Lucent Technologies MERLIN LEGEND Release 6.0 Network Reference Manual page 183

MERLIN LEGEND Communications System Release 6.0
Network Reference 555-660-150
5 System Management
General Programming in Networks
Clock synchronization derived from the PSTN, either via PRI or BRI facilities, is
always preferable to a clock source that is provided by a digital tandem facility that
is not connected to the PSTN. Networked systems, however, may not have an in-
service digital PSTN facility available or active. For this reason, clock
synchronization in some private networks requires choosing from among other
clock sources. This is accomplished by programming the clock sources as local
(clock synchronization if provided by a 100D module installed in the local system)
or loop (clock synchronization is provided by a DS1 module installed in a non-
local system). There should be no more than one local clock source for digital
tandem facilities in a network, and all other tandem facilities are assigned as loop.
A local clock source in a network is not required; all can be programmed as loop.
In a network with three or more systems, it is best if all clock sources for the
network are on either a hub system (star configuration) or a system that connects
two other switches (series configuration). If the primary clock source is not
functioning, then a secondary or tertiary source on such a system can serve either
all other systems in the network or two other systems in a network. The following
examples illustrate how clock synchronization can be implemented in a network.
100D
System A
Primary: Loop
Secondary: Local
Tertiary: ______
1. If tandem digital facilities link the systems in a network and a non-local
system is connected to functional digital PSTN facilities, a system with no
digital PSTN facilities assigns its digital tandem lines as loop to derive the
clock source from the system connected at the other end of the link.
Synchronization is derived from the PSTN connection on one networked
system. The system connecting to the PSTN also assigns its clock source
as loop because its clock source at the far end of its PSTN facility. In the
diagram above, notice that System B has three 100D modules (and
therefore three ports) to provide synchronization. (See the diagram above.)
PSTN
100D
tandem
100D 100D
PRI
System B
Primary: PSTN Loop
Secondary: Local C
Tertiary: Local A
February 1998
PSTN
100D
100D
tandem
PRI
System C
Primary: Loop B
Secondary: PSTN Loop
Tertiary: Local B
Issue 1
Page 5-7