Alcatel-Lucent 1643 AMS User's Operation Manual page 310

Timing provisioning
SEC
An SDH network element has its own internal oscillator, called the SDH equipment
clock (SEC). The accuracy of a SEC is lower than the accuracy of both the SSU and
the PRC.
Network example
The next figure gives an example of a network. Four network elements (NEs) of a
large network are drawn, plus a master clock (PRC) and a SSU.
SDH
Network
Line B
NE
Line A
....................................................................................................................................................................................................................................
7-8
SSU
Station clock Station clock
output input
NE
Line A Line B
Working Synchronization
Stand-by Synchronization
Line B Line A
NE
Alcatel-Lucent - Proprietary
See notice on first page
SDH
Network
Station clock
Line A
input
NE PRC
Line B
Master
Clock
Network synchronization
365-312-807R7.2
Issue 4, May 2007