By Sanjeev Sawai
A few weeks ago, I was at a telecom conference, and I overheard a pair of grizzled old telecom engineers moaning about SIP (Session Initiation Protocol, in case you’ve been living under a rock for the past few years). What follows is a portion of their conversation.

“SIP, Ha! SIP only provides five basic functions, user location, user availability, user capabilities, session setup and session management. It doesn’t determine what kind of applications can be sent back and forth. It doesn’t even affect how the information is passed,” said the first guy.

“Tell me about it,” the other said. “SIP doesn’t even come close to supporting the number of functions that our 10-year-old TDM systems do.”

“Man, What’s up, or should I say, ‘WhatSIP’ with all this hype over session initiation protocol?”

Unfortunately these guys had totally missed the point. SIP wasn’t designed from the top down to be everything for everyone. And, while SIP doesn’t support the full 500-feature set of capabilities in a traditional TDM system, who cares? Its potential to redefine communication means that it has far superior capabilities. SIPerating it from other protocols and standards is its flexibility. (OK no more SIP puns)

If you think about it, with all their complaints, those legacy traditionalists were actually praising SIP. SIP is just a medium for handling session management for any media type. It can perform as a connection protocol for voice, but for other media types as well, such as text messages or video.

When the IETF began designing SIP, they weren’t trying to control or limit what kind of applications and data could utilize the protocol, and they weren’t looking to confine the transfer of information to one domain or another. Compare SIP with the ITU standards that were developed to essentially mimic services provided by ISDN. Those standards were expected to provide a full feature set, but they proved to be so complex and inflexible that the protocol couldn’t be easily integrated with the advanced voice applications promised by voice over internet protocol (VoIP).

Conversely, with its flexible header-based definition, SIP has evolved into a feature-rich protocol. While it is true that SIP doesn’t support all of the features of your old TDM system, it does coverabout 90%of the telephony features used in today's TDM-based applications.But don’t fret, if you are worried that you’re going to miss your old TDM system,take a look atthe feature set offered by any modern PBX.See how many feature names you recognize,let alone use on a daily basis, and you’ll realize that there isn’t too much to miss yet there is so much to be gained. While SIP may lack 10% of the features supported by a legacy TDM, it offers capabilities previously undreamt of.

SIP’s true value is that it enhances interoperability, provides open-source alternatives and promotes portability across telecommunications and applications. In fact, SIP has the promise to deliver any-device-any-location real-time connectivity. So, if communicating is your thing, you’ll probably like some of the features and applications that the SIP standard enables.

Because it’s open and extensible, SIP enables developers to create innovative applications that work with standard IP networks. So, if you’ve got some development experience, SIP will unleash your creative ability. And, you get to run the application wherever you have IP network connectivity – integrating PCs, mobile devices, SIP phones and other end-points of communication. SIP allows all these end points to co-exist and use their capabilities to the fullest because it uses the ‘discovery’ philosophy for end-points, rather than the prescribed capabilities followed by the TDM world. As a result, a SIP end-point will declare its capabilities each and every time it negotiates a session connection with other end-points, allowing the best possible communication to occur.

Utilizing proxy servers and text-based messaging, SIP-based softphones and hardphones can establish, modify and terminate IP conferencing, IP telephony, unified messaging, IM, presence management and event notification. IP telephony applications use SIP to initiate information transfer, provide call setup and tear down among participants, route requests between locations, validate users and provide features.

All this translates into an exciting age for communication. SIP is the common link that connects phone capability with the IP network and enables developers to embed voice capability into everything from CRM systems to email packages. Wherever there may be a benefit to having voice communication at your finger tips, it is within reach. Like the standards that laid the foundation for the internet, SIP is a protocol that is easy to understand, easy to extend and easy to implement. Today, SIP has become the standard protocol for VoIP, but its design and flexibility enables all types of real-time communications, not just voice.

Included among these are:
· Instant Messaging (IM)
· Text messaging
· File transfer
· Application sharing, collaboration on a single document
· Whiteboarding, writing and drawing on a common virtual whiteboard
· Video conferencing
· Machine-to-machine real-time communication
· Alerts and notifications sent to multiple devices. Alerts can be helpful in the case of a prescription that is ready for pickup at the pharmacy and absolutely necessary if you’re saving a city from impending doom.

SIP promises to open the doors to a new world of presence-based communication systems that can be extended to every person in your organization resulting in truly unified communications (UC). If you haven’t crossed the UC threshold yet, SIP’s flexibility will push your company through that door of opportunity.

Third party developers can create targeted, vertically oriented applications. Whether you’re a financial services provider or a graphic design firm, SIP enables specialized independent software vendors to develop applications specifically tailored to meet the needs of your market.

This shift to an open application development environment is accompanied by support for protocol extensions, meaning that applications can support advanced features while still interoperating with other less functional applications. Unlike the “least-common denominator” approach of old, SIP enables three sales reps to be on a conference call with two utilizing video conferencing while the third (whose phone doesn’t support video capabilities) can participate on a traditional audio call.

With SIP, the possibilities are endless. Consider the following scenarios enabled by SIP:
· Find me/Follow me functions can be set up to drive presence management beyond the “offline” or “online” descriptions of yesterday. An end user could be in a conference call and receive a call from someone who is supposed to be in the same meeting. The call processor could directly add that caller into the conference while sending all other calls to voicemail.
· An office worker leaves the office for lunch and a call comes into her desk. Her moving cell phone could prompt a SIP-enabled call processor to route that incoming call to her mobile phone rather than let it go to voicemail.
· Or, imagine being on a Web-conference, editing an important product development worksheet. You need to leave the meeting before it concludes to catch a train. Thanks to SIP, you can seamlessly transfer the audio from the conference to your cell phone, and use your PDA to continue analyzing the document with your colleagues. SIP will treat it all as one call.

With SIP, all forms of communication are treated as just another packet stream – with an IP infrastructure you will have no problems utilizing applications that involve all types of multimedia solutions, from voice to video to data. So say goodbye and good riddance to the days of TDM, when bringing data and video together required several different gateways and a deployment process that would make you cry, not to mention the operations headache that came with maintaining it.

So when that crusty old telephony developer asked, “WhatSIP (sorry, I know I promised no more puns) with session initiation protocol,” he missed the point entirely. It’s not about the features you had on your old TDM system that didn’t carry over. It’s about a future that promises “smart,” presence-based communication available at your finger tips on whatever device you are using at the time.

For all those old-school telephony folks out there, I suggest you take inspiration from the character in that old Clovers hit, ‘Love Potion No. 9.’

Remember what he did?

“I held my nose. I closed my eyes… I took a SIP.”


Sanjeev Sawai is the CTO and Vice President of Research and Development at Envox Worldwide, a leading global provider of IP-based voice solutions. Sanjeev has written and lectured extensively on the subjects of IVR and CTI and readers can see more of his work at www.envox.com