Conversion/Mapping of PDH Rates to SDH

Presented By:Dr Muhammad Khalil Shahid

PTCL Training & Development

MappingMapping

Process of adapting tributaries into Virtual Containers

(VCs) by adding justification bits and Path Overhead

(POH) information

To make the various tributary signals synchronized

with related virtual containers

VC can be an independent entity in the transmission,

multiplexing and cross connection

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Low Rate SDH → High Rate SDH: Byte Interleave PDH → STM-N: Synchronous Multiplexing &

Flexible Mapping– 140M→STM-N– 34M→STM-N– 2M→STM-N– No container for E2 (8 Mbps)

AlignmentAlignment

Process of including in a Tributary Unit (TU) or an

Administrative Unit (AU) Pointers

To allow the first byte of the Virtual Container to

be located

Provide a flexible and dynamic method for

alignment of VC in the unit (TU or AU-4) frame

Multiplexing

Process of adapting multiple lower-order path

layer signals into a higher-order path signal

When the higher-order path signals are adapted

into a Multiplex Section

This type of multiplexing comes under

synchronous multiplexing category

Stuffing

After multiplexing & aligning, some spare

capacity is required to provide space for various

tributary rates

This space capacity is filled with "fixed stuffing"

bits that carry no information

Required to fill up the particular frame

Virtual Container (VC)Virtual Container (VC) The digital flow from the standard container

combined with path overhead forms a virtual container (VC)

C-4 + POH (9 bytes) = VC-4 (9x261 bytes)

C-3 + POH (9 bytes) = VC-3 (9x85 bytes)

C-12 + POH (1 byte) = VC-12 (35 bytes) It is the most important information structure in

SDH which supports path layer connection