PRI vs. SIP Trunking: What's the Difference and Which is Best?

PRI vs. SIP Trunking: What's the Difference and Which is Best?

If you're looking for a replacement for your business phone system or just starting a business and looking at what phone system to purchase, you're probably swimming in what may seem like a sea of acronyms. 

But, it all really boils down to two choices... Primary Rate Interface (PRI) phone systems (traditional telephony), and voice-over-IP (VoIP) phone systems delivered over Session Initiation Protocol (SIP).

As organizations realize the cost-cutting and productivity-boosting benefits of cloud communication tools, many are making the switch from PRI phones to SIP. However, others are choosing to stay with legacy phone systems, while others are still using hybrid solutions that blend legacy and IP phones into a single system.

In some ways, PRI and SIP phones both serve the same core purpose: allowing employees at the enterprise to place and receive business phone calls.

What’s the difference?

More importantly, is PRI trunking a better fit for your needs, or is SIP trunking?

PRI vs. SIP Trunking: Which is Best?

Primary Rate Interface (PRI) is an interface standard used to deliver multiple voice lines over physical copper lines that are part of your building’s physical infrastructure. Session Initiation Protocol (SIP) trunking is a set of technical standards that support VoIP calls by initiating and ending calls between a VoIP line and the PSTN.

While both PRI and SIP have their uses, "which is best" could be neither today. With newer technology being deployed nationwide, advancements are available that can drive your organization's communications with minimal changes, for both on-premises and remote employees. Check out some of this new technology here.

What is PRI Phone Service?

PRI is a T-1 transmission technology that has been widely used to support voice communications for over 40 years.

A PRI circuit includes 23 voice channels to support 23 concurrent calls, and one data channel to support call-related functionality like caller ID. Voice calls that are supported through PRI technology are submitted as electrical pulses and routed through traditional telecommunications carriers. Traditional telephony requires a relationship with a telecommunications company and on-site servicing of cabling to add lines or upgrade equipment.

PRI is an alternative to IP-based phone technologies, including SIP trunking.

Pros of PRI

  • Does not rely on data bandwidth to support voice calls
  • High quality via dedicated line structure
  • Can be made redundant via the addition of a second PRI circuit for failover

Cons of PRI

  • PRI is expensive to implement and upgrade and requires costly monthly phone service
  • May require long-term contracts with traditional telecom companies for local and long-distance calling
  • Requires dedicated capacity that can only be purchased in 23 line units
  • Slow to scale, modifications to infrastructure may take weeks of waiting.

Best Uses Cases for PRI Technology

  • Organizations with legacy PRI infrastructure and limited access to fiber-optic internet connectivity or sufficient bandwidth to support IP-based phones.
  • Hybrid PRI and SIP trunking implementations, where organizations retain legacy PRI technology for local calls while using SIP for multimedia communications and saving costs on long-distance/international calling.



What is SIP Trunking or a SIP Phone?

SIP supports the transmission of voice calls as data as well as other types of multimedia communications. SIP is a phone technology, but it supports the transmission of Unified Communications, including video conferencing, SMS messages, data transmissions, and more.

For organizations with hosted phone communications, SIP trunking equipment is generally hosted and maintained by the vendor to manage the transmission of voice data. SIP is an alternative to PRI in that it completely eliminates the need for traditional phone infrastructure, including circuits.

Pros of SIP Trunking

  • Sold by vendors on a per-channel basis on-demand, so you only pay for the capacity needed.
  • Much cheaper; cost savings vary but can be as much as 30-40% cheaper than PRI phones
  • Offers failover to mobile phones in case of loss of office data connectivity
  • Includes easy-to-use administrative portals for easy management
  • May be offered via the cloud as part of a Unified Communications (UC) implementation
  • Can be integrated with multimedia communications for collaboration and productivity
  • Offers simple support for multiple sites and remote workers
  • May include rich mobile features and mobile-first design
  • Integrates with PRI phone lines for hybrid phone systems


