!" O< #!EE* #I'NAL# 2=E($>I"!O(TANT3

"ost of the significant spectral components of speechsignals are contained in the range 0-->0?-- *6

Ny7uist (ate @ /10?-- @ ,B k*6

!ractical #ampling (ate fs@ B k*6 2C*$,,3

Number of 7uanti6ation levels @ /

Number of %its8#ample n @ B 2log// 3

Data (ate @ nfs@ B1B--- @ ? kbps

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!" O< #!EE* #I'NAL# 2=E($>I"!O(TANT3

Bandwidh R!"ui#!$!n

ommunication theory tells us that we can transmit errorfree atmost two pieces of information per second per hertz bandwidth(lathi pg. 260)

Therefore the minimum re7uired band+idth for transmission of a!" speech signal %Cmin @ ?8/ @ 0/ k*6

Ce may re7uire more band+idth but the signal is no+ digital and

+e no+ have the ability to manipulateF storeF regenerate the data,2see advantages of Digital ommunication pg /0 of lathi3

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!" %A#ED TD" #$#TE"#

!" is +idely used in transmission of speech signals in fi1ed linetelephone system,

An e1ample !"F the T. carrier system +hich +as developed at%ell labs in the U#, And is still in use today in the U# and Gapan,

A similar scheme called the E. is used in Europe and !akistan,

These schemes are used to multiple1 the speech from multiplesubscribers and transmit them to their destinations over a commonHTime #hared channel, *ence the name time division multiple1ing2TD"3,

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.0

!(I"A($ "ULTI!LEJIN'T(UN& NETCO(& 2T. @ %ELL D/3

Digital

switch

Digital

switch

n*23*64 Kb/s

n*1544 Kb/s

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!" %A#ED TD" #$#TE"# T.

The sampling rate used for voice @ B--- samples8sec

ThereforeF #ampling Interval @ .8B--- @ ./Ks

This means that the time bet+een t+o consecutive samples2from the same source3 is ./Ks, TD" systems e1ploit this factand utili6e this interval to sample signals from other subscribers,In T. systems the signals from /? subscribers is sampled in./Ks,

The samples are 7uanti6ed and then converted into a bitstreamfor transmission over the channel,

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!" %A#ED TD" #$#TE"# T.

As mentioned previouslyF sampling rate used for voice @ B---samples8sec

Every sample is represented by B bits

ThereforeF

Data rate of . voice channel @ B1B--- @ ?kbps

In the T. system /? voice channels are multiple1ed in time

thereforeF

Data rate of a T. stream %h&uld b! @ /?1?kbps @ .,0 "bps

*o+everF the a'ual daa #a!@ .,??"bps

The e1tra b*%2.,??>.,0@,--B"bps3result from the overhead bits+hich are inserted alongside the data 2details ahead3,

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!" %A#ED TD" #$#TE"# T.

The T. carrier system multiple1es binary code +ords corresponding tosamples of each of the /? channels in a se7uence,A segment containingone codeword (corresponding to one sample) from each of the 24channels is called a FRAME.

Each frame has +- . 1/+daa bi%and takes ./Ks,

At the receiver it is also necessary to kno+ +here a frame starts in orderto separate information bits correctly,

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!" %A#ED TD" #$#TE"#T. *ook signalsF Alarm signals etc,

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!(I"A($ "ULTI!LEJIN' E.

The international standard for primary ratetelephone multiple1ing uses /-?B &b8s 2E.3links, Each E. link carries 0/ channels at ?&b8s each, 0- channels are used for carrying

voiceF one for signaling and one forsynchroni6ation and link management,

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.M

!(I"A($ "ULTI!LEJIN'T(UN& NETCO(& 2E. @ E!T0-3

Digital

switch

Digital

switch

n*30*64 Kb/s

n*2048 Kb/s

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/-

"ULTI!LEJIN'

Optical Fiber or Microwave Link

Digital

switch

Digital

switch

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/.

"ULTI!LEJIN'O< AL"O#T #$N*(ONOU# DATA

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P!ES$"CH0"%"S D$$T#! H$E0#0CH2

(PDH)

The Plesiochronous Digital Hierarchy (PDH) is a

technology used in telecommunications netor+s to

trans'ort large &uantities o* data o3er digital trans'ort

e&ui'ment such as *ire o'tic and microa3e radio systems.

