Even though Session Initiated Protocol (SIP) has been around for a several years, we’ve seen the intensity of interest pick up drastically over the past several months.
And the reason is pretty darn simple. In the history of telephony, SIP represents only the third fundamental change in how information is controlled for automated switching within the network. (We’ll ignore the “zeroth” generation was not automated and the caller interacted with a live operator who would connect circuits.)
The first generation, of course, was designed for automated switching of analog calls. Calls were controlled by mechanical switches, and each individual analog circuit was physically connected. If you’re unfamiliar with the story of how two undertakers and an uncooperative operator led to the basic development of these switches, check out the story of Almon Strowger.
The second generation was the introduction of electronic switches. And hand-in-hand the capabilities for customers to have a trunk with multiple conversations between the customer premises and the “telephone company” came along. Prior to electronic signaling, each individual analog circuit had to go directly to a central office, leading to miles and miles of copper for a corporation.
The particular significance for electronic signaling was that there were several options for passing the signaling to the central office, and then the signals were likewise controlled electronically within the telephony network. The key point here, though, is that these signaling methods were all developed for switching TDM circuits with a fixed bandwidth of 64Kbps per call.
SIP now offers the same type of capabilities for controlling packetized calls, especially initially VoIP. This is a monumental change in that the bandwidth per call can be variable, and the call might be a voice call, a multimedia call, or any other type of “session.”
And perhaps most importantly, the major carriers are now rolling out “SIP trunks” that allow a company to connect to the PSTN (as we probably will continue to know telephony companies for quite a while) using a packetized rather than TDM service.
We’ll be continuing to look at SIP trunking on a regular basis. In the meantime, you might particularly enjoy the paper “SIP Trunking – Addressing the Hidden Costs of Telephony Networks.”
