If you’re looking for the zeitgeist of the IT industry today, you don’t need to look any further than XML and SIP. In just a few years, XML has come from nowhere to being a key way of representing data. You'll find XML inside databases, configuration files, describing APIs (for example in Web Services>), and in derived forms like VoiceXML and CCXML it can even describe a procedure, and execution flow of a script. In the areas of blogging and podcasting, RSS and OPML are relatively new uses of the structuring capabilities XML to make sure you get automatic updates to your favourite column or show.

Meanwhile SIP has been quietly revolutionizing the flow of signalling information. Of course SIP was invented as a way to perform VoIP signalling tasks, but has now grown far beyond this. With the SIMPLE (SIP Instant Messaging and Presence Leveraging Extensions), it can be used to exchange instant messages, and can also provide the infrastructure so that you can see when people on your buddy list go on and offline. SIP signalling is used for video and conferencing, as well as basic telephony. The Next Generation telcos are looking to IMS (IP Multimedia Subsystem) to replace legacy digital switching, and this all depends on SIP.

Now increasingly SIP is used as a transport for other types of signalling flows, for example in MSML (Media Server Markup Language) and CSTA (Computer Supported Telephony Application). These even have the ultimate in buzzword convergence, using both XML and SIP in the same protocol. Today SIP is where all the tunneling action is taking place, now more fashionable than tunneling with PPP.

Both XML and SIP have come into their prime, and we’re not done yet inventing new uses for either framework. I have heard people talking about using SIP to switch lightbulbs on and off. Personally, I think this is going a bit too far (a TCP/IP stack in a lightbulb?), but I'm sure the applications of SIP will continue to surprise.