PRI vs. SIP Trunking: Unveiling the Telephony Battle

7 min readApr 5, 2024

In today’s ever-changing business communications environment, businesses must decide about their phone system. Whether you go with the tried-and-true PRI (Primary Rate Interface) or the more flexible SIP (Session Initiation Protocol) trunking, it can significantly impact your company’s communication. This comparison will help you understand how PRI works, the differences, and if it’s right for your business.

What is PRI?

PRI is a telecom technology that lets you make and receive 23 simultaneous voice and data channels on one line. It was created to replace the traditional POTS network, which only allows you to make and receive analog calls through the PSTN. Using a T-carrier system lets you send digital data over the PSTN. The ISDN, or Integrated Services Digital Network, is a PRI version designed for businesses needing multiple lines. PRI also has Direct Inward Dialling (DID), which gives each user their unique extension, making it easier for customers to contact you immediately.

How Does PRI Work?

PRI connects two pairs of copper wire (PRI circuits) to a physical PBX phone system, which is then connected to a virtual PSTN. This creates a dedicated network that runs on duplex data. Each PRI circuit has 23 channels (called B-channels) and one more channel (called D-channels). The 24th D channel isn’t used for communication but supports signaling, control, and call functions like call hold and call ID. There are two kinds of PRI circuits — the E1 one for Europe and Australia and the T1 one for other countries. The main difference between the two networks is that the E1 network has eight more channels (31) than the T1’s 23. You can also add more PRI circuits to connect multiple PBX systems, access an extra 23 channels, or provide a failover during a network outage. PRI lines, or PRI Trunks, work with analog PBX phones and IP PBX systems but must always be connected to the network.

What is SIP?

SIP is a communication protocol that allows people to talk to each other over the Internet. It works by connecting two endpoints and then ending the connection. It’s not just for voice calls but also for video calls, faxes, instant messaging, and more. Plus, it’s not limited to wired, rugged phones — it can be used with any device with an internet connection. The reliability of the phone network depends on the provider, but they also offer failover plans and backup power supplies.

How Does SIP Work?

SIP makes it possible to send and receive business communications over the Internet instead of through the PSTN’s physical lines and circuits. Not only does it make cloud communication more accessible, but it also gives older phone systems and landlines the same features and scalability as VoIP. But how does it work? The SIP signaling protocol gathers data to make a virtual session happen. Most of it is in a user’s IP address. Still, it also includes user location, availability, and compatible codecs. These codecs (rules for how endpoints talk to each other) make it possible to transfer data and have two-way IP communications through packet switching.

What is the difference between PRI and SIP trunk?

The main difference is the infrastructure and technology behind it. PRI uses copper or fiber lines to send and receive signals. In contrast, SPP Trunking uses virtual connections made over the Internet.

Scalability: Each PRI trunk has 23 channels, so if you want to scale up, you’ll need to order more trunk lines, which can take 2–3 weeks to get up and running. With a SIP trunk, you can order as many as you need and get it up and running in several days or hours — making it a more versatile telephony solution.
Security: It’s common to think that a PRI trunk is more secure than a SIP trunk because the former can be exposed to security risks when using VoIP over public internet connections. But a SIP trunk can be as secure or better with good network security.
QoS (Quality of Service): Since a PRI trunk has a separate connection for voice, it usually has better QoS than a SIP trunk, which often has to compete with other data sources for bandwidth.
Costs: The cost is one of the most critical factors regarding SIP and PRI. SIP is usually cheaper because it uses shared internet connections. On the other hand, PRI might cost more to set up and maintain because it has its dedicated infrastructure.
Reliability: Regarding telephony, reliability is one of the most important things to consider. PRI is usually seen as more reliable because it runs on a dedicated, closed system, so you don’t have to worry about missing calls. SIP, on the other hand, depends on how good your internet connection is. So, when it comes to choosing between the two, it’s essential to understand their differences to make the best decision for your business. In the following sections, we’ll go into more detail to better understand what PRI is and what SIP is so you can pick the right one for your unique communication needs.

Benefits of PRI

Good call quality and stability: Since the call is made over a wired connection, the quality of the ring stays mostly the same. Unless something disrupts the physical networks that make up the call (which isn’t likely), you’ll get a consistent, high-quality audio signal and a reliable connection.
Traceable calls: PRI trunk calls can be tracked quickly. This is great for emergency calls because it’s easy to send a call to the closest dispatch center and figure out where to send help.
Secure calling: It’s more complicated. You can only pick up a call from a PRI trunk if the call is sent to an internet connection. If you wanted to listen to a call, you’d need to plug into the copper wire on the trunk. There’s little chance of a call being picked up.

Drawbacks of PRI

Difficult to scale: If you want to make more than 23 calls in one go or 100 phone numbers in one go, you’ll need to add another trunk to your PRI system, which means you’ll need to run another set of cables. You’ll need to add 23 connections or 100 phone numbers at once, and it’ll take a lot of work to install each new cable pack.
Not super flexible: Yes, you can change the phone numbers on your PRI trunk. But it’s a bit more complicated than that because you need to manage the physical connections. You’ll need to be patient if you must change phone numbers frequently.
Limited voice channels: As we said, a PRI trunk can only handle 23 calls at once. If you only have 100 phone numbers, you might need to add extra trunks to cover your call volume. This is especially true if you’re running a call center or other business that must simultaneously make many calls.
Can be expensive: Unfortunately, running new cables can be costly. That’s why upgrading a phone system built on a PRI trunk can cost a lot of money. The good news is that most of these costs are just one-time costs for building the physical infrastructure for the PRI trunk.

In the end, PRI provides good call quality and protection, but it’s best for businesses with a fixed phone system and only make a few calls at a time. PRI could be better at flexibility or scalability, so if that’s what you’re looking for, then SIP trunking might be the way to go. It’s much simpler to switch up virtual connections.

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