All Synchronous Digital Hierarchy (SDH) How do you compare SDH and other alternatives for PDH transmission and migration? Powered by AI and the LinkedIn community 1 PDH overview Be the first to add your personal experience 2 PDH limitations Be the first to add your personal experience 3 SDH overview Be the first to add your personal experience 4 SDH advantages Be the first to add your personal experience 5 SDH adaptation of PDH Be the first to add your personal experience 6 SDH alternatives Be the first to add your personal experience 7 Here’s what else to consider Be the first to add your personal experience Share your insights alongside other invited experts Scroll to add your perspective to any article section. Member profile image Earn a Top Voice profile badge when you make quality contributions. Start a contribution See what others are saying 1 PDH overview PDH is a method of multiplexing different data streams into a single signal, using different bit rates and clock frequencies. PDH uses time division multiplexing (TDM) to combine lower order signals into higher order ones. For example, 30 voice channels of 64 kbps each can be multiplexed into a 2.048 Mbps signal, known as E1. PDH has been widely used for voice and data transmission over copper wires and microwave links. 3 SDH overview SDH is a method of transmitting digital signals over optical fiber networks, using a common clock frequency and a standardized frame structure. SDH uses synchronous TDM to multiplex lower order signals into higher order ones. For example, 63 E1 signals of 2.048 Mbps each can be multiplexed into a 155.52 Mbps signal, known as STM-1. SDH has been widely adopted for backbone and metropolitan area networks.

1. SDH BASICS
Niranjan B
Regional Telecom Training Center
Mysore

4. DISADVANTAGES OF PDH
• NO UNIVERSAL STANDARD
• DIFFERENT HIERARCHIES AROUND THE WORLD
• PDH NETWORK MANAGEMENT IS PROPRIETARY
• DROPPING OF INDIVIDUAL CHANNELS IN HIGHER
ORDER STREAM
• NON-HOMOGENEITY OF EQUIPMENT
• CHANNEL SEGREGATION PROBLEM
• PROBLEM OF CROSS CONNECTION

5. S.D.H. Evolution
• Fibre Optic Bandwidth :
• Technical Sophistication.
• Intelligence :.
• Customer Service Needs

10. SECTION OVER HEAD(SOH)
• SOH bytes provide communication channels to cater for:
• OA&M facilities.
• user channels.
• protection switching.
• section performance
• frame alignment
• other functions.

12. For 1.544 Mbit PDH signal (North America and
Japan Standard), there are 25 bytes in 125 micro
second and for 2.0408 Mbit per second signal,
there are 32 bytes in 125 micro second.
Taking some additional bytes for supervisory
purposes, 27 bytes can be allotted for holding
1.544 Mbit per second signal, i.e. 9 rows x 3
columns. Similarly, for 2.048 Mbit per second
signal, 36 bytes are allotted in 125 micro
seconds, i.e. 9 rows x 4 columns. Therefore, it
could be said 9 rows are matched to both
hierarchies.

13. SDH STANDARDS
STM-1 155.52 Mbps
SMT-4 622.08 Mbps
STM-16 2588.32 Mbps 2.5G
STM-64 9953.28 Mbps 10G
STM-0 =
1/3rd of STM-1
51.840 Mbps Used in SONET

14. Synchronous Transport Module-STM
• This is the information structure used to
support information pay load and over head
information field organised in a block frame
structure which repeats every 125 micro
seconds

15. BASIC DEFINATIONS
• Container: First Entry point of PDH signal, in which signal is
prepared ( adding fixed stuff, JC, Justification Opportunity
byte) so that it can enter in to VC stage .32 to 34 byet fo 2Mb

16. MUTIPLEXING PRINCIPLE
CONTAINER
SIGNAL
Container-n( n=1-4 ): A container is the information structure
which forms the network synchronous information payload for
a virtual container
2Mb

