Trunk prefix

A trunk prefix is a digit sequence to be dialed before a telephone number to initiate a telephone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed.

In most countries, making a domestic telephone call requires the dialing of a single digit preceding any area codes and the destination subscriber number. In most countries, such as Australia, Germany and the United Kingdom, the trunk prefix is 0. In the North American Numbering Plan it is 1. When the same telephone number is called from another country, the national trunk prefix is not dialed; instead, for international calls, an international trunk access code is typically required. Many countries use the sequence 00, but in the member states of the NANP, such as the US and Canada, it is 011.

Example

Assume that a call is to be made to a customer in the Australian Area/State of Queensland with the local number of 3333 3333 and the "Area Code" of "7".

A caller from outside Australia must dial the International Call Prefix of the originating country, plus the Country Calling Code (in the case of Australia - 61), plus the Area Code (in this case - 7), and then the local number. Therefore a caller in the UK must dial 00 61 7 3333 3333, while a caller in the USA must dial 011 61 7 3333 3333.

SIP trunking

SIP trunking is a Voice over Internet Protocol (VoIP) and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based private branch exchange (IP-PBX) and Unified Communications facilities. Most Unified Communications software applications provide voice, video, and other streaming media applications such as desktop sharing, web conferencing, and shared whiteboard.

Domains

The architecture of SIP trunking provides a partitioning of the Unified Communications network into two different domains of expertise:

The interconnection between the two domains must occur through a SIP trunk.