Building-Integrated Timing Supply (Bits); Network Element Synchronization Modes - Nortel NTRN10AN Planning Manual

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
• external timing. See
• line timing. See
• tributary timing. See
See Figure 2-49 on page
Internal timing
Internal timing is shown in
Internal timing is provided by a SONET-compliant free-running clock within
the network element.
Planning and Ordering Guide—Part 1 of 2 NTRN10AN
Operation, administration, and maintenance (OAM) features 2-153
Internal timing on page
External timing on page
Line timing on page
Tributary line timing on page
2-155.
Figure 2-49 on page
2-153.
2-154.
2-154.
2-155.
2-155, example (a).
Rel 12.1 Standard Iss 1 Apr 2004