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 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. Cheers, Neil. -- Ubiquity Software Corporation, UK http://www.ubiquity.net
