Session Initiation Protocol (SIP) trunks are direct connections between a business and an Internet telephony service provider (ITSP), also known as Voice over Internet Protocol (VoIP). It has the ability to extend VoIP beyond a company's firewall without requiring an IP-PSTN gateway. SIP trunks are capable of carrying Enhanced 911 (E911) emergency calls, user presence information, multimedia conferences, instant messages and other real-time communications services that are SIP-based. SIP trunks is able to provide a fast return on investment for the companies that use them. There are two main reasons for this. First, ITSPs provide services that are very affordable. Secondly, SIP trunking is simpler to configure and inexpensive to upgrade, maintain, operate and design.
The "trunk" in SIP trunking is term that is commonly used in the world of circuit-switched telecommunications. It is a reference to a dedicated physical line that is used primarily to link switching equipment together. A SIP trunk is a connection between telecommunications systems. In this way, it strongly resembles its circuit-switched predecessor. However, the primary difference between the two is that a SIP trunk uses a virtual connection that is able to be made over a line that is designed to be specifically used for SIP trunking, over the Internet via a virtual private network (VPN) or over a dedicated line that carries other IP traffic along with SIP trunking.
Let's take a look at the plans that are currently offered by some of the major SIP trunk providers: