PDH & SDH
Delivered by: Dr. Erna Sri Sugesti

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

EUROPEANPDHHIERARCHYWITHBITRATES
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 Order
Mux
480 Chls
IV Order
Mux
1920 Chls
Primary
Mux
30 Chls
II order
Mux
120 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.

PROBLEMSINVOLVEDINHIGHERORDERMULTIPLEXING
ANDSOLUTIONSFORTHEM
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.

DISADVANTAGESOFPDHSYSTEM
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

EXISTINGNETWORK
•
4 RTH ORDER
3RD ORDER
2 ND ORDER
5 TH ORDER
2 Mbps
8 Mbps
34 Mbps
140 Mbps
5
6
5
m
b
/
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 BANDWIDTH
10. 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 overhead
MSOH: Multiplex section overhead
Payload: Area for information transport
Transport capacity of one Byte: 64 kbit/s
Frame capacity: 270 x 9 x 8 x 8000 = 155.520 Mbit/s
Frame repetition time: 125 µs
1
3
5
9
4
270
270 Columns (Bytes)
1 9
transmit
row 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 I
9 261
PAY LOAD
S
O
H
I I
270
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-12andC-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-16
STM-64
2488320
9953.28

SOH BYTE ALLOCATION
A1A2 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-12
VC-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 followingare the different stepsin the
mappingof 2Mbpsstream
• Formation of container C12
• 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 MULTIPLEXER
SYNCHRONOUS DIGITAL CROSS CONNECT
REGENERATOR
NMS

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 SIGNAL
SDH(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
TM
ADM 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
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.