Subject: RE: [SIP] Questions about session timer

From: "Chen, Xin (Xin)" <[email-masked]>
Date: Tue, 24 Apr 2001 09:43:40 +0100

Dean,

Thanks for your answer. In the session timer draft, it says "a proxy MUST
NOT send a BYE request once the session
expires." Why? What do I miss here?

Thanks

Xin Chen

Lucent Technologies
Tel: +44 1793 883137
Mobile: +44 7799 034668

-----Original Message-----
From: Dean Willis [mailto:[email-masked]]
Sent: 23 April 2022 5:37
To: Chen, Xin (Xin); [email-masked]
Subject: Re: [SIP] Questions about session timer

If the endpoints have started ignoring record-route and started talking
without the proxy in question, it's fairly clear that they don't really
think they NEED the proxy to hang around and proxy messages for them
anymore, so the proxy can probably just give up and go home. On the other
hand, if they DO really need the proxy (because it controls resources they
need) and they start ignoring record route, it's fairly clear that they're
not exactly playing by the rules and may need this pointed out to them . . .

The only "state" that a proxy can safely control is the state of signaling
that has passed through that proxy -- in essence discarding state means
knowing when it's OK to give up on the signaling because the clients don't
appear to be using that proxy anymore.

For example, a proxy which uses call state to maintain a set of pinholes in
a firewall needs to know when it can safely close those pinholes. It
normally does this when it sees a "BYE" on the call associated with those
pinholes. Of course, it could also decide to close the pinholes because it
hasn't seen media in a whiole, or because it hasn't seen signaling in a
while, or because the credit for the call has been used up, etc. What the
session-timer mechanism does is allow a proxy to inform clients that it WILL
be giving up on them if they haven't sent signaling (the INVITE sequence) in
some reasonable period of time. If a client fails to heed this warning, it's
entirely possible that the network experience it receives won't be what it
was hoping for.

And yes, there is generally a am interface between a proxy and a middlebox
(such as a firewall) which is working with that proxy to enforce some sort
of network policy.

--
Dean

----- Original Message -----
From: "Chen, Xin (Xin)" <[email-masked]>
To: <[email-masked]>
Sent: Friday, April 20, 2001 8:11 AM
Subject: [SIP] Questions about session timer

>
> In session timer internet draft, it says: "Similarly, if a proxy doesn't
> receive a re-INVITE before expiration of the session, it MAY remove
> associated call state, and MAY free any resources associated with the
call."
>
>
> The question is since proxy server might not be in the session traffic
path,
> caller and callee can still talk each other. How can the proxy release the
> resource (such as RSVP) for traffic transmission between the caller and
> callee if it is not in the traffic path?  According to my understanding,
one
> way to achieve this is the proxy has to been in the traffic path, itself
> also has to been a NAT/Firewall, so that it can close the holes and
release
> the address binding for traffic transmission on NAT/Firewall. If the proxy
> is not in the traffic path, there has to be an interface between the proxy
> and a NAT/Firewall which is in the path, so that the proxy can instruct
the
> NAT/Firewall block the traffic.
>
> Who can please clean my confusion about this? Please give me some detail
on
> how the proxy free ANY resources associated with the call.
>
> Also, is there a way that a proxy can release an established session when
> session timer is not supported in the proxy? Can the proxy act like a
B2BUA
> and send Bye to both ends?
>
> Thanks
>
> Xin Chen
>
> Lucent Technologies
> Tel: +44 1793 883137
> Mobile: +44 7799 034668
>
>
> _______________________________________________
> This list is for continuing development of the SIP protocol.
> The sip-implementor's list is the place to discuss implementation,
> and to receive advice on understanding existing sip.
> To subscribe to it, send mail to
> [email-masked] with "subscribe" in the body.
>

_______________________________________________
This list is for continuing development of the SIP protocol.
The sip-implementor's list is the place to discuss implementation,
and to receive advice on understanding existing sip.
To subscribe to it, send mail to 
[email-masked] with "subscribe" in the body.

_______________________________________________
This list is for continuing development of the SIP protocol.
The sip-implementor's list is the place to discuss implementation,
and to receive advice on understanding existing sip.
To subscribe to it, send mail to 
[email-masked] with "subscribe" in the body.

---

From: "Brett Tate" <[email-masked]>
Date: Tue, 24 Apr 2001 11:06:49 -0400

> expires." Why? What do I miss here?

A proxy should not trample on the CSeq of a UA.  
Thus on a given call-leg, a proxy can only 
generate responses, ACKs and CANCELs.

---

From: "Dean Willis" <[email-masked]>
Date: Tue, 24 Apr 2001 10:42:31 -0500

Right. The proxy doesn't send a BYE on the expiration of the session-timer.
It just quietly cleans up and discards whatever call state it is holding.

--
Dean

----- Original Message -----
From: "Chen, Xin (Xin)" <[email-masked]>
To: "'Dean Willis'" <[email-masked]>; "Chen, Xin (Xin)"
<[email-masked]>; <[email-masked]>
Sent: Tuesday, April 24, 2001 3:43 AM
Subject: RE: [SIP] Questions about session timer