When setting up a communications system for your team, you’re bound to encounter two main connectivity options: Primary Rate Interface (PRI) and Session Initiation Protocol (SIP).
Think of PRI as the traditional, old-school method that relies on physical landlines to connect to the Public Switched Telephone Network (PSTN) circuit system. SIP, on the other hand, represents a newer, internet-based solution that uses Voice over Internet Protocol (VoIP) technology to connect calls over a virtual, cloud-based network.
While PRI still remains a viable option for business owners today, SIP is rapidly outpacing the copper wires of yesteryear. This is especially true in terms of cost efficiency and compatibility with other advanced phone solutions like video conferencing and call recording. As a result, we will soon witness a phenomenon that many are calling the copper sunset—the inevitable end of landline-based telephone systems.
In fact, a worldwide shift has already begun. For example, Norway abandoned its PSTN systems as early as January of 2023, and the United Kingdom is set to do the same by the end of 2025.
In the United States, the Bureau of Labor Statistics reports a 36 percent increase in the cost of landline connections over the past decade. Meanwhile, 66 percent of subscribers stopped their service. Furthermore, the FCC has clearly communicated its disinterest in protecting telecom users who prefer the traditional circuit-switched systems to the latest alternative options.
As for businesses that once invested heavily in a PSTN-reliant infrastructure, the copper sunset could pose a big problem. However, certain players in both the telecom and VoIP space have stepped up to the challenge of creating transitional services so that organizations can minimize the pains and costs of switching to modern technologies.
Background on PRI vs. SIP
A PRI system relies on a wired connection to the PSTN, which is established through a telecom provider. Since a single PRI line can only connect one caller to another, it’s common to have a bundle of lines (known as a PRI trunk) that can serve a small team of users by connecting up to 23 separate voice channels.
When one team member places a call on a PRI system, an electric signal sends that person’s voice across the copper wires along the circuit-switched network. The term ”circuit” refers to the dedicated physical connection between the caller and recipient. Meanwhile, up to 22 other team members can make or receive calls simultaneously on the same trunk line without service interruption.
Similar to the older PRI system, a SIP line connects only one incoming or outbound call within the larger SIP trunk or bundle of lines. Unlike PRI methods, however, a SIP trunk is powered by VoIP technology and can manage a much larger volume of lines via a simple modem setup.
As a result, rather than having 23 dedicated (and unchanging) lines available at all times, a SIP trunk establishes a connection only when a line is immediately in use. As part of what’s called a packet-switching system, each line transmits voice signals as digital data packets over the internet and may also be used to send other types of data, including text, video, images, and documents.
It’s worth noting that PRI systems can also manage voice or video calls, but the quality is often far below what SIP-based networks can provide.
Limits of PRI vs. SIP
Since a PRI system is reliant upon physical connectivity, it cannot perform beyond the limits of the PSTN network. While this older tech is still in use for a number of businesses today, most organizations are likely to feel restricted by the number of drawbacks that consistently outdate this model.
With PRI, your available number of voice channels is limited.
In North America, telecom providers largely rely on T1 PRI lines, each offering 24 channels—23 for voice signals and one that operates as a dedicated data channel. This means that only 23 team members can use the phone at the same time.
Therefore, if you need more lines, you’ll have to order more PRI trunk bundles from your provider and wait days for them to set it up. That’s often much costlier than VoIP options already. On the other hand, a SIP trunk can offer quote-unquote “unlimited” channels that can easily be amended at any time directly through the platform interface—and this is all determined by the VoIP vendor licensing and your available internet bandwidth.
With SIP, you only pay for the lines you actually use.
The old PRI system dictates payment for every trunk, every month—whether you use it or not. Thus, you’re effectively paying to hold any extra lines you aren’t using just in case you need them.
In comparison, a SIP trunk establishes each line as needed, with pricing models based on minutes of use rather than the number of lines, which creates a far more cost-effective model.
SIP is far easier to scale as your business grows.
When relying on PRI, any changes to your service must go through your phone provider. For instance, if you want to add or remove a trunk line, you’ll have to get in touch with a representative from your provider, schedule a date of service, and then wait for a technician to become available for onsite installation.
With SIP, however, such changes are managed in real time through a simple click of a button on your VoIP interface. This leaves you with a far more customizable and efficient system that can grow with you naturally.
When a PRI system goes out, your business is stranded.
Inclement weather and other issues can affect your PRI service, leaving you at the mercy of the phone company to get its service up and running again. Until then, you’re simply stuck and unavailable to your customers.
A SIP trunk is far less vulnerable to the effects of storms or aging infrastructure. It’s still true that the internet can go out from time to time, but many VoIP vendors will suggest solutions like splitting your network between two service providers or auto-routing calls to a predetermined destination in the event of an outage.
Migrating From PRI to SIP
As the United States approaches the copper sunset, various cities and state bodies are choosing not to continue investing in outdated infrastructure. At the same time, the costs associated with PSTN services are rising. These aspects, combined with the many benefits of SIP technology, make it the right time for many businesses to make the switch.
Fortunately, there are a few modern options designed to facilitate this migration process by reducing the stress and cost of replacing legacy phone systems.
A hosted Private Branch Exchange (PBX), for example, utilizes a combination of VoIP technology and PSTN networks, establishing a cloud-based phone system that works in sync with your current landline service. Another approach, pioneered by leading VoIP vendors and telecom providers alike, is to replace your Plain Old Telephone Service (POTS) system with a “POTS in a box” solution that connects your existing devices to the digital network.
With a fairly quick setup similar to that of an internet modem, these terminals can even remain compliant with landline-based fire, security, and emergency alarm systems that might otherwise be extremely cost-prohibitive to replace. They can also transmit legacy fax and analog data in addition to providing a network failover mode that offers extra support in the event that your service is interrupted.
Alternatively, many business owners choose a hosted VoIP service as opposed to a service run on their own centrally-located hardware system. In addition to substantially lowering telecom costs by as much as 85 percent in some cases, this remotely hosted option offers an infinitely scalable alternative. It’s also convenient, portable, and often comes with far better call quality and faster data transfer. Lastly, these VoIP services tend to blend seamlessly with modern tools that drastically expand your team capabilities—including video conferencing, predictive dialing, voicemail to text, and call recording.
As the United States moves away from the older infrastructure of copper wire communications systems, the choice between PRI and SIP technology may not exist much longer. If your business has long been established on the circuit-based network, now may be the time to explore newer “POTS in a box,” hosted PBX, and VoIP options. The long-term cost savings and ample benefits for a team of any size will make these solutions well worth it in the long run, particularly as the traditional alternatives disappear.