Day two opens with a keynote from Jonathan Rosenberg, one of Henning Schulzrinne’s early collaborators on SIP. Rosenberg went on from Columbia University to Dynamicsoft, later Cisco Systems where he is now a Fellow. Rosenberg is still active in IETF work related to SIP, and was principal author of NAT traversal techniques, STUN and ICE.

Rosenberg touched on many topics in his presentation on the challenges for IP telephony, but of course one of the challenges he talked about was SPIT or voice SPAM. He said that one basic decision point is whether you know the caller or not. As long as we have strong identity on VoIP networks, it’s possible to keep a white list of permitted callers. Then the problem becomes how to enroll people on to that list in the first place.

Safely letting in people that you don’t know opens the field to a whole range of different techniques. Some that he mentioned include: consent and reputation systems; CAPTCHAs; computational puzzles and payments at risk. Some of these he outlined as more promising than others, but the point is that this problem is not solved yet, and in fact is an ongoing discussion in the IETF and elsewhere.