Ask Mr. Andrews: What is SIP Trunking and Can it Save My Business Money?

October 22, 2008 by Garrett Smith

Q: Hey, Mr. Andrews. 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 maintain 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.

Why would I want 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.

How do I setup SIP Trunking on my IP PBX?

Actual trunk configuration will vary depending upon the make and model of IP PBX you are using. For the purposes of this article I will not get into specifics on configuring SIP trunks. If you are interested in getting SIP trunking in place feel free to shoot me an email at [email protected] and I will be happy to share some instruction for you specific PBX platform. 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 dialplan 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 dialplan 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.


6 Comments

  • Lucy

    One word of caution about SIP trunks. We ran into trouble because our office is in a rural location and the internet provider did not offer Quality of Service (QOS) on the T-1. We spent hours with the SIP provider (different company) trying to figure out call quality issues before we finally narrowed it down to QOS. Unfortunately, we did not have the option to switch to another T-1 provider in our area. Bottom line – we lost a lot of time and money.

  • Cory Andrews

    Lucy – I feel your pain. In a perfect world our last mile data provider would also be the one providing our SIP trunks, and managing QoS end to end….but then, I guess, we’d be right back where we started before telecom deregulation and the rise of alternative telephony options. It’s a bit of a conundrum. I know of a SIP trunking provider in Canada who has partnered with Bell Canada….thy provision SIP trunks over Bell Canada ADSL service which has been engineered in such a way as to provide a dry loop connection back to the NOC. They actively manage QoS on the DSL circuit, and it is put in and provisioned exclusively for voice, no data at all. They charge a flat rate for the ADSL circuit, which will accomodate 6-8 SIP trunks. So you pay a fixed amount of money, per month, for the circuit and the trunks and an affordable CPM for LD and international calls. I’d love to see more providers in the US figure out a way to partner with the network operators for mutual benefit. Bandwidth.com also does a great job with their SIP trunking and offer a solid SLA which minimizes risk due to lack of performance.

  • Frank

    Lucy:

    What kind of T-1 is this? Was it an internet T-1? If that’s the case, then why would you expect the ISP to apply QoS to the traffic, end-to-end? Was it a PtP T-1? If that’s the case, where did the far end go back to? Ideally it would go back to the SIP trunk provider.

  • Chris

    Before jumping in on the SIP you should check out your internet connection. Simplying Googling “internet connection test for SIP” will yield some results, and will test your line. My VoIP sip that uses internet is 10x better than my cell phone, and my router handles the QoS

  • Sylvain

    Mr Andrew, Can you let me know what such provider has partnered with Bell Canada? i’m much interested in having SIP trunk for all our retail location in Canada.

    Thanks!

  • Martin Ramjit

    Hi Cory,

    I work for TeraGo Networks and we are delivering SIP trunking over our FIXED WIRELESS BROADBAND services. We differentiate in many ways compared to our peers. For example we control the last mile 100% to offer a 99.9% availability and a 3 hours MTTR ( to repair not respond) We will fix the problem in three hours. Local DID’s in north america and globally.

    If you have inquiries on your boad please refer them to me and I can help out where I can. I have 3 bands for SIP that are pretty standard.
    5-10 SIP on a 3 yr plan $35.00
    11-25 SIP on a 3 yr plan $30.00
    26-50 SIP on a 3 yr plan $22.00
    Also burstable option at $3.00 per channel

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