[Sip] Diagnostic idea

["Dale Worley" <dworley at nortel.com>]

I've been considering the following idea for a diagnostic tool, and I'd
like to get some feedback on it.

The goal is to be able to trace the progress of a SIP request through
the network, including seeing the forking structure.  We first need to
pick a provisional response codes.  It appears that "170" is not
currently used.  This response code is also used as an option-tag for
this feature.  The processing is that whenever a SIP element receives a
request that contains "Supported: 170", the element will immediately (in
addition to anything else that it would do with the request) send a 170
response upstream, containing the request as its body (media type
message/sipfrag).

Dale