Chapter 26: Connection Admission Control
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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The guidelines below provide settings for PacketCable CAC thresholds that should not be exceeded so that the channel can
be managed effectively. Exceeding the guidelines could result in a channel becoming overloaded and prevent dynamic
service flow set up and tear down.
Note: PacketCable voice limits do not apply to PCMM unless the gate is specified as a voice flow (Unsolicited Grant
Service (UGS) for upstream, or constant bit rate for downstream). The C4/c CMTS treats non-voice PCMM flows as normal
data flows.
CAC handles PacketCable MultiMedia priorities and preemption similar to the way they are handled by PacketCable DQoS
calls. SIP/PCMM VoIP calls using voice flows are also handled this way. The PCMM specification defines eight levels of
priority. On the C4/c CMTS, these eight levels are mapped to only two priority levels used for PacketCable DQoS calls. One
is for normal calls and the other is for emergency calls. Session classes of 0 and 1 for the PCMM gates are mapped to
normal calls and all other values are mapped to emergency calls. Downstream PCMM flows that look like constant bit rate
(i.e. having equal max and min bit rates) are treated by CAC as voice flows so that the voice limits can be used to prevent
downstream channels from being oversubscribed.
By default, the C4/c CMTS allows emergency calls to preempt normal calls if a channel has reached the Max Allowed Total
Bandwidth (BW). In general, operators should configure the Max Allowed Emergency BW to be equal to the Max Allowed
Total BW so that emergency calls always go through, provided there is enough bandwidth available on the channel for
voice flows. A normal call that is preempted by an emergency call is counted as a failed normal call.
Multicast CAC Description
Multicast CAC provides a way for MSOs to manage IP Video services in their network.
Characteristics of multicast CAC:
Feature is disabled by default; enabled using SNMP or CLI
Applies to downstream only
Has its own threshold separate from the voice thresholds
Applies to bonded and non-bonded flows
New emergency or normal VoIP call flows may not preempt an existing multicast flow (also known as Group Service
Flow)