SIP Trunking vs PRI - Connecting Businesses to Customers

November 22, 2016 mrmardis

SIP Trunking vs PRI - Connecting Businesses to Customers
Melissa Coen
Tuesday, November 22, 2016 - 12:30 SIP Trunking vs PRI

Enterprises often wonder what type of connectivity would work best for their telecommunications needs, promoting high levels of customer service and agent productivity. Terms like Session Initiation Protocol (SIP) and Primary Rate Interface (PRI), and cloud and physical connections, are tossed around in comparing the different options available for voice communications. But how do we determine which voice interface will make the most sense for our organization and be the best overall fit?

Information gleaned from a recent SIP vs PRI Infographic created by Irish Telecom helps to breakdown and compare some of the major differences between the two types of service, and make it easier to determine whether SIP Trunking or PRI is the right IT solution to connect your business and customers.

SIP Trunking and PRI Defined

SIP (Session Internet Protocol) Trunking is used to form a voice communication session across a data network, over the internet. Some examples might be: a voice over IP (VoIP) call between two users or a conference call comprised of several users. Essentially, a SIP trunk is a virtual phone line instead of a physical wire.

PRI (Primary Rate Interface) is also a telecommunications interface standard that carries multiple voice and data transmissions between the user and the network. Using PRI, a business can conduct up to 23 simultaneous calls. In plain terms, PRI makes a physical connection to the Public Switched Telephone Network (PSTN) across a voice-dedicated line.

Examining the Functionality of SIP Trunking vs. PRI

With SIP, data is transmitted across the Internet, which acts as the data connection. On the other side of the connection, the SIP trunk transmits voice between the company and its carrier’s data and SIP network. The two sides are connected via the carrier, who delivers the connection to the voice endpoint which is the business’s phone.

A PRI-based network, in contrast, consists of the internet data connection plus the PRI telephone connection that links your enterprise and carrier to a customer’s phone. Typically this line is a T1 connection with 23 voice channels and one control channel. No matter the setup, both SIP and PRI make connections between a company, a carrier (the PSTN) and the customer or endpoint’s phone.

Required Hardware

SIP connections are hardware independent since they are virtual. The number of possible trunks is limited only by the amount of available bandwidth. Therefore, adding more bandwidth allows businesses to expand the number of SIP trunks. On the other hand, PRI connections rely on physical circuits for connectivity, as well as termination hardware.

Scalability and Cost

SIP trunking is extremely scalable and can be sized up or down quickly and easily with a simple software configuration modification. On the other hand, in order to expand the capabilities of PRI, new circuits and termination hardware must be installed.

As there are no associated hardware costs required for SIP trunking, it generally costs less than PRI circuits and their termination hardware. PRI charges per circuit per month. And of course, adding additional PRI circuits increases that cost upon expansion.

Backups and Business Continuity

In the event of a disruption to the network, SIP trunks automatically reroute their IP paths according to what makes sense geographically to/from the PSTN. Calls can also be distributed through multiple service providers if necessary. In order to provide a duplicate backup network using PRI, additional PRI backup circuits need to be purchased and installed. It is possible to reroute calls with PRI, but it is difficult and expensive.

Quality of Service (QoS)

Voice connections using SIP trunking are sent like data packets and are therefore also vulnerable to packet loss and delays. As a result, SIP trunking does not have guaranteed QoS. However, PRI circuits are able to guarantee a high QoS levels since they always have a certain amount of bandwidth reserved for each call.


Cloud services through SIP trunks provide a lot of benefits to enterprises, including a large amount of flexibility, scalability and disaster recovery solutions, without the high costs involved with adding additional hardware to your company network. To also achieve a high level of guaranteed QoS, the best solution may be to integrate SIP trunks with any existing on-premises equipment.

Services like West’s MaxxConnect empower your organization to maximize infrastructure investments while offering all the benefits that a cloud-based system can provide. Merging MaxxConnect with your onsite PBX provides reliable, secure and cost-effective connections to your customers and vendors. West can help your enterprise optimize the connection to your customers today.

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