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Internet Telephony: The Evolution to a Service-Oriented Architecture

by Vijay K. Gurbani and Xian-He Sun

The field of telecommunications has evolved to resemble the distributed computing domain, where general-purpose computers communicate over a common network. This evolution has culminated in the Third-Generation Internet Multimedia Subsystem (3G IMS) Architecture. In the computing domain, the Web Services Architecture or, in general, the Service-Oriented Architecture (SOA) is the modern trend in distributed computing today. Both the IMS and the Web Services Architecture provide services built on common, standardized, and well-known protocols. In this chapter, we present our views on the continuing evolution of these two architectures as the boundary between telecommunications and computing services continues to blur. We provide a high-level architectural overview of both the telecommunications and Internet networks to provide a context for the requirements we derive for a telecommunications SOA.

1. Introduction
Until recently, the line between the telecommunications network and the Internet was well demarcated. The former was a special circuit-switched network, tuned to transporting one media: voice. Over the years, it had also evolved to provide voice-related services to its users - colloquially known as subscribers - such as call forwarding, call waiting, and other services. In the telecommunications network, intelligence was concentrated in the core of the network, with the edges (phones) being very simplistic. The Internet, on the other hand, resided at the opposite spectrum from the telecommunications network. It was designed as a packet-switched network that would transport any type of media - voice, video, gaming, text - in a packet. The core of the Internet was relatively simple and stateless - it only performed the routing of packets; the intelligence resided at the edges of the network in the form of powerful general-purpose computers.

More recently, the established lines between the Internet and the telecommunications network have started to blur. Today's 3G cellular phone is capable of providing many Internet services: e-mail, presence, Web browsing, and instant messaging, to name a few. On the other hand, transporting voice, which was once thought to be the domain of the traditional telephone network, is now done by the Internet. Two recent advances in technology have aided in this shift. The first advance is related to the form factor of what constitutes a computing device. Moore's law and other advances have continued to shrink hardware components to the point that a fairly sophisticated computer can be embedded in a handheld telephone. Second, the advances in the field of networking have made the Internet faster and more pervasive than ever. These two advances have caused each of the networks to steadily encroach on the principles held dear by the other.

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About the Author

Measuring and Improving Performance: Information Technology Applications in Lean Systems
From Architecting the Telecommunication Evolution: Toward Converged Network Services by Vijay K. Gurbani and Xian-He Sun. Auerbach Publications, 2006.

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