Businesses need to connect with people all over the world on a daily basis. The traditional way of making such connections has been through the Public Switched Telephone Network (PSTN) aka Plain Old Telephone System (POTS).

The PSTN was originally based on analog technology. The transition to digital technology brought better quality and was delivered through ISDN-based BRI and PRI connections.

The IP-networking revolution brought a host of technologies that transformed the voice and data networking space. It offers SIP-based communication services for multimedia including voice, video, messaging and much more.

Which technology – PRI or SIP – should you choose? In this article we will highlight some of the benefits of SIP-based communications systems.

What is PRI?

Primary Rate Interface (PRI) is a standard for digital voice connections between your business and the PSTN. A single PRI connection can carry 23 concurrent voice calls. A Private Branch Exchange (PBX) at your business site is connected to all the phones at your office and to the PRI trunk (so-called as it carries multiple calls). The PBX makes routing decisions based on whether a user calls another office user, or calls someone outside the office.

PRI offers several benefits including high quality via dedicated circuits and redundancy through multiple PRI lines. PRI does not rely on data bandwidth for voice calls.

PRI also has some drawbacks: it is comparatively more expensive, difficult to scale, and changes may take an inordinate amount of time to implement.

What is SIP?

SIP is a protocol that enables multimedia connections over data networks. The network can be private, or public like the Internet.

There are two types of SIP-based voice solutions

  • Hosted: the SIP server is hosted by the service provider, and is connected to your users over the Internet or through a data connection such as MPLS.
  • On-premise: the SIP server is located at your premises, and is connected to the service provider over the Internet or a dedicated data connection.

SIP offers several advantages including lower cost, scalability, flexibility and the ability to use any device – IP phones, laptops, smartphones etc. – for making voice and video calls. Some important things you should consider before implementing SIP to ensure its advantages.

Choosing between PRI and SIP

Choosing between PRI and SIP

There are inherent advantages of choosing SIP over PRI. SIP is a popular choice amongst organizations that are either setting up new IP PBX systems or are replacing their legacy PBX systems.

Lower Total Cost of Ownership

You can get a hosted SIP solution with a very low upfront cost: the SIP server is hosted at the service provider who bears the cost of maintenance and all hardware / software upgrades. You can start making calls as soon as your site is connected to the service provider over the Internet or through a dedicated data connection.

In contrast, you would have to procure a PBX for a PRI-based system. You would have to bear the cost of hardware maintenance and all software upgrades. Upgrading to a new system would also be costly. Furthermore, it takes significant time to provision and connect PRI lines. Overall, this would be a costly and time-consuming process.

If you use PRI, you have to buy capacity in multiples of 23 lines (or 24). This is costly and inefficient. In comparison, with SIP you can add one line for a month and then get it disconnected when it’s no longer required. In other words, you can scale up or down i.e. add or remove lines as needed, which is much more cost-effective. Long-distance calling through SIP is also much cheaper compared to PRI.


SIP is based on a packet-switched network. The number of concurrent connections is limited only by the bandwidth of the Internet or data connection. Increasing the channels for communication simply requires a network bandwidth upgrade.

On the other hand, PRI is restricted by the number of physical channels: new lines have to be provisioned for increasing the number of available voice connections, which is costly and time-consuming.


An enterprise using a SIP-based infrastructure can


  • Use multiple Internet/data connections to the service provider.
  • Contract with multiple service providers.

These measures will ensure that the communications network does not suffer a total outage due to the unavailability of any single link or an outage suffered by a service provider. We certainly recommend a multiple provider solution should you have call centers or critical sites that must always have phone service.

This configuration can be a bit tricky but with proper guidance, you can have full diversity along with automatic call routing to the alternative provider in the event of an outage. SIP call plans (from the carrier) are critical here.

Easy Upgrades

PRI connections are physical whereas SIP connections are virtual. Costly physical connections and termination software are needed for each circuit when it comes to PRI connections. This is not the case with SIP systems. The number of available trunks is a function of the available bandwidth instead of hardware or physical termination circuits.

Simpler Capacity Planning

For a PRI system, there is a need to plan the capacity in advance as considerable time goes into ordering, installing, and commissioning new circuits. There is a need for capacity planning in SIP as well.

However, the entire process is easy and quick as it can be managed through a simple software configuration. The capacity can be also increased for brief periods whenever there is a sudden increase in utilization.

Hybrid Trunking

It is possible to have a hybrid setup that uses both PRI and SIP trunks. You can save a lot of money by using PRI for local calling and relying on a SIP trunk using a hosted VoIP service for making international calls. PRI is still useful for industries such as healthcare who are still high volume users of fax services due to HIPAA.

Additional services offered by SIP trunking

Additional services offered by SIP trunking

  • Encryption of voice calls for the purpose of security
  • Routing calls with accurate caller location information
  • Failover to backup locations and trunks
  • Offers security against toll fraud
  • DoS/DDoS protection
  • Performance and usage reporting
  • Easy provisioning using a web-based interface.


Which technology is best for your business? The answer is that it depends. In some cases, PRI might be the ideal solution for you and your business. In other scenarios a hybrid solution works best. However, as it offers numerous advantages over PRI, SIP will be technology of choice for most enterprises, whether they are just starting out or have been in business for some time.

The team at Carrierbid can help you understand how SIP fits into your specific environment and business needs. We can perform detailed assessments and help you in determining the solution that is right for you. Our domain experts can be reached directly at 1-888-706-5656 or through our website at

Call us at


for immediate service or fill out the
form and we’ll be in touch right away.

  • Please describe how we can help:
    What services are you considering to drive your business higher?
    What challenges are you currently facing?