SIP Trunking vs. PRI: What should you to?

PRI and SIP are both ways to connect your organization to the Public Switched Telephone Network. Which one should you use?
PRI vs. SIP: Two women talking around a table

What is PRI?

PRI stands for Primary Rate Interface, and is the older of the two technologies. PRI uses a physical, wired connection to transmit calls, messages, and data. It gained popularity among businesses as a higher capacity form of TDM, or time-division multiplexing, connection.

If you ever got online in the 90s, you probably recall dial-up internet and the trauma of getting booted offline when someone picked up the telephone. PRI technology was an advancement in this plain old telecom (POTS) technology and allowed businesses to support up to 23 concurrent communication channels. PRI systems rely on physical circuits to route voice and data calls through your service provider (i.e. your telephone line).

What is SIP Trunking?

SIP stands for Session Initiated Protocol, and is a wireless technology that uses the internet rather than a physical connection. SIP Trunking, then, refers to virtual phone lines you can use to make phone calls over the internet.

SIP is often referenced in conjunction with VoIP (voice over internet protocol). You’ll often hear the two terms SIP and VoIP used interchangeably.

While there are nuances that separate SIP from VoIP, they are very similar concepts for our context here. Just think about SIP as the technology that enables VoIP. A SIP connection, or SIP trunk, exists virtually. Transmissions are made and received using devices and platforms that connect to the internet like VoIP phones and softphones running through UC platforms, such as Microsoft Teams.

The benefits of SIP trunking

Both SIP and PRI systems can provide solid call quality, but we’ve begun to see a trend with businesses ditching their POTS lines for SIP-based telecom.

Why is that? There are a variety of reasons, but the primary benefits of SIP trunking are availability, scalability and cost, and access to the benefits of current and future technologies.

1. Availability & reliability

Both SIP and PRI systems can be vulnerable to disruptions due to inclement weather, power outages, or service interruptions with the carrier or provider. A down phone system means lost revenue, and severed connections with your customers so it is important to consider resiliency when evaluating PRI vs. SIP.

There is a school of thought that PRI lines tend to be more reliable because they will continue to work in the event of a power outage, and aren’t reliant upon the internet as yet another factor in connectivity. It is true that analog phone systems, transmitting signals through copper wire connectivity, will continue to stay connected to the PSTN when the power goes out or during an internet service provider outage; whereas digital VoIP phone systems, which are SIP-based, rely on power and internet connectivity to transmit a signal.

With SIP, however, connectivity problems can typically be diagnosed and repaired remotely. And in the meantime, you’ve got a digital address for that call destination vs a physical one, so you’re able to reroute those SIP calls to a failover destination of your choosing. That way you have a contingency plan, and you don’t have to worry about your dream client slipping through your fingers during an outage. Like many other aspects of business operations, the key to getting the most out of your SIP phone system is selecting a provider with excellent, highly responsive customer service.

Because PRI is a wired connection to a circuit, any maintenance and repairs will have to be completed in person by a technician or an in-house IT team. Purchasing additional PRI circuits will provide you with backup lines that can come in handy in case of an emergency, but unfortunately, a total outage in a particular location would leave business communications down until the factors outside of your control were resolved.

Enterprise Communications Landscape 2024

Hear how 1,000 IT leaders are using SIP trunking at their organizations.

2. Security

PRI is often considered the more secure option as it is a physically wired connection that is not as vulnerable to internet hacking as SIP is. This view does not tell the full story, however. For instance, a standard copper line can be intercepted via wiretapping and is susceptible to interference.

A SIP-based system relies on network security in the form of firewalls, firmware, authentication practices, and traffic monitoring to protect information. In short, SIP is as secure as your network makes it. So while PRI may seem like the more secure option at first blush, the reality is somewhat more nuanced and likely depends on the individual use case.

3. Scalability & cost savings

Two of the key differences between PRI vs SIP connectivity is the ability to scale and expand or throttle capacity as needed to meet demand (i.e. how many calls can be handled simultaneously). PRI systems can support 23 channels per physical circuit, so if businesses need additional capacity, then that means they’ll need to install and maintain additional circuits and hardware to support.

SIP, on the other hand, represents a digital call path and therefore is easier to scale up and down with seasonal demand. With PRI systems, enterprises run the risk of incurring costs for their highest demand on concurrency year-round, whereas with SIP, enterprises can pay for what they use and need. In addition to the appeal of the more flexible and scalable SIP cost structure and billing model, all the new industry-leading Unified Communications and Contact Center platforms are being built in the cloud and reflect the trend towards SIP-based telephony systems.

4. New technologies

Enterprises that have yet to fully transition from PRI to SIP for a cloud-ready telecom stack are reaching an inflection point of old and new technologies, especially as they look to gain control over their corporate communications by moving to a UCaaS, CCaaS, and Meeting Solutions platform like Microsoft Teams, Genesys Cloud, Zoom, etc. To put it simply, old school just doesn’t work with these new school platforms.

PRI vs SIP: What’s the difference?

Now that we’ve discovered what PRI & SIP are, let’s explore how they stack up.

What does it stand for?Primary Rate InterfaceSession Initiated Protocol
How does it connect?Connection is made through copper wires to a physical PRI circuit.Connection is virtual and can be hosted with an off-site provider or managed in-house.
What kind of hardware is needed?A PRI circuit is installed at your place of business, and calls are made via landline or plain old telecom (POTS) phones.It depends. No hardware (other than the calling device) is needed for a fully hosted SIP solution. On-premise SIP systems would require more infrastructure.
Is it scalable?Yes, but more manually so. PRI is a form of TDM and can support up to 23 wired phone lines. Additional lines require additional physical circuits to be installed.Yes, and quickly. The number of available communication channels (SIP trunks) can be adjusted virtually, and is really only limited by access to bandwidth and need.

Start switching from PRI to SIP

For all the reasons listed above and more, SIP is generally accepted as the new industry standard. As your enterprise continues to navigate and undergo digital transformation, you’ll most likely encounter an inflection point for your telecom infrastructure. You’ll be presented with the opportunity to migrate your telecom to the cloud.

However, as we all know by now, migrations can be a REAL pain in the… you know what… So while you fully understand and buy into the business case for migrating and consolidating your telecom to SIP, the path to get there may be daunting or unclear depending on your current situation.

Good news, we’ve got experience here, and in Part 2 we’ll share some of our best practices for your SIP migration and cloud-bound future. Can’t wait?

Reach out to our experts