17. C-4
SIGNAL
C-3
SIGNAL
C-12
SIG
MUX PRINCIPLE: CONTAINERS(C-n)

18. BASIC DEFINATIONS
• Virtual Container(VC):
• VC= Container(C) +POH (path over head)
• 35 byte for 2Mb

19. MUX PRINCIPLE: VC-n
Virtual Container-n(VC-n):It is the information structure used
to support path layer connections in the SDH.
Two types of VCs: Lower order VC-n(n=1,2)
Higher order Vc-n(n=3,4)
CONTAINER
P
O
H

20. Tributary Unit
• A tributary unit is a information structure which provides
adaptation between the lower order path layer and the higher
order path layer. It consists of a information pay load (lower
order virtual container) and a tributary unit pointer which
indicates the offset of the pay load frame start relating to the
higher order VC frame start.
• Tributary unit 1 for VC-1 and Tributary unit 2 is for VC-2 and
Tributary unit 3 is for VC-3, when it is mapped for VC-4
through tributary group-3. TU-3 pointer consists of 3 bytes
out of 9 bytes. Three bytes are H1, H2, H3 and remaining
bytes are fixed bytes. TU-1 pointers are one byte interleaved
in the TUG-2.

21. CONTAINER
P
O
H
P
T
R
MUX PRINCIPLE: TU-n/ AU
•It is an information structure which provides adaptation between two
layers: -Between lower and higher order path layers for TU
-Between higher order path layer and section layer for AU
POINTER is an indicator whose value defines the frame offset of a VC with
respect to the frame reference of the transport entity on which it is supported

22. BASIC DEFINATIONS
• Tributary Unit(TU): Adaptation between lower order path and higher
order path
• Pointer
• An indicator whose value defines frame offset of a VC with respect to the
frame reference of transport entity, on which it is supported.
• Administrative Unit
• It is the information structure which provides adaptation between the
higher order path layer and the multiplex section layer. It consists of
information pay load and a A.U. pointer which indicates the offset of the
pay load frame start relating to the multiplex section frame start. Two AUs
are defined (i) AU-4 consisting VC-4 plus an A.U. pointer indicating phase
alignment of VC-4 with respect to STM-N frame, (ii) AU-3 consisting of VC-
3 plus A.U. pointer indicating phase alignment of VC-3 with respect to
STM-N frame. A.U. location is fixed with respect to STM-N frame.

23. BASIC DEFINATIONS
• Tributary Unit(TU): Adaptation between lower order path and higher
order path
• Pointer
• An indicator whose value defines frame offset of a VC with respect to the
frame reference of transport entity, on which it is supported.
• Administrative Unit
• It is the information structure which provides adaptation between the
higher order path layer and the multiplex section layer. It consists of
information pay load and a A.U. pointer which indicates the offset of the
pay load frame start relating to the multiplex section frame start. Two AUs
are defined (i) AU-4 consisting VC-4 plus an A.U. pointer indicating phase
alignment of VC-4 with respect to STM-N frame, (ii) AU-3 consisting of VC-
3 plus A.U. pointer indicating phase alignment of VC-3 with respect to
STM-N frame. A.U. location is fixed with respect to STM-N frame.

24. Tributary Unit Group
• One or more tributaries are contained in
tributary unit group. A TUG-2 consist of
homogenous assembly of identical TU-1s or
TU-2.
• TUG-3 consists of a homogenous assembly of
TUG-2s or TU-3.
• TUG-2 consists of 3 TU-12s (For 2.048
Mbit/sec). TUG-3 consists of either 7 TUG-2 or
one TU-3.

