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PRI Circuit for Business: Options, Alternatives, and Cost

PRI Circuit for Business: Options, Alternatives, and Cost

Primary Rate Interface (PRI) circuits are a well-established technology for business phone systems. Investing in PRI can seem like a low-risk way to meet your company’s need for reliable, quality voice communications.

While PRI circuits are stable, they have some limitations compared to alternatives such as SIP Trunking for business. Before investing in PRI Lines, it's important to understand costs, how the technology works, and potential challenges.

As SIP trunking and VoIP in general have become the most prevalant way to deliver telephone, PRI circuits are the right choice only for some specialized use cases or if you are unable to abandon your legacy digital PBX. To determine whether your business is best served by PRI, SIP, or a hybrid mixture of cloud and traditional phone technology, read on.

PRI Circuits: Top 7 Customer FAQs Answered

In this post, we'll answer some of the most frequently asked questions regarding PRI circuits.

  1. What is a PRI circuit?
  2. How do PRI circuits work?
  3. How is a PRI circuit different than SIP trunking?
  4. How many phone numbers do PRI circuits support?
  5. How hard is it to scale PRI lines?
  6. How much does a PRI circuit cost?
  7. Is PRI circuit investment the right choice?

1. What is a PRI circuit?

PRI, short for Primary Rate Interface, is a telecommunications interface standard. It is used on an Integrated Services Digital Network (ISDN) and carries multiple DS0 voice and data transmissions between the network and a user. PRI circuits are physical technology for voice communications which provide a total of 24 channels. 23 of these channels operate as dedicated voice paths, and the remaining channel is reserved for signaling call data such as caller ID. For several decades, it was the standard for providing telecommunications services to enterprises and the business office. It is based on T- carrier (T1) transmission in the United States.

2. How do PRI circuits work?

PRI circuits link a company’s private branch exchange (PBX) to a telecommunications provider and the public-switched telephone network (PSTN). The circuit uses the PRI telecommunications standard to control the transmission of voice and data over copper cabling for voice communications in the form of electrical pulses. PRI circuits enable businesses to make and receive phone calls.

3. How is a PRI circuit different than SIP trunking?

PRIs do not rely on data connectivity for voice communications. Instead, voice communications are placed through Time Division Multiplexing (TDM), traditional telecommunications switches and physical cabling infrastructure. In contrast, SIP Trunking uses Internet Protocol (IP) to support voice calls and other forms of multimedia communications.

The fact that PRI circuits are not dependent on data connectivity provides some benefits. If an internet connection is lost, the phone system will not go down. Organizations with insufficient bandwidth or a lack of fiber access are generally still able to support quality voice communications. However, there are also significant tradeoffs when comparing PRI to SIP. Factors such as cost, flexibility, and the ability to scale the technology typically tip the scales in favor of SIP, particularly as the world and workforces rely more on digital tools that can scale up quickly and cost-effectively.

For example, more companies are allowing employees to work remotely. SIP opens up functionality for remote workers, such as integrations with Microsoft Teams and other multimedia communications platforms, as well as rich mobile features, mobile-first design, and simplified customer support.

Plus, SIP is sold on a per-channel basis on-demand, so you only pay for the capacity needed and without the need to add costly circuitry or purchasing work-only phones for remote employees.

For a more in-depth look at how PRI circuits and SIP trunking stack up, we recommend PRI vs. SIP Trunking: What’s the Difference and Which is Best?

4. How many phone numbers do PRI circuits support?

While a PRI circuit can support 23 concurrent voice calls, it can support more than 23 direct inward dialing (DID) numbers. A DID is the number someone outside the organization uses to dial in to reach a department or individual. One of Atlantech's DIDs is (301) 589-3060.

PRI circuits offer flexibility in how businesses allocate DID numbers according to PRI circuit. A company with relatively low call volume may still have 20 or even over a 100 DID numbers on a single PRI circuit. However, if a customer tries to reach a number when all 23 channels are busy, they'll get a service unavailable message.

Adding lines when relying on PRI can be challenging, and isn't necessarily straightforward. If call volume spikes, organizations may need to purchase an additional PRI circuit to ensure all numbers have sufficient coverage. And, the PBX will need to be able to support a second PRI. Typically, this results in a second line card in the PBX. 

