SIP trunking is a Voice over Internet Protocol (VoIP) service based on the Session Initiation Protocol

Session Initiation Protocol

The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...

 (SIP) by which Internet telephony service provider

Internet telephony service provider

An Internet telephony service provider offers digital telecommunications services based on Voice over Internet Protocol that are provisioned via the Internet....

s (ITSPs) deliver telephone services and unified communication to customers equipped with private branch exchange (IP-PBX) facilities.

Domains

The architecture of SIP trunking provides a partitioning of the voice network into two different domains of expertise, which consist of:

• Private Domain: a VoIP solution realized at the customer's home that takes advantage of phone and unified communication services;
• Public Domain: full VoIP access solution to the PSTN / PLMN property and responsibility of the ITSP that provides phone service. The interconnection between the two domains must occur through a SIP trunk.

The interconnection between the two domains, created by transport via the Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 (IP), involves setting specific rules and regulations as well as the ability to handle some services and protocols that fall into the well-defined name of SIP trunking.

ITSP is completely responsible towards the authority regarding all the following law obligations of the Public Domain :

• Tracking traffic;
• Identification identity of users;
• Implementation of the lawful interception mechanisms.

The private domain instead, by nature, is not subject to particular constraints of law, and may be either the responsibility of the ITSP, the end user (enterprise) or of a third party who provides the voice services to the company.

Architecture

In each domain there are elements that perform the characteristic features requested to that domain, in particular the result (as part of any front-end network to the customer) is logically divided into two levels:

• The control of access (Class 5 softswitch
  Softswitch
  A softswitch is a central device in a telecommunications network which connects telephone calls from one phone line to another, typically via the internet, entirely by means of software running on a general-purpose computer system...
  
  );
• Network-border elements that allow to separate the Public Domain from the Private one implementing all the appropriated ITSP phone security policies.

The private domain consists of three levels:

• Corporate-Border Element that allow to separate the Public Domain from the Private one implementing all the appropriated Company security policies.
• Central Corporate Switching Node;
• IP-PBXs.

External links

• (ITU-T | Kaleidoscope event 2010 | conference)