Chapter 13: CAM Sparing
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
378
Guidelines for Upstream Spare Groups
An upstream spare-group must be homogenous: a 12U CAM can spare only for other 12U CAMs; a 24U CAM can spare
only for other 24U CAMs.
Upstream CAM spare-groups are designated by the lowest-numbered slot in the group. The spare-group leader of an
upstream spare-group is always the lowest-numbered slot in that group.
Guidelines for Downstream Spare Groups
An downstream spare-group must be homogenous: a 16D CAM can spare only for other 16D CAMs; an XD CAM can
spare only for other XD CAMs. All the XD CAM slots in a spare-group must also be provisioned for the same annex.
Downstream CAM spare-groups are named for the highest-numbered slot. The group leader of a downstream spare-
group is always the highest-numbered slot in that group.
Calculating Signal Loss During Failover
When failover occurs the RF signal to 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.
Configuration Example
The figure below provides an example of a chassis equipped with 24U and XD CAMs arranged in spare-groups. Note that
the 24U CAM spare-group builds from left to right: its spare is the lowest-numbered CAM in the group. The XD spare-group
builds from right to left: its spare is the highest-numbered CAM in the group.
For the CAM sparing shown in Figure 11-1 you would need seven non-spare upstream CAM PICs, six non-spare
downstream CAM PICs, and two sparing PICs. The five different types of CAM PICs are listed below.