A recent post entitled VoIP Technical Details caught myeye because of some minor inaccuracies and inconsistencies about SIP and H.323 protocols commonly used in VoIP. I posted Protocol Playtime in reponse. In that response, I promised a series of articles digging into VoIP protocols in more depth over the weeks and months ahead. The first paper, A Look at Session Initiation Protocol (SIP), is the first of those papers. It's now available online here. 

A Look at Session Initiation Protocol

By Ken Camp

As a follow-up to recent online conversations, this article begins an exploration of common VoIP protocols. This first installment of an ongoing exploration of the technical workings of VoIP protocols will explore Session Initiation Protocol (SIP). As this is the first paper in the series, it will begin with an overview of how the open standards widely used in the Internet are developed.

Standards used in the worldwide Public Switched Telephone Network (PSTN) are products of the International Telecommunications Union-Telephony (ITU-T) sector, formerly known as the CCITT. This group operates under the auspices of the United Nations (UN), which is important to note because this body acts in many ways as an administrative unit focused more on international interoperability than other areas. Although this group has responsibility for telephony standards, they have not historically been known for being quick or nimble at responding to technology needs. ISDN standards took 10 years to get through this group. There are many different international political agendas that come into play when dealing with the UN, and change takes time.

Internet standards are a much different story. TCP/IP standards used throughout the Internet are primarily the work of the Internet Engineering Task Force (IETF). This group is also global—primarily an organization of volunteers. Any interested party can join the IETF and participate in standards development, and many do every year. The IETF working groups are made up of technology specialists from colleges and universities, hardware and software vendors, telecommunications providers and competitive local exchange carriers (CLECs), Internet service providers (ISPs) and Internet telephony service providers (ITSPs), government organizations, and a variety of other interested parties. Because the organization is voluntary and created by technologists focused on progress and efficiency, the structure of developing IETF standards is much different than that for the PSTN. [read the whole article...]

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