PRI vs SIP: Which Is Right for Your Business?

September 3, 2018 11 min read

Cameron Johnson

Cameron Johnson

As technology sprints ever forward, many businesses are examining the effectiveness of their phone systems. What’s the impact on the customer experience? What are the costs?
While some look to upgrade their old analog systems, others are looking to upgrade from a PRI system to something better, like SIP. Some businesses even choose to utilize a hybrid of the two.
But how do PRI and SIP trunk providers work? What’s the difference? And which is better?

Let’s tackle these questions and more as you decide which is the best solution for your business.

Table of Contents


Before we dive into the comparison of SIP vs PRI, let’s be sure we’re clear on what each of these acronyms really mean. Each system is distinct and works with different technology backing it.
Session Initiated Protocol = SIP
SIP is the method of sending voice communications via a data network (internet). These communications can include voice calls, instant messages, video chats, or data transfers.
SIP is considered network technology, as opposed to telephone technology, since its action is happening over a data network instead of a telephone line. These communications don’t necessarily require a telephone at all – any internet-ready device could have the ability to process SIP communications.
Each communication channel in SIP is called a trunk, hence the phrase ‘SIP trunking’. SIP trunking can deliver near-limitless channels to a business.
how SIP trunks work as opposed to PRI
Primary Rate Interface = PRI
A PRI is a digital, end-to-end connections that allows for multiple, simultaneous voice, data, or video transmissions. This is achieved through a physical line or circuit.
The physical circuit, a cable containing two pairs of copper wires, provides 23 channels for data and or voice. This means up to 23 concurrent conversations (or chats, videos, etc.) can occur. More than 23 transmissions would require an additional PRI circuit. These circuits require physical, on-site installation.
PRI technology has been around for several decades, making it substantially older than SIP trunking.

Functionality of SIP and PRI

At this point we’ve covered the basic definitions; now let’s take a bit more practical look at how each system works.
If you’re on a SIP system, here’s how a phone call works:

  1. You pick up the phone and dial a number or extension.
  2. The call is transmitted through your internet connection to the service provider (carrier).
  3. The carrier, also using an internet connection, then sends the call on to the person you dialed.

Calling on a PRI system looks more like this:

  1. You pick up the phone and dial a number.
  2. The call is transmitted through hardwire (a T1) to your service provider.
  3. The provider then transmits the call to the person you dialed.

Main differences Between PRI and SIP

So what makes PRI and SIP so different? After all, they’re both just phone systems, right?
Yes, they’re both phone systems. Both allow you to make a voice call to another person, but the technology is quite different. Take a look at some of the key factors that distinguish SIP from PRI.



ConnectionPhysical connection through PRI circuitVirtual connection through network
TransmissionCalls are transmitted through physical circuitsCalls are transmitted via data packets on the virtual network
ScalabilityLimited by the number of wired phone linesLimited only by bandwidth

Comparison: PRI vs SIP

Here we’ll put PRI and SIP head to head, comparing features, flexibility, and service.


When it comes to the hardware associated with each of these systems, there are a few things to keep in mind. First, cost – Hardware costs money. Second, maintenance – Hardware requires upkeep. And finally, space – Hardware is a physical thing that takes up room in your business.
Here you have two options: hosted or on-premise. Hosted solutions cost very little upfront and require minimal hardware and maintenance. In fact, the only hardware you need is a phone. Your provider and the data centers they use will handle everything else. For these reasons we highly recommend hosted VoIP.
On-premise solutions, on the other hand, require physical servers to be stored on-site. All connections, however, are virtual. Beyond installation of the SIP server, there will be no additional installation required for cables, wires, or other equipment.
on-premise SIP technology
PRI’s require physical connections. These are actual cables installed on your site. Since each connection can only handle 23 channels, the number of circuits installed will depend on your business’s needs.
Since this is a physical install, the hardware alone can be costly. And if additional lines are ever needed then installation costs will be incurred again. This is one of the major limitations of PRI systems.

Backup and redundancy

Lots of things can cause a disruption in your phone service. It could be because of bad weather, a power outage, internet issues, or even a stomach bug that knocks out your call center staff. Your phone system needs to be able to handle this and handle it well.
SIP trunks can be rerouted easily and with little impact. In the event of an emergency, calls can be routed to predetermined destinations, like a third-party answering service. Business can carry on as usual until your problems are solved and calls can be rerouted to your office.
Additional PRI circuits can be added to help with redundancy. But if your PRI system goes down completely? Not a great situation. Calls on a PRI cannot be rerouted.


