SDH

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