PDH & SDHPDH & SDH

PDH PLESIOCHRONOUS DIGITAL HIERARCHY. A TECHNOLOGY USED IN TELECOMMUNICATIONS

NETWORK TO TRANSPORT LARGE QUANTITY OF DATA OVER DIGITAL TRANSPORT EQUIPMENT SUCH AS FIBRE OPTIC AND MICROWAVE RADIO WAVE SYSTEMS.

THE TERM “PLESIOCHRONOUS” IS DERIVED FROM Greek plesio which means near, and chronous, time.

IT MEANS THAT PDH NETWORKS RUN IN A STATE WHERE DIFFERENT PARTS OF THE NETWORK ARE ALMOST, BUT NOT QUITE PERFECTLY SYNCHRONISED.

PDH

SENDING A LARGE QUANTITY OF DATA ON FIBRE OPTIC TRANSMISSION SYSTEM.

TRANSMISSION AND RECEPTION ARE SYNCHRONIZED BUT TIMING IS NOT.

THE CHANNEL CLOCKS ARE DERIVED FROM DIFFERENT MASTER CLOCKS WHOSE RANGE IS SPECIFIED TO LIE WITHIN CERTAIN LIMITS. THE MULTIPLEXED SIGNAL IS CALLED A “PLESIOCHRONOUS” SIGNAL.

PDH SIGNALS ARE NEITHER SYNCHRONOUS NOR ASYNCHRONOUS.

PDH PDH ALLOWS TRANSMISSION OF DATA

STREAMS THAT ARE NOMINALLY RUNNING AT THE SAME RATE, BUT ALLOWING SOME VARIATION ON THE SPEED AROUND A NOMINAL RATE.

BY ANALOGY, ANY TWO WATCHES ARE NOMINALLY RUNNING AT THE SAME RATE, CLOCKING UP 60 SECONDS EVERY MINUTE.

HOWEVER, THERE IS NO LINK BETWEEN WATCHES TO GUARANTEE THEY RUN AT EXACTLY THE SAME RATE.

IT IS HIGHLY LIKELY THAT ONE IS RUNNING SLIGHTLY FASTER THAN THE OTHER.

VERSIONS OF PDH THERE ARE TWO VERSIONS OF PDH NAMELY 1) THE EUROPEAN AND 2 ) THE AMERICAN. THEY DIFER SLIGHTLY IN THE DETAIL OF

THEIR WORKING BUT THE PRINCIPLES ARE THE SAME.

EUROPEAN PCM = 30 CHANNELS NORTH AMERICAN PCM = 24 CHANNELS JAPANESE PCM = 24 CHANNELS IN INDIA WE FOLLOW THE EUROPEAN PCM

OF 30 CHANNELS SYSTEM WORKING.

EUROPEAN DIGITAL HIERARCHY

• 30 Channel PCM = 2 Mbps• 2 Mbps x 4 = 8 Mbps• 8 Mbps x 4 = 34 Mbps• 34 Mbps x 4 = 140 Mbps• 140 Mbps x 4 = 565 Mbps

EUROPEAN PDH HIERARCHY WITH BIT RATES

MUX BIT RATE PARTS PER MILLION

CHANNELS

2 Mbps 2.048 Mbps +/- 50 ppm 30

8 Mbps 8.448 Mbps +/- 30 ppm 120

34 Mbps 34.368 Mbps +/- 20 ppm 480

140 Mbps 139.264 Mbps +/- 15 ppm 1920

DESCRIPTION OF EUROPEAN E-CARRIER SYSTEM

THE BASIC DATA TRANSFER RATE IS A STREAM OF 2048 KBPS.

FOR SPEECH TRANSMISSION, THIS IS BROKEN DOWN INTO 30 X 64 KBIT/S CHANNELS PLUS 2 X 64 KBPS CHANNELS USED FOR SIGNALLING AND SYNCHRONIZATION.

ALTERNATIVELY, THE WHOLE 2 MB/S MAY BE USED FOR NON SPEECH PURPOSES, FOR EXAMPLE, DATA TRANSMISSION.

THE EXACT DATA RATE OF THE 2 MBPS DATA STREAM IS CONTROLLED BY A CLOCK IN THE EQUIPMENT GENERATING THE DATA.

THE EXACT RATE IS ALLOWED TO VARY SOME PERCENTAGE (+/- 50 PPM) EITHER SIDE OF AN EXACT 2.048 MBPS.

