What is a SIP Trunk?

A SIP Trunk is a VoIP (Voice over Internet Protocol) service which streams media based on the Session Initiation Protocol. SIP is often used to control voice and video calls or other communication sessions over Internet Protocol. The protocol can be used to both create and terminate sessions, or modify them whether they be unicast or multicast or over one or several media streams. Instant messaging and online games also use SIP.

Using SIP Trunking, internet telephony service providers can deliver unified communications to customers who have available to them SIP-based private branch exchange (IP-PBX) and Unified Communications facilities. Generally, voice and video streaming media applications are made available by Unified Communications software applications, as well as other streaming media applications such as web conferencing or desktop sharing.

Both individuals and companies can take advantage of the existence of SIP Trunks, as these can be used in either situation. Within a customer’s home, a VoIP solution uses the phone and unified communication services that are there, whereas in a Public Domain, a company has full VoIP access to the whole PSTN (Public Switched Telephone Network)/PLMN (Public Land Mobile Network) property as well as responsibility of the ITSP (Internet Telephony Service Provider) which provides the telephone services. The private domain isn’t personally responsible for complying with the law, but is rather the responsibility of the ITSP, a third party providing the voice services to the company or the end user.

Usually, a business is delivered bundles of wires by the service provider. By using a SIP Trunk, the business can replace these PSTN lines, instead using the SIP Trunking service provider to gain connectivity to the PSTN.

A business needs three things to put into place SIP Trunks. Firstly, a PBX (Private Branch Exchange) which has a SIP-enabled trunk side, an enterprise edge device which understands SIP and an Internet telephony or SIP Trunking service provider.

SIP Trunks are used in great part to save money, as they remove the need for PSTN gateways, expensive ISDN BRIs (Basic Rate Interfaces) and PRIs (Primary Rate Interfaces).

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