The Session Initiation Protocol (SIP) has come to prominence primarily as the focus of VOIP technology development has shifted from creating low cost solutions to adding value. It is a text-based protocol that is easily programmed, highly flexible and readily scalable – all attributes where it differs from its closest rival in the IP telephony services arena: the ITU’s H.323 umbrella recommendation. Further, SIP is a lightweight client easily embedded in end-user devices. This means that, wherever there is a requirement for real-time sessions to be established, SIP can be placed in the communications device to handle them.

These attributes open up a wide range of new possibilities for services with revenue-generating potential - on-line gaming, click-to-dial for web commerce, IP Centrex, instant messaging, presence management, desktop call management and unified messaging, to name a few.

However, what if an instant message service could be combined with an online translation facility so that it was instantly translated into another language? Such is the promise offered by SOAP - Simple Object Access Protocol. Is SOAP then a suitable way to extend SIP-based applications?

What's it for?

Like SIP, SOAP is a simple, lightweight protocol that facilitates exchange of information in a decentralised, distributed environment. It is based on XML, which means it is highly flexible and extensible. It is also firewall-friendly and platform independent. It can be used not only as a data carrier, but also and more importantly for invoking remote procedures on servers, services, components and objects written in any language and running on any platform. It is an open standard and, as such, is aimed at simplifying information exchange and providing interoperability across a variety of platforms.

It has gained a lot of interest over the last year, especially since the World Wide Web Consortium (W3C) undertook its standardisation and Microsoft decided to incorporate it into its products (such as DNA 2000 and the Microsoft.Net framework) for the development of web services. Above all, it can jump through firewalls and proxy servers.

SOAP enables interoperability by providing a generalised specification for invoking routines on objects and components using the ubiquitous Hypertext Transfer Protocol (HTTP) and Extensible Markup Language (XML) data formats. Having now obtained support from the likes of IBM and Sun Microsystems, it also promises to be a major industry standard in the future.

SIP and SOAP: working together

SOAP defines the use of XML and HTTP to access services, objects and servers in a platform-independent manner. It can therefore act as the glue between heterogeneous software components. So, if developers can agree on HTTP and XML, SOAP offers a mechanism for bridging competing technologies in a standard way. It is therefore highly suitable as a lightweight protocol for the customisable exchange of information in a decentralised, distributed environment where many components can be arranged to collaborate to provide features and functionality.

The platforms supporting services in the future will increasingly be decomposed into many unique components – allowing the specialisation of separate service components such as text-to-speech engines, web application servers, Voice XML servers and conference servers. While SIP then provides the capabilities for finding the particular components required and controlling the session, SOAP can provide a means to access them.

Take the example of an instant message translation. The basic messaging service is provided using SIP functionality. The translation facility could then be on an independent, remote web-based server which is integrated into the application by using SOAP to access it. As a result, when the message is sent it can be translated in real time either word by word or phrase by phrase so that it appears at the receiving end fully translated. Since the translation server can be chosen according to immediate requirements, it may be a specialist facility focusing perhaps on a particular industry and its special terminology. In principle, this even provides the means for several people each speaking a different language to take part in an instant message chat or conference with each using his or her own language only. A powerful facility indeed.

A further example might involve a courier service delivering a gift or other important package – an urgent specification say. When the gift is delivered, the user receives an instant message notification that includes a URL. By loading this URL, a web page is displayed which allows the user to request that a call be set up to the gift’s recipient as a click-to-dial facility. SOAP could be used to instruct the communications channel to connect accordingly, with SIP choosing the right device for the recipient to receive the call on. As soon as the package is delivered, then, the person sending it can call the person receiving it. 

Watch this space

SOAP is simple. It is nothing more nor less than a standard protocol that defines how to access services, objects and servers in a platform-independent manner using HTTP and XML. As such, it offers several benefits over proprietary XML vocabularies. When combined with SIP-based communication applications, even in these early days of use it is already demonstrating great potential for creating new and innovative revenue-generating services quickly and at low cost. 

© e-principles 2001

Robin Duke-Woolley

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