What is a SIP Trunk?

SIP: Session Initiation Protocol


A SIP trunk is a direct connection between your organization and an Internet telephony service provider (ITSP). It is a form of a circuit, or “trunk” that delivers voice and data abilities to a company. A SIP trunk provides the same service as an analog (POTS) phone line, but it is a virtual line rather than a physical wire, and sends voice and information in data packets over the internet. This basically means it is the technology that turns all office calls into cheaper internet calls.

SIP trunks allow voice to go past the firewall security in a company without a special gateway, making them easier and less expensive to design, operate, maintain, and upgrade.

SIP trunking is becoming increasingly common in the world of business phone systems, and unified communications (UC). SIP Trunking is completely replacing the need for PRI services because it is more intelligent, more flexible, less expensive, and technically superior in many ways to PRI or T1 circuit. In addition to voice calls, SIP trunks can also carry instant messages, multimedia conferences, user presence information, Enhanced 911 emergency calls, and other SIP-based, real-time communications services. This makes them a valuable addition to Unified Communications and business phone systems.

As SIP-based communication technologies advance and SIP trunking becomes commonplace, additional services are likely to become available.


SIP trunking can greatly assist an organization in simplifying their telecommunications and enabling the latest advancements in Unified Communications (UC). While it allows for greater flexibility in your communication and collaboration abilities, SIP trunking also represents immediate and substantial cost savings.

Advantages that lead to savings:
Cheaper than PRI Circuits: If your organization has or needs a PRI, find out if a SIP trunk is an option in your area as it has a greater capacity at a lower price.
Only pay for what you need: With SIP trunking, you don’t need to buy phone and data lines in blocks of 24 or 32, but rather, you can buy the bandwidth you need in the increments you need.
Scalable: Since the connections are virtual, scaling up or down can be as simple as a software configuration adjustment, and doesn’t require any physical hardware or circuits
Save money on long distance service: Long distance service typically costs significantly less with a SIP trunk connection.
Eliminate IP-PSTN gateways: Because SIP trunks connect directly to your ITSP without traversing the publicly switched telephone network (PSTN), you can eliminate the cost and complexity of IP-PSTN gateways.
Eliminate a redundant network: For business continuity and a back up plan in the event of failure, many companies used to employ backup data and telephone networks. With SIP trunking, however, the network is IP based and can potentially eliminate that need.
There are circumstances where a PRI circuit would be a better fit for a business however, depending on what the company’s priorities and bandwidth are. To find out what is the best fit for your business, talk to an experienced telecommunications consultant today.