SIP session lives on after container callback to sessionExpired (Issue 1265)

Description

This is an intermittent issue. The SIP container intermittently responds with a 500 Server internal error message instead of a 481 Call/Transaction does not exist message when there is a race condition between the 200 for NOTIFY indicating that the session has been removed, and the SUBSCRIBE sent by the client when receiving that NOTIFY.

Solution

The client needs to the refresh SUBSCRIBE much before the subscription expires.