SIP Trunk FAQ

A SIP Trunk is a concurrent call routed over a VoIP provider’s IP backbone. SIP Trunks are used in conjunction with an IP-PBX as replacements for traditional PRI or analog circuits. The popularity of SIP Trunks is due primarily to the cost savings of SIP, along with the increased reliability as backed by the SLAs of SIP Trunk Providers.

SIP Trunks realize their primary benefit over PRIs from cost savings. SIP trunks typically cost $20 to $30 per trunk for unlimited inbound and local calling along with a long distance rate that can be under 2 cents per call. When coupled with line oversubscription (e.g. a 30 person company purchasing just as many SIP trunks as they anticipate having concurrent calls, typically 8 to 10), SIP Trunks are a very cost effective way for a business to save money. SIP Trunks can be purchased in increments of 1, whereas PRIs have to be purchased in increments of 23 channels.

SIP Trunks are less expensive than analog circuits while maintaining the same service quality that businesses expect from line quality. SIP Trunks cost approximately $20 to $30 per trunk, versus $40 per analog circuit. In addition, long distance termination charges associated with SIP Trunks are much more cost-effective than traditional analog or TDM rates.

A business should look into purchasing SIP Trunks when they decide that their needs are best met with a premise-based system. This system is often referred to as an IP-PBX. Coupled with SIP Trunks, an IP-PBX serves up similar features to hosted solutions. SIP Trunks typically save a business customer money over a hosted solution in that a SIP Trunk can serve the needs of three to four employees (depending on oversubscription) while a hosted seat is needed for each employee.

SIP Trunks can work with a SIP-ready PBX. SIP Trunks can also be made to work with traditional analog or key systems with an IAD (Integrated Access Device). The SIP Trunk service provider will need to interoperate with the underlying equipment manufacturer. However, it should be noted that with the advent of standards around RFC and SIP Connect, the challenge of finding SIP Trunk Service Providers with SIP Trunk compatible equipment is significantly decreased.

SIP Trunks are virtual circuits delivered over an Internet Access line. Depending on the number of SIP Trunks purchased, and the amount of excess Internet connectivity, a business should consider purchasing more Internet access. However, it’s important to know that when a SIP Trunk is not being used, the bandwidth otherwise allocated to a SIP Trunk is freed up for use in less intensive applications, such as e-mail and general web use. This dynamic allocation of bandwidth is yet another feature of SIP Trunks versus more traditional technologies, such as analog or PRI circuits.