Brett Tate wrote:
>
> > In testing labs I am seeing a worrying number of UA
> > implementations making the same mistake of sending requests
> > to a Proxy where the Request-URI is in the form
> > sip:user@<proxy-address>. I think some of the confusion may
> > be traced back to early SIP message flows which showed this
> > behaviour. I urge implementers to rectify this situation as
> > we are seeing this cause a great deal of confusion to
> > the first commercial adopters of SIP technology. These people
> > are not SIP protocol experts and just expect this technology
> > to work.
> >
> > It is often seen when using a local out bound proxy. The
> > situation is that the UA takes a configuration parameter
> > for the local proxy. You can then dial by keying in just the
> > user part of a SIP URL. The UA then builds a complete URL by
> > adding the Proxy's address and sends the message to the proxy.
> > The Proxy then receives an INVITE of the form
> > sip:user@proxy-ip - according to the protocol spec the Proxy
> > will route this request to the server at the given IP address.
> > This is obviously itself so an illegal loop is created. A
>
> An outbound proxy for userA can be configured
> to translate upon a received outgoing message
> from known userA however it wishes. UserA
> dialing *69 on a phone can be sent to outbound
> proxy with Request-URI of *69@outboundProxy-Ip.
> Assuming the outbound proxy knows userA, it can
> change the Request-URI into the last "known"
> user@host that called userA.
According to the SIP spec sip:*69@outboundProxy-Ip
does not map onto the last incoming caller's sip URL
this is specialised logic. It may exist but a truly
interoperable UA must still be able to work if it
doesn't.
The point I was really trying to make is that a UA
should not write Request-URIs out to be the destination
of where they are being sent in the hostport when using
a local outbound proxy.
Say I want to dial sip:[EMAIL PROTECTED] but
the UA configured with a local outbound proxy setting
of proxy.this-domain.com actually sends the INVITE
out as:-
INVITE sip:[EMAIL PROTECTED] SIP/2.0
To: sip:[EMAIL PROTECTED]
From: sip:[EMAIL PROTECTED]
....
This will either result in a 404 response, possibly
482 if the Proxy sends on to itself, or go to the
wrong jsmith. If a UA can only send out INVITEs
with Request-URIs like this it is broken.
Cheers,
Neil.
--
Ubiquity Software Corporation, UK http://www.ubiquity.net
