Chapter 13: CAM Sparing
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 377
Signal Loss during Failover
When failover occurs the RF signal to/from the failed CAM is rerouted from the PIC of the failed CAM through the
intervening PICs and backplane to the PIC of the now-active spare CAM. This longer path produces some signal loss.
Although station maintenance begins immediately and compensates for the upstream loss, there is a period of at least a
few seconds, depending on the number of modems supported, that the signal is weakened.
Guidelines for CAM Spare Groups
A spare-group consists of one spare CAM (the spare-group leader) and one or more active CAMs protected by the spare-
group leader.
CAMs are not required to be part of a spare-group.
A chassis may have several spare-groups, depending on how many slots are used as spares and on the size of the spare
groups.
Any CAM can be used as spare-group leader, but it must be the first CAM added to the group.
The spare-group must be homogenous: the group leader and all of the members of the spare-group must be the same
type of CAM.
CAMs from two different spare-groups cannot be interspersed. If slot 8 has been added to spare-group 0, then CAMs 1-
7 cannot belong to any CAM spare-group except 0. In the same way, if slot 9 has been added to spare-group 15, then
slots10-14 can only be added to spare-group 15.
There can be an unspared CAM or an unpopulated front slot within a spare-group, but the rear slot must have the
correct PIC in it. For example, slot 0 can be the upstream spare-group leader for slots 1, 2, 3, 4, and 6, with slot 5 being
either unpopulated or not added to any spare-group. In this case in which slot 5 is unpopulated, rear slot 5 must be
equipped with an upstream non-spare PIC. If it is not, a failover from CAM 6 to the spare-group leader in slot 0 would
not succeed because traffic on CAM 6 could not be re-routed through the backplane from slot 6 to slot 0.
The spare-group leader must have a special Physical Interface Card called a sparing PIC. The upstream sparing PIC is a
different card than the downstream sparing PIC.
If you decide to turn a sparing leader slot into an active one, you may use the same CAM but you must replace the
sparing PIC with a non-sparing PIC.
To Next Page
Loading...
