With CAC, you can specify several types of limits on Locations.

An overall limit, Total Bandwidth, constrains the total bandwidth used for calls traversing the link of the location.

The multimedia sub-limit, Multimedia Bandwidth, restricts calls that are not audio-only, such as video calls, to less than the full capacity of the location. The sub-limit prevents a few large video calls from exhausting the link and preventing audio calls from being made.

CAC also provides per-call parameters such as Maximum Multimedia Bandwidth to be specified at a location level. The Maximum Multimedia Bandwidth value limits the bandwidth allowed to a single call to create room for more calls along a link by restricting video quality.

Each of these limits may be specified or left blank for any given location.

CAC operates by inspecting Session Description Protocol (SDP) contained in SIP messaging for calls. SDP identifies both the source of media (by IP address, which maps to Location) and the amount of bandwidth consumed. SDP manipulation is also used to reduce bandwidth consumption for limit enforcement. CAC allows the specification of default bandwidth assumptions for calls with unrecognized SDP, specified per Location (Default Audio Bandwidth). CAC also allows a per-location restriction on how much a multimedia stream can have its bandwidth reduced (Minimum Multimedia Bandwidth) before it should be removed entirely. This is required for maintaining a minimum level of video quality.

CAC provides alarm notifications when the bandwidth usage of a location remains above a certain threshold for a sustained period of time. Snapshots of current usage are taken every 60 seconds, and if successive snapshots remain above the threshold, the alarm is raised until usage drops below the threshold. For each location and limit type, you can administer the number of snapshots and threshold required to raise the alarm. You can monitor the real-time bandwidth usage in the Managed Bandwidth Usage page.

Two additional settings can change the way Session Manager performs Call Admission Control.

• Audio Calls Can Take Multimedia Bandwidth, when not selected, specifies that only multimedia calls will fill the Multimedia Bandwidth bucket, while audio-only calls will be limited to the bandwidth specified by Total Bandwidth – Multimedia Bandwidth. When selected (default), audio-only calls can consume all of Total Bandwidth, and Multimedia Bandwidth functions as a sub-limit for calls containing non-audio media.

• Based on the Ignore SDP for Call Admission Control option in the Global Settings section on the Session Manager Administration page, all Session Manager instances interpret that all calls lack SDP. This option causes every call to be regarded as an audio call using bandwidth defined as Default Audio Bandwidth under the originating location of the call.

  • This setting can be used to transform CAC into a call count enforcer. Because each call is counted equally, the limit enforced is a limit on the number of calls allowed to or from a location. By assigning SIP entities to unique locations, you can limit the number of calls to or from an entity.

  • Session Manager ignores SDP. When upgrading System Manager from 6.0 to later versions, the previous administered behavior will be preserved. Otherwise, this option is disabled by default.