So you'd like your SIP phones to all work together, eh? And you'd like your SIP phone from Vendor A to work with the SIP phone of Vendor B and yet give you the business functionality that you used to have in the PBX from Vendor C?
Yes, they will (or should!) all work together for basic call functions, but if you want to do more than just the very basics, you rapidly wind up in the realm of incompatible SIP implementations. Different vendors support different RFCs... or interpret RFCs differently. It's a challenge to go beyond basic functionality.
Enter "BLISS", one of the latest working groups coming out of the IETF. It stands for "Basic Level of Interoperability for SIP Services" and, as noted in its charter, the intent is to define a basic set of functionality ("minimum interoperability requirements") to allow SIP endpoints to interoperate on 4 specific telephony services:
- Bridged/Shared Line Appearance (BLA/SLA)
- Call Park/Pickup
- Do Not Disturb (DND)
- Call Completion to Busy Signal/Call Completion on No Reply
More details are on the charter page. These are just the initial four issues chosen to be addressed and Internet-Draft documents are already circulating on some of the items. I see it as a necessary group if we are to actually have real interoperability between SIP endpoints, and I commend the group organizers on scoping it to an initial 4 issues (rather than making it wide open).
If you work with SIP, I'd encourage you to check out the BLISS web site, read the "problem statement" and charter... and then join the mailing list (and please read the archives to see what's happened so far). I've joined the list... and would encourage others to consider doing so. If we do want real SIP interoperability, we need to hammer some of these things out.
For more information, you can download the set of slides presented by Jonathan Rosenberg of Cisco at the IETF 68 meeting stating the problem and why the BLISS working group is needed. To make it easy to see them, I'm going to embed a SlideShare version here:
See you on the list...