Medias Mediatrix 1204, Reference Manual

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Session Timers Reference Manual (SIP Version)
Mediatrix 1204 221
Session Timer Version
You can select the version of the session timer draft that the Mediatrix 1204 uses. Session timer versions other
than those provisioned may not work because of backward compatibility issues between the versions.
This feature is currently located under the mediatrixExperimental branch of the MIB structure. See “MIB
Structure” on page 111 for more details.
The Mediatrix 1204 supports the following session timer versions:
X
To set the version of session timers supported:
1. In the sipInteropMIB , set the sipInteropSessionTimersVersion variable with the proper version.
• sessionTimer04
• sessionTimer08
Background Information
The following explains how the session timers are used.
SDP in Session Timer reINVITEs
The reINVITE is sent with the last SDP that was negotiated. Receiving a session timer reINVITE should not
modify the connection characteristics.
Relation Between Minimum and Maximum Values
A user agent that receives a Session-Expires header whose value is smaller than the minimum it is willing to
accept replies a “422 Timer too low” to the INVITE and terminates the call. The phone does not ring.
It is up to the caller to decide what to do when it receives a 422 to its INVITE. Mediatrix units will automatically
retry the INVITE, with a
Session-Expires value equal to the minimum value that the user agent server was
ready to accept (located in the Min-SE header). This means that the maximum value as set in the Mediatrix
unit might not be followed. This has the advantageous effect of establishing the call even if the two endpoints
have conflicting values. Mediatrix units will also keep retrying as long as they get 422 answers with different
Min-SE values.
Who Refreshes the Session?
Re-sending a session timer INVITE is referred to as refreshing the session. Normally, the user agent server
that receives the INVITE has the last word on who refreshes. Mediatrix units always let the user agent client
(caller) perform the refreshes if the caller supports session timers. In the case where the caller does not
support session timers, the Mediatrix unit assumes the role of the refresher.
Standards Supported • draft-ietf-sip-session-timer-08.txt
• draft-ietf-sip-session-timer-04.txt (expired)
Table 139: Session Timer Versions Supported
Version Description
sessionTimer04 The Mediatrix 1204 uses the session timer extension as described in the now expired
draft-ietf-sip-session-timer-04.txt . Its use is deprecated. You should use this setting for
backwards compatibility issues only.
sessionTimer08 The Mediatrix 1204 uses the session timer extension as described in the more recent
draft-ietf-sip-session-timer-08.txt . This draft version contains several enhancements over
the previous ones, including the use of the Min-SE header. Use this setting if you do not
need to interoperate with session timer v4-enabled parties.