SIP becomes the “glue” behind unified communications
Videoconferencing protocols have followed a similar evolutionary path as voice-over-data schemes. They started life as proprietary protocols, and were then standardized by telephony organizations. Finally, they were developed to run over IP.
Specifically, early VoIP systems were proprietary; later, the International Telecommunication Union (ITU) developed the H.323 protocol family for session establishment and management. Ultimately, VoIP emerged from the Internet Engineering Task Force (IETF). It was optimized for IP networks, followed the “dumb network/smart end-points” philosophy governing Internet design, and had the ability to adapt to a range of media types (including video).
One of the outcomes of VoIP’s development was the definition of SIP, the Session Initiation Protocol. Originally SIP was designed to support the needs of the mbone, an experimental multicast network for carrying audio and video over the Internet, but as developers realized the applicability of their work to emerging voice and video over IP applications, it has rapidly become an integral component of most VoIP systems.
SIP has also emerged as the basis for unified communications, enabling a standard method for interconnecting various real time communication applications including voice, video, messaging and conferencing. Via SIMPLE, any SIP-based application can share presence information with any other, while developers can deliver SIP-based clients capable of controlling any form of support communication application or even extend SIP-based applications into other systems or user interfaces. Thus, SIP becomes the “glue” behind unified communications. Hosted services for voice and video interconnectivity as well as hosted videoconferencing services are largely based on SIP as well, meaning that SIP has emerged as not only the protocol of choice for internal systems, but as the standard for interconnecting internal systems with hosted or external applications.
Videoconferencing hasn’t quite caught up on the SIP front yet, but there are signs that it will shortly. Videoconferencing systems still largely rely on H.323 or proprietary protocols for signaling and session management. Yet because of SIP’s popularity and effectiveness, many video vendors are supporting SIP as well, particularly for system integration and end-point signalling. This means many systems support both SIP and H.323. Mixed protocol architectures entail additional architectural complexity, management concerns and cost.
Over time, we expect SIP to increase in popularity across the board for videoconferencing — and that’s nothing but good news for unified communications. As videoconferencing systems increasingly become SIP-based, they can more easily integrate into unified communications, sharing presence information across applications (for example, allowing one user to see when another is in a videoconference). Videoconferencing vendors are also able to take advantage of the other benefits of SIP vs. H.323 including reduced end-point and architectural complexity, easier management, and greater extensibility. Adoption of SIP also means greater likelihood of interoperable conferencing across enterprise boundaries, either by organizations that establish direct interconnectivity between systems, or for those wishing to leverage hosted/managed services to support extranet conferencing.
Finally, standardizing on SIP reduces integration complexity by creating a single communications protocol layer for all UC elements. Enterprise IT architects can simplify deployment and management by managing one suite of protocols rather than separate protocols for each type of UC application. IT managers can also take advantage of emerging SIP-based services for extranet connectivity to support communication and collaboration sessions across company or network boundaries.
But just standardizing on SIP isn’t enough to reduce integration headaches.
First off, not all organizations are in a position to move straight to SIP. Many folks have large deployments of legacy systems that either require upgrading, or purchase of gateways to enable them to function in a SIP-based environment. Forklift upgrades, additional gateway purchases, or even software upgrades may not be feasible given tight IT budgets. Thus, the ideal approach is to create an architecture that is capable of interoperable support of existing protocols in use (e.g. SIP, H.323 or vendor proprietary alternatives) during time of transition to SIP. This strategy will reduce integration complexity by allowing IT architects to support a wider range of existing protocols for as long as necessary.
Another challenge is the fact SIP is only “kinda-sorta” standardized. More specifically, not all SIP implementations are identical, and vendors often implement their own proprietary methods for session establishment and management. (Remember that SIP doesn’t mandate a type of session, but rather controls the negotiation process, which means that session types supported in one vendor’s implementation may not be supported in another vendor’s). This means that in a multivendor environment, there’s still some integration work to do — even if all vendors support SIP.
Vendors and standards organizations are working on the problem, particularly the SIPForum, an industry consortium developing SIP implementation standards. Specifically, they’re standardizing SIP primitives that define a standard way of negotiating certain services including ringing, message wait indicators, call transfer, multi-way calling and so on. As vendors agree to implement these primitives, interoperability will improve. But in the meantime, even in an all-SIP environment, multivendor interoperability may be an issue — so communicate closely with your vendors to understand exactly what does and doesn’t interoperate.
The bottom line? SIP is poised to do for videoconferencing what it has done for VoIP: enable seamless integration of disparate systems and hosted services using a common signaling protocol optimized for IP. So as you’re assessing videoconferencing systems as part of your unified communications plans, keep SIP in mind.