You might’ve been wondering about this, especially if you’re a numbers person. Like with anything else, VoIP phone system costs will vary depending on your business’s specific needs. Here’s some general information about costs.
You don’t need a ton of extra equipment with SIP, so you’re looking at cost savings with setup and maintenance (especially if you go the hosted route). Ongoing costs will be limited to the monthly access for the service, usually charged per channel or per minute.
For a more in-depth comparison of hosted vs on-premise costs read What is PBX or check out the price comparison chart below:

on-site PBX can cost more than hosted VoIP or PRI over a 2 year period

By nature of its technology, PRI circuits are physical hardware. In addition to the cost of the hardware itself, you’re looking at installation and upkeep fees. These charges will be on top of monthly service access fees.
When you need more channels, you’ll pay for installation of one or more PRI circuits.

Flexibility and upscaling

If you plan on growing your business at any point, it will be important that your phone system can grow too. Gradually adding users, rapidly upscaling, as well as expanding to multiple locations are all considerations. It’s important to think long term here. No one wants to change phone systems every few years, so forecasting your future growth can help you make the right decision.
Need to add more users to your SIP system? Simply contact your service provider and make a request for more lines. It’s that simple. Scaling can be quick and easy with a SIP system, especially if you’re provider is super responsive.
You’ll recall PRI circuits provide 23 communication channels. If you need to add just a couple of users, you’ll still be required to purchase an additional circuit of 23 channels. The addition will then require someone to physically to visit your office to install the new circuit(s.)

Quality of service

SIP transmissions are in HD, so the quality has the potential to be excellent. Network bandwidth plays a major role, however. Poor bandwidth can result in less-than-stellar call quality.
Generally, with strong bandwidth, SIP calls are clear, HD quality.
Don’t believe us? Just hear what the Children’s Museum of Phoenix had to say about their switch to Nextiva’s commercial phone service:

PRI transmissions are not in HD. While calls are generally stable, the quality is notably less than what we’re used to with network communications. PRI calls often sound similar to an old school, analog call since they’re both transmitted with a low range of frequency.

Best use cases

So which solution is best for you? For 99% of businesses we recommend SIP, but it really depends on your business and your goals. Check out how each solution can address different needs.

PRI solution works best for

  • Organizations with little or no access to a reliable fiber-optic network
  • Organizations without sufficient bandwidth to support IP phones and equipment

SIP solution works best for

  • Businesses looking to save money on phone service
  • Businesses who make a lot of long-distance or international calls
  • Organizations with one or more call center teams
  • Businesses that are looking for mobile support
  • Businesses with remote workers (or businesses who want to have remote workers)
  • Organizations who aim to reduce workload for onsite IT staff
  • Businesses who aim to reduce day-to-day phone system management
  • Organizations interested in multi-channel communications
  • Organizations interested in a cloud communications platform or UCaaS (unified communications as a service)
  • Businesses that require the ability to scale up (or back) quickly and efficiently

Factors to consider

Before you make your final decision in the PRI vs SIP race, there are a few more things to consider.

How many simultaneous phone calls do you expect to receive?

Think about the number of people in your office. Now think about your call traffic on a normal day. How many people are usually on the phone at the same time – how many people could possibly be on the phone at the same time? This is especially important if you have a call center or sales team who are likely to be on the phone a lot.
For SIP trunking, more simultaneous phone calls mean more bandwidth. To determine if your current bandwidth is enough, run a VoIP speed test.
In the case of PRI circuits, everything is done in groups of 23. Any number of simultaneous calls, from 2 through 23, can be handled on one circuit. More than 23, you’re looking at adding another circuit. More than 46, another circuit. And so on…

How important is your call quality?

Is call quality a mission-critical element in your business? If so, you’ll need a solution that can provide 100% quality of service.
First, let’s clarify what we mean by ‘mission-critical’. Mission-critical means the quality of the audio during a call is essential to the nature of the call. Generally, ‘mission-critical’ audio quality means both parties can clearly hear and understand each other without repetition. Industries like hospitals, emergency responders, even airline communications would consider their call quality to be mission-critical.
type of business that needs SIP vs PRI
If call quality is mission critical in your line of business, the phone solution you choose should provide you with near 100% clarity. While every business can benefit from HD call quality, these businesses absolutely need it.

