Nortel Networks 553-3001-211 manual 748 of 894 NTAK79 2.0 Mb PRI card

Page 748 of 894 NTAK79 2.0 Mb PRI card

•jitter filtering

•use of an algorithm to detect crystal aging and to qualify clocking information

Reference switchover

Switchover may occur in the case of reference degradation or reference failure. When performance of the reference degrades to a point where the system clock is no longer allowed to follow the timing signal, then the reference will be said to be out of specification. If the reference being used is out of specification and the other reference is still within specification, an automatic switchover is initiated without software intervention. If both references are out of specification, the clock controller provides holdover.

Autorecovery and chatter

If the software command “track to primary” is given, the clock controller tracks to the primary reference and continuously monitors the quality of both primary and secondary references. If the primary becomes out of specification, the clock controller automatically tracks to secondary provided that it is within specifications. On failure (both out of specification), the clock controller enters the HOLDOVER mode and continuously monitors both references. An automatic switchover is initiated to the reference that recovers first. If the secondary recovers first, then the clock controller tracks to the secondary, but switches over to the primary when the primary recovers. If the primary recovers first, the clock controller tracks to the primary.

If the software command “track to secondary” is given, the clock controller tracks to the secondary reference and continuously monitors the quality of both primary and secondary references. If the secondary becomes out of specification, the clock controller automatically tracks to primary provided that it is within specifications. On failure (both out of spec.), the clock controller enters the HOLDOVER mode and continuously monitors both references. An automatic switchover is initiated to the reference that recovers first. If the primary recovers first, then the clock controller tracks to the primary, but switches over to the secondary whenever the secondary recovers. If the secondary recovers first, then the clock controller tracks to the secondary.

553-3001-211 Standard 2.00 September 2004