SDH BASICS

Niranjan BRegional Telecom Training Center Mysore

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

S.D.H. Evolution

• Fibre Optic Bandwidth :• Technical Sophistication. • Intelligence :. • Customer Service Needs

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.

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.

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

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

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

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

C-4

SIGNAL

C-3

SIGNAL

C-12

SIG

MUX PRINCIPLE: CONTAINERS(C-n)

BASIC DEFINATIONS

• Virtual Container(VC):

• VC= Container(C) +POH (path over head)

• 35 byte for 2Mb

MUX PRINCIPLE: VC-nVirtual 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

POH

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.

CONTAINERPOH

PTR

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

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.

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.

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.

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. •

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-3TUG-3

VC-4

TU-11

TU-12

TU-2

TU-3

AU-3

AU-4AUG

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-3TUG-3

VC-4

TU-11

TU-12

TU-2

TU-3

AU-3

AU-4AUG

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-3TUG-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-4AUG

STM-N

X7

X7

X1

X3

X3

XN

Generic Multiplexing Structure

9 X 3

9 X 4

Embedded Overhead Bytes

VC-11/12/ 2 POH

STM-1 SOH

J1B3C2G1F2H4F3K3N1

V5J2N2K4

AU - PTR

VC-3/4 POHA1 A1 A1 A2 A2 A2 J0 X X

D1 D2 D3

B2 B2 B2 K1 K2D4 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 bytesX Reserved for national use

SOH: Section overheadPOH: Path overhead

The overheads (SOH, POH) are used for maintenance and supervision of the SDH transmission network.

RSOH

MSOH Payload

P O

H

Pointer

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

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

Functions of Path Overhead

V5J2N2K4

J1B3C2G1F2H4F3K4N1

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 channelbetween path elements (F2, F3)

Identification of the Path Source (Path Trace J1, J2)

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.

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.

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.

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

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.

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.

Section and High Order Path Overhead BytesThe 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 MaintenanceJ0 Trace identifierK1,K2 Automatic protection switching (APS) channel.M1 Transmission error acknowledgement.S1 Clock quality indicator.* Media dependent bytes.

SDH–based Transport Network Layered Model

SDH LAYERS

LAYERED INTERFACE

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

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.

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.

ADVANTAGES OF SDH

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

services• HUB :