PINT and SPIRITS - Instant Messaging
The use of SIP by other protocols is continuing at a frantic pace, and designers of many other application environments are looking at the modularity, scalability, and transparency of SIP for their own uses.
A strong case in point: call enabling e-commerce web pages with one-click call options to a call center. SIP is perfect for this environment. Since the SIP user agent is very lightweight, and is being imbedded in many phone-type devices, it is very easy to imbed a SIP Java client in a Java servlet on the web server, which can launch requests to create phone calls on the telephone network. This is the focus of the PINT (PSTN and Internet Interworking) protocol, based on SIP.
Another SIP application: Internet call waiting. A CO switch detects that you are online when a call comes in for your phone. Understanding this line condition, the switch gateways the call over IP using SIP and signals you, while you are still online, that you have a call coming in. You are prompted at your desktop to either (1) accept the call, (2) reject the call, or (3) send the call to voicemail. This application fits into the broader context of IP-PSTN cross signaling environments. Its standardization, based on SIP, is taking place in the SPIRITS (Service in the PSTN/IN Invoking Internet Service) working group in IETF.
Perhaps one of the most exciting new applications of SIP is as a protocol platform for instant messaging. A replacement for AOL Messenger? Absolutely. The mechanism by which it routes call invitations, and reaches the user wherever he is, is fundamentally about using presence (i.e., the communications state of a person) to enable session initiation. Turning this presence information around and delivering it to "buddies" is a natural extension of SIP. It also means that a single infrastructure can be used for voice, video, presence, and instant messaging - a very appealing goal. - R.S., J.R.
