Nortel Networks NN43001-301 manual QPC471 and QPC775 Clock Controllers, Synchronization methods

158Clock Controller description and installation

ENL CC x FDL Enable Clock in side x with the force download option

If the optional parameter is not specified, then downloading is conditional. This means that the version number of the loadware on the clock controller card will be checked against the version number stored on the system disk. If a mismatch is found and the version number in the system software database is higher, then downloading will be initiated for that card. The entry for the card is not added to the PSDL tree at this time. Instead, downloading is initiated on a single card and only that card will be allowed to perform the force download option.

QPC471 and QPC775 Clock Controllers

Clock Controllers QPC471 and QPC775 will continue to function with:

•CS 1000M HG systems

•CS 1000M SG systems

•CS 1000M MG systems

Note: "Description" (page 156) for market and application availability information.

Synchronization methods

There are two common methods of operation for maintaining timing coordination between switching systems, Plesiosynchronous and Mesosynchronous.

Plesiosynchronous operation

In a Plesiosynchronous operation, nodal clocks run independently (free run) at the same nominal frequency. There are frequency differences between clocks resulting in frame slips (see "Frame slip" (page 160).) The magnitude of frame slips are directly proportional to the frequency difference. Slips are inevitable but can be minimized by using very stable clocks and elastic stores or buffers. These buffers are capable of absorbing a certain number of data bits to compensate for slight variances in clock frequencies.

Mesosynchronous operation

In a Mesosynchronous operation, nodal clocks are continuously and automatically locked to an external reference clock. With this method, frame slips can be eliminated if elastic stores are large enough to compensate for transmission variances. Mesosynchronous operation is virtually slip free.

Whenever possible the system uses the Mesosynchronous mode of operation by using the clock controller circuit cards to lock onto an external reference source (such as the Central Office, another PBX, and so on). This statement is true unless the system is used as a Master in an independent/private network (no digital links to a higher Node Category).

Nortel Communication Server 1000

ISDN Primary Rate Interface Installation and Commissioning

NN43001-301 02.03 Standard

Release 5.5 7 December 2007

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