The document discusses key concepts in digital telecommunication networks including Pulse Code Modulation (PCM), Plesiochronous Digital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH), and their frame structures and bit rates. It describes how lower bit rate signals such as E1 (2Mbps) are mapped into higher bit rate structures like STM-1 (155.52Mbps) through multiplexing techniques involving containers, virtual containers, tributary units, and administrative units. The document also outlines the section overhead bytes used in SDH for functions like frame alignment, error monitoring, and automatic protection switching.

2. Topics
 Sampling
 PCM Principles
 PDH & SDH Systems
 STM –1 Frame structure
 Bit rates of STM-1 ,STM-4 ,STM-16 ………

3. Sampling Theorem
 A bandlimited signal can be reconstructed exactly
if it is sampled at a rate atleast twice the maximum
frequency component in it.
Fs ≥ 2Fm

4. PULSE CODE MODULATION
 Developed by A.M.Reaves in 1938
 Uses TDM technique
 Voice Frequency ranges upto 4 Khz
 Sampling the Voice Signal @ 8 Khz (Ts=125 µsec)
 8 bits per sample
 Digital Bit Rate: 8000 X 8 = 64 Kbps

5. BUILDING UP THE BASE STREAM (2MB)……
One sample duration (approx) = 4 µs
Duration between samples = 125 µs

6. 30 Channel PCM System
 30 voice channels
 One channel for synchronisation
 One channel for signalling
 Totol no.of channels =32
 One frame (125 µs) is divided into 32 time slots

7. PCM bit rate
 32 time slots in a frame
 Each slot having 8 bits
 Total no.of bits per frame= 32*8 =256 bits/frame
 Total no.of frames per sec =8000
 Total no.of bits per sec =256 * 8000 =2048 Kbps

8. 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
 The basic data rate is 2.048 Mbps

9. PDH BIT RATES
(European standard)
 E1- 2048 Kbps (2Mb) [30 Voice Channel]
 E2- 8448 Kbps (8Mb) [120 Voice Channel]
 E3- 34368 Kbps (34Mb) [480 Voice Channel]
 E4- 139264 Kbps (140Mb) [1920 Voice Channel]

10. 2/8
8/34
8/2
34/8
34/140
140/565
140/34
565/140
2 Mbps
8 Mbps
34 Mbps
140 Mbps 140 Mbps
34 Mbps
8 Mbps
2 Mbps

11. PDH HIERARCHY

12. Limitations of PDH
 Specialized equipment required for interwork two
hierarchy
 Inability to identify individual channels in a higher order
bit stream.
 Insufficient capacity for network management
 Higher bit rates are difficult to achieve
 Supports only linear topology
 no common standards among vendors.

13. SDH-Synchronous Digital Hierarchy
 SDH is an ITU-T standard for a high capacity telecom network.
 SDH is a synchronous digital transport system, aim to provide a
simple, economical and flexible telecom infrastructure.
 This is the information structure used to support information
payload and overhead information organized in a block frame
structure which repeats every 125 micro seconds
 The basis of Synchronous Digital Hierarchy (SDH) is synchronous
multiplexing - data from multiple tributary sources is byte
interleaved.

14. MERITS OF SDH
 Simplified multiplexing / demultiplexing techniques
 Direct access to lower speed tributaries
 Enhance Operation , Administration & Maintenance
 Easy growth to higher bit rates in steps with evolution of
transmission technology
 Capable of transporting existing PDH
 Capable of transporting future ATM
 Capable of operating multi vendor and multi –operator
environment

15. SDH Rates
 SDH is a transport hierarchy based on multiples of
155.52 Mbit/s.
 The basic unit of SDH is STM-1
 STM-Synchronous Transport Module
 Higher rate is an exact multiple of the lower rate
therefore the hierarchy is synchronous.
STM-N
Where N =1,4,16 ,64 n is a multiples of four

16. SDH BIT RATES
SDH Levels Bit rates in Mbps
STM-1 155.520
STM-4 622.080
STM-16 2488.320
STM-64 9953.28

17. STM-1 Frame
 Synchronous Transport Module –
 A frame with a bit rate of 155.52 Mbit/s is defined in
ITU-T Recommendation G.707
 It is made up from a byte matrix of 9 rows and 270
columns.

18. 9 261
PAY
LOAD
S
O
H
270
(MATRIX REPRESENTATION)
SDH FRAME REPRESENTATION
9

19. 19
• As indicated in the figure, the STM – n signal is multiples of
frames consisting of 9 rows with 270 bytes in each row
• The order of transmission of information is first from left to right
and then from top to bottom
• The first 9 bytes in each row are for information and used by
the SDH system itself.This area is divided into 3 parts
• Regenerator Section Overhead(RSOH)
• Multiplex Section Overhead(MSOH)
• Pointers
STM-1 frame structure (contd..)

