Understanding SIP ALG Call Duration and Timeouts

The call duration and timeout features give you control over Session Initiation Protocol (SIP) call activity and help you to manage network resources.

Typically a call ends when one of the clients sends a BYE or CANCEL request. The SIP Application Layer Gateway (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 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 SIP 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 temporary openings (pinholes) in the firewall the SIP ALG opened for media are closed. The default setting is 120 seconds, and 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.
• 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, and the range is from 3 to 7200 minutes.
• t1-interval—This parameter specifies the roundtrip time estimate, in seconds, of a transaction between endpoints. The default is 500 milliseconds. Because many SIP timers scale with the T1-Interval (as described in RFC 3261), when you change the value of the T1-Interval timer, those SIP timers also are adjusted.
• t4-interval—This parameter specifies the maximum time a message remains in the network. The default is 5 seconds, the range is 5 to 10 seconds. Because many SIP timers scale with the T4-Interval (as described in RFC 3261), when you change the value of the T4-Interval timer, those SIP timers also are adjusted.
• c-timeout—This parameter specifies the INVITE transaction timeout at the proxy, in minutes; the default is 3. Because the SIP ALG is in the middle, instead of using the INVITE transaction timer value B (which is (64 * T1) = 32 seconds), the SIP ALG gets its timer value from the proxy.

Related Topics

• JUNOS Software Feature Support Reference for SRX Series and J Series Devices
• Understanding SIP ALGs
• SIP ALG Configuration Overview
• Example: Setting SIP ALG Call Duration and Timeouts (J-Web)
• Example: Setting SIP ALG Call Duration and Timeouts (CLI)