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.