Cons of SIP Trunking vs. PRI

  • Requires internet bandwidth, ideally business fiber internet, to support quality of service (QoS).
  • Needs sufficient network information security, like firewalls, to prevent cybercrime risks.
  • The quality and extensibility of service offered by hosted VoIP vendors can significantly vary

Best Use Cases for SIP Technology

  • Saving money on business phone service, especially for organizations with long-distance and international outbound calling.
  • Cost-effective support for contact centers.
  • Adding mobility features to the enterprise and supporting remote workers.
  • Reducing the burden of phone system management on internal IT personnel.
  • Moving towards hosted, multi-channel cloud communications or Unified Communications as a Service (UCaaS)
  • Gaining the ability to quickly scale business communications by adding and removing lines and features on-demand.

Is PRI vs. SIP Trunking Best for My Business?

PRI and SIP Trunking are competing approaches to phone technology that carry distinct advantages and disadvantages.

For many organizations, SIP trunking to support VoIP telephony or UCaaS is the smarter choice and enables access to the benefits of significant cost savings, improved collaboration tools, and better reliability.

For other firms, a hybrid approach to using both PRI and SIP is the right decision. Educational institutions may decide to implement Unified Communications, but maintain a few PRI lines to support legacy intercom technology and some disaster recovery planning scenarios. For other businesses still, PRI may be the right choice.

Head to Head: PRI vs. SIP on 4 Key Business Considerations

1. Cost

For the vast majority of organizations, SIP is much cheaper than PRI. Cost is an important consideration for organizations, even though it’s not the only factor to take into account when you’re investing in a business phone system. Organizations that need to scale their system, add features, and perform long-distance calling are likely to achieve massive cost savings.

There are very rare instances where PRI may be less costly than SIP. These use cases are generally limited to small, brick-and-mortar businesses with no need for advanced phone features like eFax or integrated messaging. For organizations that are not going to grow or adopt different communication technologies, maintaining an existing PRI system could be the right choice.

Who wins? SIP Trunking most of the time.

2. Information Security

PRI is considered more secure, which isn’t strictly correct. Copper cabling can be subject to a number of information security risks, including interference and interception. However, organizations that lack on-site information security expertise to achieve adequate network security and attempt to run consumer-class VoIP over public internet connectivity may be very vulnerable to security risks.

Who wins? SIP Trunking with adequate network security.

3. Flexibility

The biggest con to PRI is also among the greatest pros of SIP trunking; flexibility and scalability. With PRI, organizations are required to purchase additional user capacity in 24 lines. With SIP, organizations can add a line for a service month to accommodate a temporary or seasonal employee, and remove the line as soon as it’s no longer needed. SIP can enable organizations to unlock truly usage-paid billing on-demand, while organizations using PRI may need to wait weeks to schedule a technician for very high-cost infrastructure upgrades.

Who wins? SIP Trunking.

4. Reliability

The reliability of copper-based phone cabling can be damaged through a number of risks, including inclement weather, vandalism, or simple degradation of an aging infrastructure. While PRI is considered a very reliable technology, and it generally is, organizations will lose access to phone service if a component of their infrastructure is damaged.

SIP is reliable, provided organizations partner with a reliable vendor and invest in fiber-optic internet connectivity which is very resistant to weather and other common types of damage. With mobile failover, organizations can continue using dedicated phone lines even if there is a loss of data connectivity on site.

Who Wins? It depends. Generally, SIP wins, but some organizations may prefer a hybrid approach.

Choosing Between PRI vs. SIP Trunking

Is PRI or SIP trunking the best choice for your business? Ultimately, that depends on your organization, your goals, and your desire to adopt next-generation communication and collaboration features. The majority of organizations today have adopted or plan to switch to VoIP phones and UCaaS as a tool for cost savings, better value, and business agility. While PRI is the right choice for some select organizations, many firms find that SIP beats out traditional PRI phones.

Want a crash course in everything you need to know to drive the most value with your business investment in a new phone system? Download the free Atlantech eBook, 10 Questions to Ask Before You Buy Phone Service for Your Business.


Tom Collins
Post by Tom Collins
June 25, 2020
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.