____ _
______ _____ _____
| UAC | ______ | P1 | _______ | P2 | _______ | UAS |
|_____| |______| |_____| |_____|
Consider the above configuration -
- UAC
doesn't insert Session-Expires header in Initial INVITE.
- RFC
4028 section 8.1 says that "A proxy MAY insert a
Session-Expires header field in the request before forwarding it if
none was present in the request."
- P1 inserts
Session-Expires header.
- P2 receives
INVITE with Session-Expires header and forwards it to UAS.
- UAS doesn't
support Session-Expires so it doen't insert this header in the response.
- The response
arrives at P2. Now RFC 4028 section 8.2 says "
When the final response to the request arrives, it is examined by the
proxy.
If the response does not contain a Session-Expires header field but
the proxy remembers that it requested a session timer in the request
(by inserting, modifying, or examining and accepting the
Session-Expires header field in the proxied request), this means that
the UAS did not support the session timer. If the proxy remembers
that the UAC did not support the session timer either, the proxy
forwards the response upstream normally. There is no session
expiration for this session. If, however, the proxy remembers that
the UAC did support the session timer, additional processing is
needed.
Because there is no Session-Expires or Require header field in the
response, the proxy knows that it is the first session-timer-aware
proxy to receive the response. This proxy MUST insert a
Session-Expires header field into the response with the value it
remembered from the forwarded request. It MUST set the value of the
'refresher' parameter to 'uac'.
".
- That essentially
means neither UAC nor UAS supports RFC 4028 but P1 and P2 run the
session expiration timers as a result when the timer times out both P1
and P2 release their calls/ resources. In certain cases this could be
potential revenue loss scenario.
Is it a bug or some gap in understanding?
Dushyant P S Dhalia
Rancore Technologies,
Gurgaon, INDIA
--
"When work is a pleasure, life is a joy! When work is duty, life is slavery."
|
<<attachment: dushyant_dhalia.vcf>>
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