I've just spent the last two weeks doing interoperability testing of VoIP equipment for NetWorld+Interop. You can get the full results next month in Las Vegas at the show or in the May 10 issue of Network World, but here are some quick observations to whet your appetite:

H.323 is dead. Oh, man, is it dead! In past years, we've struggled to get H.323 devices to interoperate. They don't do it well and, what's worse, debugging is a total pain. Not so with Session Initiation Protocol (SIP)-controlled telephony. We had incredibly good basic interoperability in just minutes between SIP phones. When we wanted to debug problems, having all the control messages show up in plain text made it easier than H.323 ever was. For debugging, we used ClearSight Networks' VoIP analyzer as well as WildPackets' EtherPeek NX, but rarely needed the power and advanced features of either tool.

If you want to do a single-vendor VoIP telephony deployment, you don't care what protocol is underneath it all. Go ahead and get whatever makes sense from Avaya, Cisco, Nortel or your favorite vendor. But if you want to go for massive interoperability, mixing and matching vendors, phones and equipment, then SIP is the only way to go.

Not all phones are created equal. In the network world, we've become accustomed to treating equipment as a commodity. You can argue the fine points forever, but when it comes to most companies, it often doesn't matter what brand of network interface card, switch or server you buy. Not so with phones. We saw tremendous difference in the voice quality and performance across different products. Managing jitter across the network, encoding and decoding speech, and just sounding good or lousy - devices were all across the map. There is definitely a human factor involved with phones that's going to be unfamiliar to most IT people.

We found lots of variance in configurability and flexibility. You can tell the maturity of a product by how many knobs it has on it. Newly released, bargain-basement devices let you get on the network and little else. The battle-scarred veterans have 50 or 100 settings to tune the device for optimum performance in your network. The nice thing about SIP was that even without tuning, we had great interoperability results.