> 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.
> simple solution would appear to be to configure these UAs with
> a 'default dial domain' and for it to build URLs using this
> not the Proxy's address.
I agree that default dial domain can be used
and does more explicitly inform the proxy that
the request was intended to be processed
like an outbound-proxy instead of a regular
proxy. However I don't see that it should be
required unless the outbound proxy has problems
with spiraling.