DIFERENT 2 MBPS DATA STREAMS CAN BE RUNNING AT SLIGHTLY DIFERENT RATES TO ONE ANOTHER.

MULTIPLEXING TECHNIQUE

IN ORDER TO MOVE MULTIPLE 2 MBPS DATA STREAMS FROM ONE PLACE TO ANOTHER, THEY ARE COMBINED TOGETHER OR “MULTIPLEXED” IN GROUPS OF FOUR.

THIS IS DONE BY TAKING 1 BIT FROM STREAM #1, FOLLOWED BY 1 BIT FROM STREAM #2, THEN #3, THEN #4.

THE TRANSMITTING MULIPLEXER ALSO ADDS ADDITIONAL BITS IN ORDER TO ALLOW THE FAR END RECEIVING MULTIPLEXER TO DECODE WHICH BITS BELONG TO WHICH 2 MBPS DATA STREAM, AND SO CORRECTLY RECONSTITUTE THE ORIGINAL DATA STREAMS.

THESE ADDITIONAL BITS ARE CALLED “JUSTIFICATION” BITS OR “STUFFING BITS”

30 Chl Digital Hierarchy

III OrderMux

480 Chls

IV OrderMux

1920 Chls

PrimaryMux30 Chls

II orderMux120 Chls

X 4 X 4

2.048 Mbps 8.448 Mbps 34.368 Mbps 139.264 Mbps

DIGITAL MUX CONCEPTS• BIT INTERLEAVING:

• ALTERNATELY EACH CHANNEL CODE CAN BE SCANNED ONE DIGIT AT A TIME. THE MULTIPLEXED SIGNAL IS CALLED A “BIT INTERLEAVED SIGNAL”.

• “BIT INTERLEAVING” IS USED IN HIGHER ORDER MULTIPLEXING.

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 D1 D2 D3 D4

DIGITAL MUX CONCEPTS

• BYTE INTERLEAVING• WORD / BYTE / BLOCK INTERLEAVING:• IF THE CHANNEL TIME SLOT IS LONG

ENOUGH TO ACCOMMODATE A GROUP OF BITS THEN THE MULTIPLEXED SIGNAL IS CALLED A “ BYTE INTERLEAVED OR WORD INTERLEAVED SIGNAL”.

A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3 A4 B4 C4 D4

SLIP, JUSTIFICATION AND JITTER

SLIP – THIS OCCURS WHEN THE INCOMING BIT RATE DOES NOT MATCH WITH THE DIVIDED MUX/DEMUX CLOCK RATE. SAME BIT MAY BE READ TWICE OR LOSS OF BITS WILL OCCUR.

JUSTIFICATION:- IT IS A PROCESS OF ADDING ADDITIONAL BITS TO SOLVE THE PROBLEM OF SLIP.

JITTER:- DISPLACE MENT OF A PULSE FROM ITS NORMAL SIGNIFICANT INSTANT IS CALLED JITTER.

JUSTIFICATION -TYPES

• JUSTIFICATION

POSITIVE JUSTIFICATION

NEGATIVE JUSTIFIATION

POSITIVE-NEGATIVE JUSTIFICATION

JUSTIFICATION

IF MUX CLOCK RATE IS HIGHER THAN TRIBUTARY RATE, IT IS KNOWN AS POSITIVE JUSTIFICATION. THIS IS USED UPTO 140 MBPS SYSTEMS.

IF MUX CLOCK RATE IS LOWER THAN TRIBUTARY RATE, IT IS KNOWN AS NEGATIVE JUSTIFICATION.

IF ON AN AVERAGE, MUX CLOCK RATE AND TRIBUTARY BIT RATE ARE EQUAL, IT IS CALLED POSITIVE-NEGATIVE JUSTIFICATION.

PROBLEMS INVOLVED IN HIGHER ORDER MULTIPLEXING AND SOLUTIONS FOR THEM

1. MUX CLOCK SPEEDS SHOULD BE SAME AT BOTH THE ENDS. – SOLUTION :- THIS PROBLEM IS SOLVED BY USING P L L CIRCUIT AT TERMINAL “B” TO RECOVER THE CLOCK.

2. SYNCHRONIZATION:- SOLUTION- THIS IS SOLVED BY FRAME ALIGNMENT WORD (FAW).

3. TRIBUTARY BIT RATE AND MUX CLOCK (DIVIDED) SHOULD BE THE SAME:- SOLUTION - SOLVED BY PULSE STUFFING OR BIT STUFFING OR “ JUSTIFICATION” PROCESS. THISMEANS ADDING ADDITIONAL BITS.

