In order to gracefully end the session (which can be done at any point after acknowledging receipt of the initiation request, including immediately thereafter in order to decline the request), either the responder or the initiator MUST send a session-terminate message to the other party.
The party that terminates the session SHOULD include a <reason/> element that specifies why the session is being terminated. Examples follow.
Probably the primary reason for terminating a session is that the session has ended successfully (e.g., because a file has been sent or a voice call has completed); in this case, the recommended condition is <success/>.
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