Nortel Networks 3500, NTRN10AN manual Building-integrated timing supply Bits

Operation, administration, and maintenance (OAM) features 2-153

Building-integrated timing supply (BITS)

The building-integrated timing supply (BITS) concept requires that all digital equipment in a physical structure must receive timing from the same master clock. This master clock is the most accurate and stable clock in the structure. The BITS is driven by a Stratum 3 or better reference signal. This signal can come from the following sources:

•a timing signal derived from a SONET signal, such as the output of a BITS Out source in an OPTera Metro 3500 network element

•an external stratum clock

The BITS distributes a DS1 signal to all equipment in the same physical location.

The implementation of BITS has the following advantages.

Performance

The designation of a master timing supply for each structure simplifies and enhances the reliability of the timing distribution. The BITS concept minimizes the number of synchronization links entering a building, since each piece of equipment no longer has its own external timing source.

Utilization of resources

A single, high-quality reference timing source can be shared among many services within the office because BITS provides a large number of signals for distribution.

Operations

Record keeping for provisioning and maintenance purposes will be easier when new digital services are introduced because BITS is location-dependent, not service-dependent.

Network element synchronization modes

Different modes of synchronization are defined for the network element, depending on the timing source:

•internal timing. See Internal timing on page 2-153.

•external timing. See External timing on page 2-154.

•line timing. See Line timing on page 2-154.

•tributary timing. See Tributary line timing on page 2-155.

See Figure 2-49 on page 2-155.

Internal timing

Internal timing is shown in Figure 2-49 on page 2-155, example (a).

Internal timing is provided by a SONET-compliant free-running clock within the network element.

Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004