363-206-305
Transmission and Synchronization
5-12
Issue 3 June 2000
Timing Distribution
5
In many applications, all elements in a SONET network are directly traceable to a
single master clock via line-timing (for example, loop access networks, outside
trunks, private networks). In this environment, the high-performance
desynchronizer design of the DDM-2000 FiberReach Multiplexer allows a DS1
timing reference to be carried as a multiplexed DS1 payload to a customer
premises.
*
It is recommended that, where possible, the DS1 sources (switch,
PBX, or other equipment) be traceable to the same timing source used to time the
DDM-2000 SONET network. Multiplexed DS1 reference transport is also
consistent with current planning and administration methods. Applications include
passing synchronization from the public switched network to a PBX-based private
network (Figure 5-6). Network timing failures are identified by a DS1 alarm
indication signal (AIS) and will cause selection of an alternate timing source.
* Synchronous operation via line timing eliminates the generation of VT pointer adjustments,
thus maintaining the phase stability needed for a high-quality DS1 timing reference. Cross-
connecting at the STS-1 level also eliminates the VT pointer adjustments. While the design
of the DDM-2000 OC-3 Multiplexer maintains jitter/wander within standard DS1 interface
requirements, even in the presence of VT pointer adjustments, and while the DS1 is likely
to be stable enough for most equipment to use as a timing reference, some equipment may
have more stringent stability requirements for its timing references.
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