Note: This article was originally written by Garrett Smith, and edited by Ying-Hui (Evy) Chen

Q: We recently purchased an IP PBX, but aren’t using VoIP to send and receive calls. I keep hearing about ‘SIP Trunking’ everywhere I turn. What is ‘SIP Trunking’ and can it help my business save money on calls?

A: If you are the proud owner of a SIP compatible IP PBX and are currently using a PSTN connection, such as a PRI or a handful of POTS lines to make and receive phone calls, it might be time to give SIP trunking a look. 

Many IP PBX systems, such as Asterisk and Trixbox allow you to leverage SIP trunking, in addition to maintaining PSTN connectivity. By editing the dial plan in your IP PBX, you can dictate which types of calls you want to connect to the PSTN, and which calls you want to hand off to your SIP trunking provider for termination. Cost savings is a primary reason why SIP trunking is becoming increasingly popular with businesses of all shapes and sizes.

What is a SIP Trunk?

For enterprises wanting to make full use of their installed IP-PBXs and not only communicate over IP within the enterprise, but also outside the enterprise, a SIP trunk provided by an Internet Telephony Service Provider to connect to the traditional PSTN network is the solution. 

Unlike in traditional telephony, where bundles of physical wires were once delivered from the service provider to a business, a SIP trunk allows a company to replace these traditional fixed PSTN lines with PSTN connectivity via a SIP trunking service provider on the Internet.

Download our SIP Trunking guide here to learn more!

What are the benefits of using SIP Trunking?

There are a number of reasonable answers to that question, but the primary advantage for many users is cost savings. For example, as a business owner, I could leverage SIP trunking to bypass expensive Long Distance or International toll charges levied by my PSTN provider. The rates for domestic and international LD are typically a fraction of what can be charged by traditional Telco operators. 

Understanding that a SIP trunk is dependent upon the integrity of your data (internet) connection, it is often prudent to use SIP trunks to complement traditional PSTN circuits. This gives you the cost savings you are looking for, in addition to the fail-over and redundancy of having two call carriers available.

More SIP Trunking benefits include more flexibility, DIDs, and more. See this post to learn more: 9 Benefits of SIP Trunking

How do I set up SIP Trunking on my IP PBX?

Actual trunk configuration will vary depending upon the make and model of IP PBX you are using. 

In a nutshell, you need to configure SIP trunking using account-specific information obtained when you sign up for service with an ITSP such as Bandwidth.com. 

Next, modify the dial plan in your PBX to set up specific call rules which dictate which trunks (SIP or PSTN) calls are placed on when a user picks up a phone in your office and dials an outbound call. A very simple dial plan setup would use PSTN trunks for local calls, and SIP trunks for LD or International calls. Many businesses with multiple domestic and international locations use SIP trunking for intra-office calling as well, often leveraging their existing data infrastructure.

If you are interested in getting SIP trunking in place feel free to contact one of our VoIP experts at 1-800-398-8647 and our team will be happy to share some instruction for your specific PBX platform.