25. BASIC DEFINATIONS
• Administrative Group
• AUG consists of a homogenous assembly of AU-3s or an AU-4.
• Concatenation
• The procedure with which the multiple virtual container are associated
with one another, with the result their combined capacity could be used
as a single container across which bit sequence
• Network Node Interface (NNI)
• The interface at a network node which is used to interconnect with
another network node.
• integrity is maintained.
•

26. 1544kbps
2048kbps
6312kbps
34368kbps
44736kbps
139264kbps
C-11
C-12
C-2
C-3
C-4
VC-11
VC-12
VC-2
TUG-2
X1
X3
X4
VC-3
VC-3
TUG-3
VC-4
TU-11
TU-12
TU-2
TU-3
AU-3
AU-4
AUG
STM-N
X7
X7
X1
X3
X3
XN
1544kbps
2048kbps
6312kbps
34368kbps
44736kbps
139264kbps
C-11
C-12
C-2
C-3
C-4
VC-11
VC-12
VC-2
TUG-2
X1
X3
X4
VC-3
VC-3
TUG-3
VC-4
TU-11
TU-12
TU-2
TU-3
AU-3
AU-4
AUG
STM-N
X7
X7
X1
X3
X3
XN
C-11
C-12
C-2
C-3
C-4
VC-11
VC-12
VC-2
TUG-2
X1
X3
X4
VC-3
VC-3
TUG-3
VC-4
TU-11
TU-12
TU-2
TU-3
AU-3
AU-4
TU-11
TU-12
TU-2
TU-3
AU-3
AU-4
AUG
STM-N
X7
X7
X1
X3
X3
XN
Generic Multiplexing Structure
9 X 3
9 X 4

27. Embedded Overhead Bytes
VC-11/12/ 2 POH
STM-1 SOH
J1
B3
C2
G1
F2
H4
F3
K3
N1
V5
J2
N2
K4
AU - PTR
VC-3/4 POH
A1 A1 A1 A2 A2 A2 J0 X X
D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M 1 E2 X X
B1 E1 F1 X X
H1 Y Y H2 1 1 H3 H3 H3
Media dependent bytes
X Reserved for national use
SOH: Section overhead
POH: Path overhead
The overheads (SOH, POH) are used for maintenance and
supervision of the SDH transmission network.
RSOH
MSOH Payload
P
O
H
Pointer

28. Functions of Regenerator Section Overhead
 Parity check
(B1 calculated by regenerator and multiplexers)
 Data communication channels
(D1...D3, F1 between regenerators)
 Voice communication channels
(E1 between regenerators)
 Frame Alignment
(A1, A2)
 Section Trace
(J0 Identficationof regenerator
source)
A1 A1 A1 A2 A2 A2 J0
B1 E1 F1
D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M1 E2
AU - Pointer

29. Functions of Multiplexer Section Overhead
 Parity check (B2)
 Alarm information (K2)
 Remote error indication (M1,K2)
 Automatic protection switching
(K1, K2 Bytes)
 Data communication channels
(D4 to D12 between multiplexers)
 Clock source information (S1)
 Voice communications
channels (E2 between multiplexers)
A1 A1 A1 A2 A2 A2 J0
B1 E1 F1
D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M1 E2
AU - Pointer

30. Functions of Path Overhead
V5
J2
N2
K4
J1
B3
C2
G1
F2
H4
F3
K4
N1
VC-3/4 POH
VC-11/12/2
POH
 Parity check
B3, V5/ BIP-2 calculated by path
terminating point
 Alarm and performance information
(V5, G1)
 Structure of the VC
Signal label C2
 Multiframe indication for TUs (H4)
 User communications channel
between path elements (F2, F3)
 Identification of the Path Source
(Path Trace J1, J2)

31. SOH BYTES
• A-1, A-2 are framing bytes. Their values are :
• A1 : 11110110
• A2 : 00101000
• These two types of bytes form 16 bit Frame Alignment Word (FAW).
• FAW formed by the last A-1 byte and the adjacent A-2 byte, in the
transmitter sequence defines the frame reference for each of signal
rates.
• There are 3 A-1 bytes in STM-1 and 3 A-2 bytes in STM-1. In higher
order STM their number increases with STM order. In STM-4, there
will be 12 A-1 bytes and 12 A-2 bytes.

