PRI Vs SIP Trunking, which one is better for your company?

This article is meant to provide a very basic black and white overview of the differences between PRI Circuits and SIP Trunking.  This is by no means a thorough explanation, as there are many gray areas around both.  For example, SIP can also be used to transmit video (not just voice communication).  As such, if there is anything you’re unclear about, please email us – and we will personally answer your question!

Basic Overview of PRI VS SIP Trunking

What is PRI and SIP Trunking?

PRI and SIP Trunking are two different ways of connecting your business to the PSTN (Public Switched Telephone Network). Typically both methods, PRI and SIP Trunking, require a piece of an equipment in your office called a PBX (Private Branch Exchange). Most PBX and IP PBXs can support both PRI and SIP Trunking connections, either directly or with an adapter.

Did You Know?

The PSTN is a complex network of carriers that forms the “Telephone Cloud” that we are all familiar with.  It is the infrastructure that allows anyone to call anyone else in the entire world, whether they’re using a cell phone, land line, or VoIP.

PRI vs SIP Trunking – Main Differences

What are the Major Differences?


  • PRI (Primary Rate Interface) is a physical connection to the PSTN over a dedicated line that only serves voice transmission.
  • PRI uses a circuit switched model for making voice connections between people
  • PRI has a guaranteed Quality of Service (QoS)

SIP Trunking

  • SIP (Session Initiating Protocol) Trunking is a virtual connection to the PSTN over a physical line that is often shared over your existing data connection.
  • SIP Trunking uses a packet switched model for making voice connections between people
  • SIP Trunking is typically Best Effort

Let’s Talk – PRI

A PRI is a single line (typically a T1 connection in North America) with 23 voice channels (and a single data/control channel), that allows your business to hold 23 calls simultaneously.  This is not always equivalent to the number of phone numbers a business has.  Your business may have 100 phone numbers that are directed to come across a single PRI, however, you will only be allowed to hold 23 phone conversations at once.

pri vs sip

Get A Free PRI Circuit Quote

Let’s Talk – SIP

In short, SIP Trunking is a method of sending your voice connection over an existing data line, and therefore is commonly referred to as VoIP (Voice over Internet Protocol).


SIP Trunking is nothing more than the virtual connection between your PBX and your carriers SIP Network, over the already existing Physical Data Line.

Your call goes out over the SIP Trunk, is treated exactly like every other piece of data on that connection and is not given priority over webpages, emails, or instant messages.

pri vs sip

Once it arrives at your carriers network over the SIP Trunk, your provider’s equipment knows where to direct that call; this may either switch it over to the PSTN (so that someone with a regular phone can receive the call) or perhaps send it to a PBX at another location. A single SIP Trunk is typically limited only by the amount of bandwidth on your data connection, or in some cases, limited by the number of “call paths” you are purchasing from your SIP Trunk provider.


Expanding Your Connection

We Need To Make More Calls!

Need To Grow with PRI?

If your business requires the ability to hold more than 23 simultaneous calls, the only option for upgrading through PRI is to purchase an additional PRI line that gives you an additional 23 simultaneous calls.

Need To Grow with SIP?

This is typically as easy as calling your provider and purchasing more SIP Trunk virtual connections, or even just increasing your data connection’s bandwidth.  (Dependent again on how your carrier is selling the SIP Trunk to you).

Quality of Service (QoS)

Hello? Can You Hear Me?

Since the PSTN’s main purpose is to handle voice connections, there is always a guaranteed bandwidth capacity and availability for phone calls. Voice calls through the PSTN will always take priority over any other type of potential traffic. Likewise, PRI Circuits always have a guaranteed amount of bandwidth set aside for each call that can never be used for anything else. Therefore, your service provider can offer a very high level Quality of Service when providing a PRI connection for you. SIP Trunking, however, cannot always guarantee this QoS. Since each voice connection is sent as a packet like any other piece of data, it is subject to lag, delay, high pings, or packet loss. These are not usually issues for websites or emails, since the server will continue sending the same packet repeatedly until your computer receives it. However, with the real time transmission of Voice, these packets can typically only be sent once. If the packet doesn’t make it, it may sound a lot like when someone is on their cell phone with poor coverage. Currently the only way to provide a QoS for a SIP Trunk is to purchase an MPLS (What is MPLS?) and the circuit from the same provider offering the SIP Trunk. This is typically a much more expensive option. Since you’re using the same carrier for all of the services, they can prioritize the voice packets for you.

PRI vs SIP Trunking Choices

Which Should We Choose?

You can pay and track your bills online.

PRI Only

  • Guaranteed call quality is a top priority for your business

PRI and SIP Trunking

  • Your business loses money every second that your phones are offline.  You can have your phone calls primarily transmitted over a SIP Trunk, and if that data line goes down, the calls can be rerouted by the carrier over your PRI Line.

SIP Trunking

  • You are looking for a low cost solution, and have some flexibility on potential call quality issues

The only real answer to this is: It Depends. Before you purchase a PRI connection or a SIP Trunk, you should carefully outline your business needs.  While VoIP with SIP Trunking seems like the best new technology to have, it may not be right for you.