Understanding MGCP ALG Call Duration and Timeouts

The call duration feature gives you control over SIP call activity and helps you to manage network resources.

Typically a call ends when one of the clients sends a BYE or CANCEL request. The MGPC ALG intercepts the BYE or CANCEL request and removes all media sessions for that call. There could be reasons or problems preventing clients in a call from sending BYE or CANCEL requests, for example, a power failure. In this case, the call might go on indefinitely, consuming resources on the Juniper Networks device.

A call can have one or more voice channels. Each voice channel has two sessions (or two media streams), one for Real-Time Transport Protocol (RTP) traffic and one for Real-Time Control Protocol (RTCP) signaling. When managing the sessions, the device considers the sessions in each voice channel as one group. Timeouts and call duration settings apply to a group as opposed to each session.

The following parameters govern MGCP call activity:

• inactive-media-timeout—This parameter indicates the maximum length of time (in seconds) a call can remain active without any media (RTP or RTCP) traffic within a group. Each time an RTP or RTCP packet occurs within a call, this timeout resets. When the period of inactivity exceeds this setting, the SIP ALG gates opened for media are closed. The default setting is 120 seconds, the range is from 10 to 2550 seconds. Note that upon timeout, while resources for media (sessions and pinholes) are removed, the call is not terminated.
• transaction-timeout—The device tracks transactions between the gateway and the call agent and clears transactions when they time out. Timeout range for MGCP transactions is from 3 to 50 seconds, the default is 30 seconds.
• maximum-call-duration—This parameter sets the absolute maximum length of a call. When a call exceeds this parameter setting, the SIP ALG tears down the call and releases the media sessions. The default setting is 720 minutes, the range is from 3 to 7200 minutes.