SIP Trunking 101

February 20, 2017 Collaboration

There has been a lot of buzz recently around the idea of SIP trunking.  I thought it would be a good idea to review what SIP trunking is and how it could impact your business.  SIP (Session Initiation Protocol,) is a communications protocol that handles signaling and controlling communication sessions.  Ok, so what does that mean in practice? For a call, SIP takes care of the call setup.  Call setup involves negotiation of a call.  This handles things like ringing, and negotiating which codec (compression scheme) a call will use.  SIP works with other protocols to do this.  The codec negotiation is actually handled by SDP (Session Description Protocol,) which is sent in the SIP messaging.  Once the call is setup, RTP (Real-Time Transport Protocol) is used to carry the audio stream between endpoints.

You might wonder what the big deal is.  Traditional telephone circuits did similar things, and ISDN PRI circuits have been around for years.  They are stable and straight forward to setup.  The big advantage of SIP is the ability to use IP networks.  This removes the need for an entirely separate set of infrastructure for voice.  This is huge for the telecommunications carriers.  They can focus on optimized IP networks and do away with dedicated phone networks.  Part of the reason SIP comes with attractive pricing is the carriers can pass their savings along to you.

The next question is probably, “How do I get SIP?”  That varies by carrier, but the main element is some form of SIP trunking.  Typically, you have a data connection to the carrier although this can be done across the Internet.  SIP trunking is a logical connection between a piece of equipment at your site and a piece of equipment at the carrier site.  These devices communicate and establish calls.  In practice there can be a significant amount of complexity, but that is essentially the idea.  The devices in question can vary.  You might have a phone system capable of SIP signaling connected directly to the carrier, or you might have an intermediate device called a SBC (Session Border Controller) in place.  SBC’s can be especially important if you are using the Internet to connect for security.  You can also use a device like a voice gateway router to connect an old phone system that isn’t capable of SIP signaling to the carrier.  Your phone system connects to the voice gateway router using PRIs, and the voice gateway router connects to the carrier using SIP.  There are quite a few combinations here.  It’s important to work with someone you trust who fully understands the options to get the best outcome.

There are a couple of key elements to SIP trunking that are worth pointing out.  Using the Internet directly can have negative consequences.  There is no mechanism to provide quality of service across the internet.  This means your voice traffic can be affected by data traffic.  Someone watching videos could kill the quality of your phone calls.  There are also security risks.  When you expose your phone system to the Internet, malicious people will attempt to use it for their own purposes.  Toll fraud is a real concern.  The good news is most major carriers have an easy solution to this.  They provide dedicated data circuits to allow you to reach their equipment.  This removes the need to cross into the public Internet and removes many of the concerns associated with it.  The Internet can be used, but it’s very important to consider security and quality of service carefully.

The great news is SIP is cost effective and widely available.  In fact, carriers are phasing out their traditional voice networks in favor of combined IP networks for voice and data.  As long as you have a trusted advisor, navigating SIP Trunking setup is a straight forward.  This is the future path for voice access, and the time to migrate to SIP is now.


Curtis brings over 25 years of collaboration experience to ABS. As the Collaboration Team Manager, Curtis works to ensure that ABS is consistently providing the latest collaboration technology and support to ABS clients.