SDH path and line sections

This section describes and illustrates the SDH path and line sections.

SDH layers

SDH divides its processing functions into the following three path and line sections:

• Regenerator section

• Multiplex section

• Path

These three path and line sections are associated with

• Equipment that reflects the natural divisions in network spans

• Overhead bytes that carry information used by various network elements

Equipment layers

The following table lists and defines each SDH equipment path and line section.

Path and line sections	Definition
Regenerator section	A regenerator section describes the section between two network elements. The network elements, however, do not necessarily have to be regenerators.
Multiplex section	A multiplex section is the section between two multiplexers. A multiplex section is defined as that part of a path where no multiplexing or demultiplexing of the STM-N frame takes place.
Path	A path is the logical signal connection between two termination points. A path can be composed of a number of multiplex sections which themselves can consist of several regenerator sections.

Path, MS and RS

The following figure illustrates the equipment path, multiplex sections and regenerator sections in a signal path.

Overhead bytes

The following table lists and defines the overhead associated with each SDH path and line section.

Overhead byte section	Definition
Regenerator section	Contains information that is used by all SDH equipment including repeaters.
Multiplex section	Used by all SDH equipment except repeaters.
Path	The POH contains all the additional signals of the respective hierarchy level so that a VC can be transmitted and switched through independently of its contents.

SDH frame

The following figure illustrates the SDH frame sections and its set of overhead bytes.

Alcatel-Lucent – Proprietary

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