SIPping from a firehose
SIP stands for session initiation protocol. It is the emerging standard for Voice Over IP. It allows an open framework for the following activities (I got this from the Columbia University website)
call forwarding, including the equivalent of 700-, 800- and 900- type calls;
call-forwarding no answer;
other address-translation services;
callee and calling “number” delivery, where numbers can be any (preferably unique) naming scheme;
personal mobility, i.e., the ability to reach a called party under a single, location-independent address even when the user changes terminals;
terminal-type negotiation and selection: a caller can be given a choice how to reach the party, e.g., via Internet telephony, mobile phone, an answering service, etc.;
terminal capability negotiation;
caller and callee authentication;
blind and supervised call transfer;
invitations to multicast conferences
Here is how SIP works
SIP addresses users by an email-like address and re-uses some of the infrastructure of electronic mail delivery such as DNS MX records or using SMTP EXPN for address expansion. SIP addresses (URLs) can also be embedded in web pages. SIP is addressing-neutral, with addresses expressed as URLs of various types such as SIP, H.323 or telephone (E.164).
SIP is independent of the packet layer and only requires an unreliable datagram service, as it provides its own reliability mechanism. While SIP typically is used over UDP or TCP, it could, without technical changes, be run over IPX, or carrier pigeons, frame relay, ATM AAL5 or X.25, in rough order of desireability.
I have never seen SIP run over carrier pigeons, but it works great over most transmission protocols.
Why does this stuff matter? Because Voice Over IP is like the web was in 1995/96. It’s a wide open (and I mean OPEN) playing field where anyone can build and deploy a service without creating a lot of infrastructure to support it.
Some early VOIP players are locked into proprietary systmes and look like AOL and Prodigy did back in 1995/96. See Michael Robertson’s slam on Skype for a great example.
I see Vonage and the other consumer VOIP providers as the Earthlinks and Mindsprings, they are the carriers who are going to get everyone connected. And that’s great.
But who is going to create the real homerun business models like eBay, Yahoo!, Google, Amazon, etc? That’s a completely different issue and one that I am really interested in. If you’ve got the answers, I am all ears.