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SIP Trunking Versus PRI

SIP trunking and PRI trunking are two popular ways to connect your business to the public switched telephone network (PSTN).

In the business communications world, a “trunk” refers to a dedicated line. Using PRI and SIP trunking, businesses can exchange voice and data communications with the outside world.

PRI is an older technology (it has been used since the 1980s) while SIP is a newer technology that relies on sending communications over the internet.

Despite the fact that SIP trunking is more modern, both platforms have their own unique pros and cons. Today, we’re comparing SIP trunking versus PRI to find out what’s the right choice for your business.

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PRI, or Primary Rate Interface, is a voice technology that first became widely popular in the 1980s. Using PRI, businesses can deliver multiple lines of voice and data via one physical line through the exiting PBX.

PRI is an interface standard used on an Integrated Services Digital Network, or ISDN. It’s a high-capacity platform that carries voice and data on T1 trunk lines. Those trunk lines carry voice and data from a telecommunications center to your company’s location.

Most businesses have their ISDN PRI circuits in the form of T1 or fractional T1 lines. A T1 line carries voice and data using 24 digital channels.

As an older hardware solution, PRI has some drawbacks. It requires the installation of physical hardware, for example. That physical hardware must also be serviced by a telecommunications company and may require regular upgrading and troubleshooting.


SIP trunking is a newer telephony networking protocol that has more in common with other network protocols like HTTP and SMTP than it does with PRI. While SIP is a network technology, PRI is a telephone technology.

SIP trunks are virtual and do not require the installation of physical hardware. A business can use SIP for voice communications without needing to install an existing PBX. Many SIP providers offer hosted PBX solutions that deliver SIP trunking. So your PBX system functions exactly like a traditional PBX, but it’s all virtual.

Just like with PRI, SIP can deliver multiple lines of voice and data to an organization without the need to install multiple physical lines.

Pros and Cons of PRI and SIP Trunking

Call Quality

One of the biggest points of comparison between PRI and SIP comes down to call quality.

SIP traffic is prone to quality problems because it can be affected by network interference. Interference can lead to packet loss, jitters, and other quality problems.

PRI, on the other hand, is not a network technology, so quality is rarely an issue. Companies that require that absolute highest level of call quality at all times will often choose PRI for this reason.


PRI is also perceived to be more secure than SIP. The difference once again comes down to the use of the internet instead of traditional phone lines: PRI traffic travels through private telephone networks, which are easy to secure and monitor.

SIP traffic, on the other hand, is exposed to the internet. Just like anything on the internet, it’s susceptible to attack. If you’re going the SIP route, then security experts will recommend that you use a heavy-duty firewall to stay protected.


PRI may beat SIP in call quality and security, but SIP is the easy winner in flexibility and scalability.

If you want to change or scale your business with PRI, then you need to adjust your physical hardware. With a SIP trunk system, you can easily add more SIP trunks virtually simply by contacting your SIP provider. There’s no need for new hardware (although your SIP trunk provider will typically charge an extra few dollars per month for each extra line).

If you want to add or remove lines with PRI systems, you’ll need your PRI provider to visit your company’s location and physically install or remove another PRI circuit.


Typically, SIP trunking is the more affordable solution because it doesn’t require on-site hardware installations and ongoing maintenance. Service is delivered over the internet, allowing both the company and your telecommunications provider to minimize overhead costs.

However, it’s important to consider usage rates when weighing SIP trunking versus PRI. Some SIP and PRI trunk providers charge on a per-usage basis, while others charge a flat rate. if you have a large company or have large usage needs, then the per-usage costs could quickly inflate your bill.


One final con for SIP trunking is that your phone lines go down when your internet goes down.

Fortunately, SIP trunking providers are well aware of this limitation. And that’s why many provide redundancy using LTE or WiMAX coverage. If internet outages are frequent at your location, then make sure you work with a SIP trunking provider that has some sort of redundancy or backup system in place.

Hybrid SIP and PRI Trunking Providers

The distinction between SIP and PRI trunking providers has become increasingly blurry over the years. Today, there are many hybrid providers that offer both types of services bundled into one.

This is the best solution for some businesses. Some businesses find it advantageous, for example, to use PRI for local calling and then use a SIP trunk from a hosted VoIP service for international calls. This way, they enjoy the cheap local calling rates (typically, it’s unlimited) with PRI and then can take advantage of the affordable international per-minute rates delivered through SIP (international calling is always cheaper over the internet than through traditional phone lines).

There are also cases where companies have already invested in PBX hardware at their office and don’t want to throw that investment away. In these cases, the business may implement a VoIP gateway on the legacy PBX system to make a sort of hybrid system.

Which One is Right for You?

SIP trunks are increasingly replacing PRI systems. SIP is the newer, internet-based technology that can save a lot of money for many businesses. However, it’s not a surefire solution for all businesses – especially larger businesses that can afford to invest in physical PRI hardware.

To decide whether or not SIP trunking or PRI is right for you, here are some questions to ask:

How important is call quality to your business? If you can’t survive a little bit of interference or call quality problems, then PRI is a superior choice because data is transmitted over phone lines instead of the internet, where it could be subject to interference.

How many people are using your phone lines during your company’s busiest hours? If too many people are using your company’s phone lines with SIP, then you may run into bandwidth problems over your existing internet connection. Make sure your internet can handle a higher load. If it can’t, or if you have too many employees to reasonably transmit voice data over the internet, then PRI may be the better option.

Do you plan on growing or shrinking in the future? PRI systems aren’t as easily scalable as SIP trunking systems. With SIP trunking, adding or removing a line is as easy as logging onto your SIP trunking provider’s online portal. With PRI trunking, your PRI provider needs to install physical hardware.

Do you have an in-house IT department? Your in-house IT department may be able to support and maintain PRI trunks, in which case you can avoid one of the major drawbacks of PRI trunking systems.

Ultimately, both SIP trunking and PRI trunking have their own unique advantages. For small and medium-sized businesses, SIP trunking is often the better solution. But PRI trunking is still worth consideration in this day and age – especially if call quality is paramount.

Editor’s Note: Looking for information on VoIP Phone Systems? Use the questionnaire below and our vendor partners will contact you to provide you with the information you need:

About Johnson Hur

After having graduated with a degree in Finance and working for a Fortune 500 company for several years, Johnson decided to follow his passion by embarking on a path to the digital world. He has over 8 years of experience with large companies setting marketing strategy.

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