Critical updates to a PRI circuit can be time-consuming, challenging, and require expert assistance. Get the full story in Can You Turn Up a PRI Today?

5. How hard is it to scale PRI lines?

In order to get more channels on your PRI, you'd need to add another circuit and also have equipment that can accommodate the additional circuits. Your PBX may only be able to support 1 or 2 PRI and if you need more, you'd need to add additional cards or modules to the PBX to support the additional circuit. It may also take another 30 days to have the physical PRI installed. With SIP trunking, you can merely assign more call appearances on your SIP trunk and as long as you have enough bandwidth to support the additional call appearance (using a G.711 codec, you only need 80 Kbps per call appearance), you're good to go.

6. How much does a PRI circuit cost?

A PRI circuit can cost around $500 each month, with some variation depending on region and other factors. Assuming a business is using the circuit for just 23 lines, that comes to an average of $21.74 per phone line, which can seem like a reasonably good deal.

However, there are some other costs associated with PRI circuit investment, which aren't necessarily reflected in monthly pricing.

  1. Many organizations need to purchase a T1 card to use a PRI with a legacy PBX system, which can cost between $500-1200.
  2. Circuit installs and upgrades to physical infrastructure can be incredibly costly and may require a 30-45 day waiting period.
  3. PRI circuits require physical servicing by expert technicians, which can cost $150 per “truck roll” or site visit.
  4. Adding a single line of capacity requires the purchase of a PRI circuit and an increase in monthly costs by $500 each month.
  5. Redundancy in case of disaster or equipment failure requires the purchase of additional PRI circuits for failover, which can add $500 each month for each failover PRI circuit purchased.

Taking all of these factors into consideration, the cost of a PRI circuit is definitely not $21.74 per phone line. With redundancy, it’s $42.48, and the average costs per line only increase with site visits, capacity upgrades, or unused channels.

In contrast, pricing for IP-based phone service starts at just $12-24 each month and offers far more transparency and flexibility in costs. Organizations can add and remove phone lines upon request. Pricing is based on lines used. Cloud-based phones can be serviced remotely and don't require expensive truck rolls. The best SIP trunking providers offer automatic mobile failover for redundancy at no extra cost. For most organizations, SIP is less costly than PRI circuits.

7. Is PRI circuit investment the right choice?

When PRI circuit technology was introduced, it represented an opportunity for businesses to cut costs on business communications. Instead of paying for phone service for each business line, there were use cases in which companies with shallow inbound call volume could assign many DIDs to a single PRI circuit.

There are still some strong use cases for PRI investment.

  1. Organizations that lack data connectivity to support IP-based phones may need to rely on PRI to avoid call quality issues such as jitter, latency, or packet loss.
  2. Companies that have recently invested in a new PBX system that only supports PRI, should use PRI circuits to protect the value of the purchase.
  3. Businesses may need a limited number of PRI lines in conjunction with SIP Trunking to hybrid systems.

With SIP Trunking and other cloud-based business phone options, PRI circuits are often not the most logical investment for many organizations. SIP Trunking migration is the better choice for many businesses for many reasons:

  • Integration with Microsoft Teams, CRM applications, and more.
  • Gaining desk phone-level features on mobile devices.
  • Combining call center, messaging, and conferencing functionality.
  • Built-in video telephony video business services.
  • Cost savings vary, but can be as much as 30-40% less expensive than PRI circuits.

In short, PRI circuits are a solid option if your business needs that style and level of established technology. For all other cases, SIP trunking is one of many alternatives that can save money and provide more flexibility on the path to achieving Unified Business Communications.


Understand Your Options

While PRI Lines are low-risk and well-established, they're certainly not the only way to support cost-effective, high-quality business phone communications. Understanding your options is essential to maximizing your investment.

How do you ask the right questions to select the right phone system and telecommunications provider for your business? For expert insight and to talk through any questions you may have about PRI circuits, book a meeting with our telecom professionals today.

Tom Collins
Post by Tom Collins
January 20, 2021
Tom is the Director of Enterprise Sales & Marketing for Atlantech Online. He has over 20 years of professional experience in the Internet Service Provider industry and is known for translating technology into positive results for business. A native of Washington, DC, a graduate from University of Maryland (degrees in Government & Politics and Secondary Education), Tom is also a five-time Ironman finisher.