Nortel Enterprise 1000 Reference Manual page 180

Page 180 of 236
553-3023-211 Standard 1.00 June 2001
NTAK79 2.0 Mb PRI card
Autorecovery and chatter
See "Autorecovery and chatter" on page 31.
Holdover and free-run
See "Holdover and free-run" on page 31.
Reference clock selection through software
The NTAK79 has the necessary hardware for routing its reference to the
appropriate line on the backplane
The software is responsible for the distribution of the secondary references
and ensures that no contention is present on the REFCLK1 backplane line.
The software designates the NTAK79 as the primary reference source to the
clock controller. The secondary reference is obtained from another NTAK79
card, which is designated by a technician. No other clocks originating from
other NTAK79 circuit cards are used.
The clock controller provides an external timing interface and is capable of
accepting two signals as timing references. In this case, an external reference
refers to an auxiliary timing source which is bridged from a traffic carrying
signal. This is not intended to be a dedicated non-traffic bearing timing signal.
The clock controller uses either the two external/auxiliary references or the
NTAK79 references.