Subject: Re: [Sip] use of outbound proxies

From: Christer Holmberg <[email-masked]>
Date: Mon, 03 Sep 2001 09:26:33 +0300

Hi,

First, one could argue that this is pretty much a network architecture
question. The outbound proxy in the network is there for a reason, and
if the functionality it provides requires it to record-route it shall do
so, or the network simply won't work.

The problem with 1) could be that it if the outbound proxy is stateful,
and it may receive a BYE for a call that doesn't exist (the INVITE was
sent in the other direction, using another route). In the firewall
example that would probably not be the case, because the requests in
both directions most probably go through that same proxy. But, if the
outbound proxy is only used as a "phone book" (the UAC doesn't do DNS,
for example) incoming requests do not need to go via that same proxy.

If 2) is used, I am not sure we need to write so much about the outbound
proxy as a separate node in the first place. The request routing chapter
may simply say that the user may configure a proxy (call it outbound
proxy if you want...) which is used as the "last resort" to send
requests there.

Regards,

Christer Holmberg
Ericsson Finland

Juha Heinanen wrote:
> 
> Terry L Anderson writes:
> 
>  > draft-ietf-sip-rfc2543bis-04 appears to have contradictory rule on
>  > routing of subsequent requests.  15.4 (next to last paragraph) appears
>  > to say that whenever UAC is configured with an outbound proxy, it sends
>  > all subsequent requests there regardless of Request-URI (and so
>  > regardless of route list).
>  >
>  > But 16.4.1 appears to say the UAC does this only if there are no Route
>  > headers or UA has no support for DNS.
>  >
>  > Which is the intended behavior?
>  > 1) always route to outbound proxy
>  > 2) use outbound proxy only as last resort, for subsequent requests
> 
> i brought this same issue up before the london ietf.  i don't think that
> there is any conclusion yet.  if a firewall restricts sip traffic only
> to the outbound proxy, then 1) is the only possible choice.  one could
> argue that in that case the outbound proxy should record route, which
> would make the problem go away.  on the other hand, the outbound proxy
> may not be controlled by the same entity as the firewall and may not
> want to record route.
> 
> -- juha
> 
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