PDH &SDH FUNDAMENTALS

1. PDH & SDHPDH & SDH

2. 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.

3. 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.

4. 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.

5. 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.

6. 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

7. 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

8. 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.

9. 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”

10. 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

11. 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

12. 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

13. 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.

14. JUSTIFICATION -TYPES
• JUSTIFICATION
POSITIVE JUSTIFICATION
NEGATIVE JUSTIFIATION
POSITIVE-NEGATIVE JUSTIFICATION

15. 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.

16. 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.

17. 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

18. Fiber Optic Cable
• Fig 6.6

19. 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

20. OPTICAL LINE TRANSMISSION SUB
SYSTEM
• OPTICAL LINE TERMINATING
EQUIPMENT.
• LINE SWITCHING EQUIPMENTS
• LINE SUPERVISORY EQUIPMENTS
• ORDERWIRE EQUIPMENTS.
• SUPERVISORY SERVICE DATA
• REMOTE SERVICE DATA

21. LIMITATIONS
• LOWER CAPACITY.
• ADD AND DROP DIFFICULT.
• COMPLEX MULTIPLEXING AND
DEMULTIPLEXING.
• NO UNIVERSAL STANDARD
• INTERWORKING BETWEEN
HIERARCHIES COMPLEX.

22. 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.

23. 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

24. 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.

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

26. EXISTING NETWORK
•
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

27. 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 ?

28. 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.

29. 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.

31. • 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

32. • 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

33. STM1 Frames

34. 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)

35. (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 I270
9TH ROW
FRAME REPRESENTATION

36. 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

37. 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

38. 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)

39. SDH BIT RATES
SDH Levels Bit rates in Kbps
STM-1 155520
STM-4 622080
STM-16
STM-64
2488320
9953.28

40. 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

41. 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

42. 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

43. SDH NETWORK ELEMENTS
• The different network elements are
SYNCHRONOUS MULTIPLEXER
SYNCHRONOUS DIGITAL CROSS
CONNECT
REGENERATOR
NMS

44. 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.

45. SYNCHRONOUS MUX
• Types of synchronous
multiplexers
• TERMINAL MULTIPLEXER(TM)
• ADD DROP
MULTIPLEXER(ADM)

46. 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.

47. TERMINAL MULTIPLEXER(TM)

48. • 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’

49. • 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

50. ADM
• ADD DROP MULTIPLEXER(TM)
AGGREGATE SIGNAL AGGREGATE SIGNAL
SDH(E/O) SDH(E/O)
ADM
TRIBUTARY (PDH/SDH)

51. • ADD DROP MULTIPLEXER(ADM)
ADD DROP MULTIPLEXER(ADM)

52. • 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

53. TYPES OF NETWORK
TOPOLOGY
• STRING/BUS/LINEAR Topology
• RING Topology
• STAR Topology
• MESH Topology

54. STRING/BUS/LINEAR
TOPOLOGY
TMADM ADM ADM
REG
Aggregate
signal
Tributary
signal
(STM1/STM4/STM16)
(2/34/140Mbps/STM1(e)/ STM1(o))
TM

55. 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.

56. RING TOPOLOGY
ADM
ADM
AD
M
REG
ADM
Aggregate
signal
(STM1/STM4/STM16)
Tributary
signal
(2/34/140Mbps/STM1(e)/ STM1(o))

57. 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

58. 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.

59. STAR TOPOLOGY
• Traffic passes thru a central node
called HUB.
• The HUB is a DXC.
• If HUB fails ,total traffic fails.