One of the newest service offerings from carriers is SIP Trunking.

Like many, many other pieces of jargon in the business, many people would like to understand just what exactly it is.

SIP is an acronym for Session Initiation Protocol. This is a standards-based method of setting up Voice over IP telephone calls.

A key thing to know about Voice over IP phone calls is that once the call is set up and two people are talking, their telephones exchange IP packets with digitized speech in them directly.

One person’s telephone creates an IP packet and puts the IP address of the other person’s telephone in the destination address field. This packet is forwarded by routers directly to the other person’s phone.

To be able to do this, it is necessary to know what the other person’s IP address is!

This is the main function performed by SIP: it is an assistant to enable a caller to find out the IP address of the called party’s telephone, so they can send packets with digitized speech to that person’s phone.

Trunking is a term that has been generally used in the telecom business in the past to mean communication between telephone switches. Trunks connect CO switches, toll centers and other switches in the PSTN.

PBX trunks connect an organization’s private switch to a CO switch.

SIP Trunking is a term invented by the marketing department to mean to mean “native communication of SIP call setup messages and Voice over IP traffic between an organization’s locations, with a Service Level Agreement and transmission characteristics sufficient to guarantee the sound quality.”  And a gateway service thrown in.

Native means carrying the IP packets without converting them to an old-fashioned telephone call. The IP packets in question are at first carrying SIP call setup messages, then once the call is set up, the IP packets each contain typically 20 ms of digitized speech.

SIP Trunking replaces the previous architecture of PBX trunks.

It would be more accurate to refer to this new service as “SIP and Voice over IP Trunking” – but “SIP Trunking” rolls off the tongue better…

To learn more, attend BOOT CAMP March 27-31, or just the last two days of BOOT CAMP, which are Course 130 Understanding Voice over IP March 30-31.