You might want to know What is PRI, or Primary Rate Interface. It is best defined as a standard for telecommunications interface. It is primarily used for ISDN (Integrated Services Digital Network) to carry different DS0 data and voice transmissions across the network.

As a system that has been in use for over thirty years, PRI is mostly used by Enterprises to transmit voice and fax using a basic copper-wire connection. Here, we seek to explore the importance and applicability of PRI in today’s network environments.

What is PRI Line?

A PRI line is an end-to-end digital circuit that is typically supplied by a local exchange carrier (LEC). This circuit comprises 2 copper line pairs that connect the customer location to a time division multiplexer located in the LEC’s central office.

PRI has three main characteristics. Number one, it is based on T1 (or E1 in Europe and around the world) lines that come equipped with 24 and 32 channels, respectively. Secondly, it comprises 23 bearer channels. Lastly, it uses an out-of-band data signaling channel.

A PRI line carries multiple channels in a single circuit by applying the multiplexing and demultiplexing methodologies. As mentioned above, a PRI line comes in 2 forms (T1 or E1) with each channel in both these lines capable of providing 64 Kbps per second of data transmission.

Along with an Analog or Mixed EPABX system, a PRI line can also connect IP PBX systems although, it does require a PRI Interface for terminating the PRI circuit on the PBX.

Application of PRI in Telecom

PRI line technology was developed to cater to the requirements of industrial enterprise clients. As a result, they are designed to deliver services in high-capacity.

In addition, these can be deployed using regular T1 lines that connect your office locations to a central office nearby. Most importantly, a PRI line telecommunication service does not require the business to invest in multiple analog lines creating a complicated and often unreliable telecom landscape.

Communication-intensive, and large-scale operations like call centers run smoothly over a PRI line setup by leveraging as many PRI’s that are needed to meet their peak call volume. For example, call centers may install one PRI with 23B+D, a second PRI with 23B+Backup D, a third PRI with 24B, a fourth (etc) with 24B channels. In this example, the call center has the following voice call capacity: 23+23+24+24=94.

Even today with the advent of SIP (session initiation protocol) they are still popularly used in large organizations with wide-scale business requirements. This is primarily due to the fact that PRI telecom is capable of offering a tremendous level of very reliable voice transmission without service outages that can impact SIP and its underlying internet or MPLS service.

PRI telecom setup is versatile because it can carry 23 different communications concurrently over two copper circuit pairs. PRI lines are lower in speed in comparison to high-speed gigabit internet, but they are extremely stable making them an ideal option for enterprises requiring a hardware-based on-premise telecom solution.

What are the applications of PRI

PRI in the Medical Industry

Medical systems in the USA and around the world still rely very heavily on the use of fax transmissions due to laws such as HIPAA which is the Health Insurance Portability and Accountability Act.

HIPAA requires personally identifiable information (PII) that is received by a healthcare provider to be protected. Healthcare providers have found that one of safest options to ensure safety of PII is to continue to use “old school” fax services.

PRI’s work reliably for fax and are most often used since SIP, even though it has fax capabilities, it experiences high failure rates particularly for inbound faxing.

The reason SIP fails on inbound applications is typically due to multiple conversions from the originator’s TDM device to IP and SIP as it traverses various carrier networks through to the end destination. SIP is much more reliable for outbound faxing and is often the preferred choice due to the slightly lower cost.

Benefits of Using PRI

If your business requirements reflect what is mentioned above, then it is essential to understand what is PRI and explore its benefits. Some of which include:


Larger enterprises require concurrent communication options that are much higher in number in comparison to a smaller business. PRI offers the required scalability as business requirements increase, you can enhance the dialing capacity by easily adding another circuit and initiate inbound as well as outbound calling with 23 or 24 additional channels, thereby adding to the communication capability of concurrent instances.

VoIP Systems Interface

Enterprise customers using PRI can have a PBX system that utilizes VoIP for conducting enterprise-wide communication activity. The PBX system can be conveniently linked with the existing PRI lines resulting in a significantly increased number of channels for business communication.

T1 and E1

The overall transfer rate for T1’s is 1.544 Mbps and E1 PRI lines is 2.048 Mbps. However, they both are capable of delivering 64 Kbps file transfer rates even though E1 PRI lines have more concurrent connections. At 64 Kbps, it is known as “toll quality” which is the highest voice quality available in the network today.

Non-Reliance on Internet or MPLS Bandwidth Stability

Traditional VoIP business services rely heavily on the stability of the organization’s internet and MPLS bandwidth connection. In contrast, PRI systems are not dependent on your company’s internet or MPLS connectivity.

Since they are mainly copper wires relying on the conventional telecom system, they are only dependent on the hardware and the physical cabling of the PSTN or Public Switched Telephone Network.

Therefore, it is highly recommended for businesses that work with limited bandwidth due to their location. Such businesses can get going by simply connecting a PRI system to the existing copper wire connection of the premises.

What is PRI and is it compatible with MPLS?


Lines are considered cost-efficient since a single connection is capable of taking on the load of 23 to 30 individual lines. This translates indirectly into lower cost of services as well as simplified management thereby reducing the operational cost for the organization’s telecom.


Here again, the number of lines offered also increases the flexibility of the company’s telecommunications setup. Further, you can be more flexible while dealing with voice and data transmissions. Call hunting, direct inward dialing, caller ID are some of the other features that are offered by PRI lines.


Speed is another major advantage of PRI telecom. Users can make calls over a Primary Rate Interface that are not just speedier but also high in quality. This is delivered faster as a result of the dedicated line structure of this technology.


Unlike analog trunk lines, the PRI telecom setup is more secure and cannot be tapped into as easily. This is largely because lines are digital allowing them to ensure increased security and an additional layer of privacy to all telecommunication flowing through it. (this is another reason why the medical community uses it for faxing)

The only drawback of PRI is its dependence on hardware and physical components. Therefore, setting up PRI from scratch can be somewhat more expensive as well as equally time-consuming since each and every circuit requires a physical connection and corresponding hardware for connection termination. The good news is that this hardware has gotten less expensive over time.

As a telecom solution, PRI is not built to cater to the requirements of every organization. However, it is an excellent option if your company requires extensive usage of telephony voice and fax services accompanied by high call quality– then PRI can offer a reliable solution.

If you still have questions would like us to help you acquire these services at the best possible rate for your business, then feel free to reach out to us at CarrierBid and our experts can help you make the best decision for your business. Alternatively, please fill out the form below and we will reach out to you for an initial consultation.

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