Nortel 1000 Installation And Commissioning Manual page 159

In an isolated private network, the clock controller can operate in free run
mode and act as a master clock to be tracked by other PBX systems in
the private network.
Hierarchical synchronization
Figure 59 "Hierarchical Synchronization" (page 159)
view of the Digital Network Clock Synchronization including the four stratum
level Node Categories. Stratum 1 being the most accurate and Stratum 4
being the least accurate. System clocking meets Node Category E Stratum
4 requirements. Also shown are ways of providing a Secondary Clock
Source while preventing timing loops.
Figure 59
Hierarchical Synchronization
Copyright © 2003-2007, Nortel Networks
.
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
Description 159
provides a general