The term 'lesiochronous is deri3ed *rom ree+ 'l4sios,meaning near, and chronos, time, and re*ers to the *act that

PDH netor+s run in a state here di**erent 'arts o* the

netor+ are nearly, ut not &uite 'er*ectly, synchronised.

PDH is ty'ically eing re'laced y Synchronous DigitalHierarchy (SDH) or Synchronous o'tical netor+ing

(S"%ET) e&ui'ment in most telecommunications netor+s.

PDH allos transmission o* data streams that are nominally

running at the same rate

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/0

*IE(A(*$

Each multiple1ed section has its o+n clock

Each level of multiple1ing has its o+n clock

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!D* !(INI!LE

If +e +ant yet higher ratesF +e can mu1 together TD" signals2tributaries3

Ce coulddemu1 the TD" timeslots and directly remu1 them but that is too comple1

The TD" inputs are already digitalF so +e must

insist that the mu1 provide clock to all tributaries

2not al+ays possibleF may already be locked to a net+ork3

4R

someho+ transport tributary +ith its o+n clock

across a higher speed net+ork +ith a different clock

2+ithout spoiling remote clock recovery3

5(6)SS4NET

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!D* *IE(A(*IE#

5(6)SS4NET

? kbps

/,-?B"bps

.,??"bps

.,??"bps

,0./"bps

,0./"bps

B,??B"bps

0?,0B "bps

.0M,/?"bps

??,P0 "bps 0/,-?

"bps

MP,P/B"bps

/P?,.P"bps

E!T N,A, Gapan

?

0

/

.

-

level

Q0-Q/?

Q/?

Q?

Q?

Q?

Q?

QP

Q

Q?

Q

Q0

E.

E/

E0

E?

T.

T/

T0

T?

G.

G/

G0

G?

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!D* O=E(*EAD

Overhead al+ays increases +ith data rate 5(6)S

S4NET

(igital

signal

(ata rate

b)s'

ice

channels

erhea( )ercentage

+1 1,544 24 0,52 -

+2 6,312 .6 2,66 -

+3 44,36 62 3,86 -

+4 24,16 4032 5,88 -

1 2,048 30 6,25 -

2 8,448 120 .,0. -

3 34,368 480 10,61 -

4 13.,264 1.20 11,6 -

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OA"

analog channels and ? kbps digital channelsdo not have mechanisms to check signal validity and 7uality

thus maor faults could go undetected for long periods of time hard to characteri6e and locali6e faults +hen reported minor defects might be unnoticed indefinitely

#olution is to add mechanisms based on overhead

as !D* net+orks evolvedF more and more overhead +as dedicated to4perationsF Administration and Maintenance 2OA"3 functions

including

monitoring for valid signal defect reporting alarm indication8inhibition 2AI#3

5(6)SS4NET

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LI"ITATION# O< !D*

Three incompatible !D* standards are used globally 2NorthAmericanF GapaneseF European3

No +orld+ide optical interface standard 2vendor specific3

Insufficient capacity for net+ork management

omple1 de>multiple1ing structure to e1tract a particulartributary signal 2e,g e1tracting E. from E?3

!D* based net+orks do not meet present ) future telecomdemands 2ma1imum %C offered by !D* is E?3

Overhead percentage increases +ith rate

Inability to identify individual channels in a higher>order bitstream,

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#ONET8#D*

"OTI=ATION AND *I#TO($

5(6)SS4NET

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O"!A(IN' LO

A clock is said to be isochronous2isos@e7ualF chronos@time3

if its tic%sare e7ually spaced in time

/ clocks are said to be synchronous2syn@same chronos@time3if they tic% in timeF i,e, have precisely the same fre7uency

/ clocks are said to be plesiochronous2plesio@near chronos@time3

if the same fre7uency but are not loc%ed

5(6)SS4NET

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IDEA %E*IND #ONET

Synchronous 4ptical NET+ork

Designed for opticaltransport 2high bitrate3

Di#!'mapping of lo+er levels into higherones

arry all !D* types in &n!universalhierarchy ITU version @ Synchronous Digital

Hierarchydifferent terminology but interoperable

Overhead doesnt increase +ith rate

OA" designed>in from beginning

5(6)SS4NET

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S5NCHR4N4 HIERARCH5(SDH)