FOTS

• FIBRE OPTIC TRANSMISSION SYSTEM.• SUB SYSTEMS –• DIGITAL MULTIPLEX SUB SYSTEM.• OPTICAL LINE TRANSMISSION SUB

SYSTEM.• CENTRAL SUPERVISORY SUB SYSTEM• POWER SUB SYSTEM• ALARM SUB SYSTEM

Fiber Optic Cable

• Fig 6.6

FIBRE OPTIC CABLE

Fiber Optic Cable Consists of many extremely thin strands of

solid glass or plastic bound together in a sheathing

Transmits signals with light beams No risk of sparks, safe for explosive

environments More expensive than coaxial, but more

bandwidth Different colors of light are used to

simultaneously send Multiple signals

OPTICAL LINE TRANSMISSION SUB SYSTEM

• OPTICAL LINE TERMINATING EQUIPMENT.

• LINE SWITCHING EQUIPMENTS• LINE SUPERVISORY EQUIPMENTS• ORDERWIRE EQUIPMENTS.• SUPERVISORY SERVICE DATA• REMOTE SERVICE DATA

LIMITATIONS

• LOWER CAPACITY.• ADD AND DROP DIFFICULT.• COMPLEX MULTIPLEXING AND

DEMULTIPLEXING.• NO UNIVERSAL STANDARD• INTERWORKING BETWEEN

HIERARCHIES COMPLEX.

DISADVANTAGES OF PDH SYSTEM

PDH IS NOT IDEALLY SUITED TO THE EFFICIENT DELIVERY AND MANAGEMENT OF HIGH BANDWIDH CONNECTIONS.

PDH IS NO LONGER EFFICIENT TO MEET THE DEMANDS PLACED ON IT.

TO ACCESS THE LOWER ORDER TRIBUTARY, THE WHOLE SYSTEM SHOULD BE DEMULTIPLEXED.

BANDWIDTH LIMITATIONS – MAX CAPACITY IS 566 MBPS ONLY.

NO COMMON STANDARDS AMONG VENDORS. TOLERANCE IS ALLOWED IN BIT RATES. POINT TO POINT CONFIGURATION ( LINEAR WORKING )

ONLY IS POSSIBLE. IT DOES NOT SUPPORT HUB. NO PROVISIONING FOR NMS.

EVOLUTION OF SDH

• FIBER OPTIC BANDWIDTH:Bandwidth of the optical fiber can be increased and there is no limit

• TECHNICAL SOPHISTICATION:Using VLSI techniques which is also cost effective

• INTELLIGENCE:Availability of cheaper memory opens new possibilities

• CUSTOMER SERVICE NEEDS:Requirement of customer services can be easily met w/o much additional equipments

EVOLUTION OF SDH

TOTALLY SYNCHRONOUS SYSTEM. INTERNATIONAL STANDARD/SYSTEM – MULTIPLEXING

STANDARD. IN 1988, (ITU-T) 18TH STUDY GROUP FORMULATED

CERTAIN STANDARDS FOR MULTIPLEXING. THE MAIN AIM IS TO ACCOMMODATE THE EXISTING

PDH SIGNALS ALSO. ADOPTING THE DIFFERENT VENDORS EQUIPMENTS. DISADVANTAGES OF PDH LED TO THE INVENTION OF

SDH.

DIFFERENT SERVICES

• LOW/HIGH SPEED DATA• VOICE• INTERCONNECTION OF LAN• COMPUTER LINKS• FEATURE SERVICES LIKE HDTV• BROAD BAND ISDN TRANSPORT

EXISTING NETWORK

•

4 RTH ORDER

3RD ORDER

2 ND ORDER

5 TH ORDER

2 Mbps

8 Mbps

34 Mbps

140 Mbps

565 mb/s

565 Mbps

SYNCHRONOUS :

ONE MASTER CLOCK & ALL ELEMENTS SYNCHRONISE WITH IT.

DIGITAL:INFORMATION IN BINARY.

HIERARCHY:

SET OF BIT RATES IN A HIERARCHIAL ORDER.

WHAT IS S D H ?

WHAT IS SDH?

SDH IS A HIERARCHICAL SET OF INFORMATION STRUCTURE (DIGITAL TRANSPORT STRUCTURE) TO CARRY PAY LOAD.

