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You configure the Session Timer in the IMG 1010 - SIP Session Timer pane. SIP Session Timer is enabled by default.
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If support of session timer is disabled, the Supported header in an outgoing request will not contain the tag ‘timer’. If the incoming request has Require header that contains tag ‘timer’, the request will be rejected with 420 response code.
If support of session timer is enabled, the IMG will always request a session timer, and depending on the configuration the IMG may enforce the session timer even if the remote gateway does not support it.
Session refresh timer will be one half of the session interval. Session end timer will be the two thirds of the session interval, or the session interval minus 32 seconds, whichever is larger.
The IMG can choose to use re-INVITE or UPDATE to do the refresh. If it is configured to use UPDATE, but the remote gateway does not support UPDATE, the IMG will use re-INVITE instead.
If re-INVITE is used, there will be an SDP on it. If UPDATE is used, there will be NO SDP on it.
A re-INVITE or UPDATE request sent within a dialog for purpose other than session refreshes will also have the effect of refreshing the session, and its processing will follow the procedures described below.