32. SOH BYTES -A1, A2
• A-1, A-2 are framing bytes. Their values are :
• A1 : 11110110
• A2 : 00101000
• These two types of bytes form 16 bit Frame Alignment Word
(FAW). FAW formed by the last A-1 byte and the adjacent A-2
byte, in the transmitter sequence defines the frame reference
for each of signal rates. There are 3 A-1 bytes in STM-1 and 3
A-2 bytes in STM-1. In higher order STM their number
increases with STM order. In STM-4, there will be 12 A-1
bytes and 12 A-2 bytes.

33. SOH BYTES-J1/C1
• STM Identifier with J1/ C-1 Byte : In STM-1
there is a single C-1 byte which is used to
identify each of inter-leaved STM’s and in an
STM-N signal. It takes binary equivalent to
position in inter-leave.

34. SOH BYTES- D,E,F
• D-1 or D-12 : These bytes are for data
communication channel. In this D-1, D-2 and
D-3 are for regenerator section. It can support
192 kilo bit per section. D-4 to D-12 are for
multiplex section. They can support 576 kilo
bit per second.
• E-1 is for regenerator section order wire.
• E-2 is for multiplex section order wire.
• F-1 is used for fault control purposes

35. SOH BYTES- B1 B2
• B-1 byte are called bit inter-leave parity-8.
This is used for error monitoring in the
regenerator section. There is only 1 byte in
STM-1 or STM-4 or STM-16. On line
monitoring done in this case.
• B-2 bytes. These are used for error monitoring
in the multiplex section. There are 3 bytes for
STM-1, STM-4 and 16 will have more number
of B-2 bytes as per their order.

36. SOH BYTES- K1 K2
• K-1, K-2 bytes.
• There are 2 bytes for STM-1, 4 or 16. These
are used for coordinating the protection
switching across a set of multiplex section
organised as protection group, they are used
for automatic protection switching.

37. Section and High Order Path Overhead Bytes
The purpose of individual bytes is detailed below.
A1,A2 Frame Alignment.
B1,B2 Parity bytes for errors monitoring.
D1…D3 Data communication channel (DCC)
network management.
D4…D12 Data communication channel (DCC)
network management.
E1,E2 Orderwire channel.
F1 Maintenance
J0 Trace identifier
K1,K2 Automatic protection switching (APS) channel.
M1 Transmission error acknowledgement.
S1 Clock quality indicator.
* Media dependent bytes.

41. SDH–based Transport Network Layered Model

42. SDH LAYERS

43. LAYERED INTERFACE

44. In–Service Maintenance Signals
Major alarm conditions such as
Loss of Signal (LOS),
Loss of Frame (LOF),
Loss of Pointer (LOP)
Alarm Indication Signal (AIS) to be transmitted downstream.
Different AIS signals are generated depending upon which level
of the maintenance hierarchy is affected

45. In–Service Maintenance Signals
Far End Receive Failure (FERF) is sent upstream in the
Multiplexer Section Overhead after Multiplexer Section
AIS, or LOS, or LOF has been detected by equipment
terminating in a Multiplexer Section span
Remote Alarm Indication (RAI) for a high order path is sent
upstream after Path AIS or LOP has been detected by
equipment terminating a Path, and similarly,
Remote Alarm Indication (RAI) for a Low Order Path is sent
upstream after Low Order Path AIS or LOP has been
detected by equipment terminating a Low Order Path.

46. S.D.H. MERITS
•Simplified multiplexing/demultiplexing techniques.
•Direct access to lower speed tributaries, without need to
multiplex/demultiplex the entire high speed signal.
•Enhanced operations, Administration, Maintenance and provisioning
capabilities.
•Easy growth to higher bit rates in step with evolution of transmission
technology.
•Capable of transporting existing PDH signals.
•Capable of transporting future broadband (ATM) channel bit rates.
•Capable of operating in a multi-vendor and multi-operator environment.

47. ADVANTAGES OF SDH
• Multi-vendor environment (mid span meet) :
• Synchronous networking :
• Enhanced OAM&P :.
• Positioning the network for transport on new
services
• HUB :