SDH MULTIPLEXING:- A PROCEDURE BY WHICH MULTIPLE LOWER ORDER PATH LAYER SIGNALS ARE ADAPTED INTO HIGHER ORDER PATH OR MULTIPLE HIGHER PATH LAYER SIGNALS ARE ADAPTED INTO MUX SECTION LAYER.

POINTER DEFINES FRAME OFFSET VALUE OF A VIRTUAL CONTAINER.

SDH MAPPING:- THE PROCEDURE BY WHICH THE TRIBUTARY ARE ADAPTED INTO VIRTUAL CONTAINERS AT THE BOUNDARY OF THE SDH NETWORK.

ADVANTAGES OF SDH

1. SIMPLIFIED MULTIPLEXING/DEMULTIPLEXING TECHNIQUES.

2. DIRECT ACCESS TO LOWER ORDER TRIBUTARIES.3. ACCOMMODATES EXISTING PDH SIGNALS.4. CAPABLE OF TRANSPORTING BROADBAND SIGNALS.5. MULTI-VENDOR, MULTI OPERATOR ENVIRONMENT.6. PROTECTION SWITCHING TO TRAFFIC IS OFFERED BY

RINGS.7. ENHANCED BANDWIDTH.8. NMS FACILITY.9. UNLIMITED BANDWIDTH10. GROWTH OF THE EXISTING TO THE HIGHER ORDER

SYSTEM IS SIMPLE.

• The Container (C)– Basic packaging unit for tributary signals (PDH)

– Synchronous to the STM-1

– Bitrate adaptation is done via a positive stuffing procedure

– Adaptation of synchronous tributaries by fixed stuffing bits

– Bit by bit stuffing

• The Virtual Container (VC)– Formation of the Container by adding of a POH (Path

Overhead)

– Transport as a unit through the network (SDH)

– A VC containing several VCs has also a pointer area

• The Tributary Unit (TU)– Is formed via adding a pointer to the VC

• The Tributary Unit Group (TUG)– Combines several TUs for a new VC

• The Administrative Unit (AU)– Is shaped if a pointer is allocated to the VC formed

at last

• The Syncronous Transport Module Level 1 (STM-1)– Formed by adding a Section Overhead (SOH)

to AUs– Clock justification through positive-zero-

negative stuffing in the AU pointer area– byte by byte stuffing

STM1 Frames

RSOH: Regenerator section overheadMSOH: Multiplex section overheadPayload: Area for information transport

Transport capacity of one Byte: 64 kbit/sFrame capacity: 270 x 9 x 8 x 8000 = 155.520 Mbit/sFrame repetition time: 125 µs

1

3

5

9

4

270

270 Columns (Bytes)

1 9transmitrow by row

RSOH

MSOH

AU Pointer Payload(transport capacity)

(MATRIX REPRESENTATION)

1ST ROW 2ND ROW 3RD ROW

9 261 9 261 9 261 9 261

I I I9 261

PAY LOADSOH

I I270

9TH ROW

FRAME REPRESENTATION

STM-N AUG AU-4 VC-4

TUG-3 TU-3 VC-3

C-4

C-3

TUG-2

TU-1 VC-1 C-1

140Mbps

34Mbps

2Mbps

(REDUCED DIAGRAM FOR SDH-MULTIPLEXING)

REDUCED MUX STRUCTURE

Containers: C-3, C-2, C-12 and C-11

Container Carries signals at

C-11 1.544 Mbit/s

C-12 2.048 Mbit/s

C-2 6.312 Mbit/s

C-3 34.368 Mbit/s and 44.736 Mbit/s

C-4 139.264 Mbit/s

TERMINOLOGY & DEFINITIONS

• SDH:Set of hierarchical structures,standardized for the transport of suitably adapted pay load over physical transmission network

• STM:Synchronous transport module• It is the information structure used to support section

layer connections in SDH• VIRTUAL CONTAINER :used to support path layer connections

in the SDH• LOWER ORDER VC ( VC1,VC2,VC3)• HIGHER ORDER VC (VC3 ,VC4)

