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158 Clock 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
Copyright © 2003-2007, Nortel Networks
.