Sip Trunking

NETW320

SIP Trunk

SIP trunking is a method of combining voice and data services over a single broadband circuit. This Voice over Internet Protocol (VoIP) method and streaming video service is comprised from the Session Initiation Protocol (SIP). This method is used by enterprises that have an installed SIP based private branch exchange (IP-PBX) and that wish to make full use of it, not only for IP communications within the enterprise, but externally by an Internet Telephony Service Provider who then connects to a traditional PSTN network (What is SIP Trunking, n.d.). A SIP trunk replaces the traditional bundle of wire that were used to connect a service provider to a business by replacing the fixed PSTN lines with an Internet based SIP trunk service. By using these SIP trunks the cost savings for an enterprise can be significant because you can eliminate the need for PSTN gateways, ISDN Basic Rate Interfaces (BRI’s) and / or Primary Rate Interfaces (PRI’s).

There are three elements that are required to put a SIP trunk in place; a Public Branch Exchange (PBX) with a SIP enabled trunk side. This can be either IP based or traditional digital or analog PBX’s as long as an interface for SIP trunking connectivity is available. The second element necessary is the enterprise border element which connects the PBX to the local area network via the ITSP. The enterprise edge component can either be a firewall with SIP support or be an edge device connected to the firewall which handles the SIP traffic. The final element is the Internet Telephone Service Provider, the service provider that provides the connectivity of the internet and the communication with mobile and fixed telephones. Overall a SIP trunk is cheaper than a legacy trunk (MACHOWINSKI, M. , 2009).

The following RFC’s are associated with SIP Trunking:

1889 RTP: A Transport Protocol for Real-Time Applications

2327 SDP: Session Description Protocol

2833 RTP Payload for DTMF Digits, Telephony Tones and...