SIP stands for Session Initiation Protocol. It is designed to set up connections between devices such as computers, phones, PBXs, video conferencing units and servers.
A SIP Trunk is a virtual phone line that connects your PBX to the public telephone network. It sends the data over a data network, instead of over an ISDN circuit. SIP Trunks can be used instead of ISDN circuits to carry all of your telephone calls, or in conjunction with an ISDN circuit to provide a resilient telephony solution.
SIP trunks can offer significant cost-savings for enterprises, eliminating the need for local PSTN gateways, costly ISDN BRIs (Basic Rate Interfaces) or PRIs (Primary Rate Interfaces).
There are three components necessary to successfully deploy SIP trunks: a PBX with a SIP-enabled trunk side, an enterprise edge device understanding SIP and an Internet telephony or SIP trunking service provider.
In most cases the PBX is an IP-based PBX, communicating with all endpoints over IP, but it may just as well be a traditional digital or analog PBX. The sole requirement is that an interface for SIP trunking connectivity is available.
The PBX on the LAN connects to the ITSP via the enterprise border element.The enterprise edge component can either be a firewall with complete support for SIP or an edge device connected to the firewall, handling the traversal of the SIP traffic.
On the Internet, the ITSP (Internet Telephone Service Provider) provides connectivity to the PSTN (Public Switched Telephone Network) for communication with mobile and fixed phones.
The advantages of of using SIP Trunking rather than ISDN are that SIP Trunks utilise your existing data connection, negating the need to spend money on monthly line rental for ISDN circuits.
Calls sent over the Internet are much cheaper than calls sent over traditional telephone infrastructure, thereby saving on your monthly call costs.
Because SIP Trunks are provisioned over your existing data connection, provisioning can be done instantly as you do not need to wait for circuits to be installed.
Unlike with ISDNs where you have a maximum of 30 channels per circuit, a SIP trunk is fully scalable so you can have as many or as few as users as you want.
By retaining on of your old ISDN circuits, you can add resilience to your phone system, thereby ensuring that even if one of your connections goes down, your telephones will continue to work at all times.
Session Initiation Protocol (SIP) is an underlying protocol that makes connecting parts of an overall communications system very easy and leads to rapid service/offer deployment. SIP can reduce hardware costs; provide greater flexibility for disaster recovery; and enables businesses to take advantage of a wide variety of choices in communication devices. It has delivered on the Internet Engineering Task Force (IETF) goal of creating a simple but elegant protocol for setting up and tearing down real time communications sessions across an IP packet network. Now, by unifying communications solutions, SIP is ushering in a new era of intelligent communications.
SIP deployment encompasses four key elements:
