363-206-305
Transmission and Synchronization
Issue 3 June 2000
5-9
External Timing/Line Timing Configuration
5
The external timing/line timing configuration (shown in Figure 5-4) integrates loop
feeder and customer location networks into the digital synchronization network as
required by the SONET standard. This application is ideal for networks where only
one location has a building integrated timing supply (BITS); for example, a loop
feeder. The network is synchronized to a local central office clock via DS1
references. The local office clock should be Stratum 3 or better, with timing
traceable to a primary reference source. The local DDM-2000 multiplexer times its
transmitted signals at the low- and high-speed interfaces from the internal
oscillator that is locked on the external reference. The remote DDM-2000
FiberReach Multiplexer recovers timing from the incoming OC-N signal and
unidirectional timing path and uses this timing for its transmitted signals.
External timing is required when EC-1 low-speed interfaces are used to
interconnect the local DDM-2000 with other SONET equipment. Thus, the
external timing/line timing configuration should be the long-term goal for all loop
feeder and customer applications.
This timing configuration is also recommended for multispan topologies. Line
timing can be extended to many DDM-2000 sites without any degradation of
timing quality. In the ring topology, synchronization messaging allows automatic
synchronization reconfiguration in the event of a fiber or equipment failure.
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