2011/7/6 Martin Hoffmann martin.hoffmann@telio.ch:
Yes, SIPS: is really messy and hard to understand.
I'd argue it's completely broken like so many things in SIP. IETF went out to publish a document to fix it. After much argueing, this became RFC 5630 and people are confused as ever.
Main cause of the confussion ever after RFC 5630, is the fact that such RFC does not want to cover the ;transport=tls case in deep (which exists anyway as RFC 2543 and RFC 3261 mention it).