Subject: RE: [Sip] OUTBOUND: How far does a request go?

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Fri, 3 Mar 2006 08:20:45 +0100

Hi Dean, 

> One thing, which I haven't seen being discussed in the "Outbound and 
> STUN Keep Alive" thread:
>
> Assuming we DO use a SIP method to keep the NAT binding open, the 
> questions is whether the request should be terminated by an edge proxy

> "on the other side" (from a UA perspective) of the NAT, or if the 
> request should go all the way to the registrar (scenario shown in 
> chapter 4.3 of the draft).
>
> In IMS, the edge proxy would be the P-CSCF, while the S-CSCF would be 
> the registrar. I am not sure one would like to require the P- CSCF to 
> forward the NAT keep-alive requests towards the S-CSCF, because it 
> would only cause unecessary extra traffic in the IMS network. So, for 
> this reason methods like OPTIONS cannot be used, because OPTIONS WILL 
> be forwarded by a P-CSCF. So, either the edge proxy must know that it 
> can terminate certain requests, OR the requests must be addressed to 
> the edge proxy itself (instead of the registrar).
>
> And, IF we assume there is no proxy between the UA and the NAT, the 
> double CRLF "proxy problem" would not be an issue, since no proxy 
> would be supposed to forward the double CRLF. Of course, there may 
> still exist other issues with the double CRLF mechanism. A STUN 
> request would also be terminated by the edge proxy on the other side, 
> I assume.
>
> And, if there IS a proxy between the UA and the NAT, I guess that 
> proxy would have to send the double CRLFs. I don't really see a 
> difference whether whatever-we-come-up-with has to be implemented in 
> the UAs, or in the proxy between the UA and the NAT...

If we get into the use case of "there is a NAT between the edge proxy
and the registrar", then we have a problem if the edge proxy terminates
the keepalive.

[CHH] The use-case I had in mind is when we have a NAT between a proxy
and the edge proxy. The edge proxy would then terminate the keep-alive
messages, send by the UAs AND/OR the proxy behind the NAT.

Maybe we should use different terms for the proxies we are talking
about, depending on where they are located, in order to avoid confusion
and missunderstandings...

Regards,

Christer

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---

From: "Gary Gan" <[email-masked]>
Date: Fri, 3 Mar 2006 09:16:06 -0500

I think the proxy should not forward the keepalive. Before we were worry
about the overload of the keepalive to the edge proxy, with this, it would
overload more proxies, even the whole SIP network. One way for proxy to
proxy NAT keepalive, I think, is to keep track the list of peer proxies that
previous visited for a period of time. Each proxy maintains the peer proxy
keepalive by itself. 

- Gary Gan

-----Original Message-----
From: Christer Holmberg (JO/LMF) [mailto:[email-masked]] 
Sent: Friday, March 03, 2006 2:21 AM
To: Dean Willis
Cc: IETF SIP List
Subject: RE: [Sip] OUTBOUND: How far does a request go?

Hi Dean, 

Regards,

Christer