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
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.
11.
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
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.
•
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
POH
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.
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 :
Editor's Notes
A number of functions are defined in the overhead channels to ensure proper transport of the payload.
The Section Overhead (SOH)
The overall capacity of the SOH is 4.608 Mbit/s (9x8x64kbit/s), of which 30 bytes (1.920 Mbit/s) have fixed definitions. The remaining 64kbit/s channels are not specified. Six are reserved for national use. Although six bytes are reserved for medium dependent functions (e.g. radio link systems). The columns 1,4 and 7 corresponds also to the STS-1 frame.
Functions of the SOH:
Contains maintenance, monitoring and operational functions
Each byte refers to a 64kbit/s channel
Splitted into RSOH and MSOH
Protect the connection from point of STM-1 assembly to point of disassembly.
The Path Overhead (POH)
The POH of VC-4/VC-3 consists of 9 bytes and the POH of the VC-11/VC-12 and VC-2 consists of 4 bytes.
The RSOH is reformed (terminated) by each regenerator. Each regenerator section passes the MSOH transparently.
Section overheads (SOHs) of STM-1 are depicted by the shaded parts in the above drawing.
1.1 Regenerator SOH (RSOH), 3 rows by 9 columns, can be accessed at terminating points of a regenerator section (RS), at both regenerators and multiplexers.
1.2 Multiplex SOH (MSOH),5 rows by 9 columns, , can be accessed at multiplex section (MS) terminating points, i.e.at multiplexers only. It passes through regenerators transparently.
1.3 Information carried by RSOH and MSOH is mainly used for administration of RS and MS layer,respectively .
Marked bytes are already defined. Unmarked bytes are reserved for future use.
△ bytes are defined as Media-dependent. If necessary. (For SDH radio it is defined in ITU-R F.750)
Bytes marked are assigned for national use. Each country can define their function differently but the definition is valid within the country, not international.
Column number of STM-N is 9 x n and same byte assignment is applied but byte number of A1, A2, B2, △ and are increased accordingly.
For STM-16, 64 and 256, using some of unmarked bytes FEC (Forward Error Correction) is implemented.
The MSOH is reformed (terminated) by each multiplexer and cross connect . A1, A2 : Frame Alignment Signal (FAS)
1.1 A1: 11110110 A2: 00101000
1.2 A receiver finds the STM-N frame by detecting fixed A1....A2 .... pattern which appears periodically at 125μs interval. (Remember VC-n does not have any FAS, its frame is found by using pointer.)
J0 : Regenerator Section Trace
2.1 For verification of Regenerator Section connection
2.2 A transmitter can set an identifier (name) to STM-N signal, maximum 15 characters using J0, and a receiver compares the received ID (J0 value) to the expected J0 value, which is preset in the receiver, to verify the connection.
2.3 To carry 15 characters 16 multiframe is formed, the first J0 for FAS and error detection and 15 J0s for ID.
2.4 (Early recommendation defined this byte as C1 (STM identifier) that shows the unique order number of STM-1s in STM-N to assist demultiplexing process.)
B1, B2 : Error Monitoring
3.1 BIP-X (Bit Interleaved Parity-X) detects error occurrence.
3.2 B1: For Regenerator Section error detection by BIP-8.
B2: For Multiplex Section error detection by BIP-24N (N; STM level). Detail of BIP-X will be explained latter.
The Path Overhead is evaluated at the end point of the transmission system where the ‘unpacking’ takes place.
