SIP in the Larger Context of the Internet Protocol Suite
By Mark A. Miller, P.E., President, DigiNet Corporation
Submitted by Smoothstone
The ARPANET—the predecessor to today’s Internet—was deployed in 1969, and was originally designed to support three key applications: electronic mail, remote terminal access to host computers, and file transfers. These three applications share the common characteristic of non-real-time operation. In other words, if the email or the file transfer is delayed through the network by a few seconds, neither the application nor the end user will notice any appreciable degradation in service.
Internet technologies and protocols have matured significantly since the late 1960s, to the point that real-time applications, such as voice and video, are now quite common. Much of the current research from the Internet Engineering Task Force (IETF)—the standards body responsible for Internet process and protocol development—is focused on supporting these types of traffic. However, the basic infrastructure of the Internet, and its architecture as a data-centric, connectionless network based upon the Internet Protocol (IP), has not changed.
When operated over a connectionless environment, these real-time applications may be subject to anomalies, such as packet delay and loss, which could significantly degrade the end user’s experience. To compensate, the IETF has developed a number of additional protocols, such as the Real Time Protocol (RTP), RTP Control Protocol (RTCP), and the Session Description Protocol which enhance the functionality of the base IP infrastructure. In particular, the Session Initiation Protocol (SIP) plays some key roles in the transformation of the data-centric Internet into a broader infrastructure capable of handling both data-centric and real-time applications. In the ten years since its development, SIP has emerged as the predominant protocol to support these real-time applications, and is widely supported by hundreds of software developers, system designers, test equipment manufacturers, and service providers within their products and services
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