Sdh 2

Chapter 2

SDH Basics

Objective        

Standards Frame Structure Multiplexing Section Hierarchy Regenerator Section Overhead Multiplex Section Overhead Path Overhead Advantages

Basic data rate  

Common Characteristics

E1 and T1

a

Audible frequency range (fm)

0 - 3.4kHz ≈ 4kHz 

b

Sampling frequency (fs)

2 X fm = 8kHz

c

Number of samples per signal

8000 per second

d

Length of PCM frame

1/c = 125ųs

e

Number of bits in each code word

8

f

Telephone channel bit rate

c X e = 8000/s X 8 bit = 64kbps

Limitations of PDH  Inability to identify individual channels in a higher-order bit stream.  Multiplexing / Demultiplexing is cumbersome (Stage wise).  Insufficient capacity for network management as limited OAMP operation.  There’s no standardized definition of PDH bit rates greater than 140 Mbit/s.  There are different hierarchies in use around the world. Specialized interface equipment is required to interwork the two hierarchies.

Standards  The hierarchy is as follows: Optical Signal STM-0 STM-1 STM- 4 STM-16 STM-64 STM-256

Bit Rate 51.84 Mbps 155.52 Mbps 622.080 Mbps 2488.320 Mbps 9953.280 Mbps 39813.12 Mbps

Abbreviated as 51 Mbps 155 Mbps 622 Mbps 2.4 Gbps 10 Gbps 40 Gbps

STM-1 Frame Format

Frame =125µs

Frame =125µs

Frame = 125µs

STM-1 =  270 Columns (2430 bytes) 1 2 3

Pointers

4

Regenerato Sectio Overhea H1 H2 H

H1H1 H1 H2 H2 H2 H3 H3 H3

5 6 7

Multiple Sectio Overhea

8 9

Overhead width = 9 columns

STM-1 Frame Format

Administrative  Unit Capacity of  the Virtual  Container + Pointer s

9  Rows

STM-N Frame Format

Frame = 125µs Frame Format  STM - Section overhead and Administrative unit  Section overhead – Regenerator section overhead and Multiplex section overhead  Administrative unit – Virtual container and pointers  Virtual container - Payload and Path overhead information

    STM-N  

     

Section  Overhead

Regenerator  Overhead

Administrative        unit

Multiplex  overhead

Pointer

   Path  Overhead 

  Virtual  Container

Payload

Mapping Elements       

Container Virtual Container Tributary Unit Tributary Unit Group Administrative Unit Administrative Unit Group STM-N Frame

SDH Multiplexing

Container  

Input signals are placed into the containers It adds stuffing bytes for PDH signals,which compensates for the permitted frequency deviation between the SDH system and the PDH signal

• • • • •

C12 (2 Mbps – G.703) C11 (1.5 Mbps) C2 (6 Mbps) C3 (34 / 45 Mbps) C4 (140 Mbps

Virtual Container MAPPING : It is a process from Containers to Virtual containers.

+

POH

PAYLOAD

=

POH

PAYLOAD

ANALOGY: • • • •

Packing C2 carton box with some more packing material and labeled as VC2 box It adds overheads to a container or groups of tributary units, that provides facilities for supervision and maintenance of the end to end paths VCs carry information end to end between two path access points through the SDH system VCs are designed for transport and switching sub-SDH payloads

• • • • •

• • • •

VC12 (C12 + POH) VC11 (C11 + POH) VC2 (C2 + POH) VC3 (C3 + POH) VC4 (C4 + POH)

At each level, subdivisions of capacity can float individually between the payload areas of adjacent frames. Each subdivision can be readily located by its own pointer that is embedded in the overheads. The pointer is used to find the floating part of the AU or TU, which is called a virtual container (VC). The AU pointer locates a higher-order VC, and the TU pointer locates a lowerorder VC. For example, an AU–3 contains a VC–3 plus a pointer, and a TU–2 contains a VC–2 plus a pointer. A VC is the payload entity that travels across the network, being created and dismantled at or near the service termination point.

Tributary Unit • • •

• • •

It adds pointers to the VCs This pointer permits the SDH system to compensate for phase differences within the SDH network and also for the frequency deviations between the SDH networks TUs acts as a bridge between the lower order path layer and higher order path layer

TU12 (VC12 + pointer) TU2 (VC2 + pointer) TU3 (VC3 + pointer)

Tributary Unit Group • •

It defines a group of tributary units that are multiplexed together As a result, a TU group could contain one of the following combinations

• •

Three TU-12s (TUG – 2) Seven TUG-2s (TUG – 3)

Administrative Unit • It adds pointer to the HO Virtual containers(similar to the tributary unit)

• •

AU - 3 (VC-3 + pointer) AU - 4 (VC-4 + pointer)

Administrative Unit Group •

It defines a group of administrative units that are multiplexed together to form higher order STM signal

Synchronous Transport Module – n • • •

It adds section overhead (RSOH & MSOH) to a number of AUGs that adds facilities for supervision & maintenance of the multiplexer & regenerator sections This is the signal that is transmitted on the SDH line The digit “n” defines the order of the STM signal

SDH Multiplexing

4 columns 1 2 3 4

1 2 3

Stuffing and POH

TU – 12 9X4 9 rows

TUG-2 9 X 12

TUG-3 9 X 84 Section Over Head

P O H

P O H

P O H

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 TUG - 3

TUG - 3

(9 X 9)

TUG - 3

9 X 261

Mapping of 2Mbps into STM – N 2.048 Mbps (E1)

32

1 2 3 32 Bytes

Stuffing Bytes C-12

1 23

32 34 Bytes

POH (LowerOrder) VC-12

1 23

32 35 Bytes

Pointer TU-12 36 Bytes

TU 12 is arranged Into Matrix of 9 X 4

9 Rows

4 Columns

TU-12

TU-12

TU-12

9 Rows

4 Columns

4 Columns

4 Columns

Multiplexing

TUG-2

9 Rows

12 Columns