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Transmission and Synchronization Interfaces
5-56 Issue 3 June 2001
Network Timing Distribution 5
DS1 signals have long been used to pass timing information through the network
synchronization hierarchy. These DS1 timing references should be transmitted
between master and slave clock sources over the most reliable facilities available.
In some cases, these DS1 signals also carry traffic. The facility of choice has
evolved from T-carrier through asynchronous lightwave systems to SONET
lightwave systems. As these systems are upgraded to SONET systems, timing
distribution plans should be revisited to ensure the quality of the timing signals are
not degraded. With proper planning, SONET can be used to improve the overall
quality of the network timing.
Interoffice Timing Distribution 5
One way SONET can be used to improve the quality of interoffice network timing
is through the use of OC-N timing distribution. DDM-2000 OC-3 supports the
evolution to interoffice OC-N timing distribution by providing a DS1 timing output
derived from the incoming OC-N signal. The DS1 timing output is traceable to the
clock source that times the DDM-2000 OC-3 subnetwork and has extremely low
jitter and wander. This is true regardless of the number of DDM-2000 OC-3
systems connected in the network. This DS1 can be fed to the local BITS clock
which subsequently times the local DDM-2000 OC-3 and the other equipment in
the office. If a BITS clock is not available in the office, the DS1 timing output can
be used to time other equipment (including another DDM-2000 OC-3) directly.
DDM-2000 OC-3 can provide DS1 timing outputs in all supported topologies (for
example, point-to-point, add/drop, and ring).
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