The concept of the Service Oriented Architecture (SOA) is not new, although the reference is most commonly used in the context of modern information systems typically used in and between large enterprises. Service Oriented Architectures for information systems have largely been evolved from technologies and approaches that build popularized by the Internet. The IT industry has settled on an SOA approach that relies on the use of HTTP as the addressing and transport infrastructure and eXtensible Markup Language (XML) as a generic format for inter-process messages.
Current generation Web services-based SOA define a number of technologies that supplement standard transport protocols (primarily HTTP) to complete the architecture, such as the Universal Description, Discovery (UDDI), Integration protocol and the Web Service Definition Language (WSDL) and, optionally, the Simple Object Access Protocol (SOAP).
The combination of HTTP and XML, for example, is sufficient to allow the concept of a Service Oriented Architecture to be effectively realized through largely off-the-shelf products and widely available competence. In many cases, simple and relatively low cost upgrades of existing infrastructure are all that is needed to begin realizing a Service Oriented Architecture. There are substantial limitations to this approach, however, which make it generally unsuitable for a broad range of applications.
For a number of reasons, largely related to scale, resource efficiency, security, inter-domain interoperability and reliability requirements, real-time communications systems have not benefited from the Internet in the same way, or to the same extent, as information systems. Recently, however, a dramatic shift(fuelled by the remarkable increase in global IP network capacity, geographical coverage and the increasing power and flexibility of the computing devices available to consumers) has altered the balance of forces.
The fundamental ability to make use of the Internet (and all of its component technologies) for real-time, full-duplex exchanges of streamed data, such as voice and video, has only recently become achievable at the scale and cost levels needed to supplant legacy communications systems. The communications industry has standardized the essence of a Service Oriented Architecture of its own that, in many ways, exceeds the scope of the information systems from which it draws much of its inspiration.
This architecture is known as the IP Multimedia Subsystem (IMS).
About the IMS
There are several excellent sources for information about the IMS. I reccommend that anyone interrested in the IMS start by looking at the Wikipedia entry for IMS as a starting point.
Wikipedia - IP Multimedia Subsystem
From an industry perspective, the IMS is generating a good deal of buzz. One of the best sources for Telecom industry news and analysis is the Light Reading website (and the Heavy Reading consultancy).
A pedagogical white paper will be published in the upcoming weeks that deals with the specific comparison of IT SOA and IMS in more detail. Of particular interest is the IMS vision for Representational State Transfer (REST) "Web Services" using SIP, HTTP and XML rather than the more generalized SOAP protocol so common now in IT SOA discussions.
Reference: Michael Palmeter's Blog
