Adding Pointer Adjustments; Jitter Caused By Pointer Adjustments - Agilent Technologies OmniBER 720 User Manual

SONET_Usr.bk Page 44 Wednesday, December 13, 2000 11:11 AM
Selecting Test Features - SDH Operation

Adding Pointer Adjustments

Adding Pointer Adjustments

Introduction
Pointers perform a critical role in the error free transmission of payload data
(subscriber data) through an SDH network. They also enable individual payload
channels to be inserted or extracted from a high speed STM-n line signal (for
example the functionality provided by ADM's).
Pointer adjustments are often necessary to compensate for asynchronous operation
between different nodes within an SDH network.These adjustments however can
result in jitter being added to a PDH signal transmitted from an SDH network
element.

Jitter caused by Pointer Adjustments

Pointer adjustments are the mechanisms within SDH to compensate for frequency
and phase differences between VCs and outgoing SDH frames. These pointer
adjustments are byte wide and since they can occur randomly, they may cause
significant amounts of payload signal jitter. It is therefore necessary to control the
jitter on payload signals that is due to pointer adjustments.
Pointer adjustment activity within a network can be randomly spaced individual
pointer adjustments, pointer bursts or periodic pointer adjustments.
The ITU-T G.783 and ETSI TM-1015 recommendations define a set of pointer
sequences to be used when evaluating an NE's pointer adjustment jitter
performance.
The OmniBER 720 generates a set of test sequences which can be used to simulate
network pointer adjustment activity. This allows the amount of tributary jitter due to
different types of pointer adjustment to be measured in the OmniBER 720.
Pointer adjustment activity within a network can be randomly spaced individual
pointer adjustments, pointer bursts or periodic pointer adjustments.
The Bellcore GR-253 and ANSI T1.105 standards define a set of pointer sequences
to be used when evaluating an NE's pointer adjustment jitter performance.
The OmniBER 720 generates a set of test sequences which can be used to simulate
network pointer adjustment activity.
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