- Nortel Network Multiservice Platform User's Guide

Operation, administration, and maintenance (OAM) features 2-153
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
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.