Chapter 13: CAM Sparing
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
376
Benefits of Hitless CAM Sparing
CAM sparing is an important element of system reliability. The benefits of hitless CAM sparing include:
Uninterrupted service to the subscriber if a CAM goes down in the middle of a session where the end user is sending or
receiving data
System administrators can take active CAMs out of service without serious impact
The spare CAM is used until the failed module is diagnosed, repaired, or replaced, or until there is a software recovery.
The goal of CAM sparing is to preserve data flows such as voice calls, video, best effort, and other subscriber services.
CAM Sparing PIC LEDs
The spare-group leader CAMs are equipped with sparing PICs. Other CAM slots are equipped with regular PICs. All CAM
PICs have a sparing indicator LED. The LED indicates if the CAM is being spared for (in the case of a regular CAM PIC) or if
the spare CAM is actively sparing for a member of the spare group (in the case of a spare CAM PIC). In normal conditions
all sparing LEDs are off. When a CAM in a spare-group fails, traffic is transferred to its spare-group leader. In this case, the
sparing LEDs of the failed CAM PIC and of the spare-group leader CAM PIC are on.
Definitions
Failover — An active CAM fails and the spare CAM takes over
Failback— The recovered CAM becomes active again, taking over for the spare.
Size of Hitless CAM Spare-groups
The C4 CMTS supports CAM sparing within the following limits:
XD CAM Up to 8:1
16D CAM Up to 8:1
12U CAM Up to 11:1
24U CAM Up to 9:1
For example, the CMTS supports 8:1 CAM sparing for the 16D CAM. In other words, the largest possible 16D CAM spare-
group has eight active CAMs and one spare.