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Description:
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sipUAMaximumSessionExpirationDelay OBJECT-TYPE
SYNTAX Unsigned32 (0 | 180..3600)
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"Suggested maximum time for the periodical session refreshes.
This value will be reflected in the Session-Expires header.
Increasing the maximum will help to reduce network traffic,
but will also make 'dead' calls longer to detect.
This value is expressed in seconds (s).
To disable the session timer service, set the maximum session
timer expiration value to 0. However, this is not recommended since
it will make 'dead' calls impossible to detect.
Questions & Answers
---------------------------------------------
Q - What is the session timer extension?
A - The session timer extension allows the detection of the premature end of a
call caused by a network problem or a peer's failure.
The session timer mechanism simply resends an INVITE every n seconds.
A sucessful response (200 OK) to this INVITE will signify that the peer
is still alive and reachable. A timeout to this INVITE may mean that there
are problems in the signaling path, or that the peer is simply not there
anymore. In that case the call will be shut down using normal SIP means.
Q - SDP in Session Timer reINVITEs:
A - The reINVITE is sent with the last SDP that was negotiated.
Reception of a session timer reinvite should not modify the
connection characteristics.
Q - Relation between minimum and maximum values:
A - A UA that receives a Session-Expires header whose value is smaller than the
minimum it is willing to accept will reply a 422 Timer too low to the
INVITE and terminate the call. The phone will 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 UAS was ready to
accept (found in the Min-SE header). This means that the maximum value as set
in the Mediatrix unit might not be respected. 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.
Q - Who refreshes?
A - Re-sending a session timer INVITE is referred to as refreshing the session.
Normally, the UAS that receives the INVITE will have the last
word on who refreshes. Mediatrix units will always let the UAC
(caller) do the refreshes if the caller supports session timers.
In the case the caller does not support session timers, the
Mediatrix unit will assume the role of the refresher.
Also see sipUAMinimumSessionExpirationDelay."
DEFVAL {3600}
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