Part of what I wanted to learn was whether the VoIP signaling protocol battle was as over as it seems to be. Most consumer VoIP products use the SIP protocol (see this page of our VoIP NTK for more info.), although the older protocols continue to be used in business (PBX) VoIP and trunking applications. Competing standards usually aren't conducive to high consumer uptake, so this is an important question if consumer VoIP services are to continue to grow.

One of the most interesting sessions I attended was one that posed the question of whether the open source IAX2 (pronounced "eeks two") VoIP protocol favored by Asterisk creator and Digium founder Mark Spencer would replace SIP. Electronic Frontier Foundation (EFF) Chairman Brad Templeton pointed out that they key question most prospective VoIP users ask is "who can I talk to?", not what protocol a service uses.

Templeton noted that the free Internet telephony service Skype claims to have 600,000 active users out of the over 28 million downloads of the application - a number that dwarfs the multiple thousands of subscribers on any of the SIP-based non-PSTN services. Skype's decision to use a proprietary protocol certainly didn't seem to hold it back and probably has helped its development, since it didn't have to wait for the painfully slow standards-creating process.

Mark Spencer of Digium made a strong case for IAX over SIP, primarily on the basis of IAX's higher efficiency and ability to easily traverse NAT firewalls. But even he bows to the dominance of other protocols since his Asterisk open source VoIP PBX supports IAX, SIP, MGCP, Skinny (SCCP), and H.323 VoIP protocols. But since Spencer is a co-creator of IAX, he's not exactly a neutral observer on this topic.

The other SIP themes that seemed to emerge were that SIP implementations aren't as standard as vendors would like (or would like their customers) to believe. While interoperability of basic SIP features (call setup and teardown) is pretty good, advanced features such as transfer, conferencing, follow-me, etc. don't always work between vendors. Part of the problem may be that there is not yet a SIP certification process, although there is an industry trade organization - the SIP Forum - that has a certification working group.

Instead, SIP vendors rely on two "interoperability test events" to see how well their products play with others'. SIPit is held roughly twice a year and focuses on basic SIP functions, while the

The reality is that multiple signaling standards exist and will continue to exist for some time to come in the VoIP world, and the PSTN (that's your good ol' regular telephone in VoIP-speak) isn't going away anytime soon either. Once you dig below the surface and get into the stuff that actually does the real work in getting your VoIP call through, things get pretty messy. That world - which is something that I won't be getting into - is a patchwork of gateways that perform conversion among the various media and signaling protocols.