By Tarun Kapoor

In today’s increasingly connected world, many employees of an enterprise are computer literate enough to use the latest communications technologies, such as an Instant Message (IM) application or an IP phone. Yet they still complain that they need multiple applications to reach their colleagues or customers; one application for sending and receiving Instant Messages, one application or device for telephone and/or video calls, and another one for collaboration tools such as a whiteboard. Occasionally, they even need to use one application just to set up another application. It is even worse for system administrators who have to manage multiple, disparate systems. However, there is an answer: the “Converged Platform” where multiple features and functionalities are all combined into one client or device; a “one-stop” concept, making it a potential candidate for the next killer app. The increasing need for scalable and flexible converged communications mandates SIP as the protocol that serves as the backbone of the platform.

But before we can begin to decipher why SIP is so important to converged communications, we must first redefine the term enterprise convergence. Today, enterprise convergence is narrowly defined as the merger of voice and data networks in an IP environment. However, this limited definition distracts from the real goal of
enterprise convergence. To truly embrace network convergence, an organization must consider voice communications as simply another application. Convergence therefore should be viewed as the sharing of IP network resources and services among different applications. These applications can provide features such as voice, data, video, etc. What if you could provide all of these features on a single platform for enhanced communications, increased productivity, and a complete converged experience? This is how convergence should be viewed; the concurrent delivery of various media types to a single application (Figure 1). Leveraging the right protocol for convergence is crucial and no protocol to date can be compared to SIP; it is the key to convergence in the enterprise. SIP already has built-insupport for many convergence features and functionality such as setup and negotiations of multimedia sessions and parameters, support for Instant Messaging (IM) and Presence, and many extensions (e.g., UPDATE for conferencing) to provide other advanced features of converged communications.

This eliminates the need for multiple servers supporting multiple features and allows for easier administration of both users and features. Network service providers can benefit from having one server for all features, a “one-stop” server, to provide all the converged features, even providing them through NATs and firewalls by utilizing apersistent TCP connection to the server. SIP was initially designed to be a call setup protocol, though now it has matured to offer many different services. The main function of SIP was to set up a multimedia session between two endpoints, and even now this is still one of the strong points of SIP. The two endpoints can negotiate multimedia parameters before the session setup, during the session setup, or change the multimedia parameters in midsession. Imagine how convenient it is to be in the middle of a voice session, then change to a video session, and finally add a whiteboard to the video session, yet the user does not lose the current multimedia session if the remote endpoint cannot support a desired multimedia type. Using SIP, all this can be automated; for instance, suppose you want to change an existing voice session to a video session. You initiate the video session from your User Interface (UI), yet the two endpoints automatically determine that one endpoint does not have video capabilities and then you get notified with this information without the remote user ever realizing that you wanted to change to a video session.

With its scalable and flexible architecture, SIP easily incorporates innovative and unique features for enterprise convergence. For example, a SIP server can invite users to persistent multimedia conferences such as a “push to talk” persistent audio conference. As the server also “speaks” presence (i.e., a presence agent) by sending presence updates, it can notify existing members of the conference of the addition of new members, while simultaneously negotiating the multimedia session parameters. This powerful functionality is excellent for supporting multiple conferences and presence updates per user. As users recognize the benefits of converged communications within the enterprise, they are very likely to demand more advanced services to augment their converged experiences, such as event notifications. The event mechanism for event notifications is one of the key aspects of SIP. The events can be generated (and subscribed to) by either the server or the client. One client can notify another client about a client-specific event (e.g., when they are on the phone with a specific customer) and/or all clients can receive notifications about system-wide events (e.g., scheduled system maintenance). Since any device on the converged platform (phone, handheld device, or soft client) can subscribe to and receive different types of SIP event notifications, it can integrate the event notification with an existing feature (such as automatically invite other users to a multi-party conference) or even third-party applications such as a scheduler or automatic dialer (with additional XML support). By supporting Internet-based standards such as XML, a converged platform for the enterprise can easily integrate with various other Internet-based applications and protocols.

For example, with XML support, a SIP-based converged application can integrate with public IM clients such as Yahoo! Messenger or MSN Messenger and possibly even enterprise IM clients. Web services, XCAP-based configuration servers, even real-time streaming of live corporate video feeds… these are some of the potential services of the enterprise converged platform; they are feasible due to the inherent tying into technologies that many applications and services are using today and which users are accustomed to. Keeping in mindthat SIP was designed to be a modular protocol and that it was based on the HTTP protocol, this is a logical consequence of those decisions. The initial goal of SIP was to provide some core features and functionalities for multimedia session setup that could be leveraged by applications or devices in coordination with other protocols to provide a rich user experience (e.g., convergence). The fact that SIP has added many extensions to provide additional functionality does not alter the original concept of modularity. Yet modularity is only one key concept which differentiates SIP from other signaling protocols. For enterprise convergence, the real benefit of SIP compared to other protocols is where the intelligence for a service resides. There exists no notion of a client-server architecture, or dumb endpoint versus intelligent network concept. Depending on the type of service, the server makes the intelligent decisions (e.g., routing decisions, processing decisions, network decisions, etc.) or the client implementing the service communicates the information to the server, or it can even be two clients using a peer-to-peer mode to provide the service.

This is ideal as each feature of the converged platform can be used in different styles based on the end user expectations and network infrastructure available. For example, based on changing network conditions or endpoint mobility, either the server or the client can renegotiate the multimedia parameters in an existing multimedia session. Of course, as SIP is currently considered the foundation for the IP Multimedia System (IMS) industry, of which converged communications is a subset, it only seems logical that SIP would be used as the backbone protocol for enterprise convergence. Venture Development Corporation (VDC) estimates worldwide markets for SIP infrastructure and software to exceed $5.5 billion by 2007. This represents a compound annual growth rate of 36.1 percent between 2003 and 2007. According to Chad Hart, VDC’s Telecom/Datacom Practice Director, IMS adoption will drive SIP growth, with initial trials through 2006 and more significant deployments in 2007.

“The acceptance of IMS by both wireline and wireless carriers solidifies SIP’s role as the protocol of choice for all network operators. Most carrier-focused vendors will repackage their existing SIP offerings to cater to this rapidly emerging market.” As more and more vendors and service providers are moving towards SIP-based services and offerings, many of the drawbacks and missing pieces of SIP with regards to enterprise convergence will be resolved with extensions to the base protocol (that is not to say that there will be a day with no shortcomings in SIP). As more vendors implement converged solutions for the enterprise, they will need to provide more enhanced features and services to differentiate themselves in the marketplace. Understanding the advantages and benefits of using SIP as their foundation will have a profound impact on their ability to provide these new services to their customers.