20. THE TRUCK ANALOGY
PAYLOAD
OVERHEAD

21. THE TRUCK ANALOGY
PAYLOAD
OVERHEAD

22. THE TRUCK
PAYLOAD
OVERHEAD

23. 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)
SDH Frame Structure

24. (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

25. BIT RATE : STM-N
• NUMBER OF ROWS = 9
• NUMBER OF COLUMNS = 9+261=270
• NUMBER OF BYTES = 9x270
• NUMBER OF BITS = 9x270x8
• NUMBER OF BITS / SECOND = 9x270x8x8000
=155520000
=155.520 Mbps (STM-1)
• BIT RATE OF STM-N = (Nx155.520) Mbps

26. SDH ACCOMMODATES
EXISTING SIGNALS
C4
C3
C12
34M
140M
8M
34M
2M
8M
64K
2M
63
1
S
D
H
M
U
X
3
1

27. SDH Multiplexing
 The multiplexing principles of SDH follows these terms
 Mapping - A process used when tributaries are adapted into
Virtual Containers (VCs) by adding justification bits and Path
Overhead (POH) information.
 Aligning - This process takes place when a pointer is included in
a Tributary Unit (TU) or an Administrative Unit (AU), to allow the
first byte of the Virtual Container to be located.
 Multiplexing - This process is used when multiple lower-order
path layer signals are adapted into a higher-order path signal, or
when the higher-order path signals are adapted into a Multiplex
Section.

28. Multiplexing Structure

29. 29
Elements of SDH
• Container (C)
• Virtual Container (VC)
• Tributary Unit (TU)
• Tributary Unit Group (TUG)
• Administrative Unit (AU)
• Administrative Unit Group (AUG)
• Synchronous Transport Module - N (STM – N)

30. CONTAINER
 Input is PDH
 Provides justification for PDH signals
 Output is synchronous
CONTAINER
SDH
P
D
H
JUSTIFICATION
2Mb/s
synchronized
34 BYTES

31. VIRTUAL CONTAINER
 35 BYTES - ONE 2MB
CONTAINERPOH

32. TRIBUTARY UNIT
 When pointer is added to the virtual container ,it is called
tributary unit ( ONE 2 MB)
VCPOINTER
4 X 9
36 BYTES

33. TRIBUTARY UNIT GROUP-2
 4 X9 4 X9 4 X9
TU12
(1)
TU12
(2)
TU12
(3)
TUG-2
12 X9
TU12 CONTAINS -ONE 2 MB
TUG-2 CONTAINS THREE 2MB

34. Tributary unit group -3
 Homogeneous assembly of identical tributary units
Tug-2
(1)
Tug-2
(7)
TUG-3 TUG-3 CONTAIS 21X2MB

35. VC-4 FORMATION
 Virtual container formation
TUG-3 TUG-3 TUG-3
VC-4=261

36. VIRTUAL CONTAINER -4
 Virtual container 258C + 1C POH+ 2C fixed stuff byte
 258+1+2=261Columns
vc
FIXED
TUFF
P
O
H

37.  AU POINTER IS ADDED TO THE VC
PAYLOAD
AU Pointer

38. ADMINISTRATIVE UNIT GROUP
 SOH BYTES ARE ADDED
 270C X 9R
PAY LOADAU POINTER
RSOH
MSOH

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

40. MUX PRINCIPLE: STM-1(from C-12)
TUG-3
P
O
H
P
T
R
S
O
H
TUG-3 TUG-3
TUG-2 TUG-2 TUG-2 TUG-2 TUG-2 TUG-2 TUG-2
TU-12 TU-12 TU-12
CONTAINER-12
P
O
H
P
T
R

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. STM-1 AU-4 VC-4
C-3
VC-3TUG-3
E3: 34.368Mb/s
DS3: 44.736Mb/s
TU-3
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
Mapping of 34 Mbps stream

43. STM-1 AU-4 VC-4
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
Mapping of 140 Mbps stream
C-4 E4: 139.264Mb/s

44. SDH End-to-End Connection
PTE MSTE MSTE PTE
STM-1 STM-NSTM-N
REG
STM-N STM-1
REG
Multiplex section
Path
PDH PDHRegenerators
section
SDH

45. Section Overhead
 RSOH –Regenerator Section Overhead
 MSOH –Multiplex Section Overhead

46. SECTION OVERHEADS
A1 A1 A1 A2 A2 A2 J0 X X
B1 E1 F1 X X
D1 D2 D3
AU POINTER
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M1 E2 X X
MSOH
RSOH

47. SOH BYTE ALLOCATION
A1,A2 Frame alignment
B1B2 Error monitoring
D1..D3 Data communication channel for RSOH
D4..D12 Data communication 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