SDH BIT RATES

SDH Levels Bit rates in Kbps

STM-1 155520

STM-4 622080

STM-16STM-64

24883209953.28

SOH BYTE ALLOCATIONA1A2 Frame alignment

B1B2 Error monitoring

D1..D3 Data comm channel for RSOH

D4..D12 Data comm channel for MSOH

E1-E2 Order wire channel

F1 Maintenance

J0 STM Identifier

K1 K2 Automatic protection switching

S1 SYNCHRONISATION STATUS

M1 Txmn Error acknowledgement

Media dependent bytes

2 Mbps mapping

E1: 2.048Mb/s

STM-1 AU-4 VC-4

C-12VC-12

TUG-3

TUG-2

TU-12

x3

x7

x3

VC-n

AU-n

AUG

STM-n Synchronous Transport Module

Administrative Unit Group: One or more AU(s)

Administrative Unit: VC + pointers

Virtual Container: payload + path overhead

AUG

The following are the different steps in the mapping of 2Mbps stream

• Formation of container C12C12• Formation of virtual container VC12

• Formation of tributary unit TU12

• Multiplexing of TU12 ‘s to form TUG3

• Multiplexing of TUG3‘s to form VC4

• Formation of administrative unit AU4

• Formation of administrative unit group AUG

• Adding SOH to form STM1

SDH NETWORK ELEMENTS

• The different network elements are

SYNCHRONOUS MULTIPLEXERSYNCHRONOUS DIGITAL CROSS

CONNECTREGENERATORNMS

NETWORK ELEMENTS

• SYNCHRONOUS MULTIPLEXER• As per ITU-T Rec. synchronous

multiplexer performs both multiplexing and live line terminating functions.

• synchronous multiplexer replaces a bank of plesiochronous multiplexers and associated line terminating equipment.

SYNCHRONOUS MUX

• Types of synchronous multiplexers

•TERMINAL MULTIPLEXER(TM)•ADD DROP

MULTIPLEXER(ADM)

TM

• TERMINAL MULTIPLEXER(TM)

•TM Accepts a no. Of tributary signals and multiplex them to appropriate optical/electrical aggregate signal viz STM1,STM4,STM16 etc.

TERMINAL MULTIPLEXER(TM)

• ADD DROP MULTIPLEXER(TM)

• ADM is designed for ‘THRU’ mode of operation.

• Within ADM its possible to ADD channels or DROP channels from ‘THROUGH CHANNELS’

• ADD DROP MULTIPLEXER(TM)• At an ADM site ,only those signals that

need to be accessed are dropped or inserted

• The remaining traffic continues thru the NE without requiring special pass thru units or other signal processing

ADM• ADD DROP MULTIPLEXER(TM)

AGGREGATE SIGNAL AGGREGATE SIGNALSDH(E/O) SDH(E/O)

ADM

TRIBUTARY SIGNALS

(PDH/SDH)

• ADD DROP MULTIPLEXER(ADM)

ADD DROP MULTIPLEXER(ADM)

• CROSS CONNECT EQUIPMENT

• Cross connect equipment functions as a semi permanent switch for varying bandwidth control it can pick out one or more lower order channels for transmitting signal without transmission channels

• Channels can be 64Kbps up to STM1• Under software program the need of

demultiplexing

TYPES OF NETWORK TOPOLOGY

• STRING/BUS/LINEAR Topology• RING Topology• STAR Topology• MESH Topology

STRING/BUS/LINEAR TOPOLOGY

TMADM ADM ADM

REG

Aggregate signal

Tributary signal

(STM1/STM4/STM16)

(2/34/140Mbps/STM1(e)/ STM1(o))

TM

RING TOPOLOGY

• Ring is a linear network looped back to itself

• Network elements are ADM’s or REGENERATORS

• Every node on a ring has two communication paths to each other node via the two directions around the ring.

RING TOPOLOGY

ADM

ADM

ADM

REG

AD

M

Aggregate signal

(STM1/STM4/STM16)

Tributary signal

(2/34/140Mbps/STM1(e)/ STM1(o))

RING TOPOLOGY

• Ring network is self healing type(allowing rerouting of traffic when a link fails).

• The simple topology of a ring facilitates the implementation of protocols that can detect failure of a fiber segment or node and rapidly reestablish communications, typically in timeframes on the order of milliseconds. This is referred to as protection or protection switching

RING TOPOLOGY

• Rings gives greater flexibility in the allocation of band width to the different users.

• Normally used in LAN,WAN, Core Network,Regional Network etc.

STAR TOPOLOGY

• Traffic passes thru a central node called HUB.

• The HUB is a DXC.• If HUB fails ,total traffic fails.