Synchronous o'tical netor+ing (S"%ET) and

synchronous digital hierarchy (SDH) are standardi5ed

multi'le6ing 'rotocols that trans*er multi'le digital it

streams o3er o'tical *ier

!oer data rates can also e trans*erred 3ia an electricalinter*ace

Di!#!n'! #&$ PDH S"%ET7SDH are tightly synchroni5ed across the entire netor+

reatly reducing the amount o* u**ering S"%ET and SDH can e used to enca'sulate earlier digital

transmission standards

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0?

*IE(A(*$

STM-1 STM-1

' to 89 channels at : M7s

+he entire tr!n netwr has ne clc

#!lti)lee( stream base( n 125 S frames

Different channels can each hae their wn

asnchrn!s clc,

$(((r) m!lti)leers

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STANDARDS ANDAPP>ICATI4NS 4F SDH

V Chy #ONET8#D*

V #ONET8#D* solution

V #D* format

V #D* mapping8multiple1ing

V #D* pointer application

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WH5 S4NET2SDH

ONET8#D*s goal

implify interconnection bet+een net+ork operators1pand the compatibility

perfection of !D*

hree different regional digital hierarchiesate )

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B#S$C %$T "; ;0#M$% $% SDH

The asic unit o* *raming in SDH is a STM-1 (Synchronous

Trans'ort Module, le3el 1), hich o'erates at 1

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S4NET2SDH S4>.

#T">?

#T">.

#T">?

.,B?

.,/

//,-B

/?BB,0/

MM0,/B

.,/

//,-B

/?BB,0/

MM0,/B

#peed Unit 2"bps3

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S4NET2SDH S4>

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S4NET2SDH BENEFITS

V (educe costs

simplified standard interfaces eliminate vendor proprietary interfaces

V Integrated net+ork elements

enhanced operations capabilities

V #urvivability

grants upgradability 2modularity3

V No band+idth bottlenecks

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#ONET8#D*

A(*ITETU(E

5(6)SS4NET

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LA$E(#

#ONET +as designed +ith definite layering concepts

!hysical layer R optical fiber 2linear or ring3 +hen e1ceed fiber reach R regenerators regenerators are not mere amplifiersF regenerators use their o+n overhead fiber bet+een regenerators called section2regenerator

section3

Line layer R link bet+een #ONET mu1es 2Add8Drop Multiple1ers3 input and output at this level are ?irtual Tributaries 2?Cs3 actually / layers

lo+er order = 2for lo+ bitrate payloads3higher order = 2for high bitrate payloads3

!ath layer R end>to>end path of client data 2tributaries3 client data 2payload3 may be

!D*AT"packet data

5(6)SS4NET

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#ONET A(*ITETU(E

#ONET 2#D*3has at 0 layers

path R end>to>end data connectionF mu1es tributary signals path section

there are #T# paths W =irtual Tributary 2=T3 paths

line R protected multiple1ed #ONET payload multiple1 section

section R physical link bet+een adacent elements regenerator section

Each layer has its o+n overhead to support needed functionality

#D* terminology

5(6)SS4NET

PahT!#$inai&n

PahT!#$inai&n

>in!T!#$inai&n

>in!T!#$inai&n

S!'i&nT!#$inai&n

path

line line line

AD" AD"regenerat

or

section section sectionsection

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#T#F OF ET,

A #ONET signal is called a Synchronous Transport Signal

The basic #T# is #T#>.F all others are multiples of it > #T#>N

The 2optical3 physical layer signal corresponding to an #T#>N is anO>N

5(6)SS4NET

SONET Optical rate

S+S1 C1 51,84#

S+S3 C3 155,52#

S+S12 C12 622,080#

S+S48 C48 2488,32#

S+S1.2 C1.2 ..53,28#

Q 0

Q ?

Q ?

Q ?

