Transcending Boundaries with SIP
By Eric Ransdell, Thu Apr 25 00:00:00 GMT 2002

SIP has the potential to realize the long sought-after dream of a "one-number world."


There’s an offer on the table and you have 15 minutes to make a decision. But first you need input from your CEO, COO and corporate counsel who, at this particular moment, happen to be away on other business in three different countries. Not a problem. You step out of the meeting and check each of their mobile handsets to make sure they are on and available. You then send an instant message asking if they can join a conference call. When the responses come back affirmative, you choose the “Auto-Conference” option, highlight their names on your buddy list and press “Send”. In the time it takes to place a phone call, you’ve enabled a conference call. Fifteen minutes later, you’ve got a deal.

Sound like something out of the 3G fantasy book? It’s not. Currently there are more than 100 companies working to make this scenario possible over existing wireless infrastructure. How? By using a new technology called Session Initiation Protocol or SIP. You may not have heard of it yet, but many inside the industry believe that SIP has the potential to be to wireless what Hyper Text Transfer Protocol (http) was to the computing industry.

How it works?


In fact, with its open, client-server architecture SIP could be considered a close cousin of http. And that is what makes it so revolutionary. Just as computer programming was the exclusive domain of computer scientists and engineers before the advent of http, telecom protocols and APIs are currently either proprietary or so difficult to learn and navigate that only highly trained personnel can use them. SIP promises not only to change all that, but in the process, change the way we communicate.

Jonathan Rosenberg is one of the people who invented SIP while he was a member of the Internet Engineering Task Force (the same body that gave the world the Internet Protocol and http). He believes SIP will profoundly change the communications landscape in three ways.

“First,” says Rosenberg, who is now chief scientist for dynamicsoft, a SIP developer based in New Jersey. “its grounding in web technologies will enable the kind of innovation in telecom services that we have seen in web services. Second, it will finally integrate what has traditionally been disparate communications modalities - voice, video, messaging, and presence. Third, it will unify wireline, wireless, and PC-based communications onto the same technologies, so that users can finally have a consistent experience across all access types.”

SIP works much like http in that it is used to initiate, establish and maintain real-time peer-to-peer communications across IP networks. But its flexibility as a protocol takes it well beyond http in that it can be applied to voice, messaging and presence using the same network servers.

“Http connected computers in a way that enabled them to exchange information about HyperText delivered up by Web servers, so what once was the dim world of slim white command lines on black monitors became the bright world of hyperlinked pages in cyberspace,” explains Tom Mueck, editor of SIP Forum. “Now you have discrete islands of different communications media - SMS, video/voice over IP, chat rooms, phone calls on POTS (plain old telephone lines) and presence - and what SIP does is to string them all together.”

Not only does it bring together different forms of communication over networks, but because it runs over the Internet, SIP also connects fixed and mobile messaging. Which means that SIP-enabled computers will be able to communicate in real-time with SIP-enabled mobile handsets. “It's the integration of the fixed and mobile worlds into one messaging universe,” says Margaret Hopkins, principal analyst with Analysys, a London-based telecom consulting and research firm.

SIP’s killer apps


It’s that crossing of the communications equivalent of the blood-brain barrier that has so many people excited about SIP. One of SIP’s killer apps, many industry analysts believe, will be instant messaging and buddy lists. After email, instant messaging is the most popular form of online communication with more than 50 million users worldwide. But with email now available over some mobile handsets, instant messaging remains firmly rooted in the home or the office. What SIP will do is to make instant messaging mobile and extend its ability out to a global wireless population of 1 billion users.

Though instant messaging is free, what SIP brings to network operators is a chance to monetize it in the same way users are charged for sending SMS messages. “There are such huge numbers of SMS messages floating around, that only terminating a small proportion of them on SIP makes it worth having as an SMS-to-SIP gateway,” says Hopkins. “There is only revenue for the network operators on the mobile side, so linking instant messaging to SMS creates a chance for them to generate new revenues.”

Another of SIP’s killer apps is its ability to detect presence over networks. Users of Web buddy lists are already familiar with presence awareness, which usually takes the form of icons showing whether another user is online or offline. SIP’s peer-to-peer capabilities not only allow it to detect another user on a network, but also to show the status of their mobile handset - for example, whether it’s on or off, set to Silent ring (meaning they wish not to be disturbed) or is out of money.

And that’s only with mobile handsets. The implications become huge when you consider SIP’s ability to detect the presence of anything over a network – be it a computer, a PDA or a fixed line phone. All that’s required is that the device in question be SIP-enabled and have a SIP URL, which is similar to an email address but is prefaced with sip (for example sip:joe@thefeature.com). SIP also supports phone numbers in its URLs.

Because it’s the address and not the device, SIP will enable what its proponents describe as “service mobility”. “SIP will enable the kind of mobility that transcends device boundaries,” explains Henning Schulzrinne, another of SIPs inventors and Associate Professor of Computer Science and Electrical Engineering at Columbia University.

“I can tell people the same number (SIP URL) whether I'm using the hotel phone while traveling, my home phone, my office phone or any other device that I use permanently or temporarily. The same identifier can reach several devices, so that my SIP URL makes both my home and my office phone ring, regardless of whether they are operated by the same company or not.”

A reality check


So does SIP have what it takes to become the http of the wireless world? Some biggest players seem to think so. Microsoft has already incorporated SIP into its Windows XP communications platform as the technology to provide presence awareness, instant messaging and voice capabilities. AOL has announced that it will use SIMPLE (SIP for Instant Message and Presence Leveraging) as a means of allowing its users to send instant message to other services. Nokia, Ericcson and Motorola are also helping to develop a SIP-based messaging system through their Wireless Village initiative. And in what may be the most important show of support, the 3G wireless standards bodies, the Third Generation Partnership Project (3GPP) and 3GPP2, have designated SIP as the call control standard for 3G networks.

In her report “Session Initiation Protocol: SIP-related European revenue forecasts 2002-2007”, Analysys’ Margaret Hopkins estimates that SIP-related revenues in Western Europe could hit 2.9 billion euros in 2007. In that best-case scenario, SIP clients would number 200 million.

But SIP is still a technology in development. The biggest issues the IETF currently confronts are those of security and privacy. The latter is a particularly thorny problem because of SIP’s presence awareness capabilities. For example, what if you don’t want your boss to know your phone is turned on. SIP’s ability to enable a single number for different devices also comes with a steep downside in terms of spamming.

SIP adds value


Some of those issues will have to be addressed by governments. For example, the EU is considering making location-based marketing messaging a user opt-in system. But the SIP technology will also provide solutions. “With SIP you can finally have a "block list" which blocks certain people from sending you IM, but also blocks them from calling you, or from adding you as a buddy,” says Rosenberg. “It’s this consistent and coherent behavior across multiple communications modalities that is one of SIP’s primary value propositions.”

SIP’s greatest value, however, may be its ease of use as a text-based programming language. In effect, SIP is to H.323, the current standard protocol, what http was to UNIX – a simple, interoperable standard that has the potential to revolutionize the industry. And because it is based on http, the tens of thousands of web developers already in existence will find it easy to make the transition to developing applications for the wireless world, which could throw open the floodgates to new innovations the same way http did with the Web.

“By making it easy for new applications to be built, SIP allows the killer app to come from some place you might not expect it,” says Rosenberg. “After all, isn't that the definition of a killer app?”

Eric Ransdell is the former Silicon Valley Bureau Chief for US News and World Report magazine. Now living in Shanghai, he covers mobile technology in Asia.