AT&T 76450 manual Synchronization/Timing Standards, Termination of timing leads

Common Systems Connection Standards	AT&T Services, Inc
Date: August 31, 2007	ATT-TP-76450, Issue 9

3 Synchronization/Timing Standards

The Building Integrated Timing Supply (BITS) concept is the method of providing Phase and Frequency synchronization. The BITS plan details that each office have one Primary Reference Source (PRS)/(Stratum-1) traceable office master clock called the BITS. Under the BITS concept, each/every timing capable Network Element (NE) in the office should derive its timing from that single source within the office. A timing capable Network Element is defined as any digital equipment piece that is capable of conforming to the BITS concept by accepting timing from an external source. A Network Element is still timing capable even if it is not currently configured or equipped to accept external timing via AT&T approved, adequately protected wire-wrap connections; as long as the option exists to allow it to be so equipped.

3.1Termination of timing leads

All critical network element timing signals lead termination points shall terminate only on the BITS/TSG office master shelf or one of its expansion shelves or a Remote Master shelf equipped with oscillators that can maintain phase alignment.

3.2Primary and Secondary Interfaces

A Network Element should be equipped with separate external primary and secondary timing interfaces.

3.3Clock output lead cabling

Clock output leads to network equipments shall be cabled with physically diverse routing. The primary and secondary input leads for a NE must have physically separate paths/routes with a minimum of six-foot separation. If physically separate paths/routes do not exist, running leads on opposite sides of the cable rack is acceptable.

External Clock Wire Wrap pins on the backplane of shelf are the AT&T standard and preferred method but the use of a wire wrap adapter kit or equivalent is acceptable. To be compliant to GR-1244, R3-10, no DB or RJ type connectors would be allowed

Each terminal shall consist of three pins designated “TIP”, “RING” and “SHIELD.”

Note that while GR-1244 R3-10 [11v2] and R3-11 [108] do not require that the wire-wrap terminals be located on the backplane of the equipment, AT&T requires hardware, backplane chassis integration, rather than having the terminals located close to the equipment in order to facilitate trouble-shooting and maintenance procedures. Also note that R3-11 [108] applies independent of whether the NE itself supports the external timing mode (e.g., it would apply to a line-timed NE that supports the capability to generate an external timing signal for use at another NE).

3.4Redundancy of timing inputs

Each Switch (Host, or Remote, where applicable) or each Transport Network Element requiring redundant timing inputs (for instance, a SONET ADM/DCS) shall be individually timed from the

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