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#ONET8#D* T(I%UTA(IE#

E0 and T0 are carried as *igher Order !aths 2*O!s3E. and T. are carried as Lo+er Order !aths 2LO!s3

2the numbers are for di#!'mapping3

5(6)SS4NET

SONET SDH T1 T3 E1 E3 E4

S+S1 28 1 21 1

S+S3 S+#1 84 3 63 3 1

S+S12 S+#4 336 12 252 12 4

S+S48 S+#16 1344 48 1008 48 16

S+S1.2 S+#64 536 1.2 4032 1.2 64

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NO O""ON #TANDA(D

%efore #D* there +ere no standards toensure that e7uipment from differentvendors inter+orked on the same system,

=endors can have their o+n uni7uedesigns +hich means +e have to buy thesame vendors e7uipment for both endsof the line,

Ideally +e +ould like to shop around forthe most suitable e7uipmentF +ithouthaving to keep to the same supplier,

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AD=ANTA'E# O< #D*

Designed for cost effectiveF fle1ible telecoms net+orking Rbased on direct synchronous multiple1ing,

!rovides built>in signal capacity for advanced net+orkmanagement and maintenance capabilities,

!rovides fle1ible signal transportation capabilities R designed

for e1isting and future signals, Allo+s a single telecommunication net+ork infrastructure R

interconnects net+ork e7uipment from different vendors

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AD=ANTA'E#O< #D* #D* integrates three maor digital hierarchies of the +orld

#D* offers standard optical interfaces 2ITU>T based3

#imple and direct multiple1ing 8 de>multiple1ing method foradding or dropping electrical signals

(ich overhead bytes 2OA"@?S3 for managementFmaintenanceF and operation, #upports po+erful net+orkmanagement system,

#upport fle1ible and self>healing net+orks 2protection3

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AD=ANTA'E#O< #D*

%oth synchronous and plesiochronous operationsare possible,

%it rates e1ceeding .?-"b8s are standardi6ed ona +orld+ide basis,

All current !D* signals can be transmitted +ithinthe #D* e1cept B "b8s 2E/3 +hich has nocontainer,

A reduction in the amount of e7uipment ) anincrease in net+ork reliability,

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DI#AD=ANTA'E# O< #D*

%and+idth utili6ation is comparatively poor than!D* 2+aste of %C due to various managementoverhead bytes3

#D* e7uipments are complicated to deal +ithdue to variety of management traffic types andoptions,

#D* adopts large>scale soft+are control +hich

makes it vulnerable to man>made mistakesFsoft+are bugsF configuration problemsF etc,

,

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C*E(E I# #D* U#ED

#D* can be used in all of the traditionalnet+ork application areas,

A single #D* net+ork infrastructure istherefore possible +hich provides an efficient

direct interconnection bet+een the threemaor telecommunication net+orks,

#D* (IN'#

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E/

#D* (IN'#

9= M7s : M7s

#D* (IN'#

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E0

#D* (IN'#

#D* (IN'#

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E?

#D* (IN'#

#D* (IN'#

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EE

#D* (IN'#

CT >

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NOTE# ON #D* (ATE#

The most common #D* line rates in usetoday are .,/ "bpsF //,-B "bpsF /,'bpsF .- 'bps,

#D* is a structure that is designed for the

futureF ensuring that higher line rates can beadded +hen re7uired,

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#U""A($ !" is +idely used in transmission of speech signals in fi1ed line telephone

system, E1ample of is !"F the T. and E.

The nominal data rate on the multiple1ed 2T.3 link is .?? &b8s +hich is theresult of multiple1ing /? channels at ? &b8s

Each E. link carries 0/ channels at ? &b8s each, 0- channels are used forcarrying voiceF one for signaling and one for synchroni6ation and linkmanagement,

Digital #ignal 0 2D#03 is a digital signal level 0 T> arrier, It may also be referredto as a T0 line, The data rate for this type of signal is ??,P0 "bit8s,

PDH allos transmission o* data streams that are nearly running at the same rate re'laced y SDH Synchronous o'tical netor+ing (S"%ET) and synchronous digital hierarchy (SDH) are

standardi5ed multi'le6ing 'rotocols that trans*er multi'le digital it streams o3er o'tical *ier

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@