Is scaling important?

If the need to scale your business is most important to you, SIP is the hands down winner.
Scaling a PRI system is cumbersome, requires physical installation of equipment, and can be costly. Not to mention you’re roped into scaling 23 channels at a time. That’s fine if you’re growing at that rate. But if you’re growing at a slower pace, you’ll be forced to buy channels you don’t need.
On the other hand, SIP is highly scalable. You can easily add one trunk or many simply by contacting your service provider and making the request.

Is your existing system compatible?

Ask your current phone provider if your existing system is compatible with VoIP gateways. If not, it’s probably pretty old. In that case, it may be in your best interest to get rid of the system and start from scratch with a SIP-enabled solution. After all, it is the more current technology.
If your system is modern enough to be upgraded to work with PRI circuits and you’re willing to make the investment, you could always choose PRI. Just remember that you’re investing in outdated technology.

Do you have in-house IT support?

A hosted SIP trunking system requires little involvement from an on-site IT staff. Nearly everything is handled by the service provider (host). This would be an ideal choice for a small company with little to no on-site IT support or a medium-sized company with a small IT team.
A PRI system, on the other hand, requires dedicated time from on-site staff. Your IT team will be responsible for maintaining, upgrading, and troubleshooting the system. They’ll also work directly with the carrier on any deployments. PRI really only works well when there’s one or more IT folks dedicated to its upkeep.

Verdict: Which is the better choice?

Both PRI and SIP trunking will help you achieve your goal of making and receiving business calls. There are, however, distinct advantages and disadvantages to each. And one solution’s advantages far outweigh the other’s – SIP trunking.

SIP Trunking

sip trunking diagram

For many businesses, SIP trunking will be seen as the clear choice. It’s the more current technology and is highly scalable. Its costs are generally much lower than a PRI in deployment, ongoing maintenance, and scaling.

Hybrid PRI – SIP trunking

Sometimes a hybrid solution may be preferable. This may be the case if an organization has an existing PRI system and wishes to do a partial upgrade. Or, maybe the company is not ready to make the full leap to cloud technology.
In this situation, an organization can use a PRI system for local and toll calling while also using SIP trunking for long distance and international calling. The same advantages and disadvantages of each solution apply, but they can be somewhat offset.

Risks with SIP

SIP trunking is not a new technology, so the risks are minimal. SIP best practices are modeled after networking best practices, so they’re tried and true.
The only risk you really have to consider is which provider you go with. You want a provider that has:

  1. Exceptional customer support (since the provider is essentially an extension of your IT department)
  2. A proven track record in the industry
  3. Virtually zero downtime

Choosing a provider

In the sea of telecommunications providers, there’s one that stands apart – Nextiva.
Along with industry-leading hosted VoIP solutions, Nextiva offers SIP trunking that works alongside your existing PBX system. You’ll be in the cloud in no time.
Your current system – even if it’s old-school – can be transformed into an IP-based communications powerhouse. Use your own existing equipment and get started with no upfront investment.
Power outage? Company-wide meeting? No problem. Nextiva’s SIP trunking technology can route your calls to another location.
Worried about a disaster? Don’t. Make use of Nextiva’s seamless call routing, load sharing, and failover procedures.
To recap:

Why is SIP trunking better than PRI?

Primary Rate Interface (PRI) is a legacy technology that requires physical wiring from the local telephone company. It supports up to 23 concurrent calls per circuit.
SIP trunks offer greater flexibility than PRI by connecting calls over the internet using an internet connection. It handles as many concurrent calls as your PBX and bandwidth supports.
IT experts enjoy SIP trunk services because they maintain full control of their PBX and pair it with the scalability of the cloud. No on-site installation or troubleshooting obsolete hardware, either.
The bottom line is using a SIP trunking provider is the best alternative to traditional phone lines. Nextiva’s reliable VoIP network connected more than 1 billion calls last year alone.
Related: What Is Session Initiation Protocol (SIP) & How Does It Work?

Cameron Johnson


Cameron Johnson

Cameron Johnson is a market segment leader at Nextiva. Along with his well-researched contributions to the Nextiva Blog, Cameron has written for a variety of publications including Inc. and Cameron was recently recognized as Utah's Marketer of the Year.

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