PRI vs. SIP vs. IP Trunking: What’s the difference?

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Let’s face it. Your company needs a robust communications system to operate. Most businesses still rely on a customer being able to pick up the phone and talk to someone live. The choices you make about your telephony systems can have a meaningful impact on your revenue, employee productivity, and future growth. What are the options? This article looks at the basics of IP Trunking, Session Initiation Protocol (SIP) trunking, and Primary Rate Interface (PRI)

SIP trunking and IP trunking are not competing technologies. If your business is being asked to pick a telephony service based on either SIP or IP trunking, it is time to find another provider. That said, for businesses that want to migrate from a legacy phone system to a modern communications solution, it is easy to see how these terms enter the discussion. There is an incredible number of options available for business communications. The options range from completely online to the traditional PBX. The best solution for your business depends on the level of technical resources available within your company and the functionality you need for your communications. 

What is IP trunking?

Most users think of voice over internet protocol (VoIP) as offering the most features at the best price and requiring the least onsite support. This is also where “IP trunking” comes into the equation. IP trunking is when an organization is using VoIP for their communications and needs to connect all the phones into their IP network. 

To add a little further clarity, a “trunk” referred to a bundle of lines that are shared by a group of users. You can think of it like a massive tree and the branches are the lines going to the individual office phones. You might hear IP trunking used interchangeably with VoIP for this reason. These services tend to go hand in hand.  

What is SIP trunking?

SIP trunking is also a VoIP technology based on session initiation protocol (SIP). SIP is a type of communications protocol that enables multimedia communications. In this model – the business is buying raw connectivity. The SIP trunk would likely connect into an onsite IP PBX to deliver advanced voice services. 

SIP trunking: Flexibility and functionality 

Newer to the marker is Voice over Internet Protocol (VoIP) delivered through SIP trunking. SIP trunking is a hosted cloud service that runs your calls, in addition to a variety of other communications formats, over the internet. There are a few reasons why you may want to choose SIP trunking for your company:

  • SIP trunking uses a VoIP line to initiate and end calls, but it also supports a variety of other transmissions, including SMS messages, video conferencing, and data transmissions. For companies prioritizing unified communications, SIP trunking provides the right technology. 
  • You only pay for the number of SIP trunking channels you need, when you need them. If you need 23 channels, you pay for 23 channels. If you need 28, then you pay for 28. This flexibility could lower costs by up to 30 – 40 percent when compared with PRI trunking and integration with other communications tools.


Organizations that choose a SIP trunking service need to be sure they have the necessary bandwidth, as well as sufficient network security. The SIP trunking vendor selection matters and should include consideration of a variety of factors because quality levels and service levels can differ dramatically.

Choosing SIP trunking helps relieve maintenance of the phone system from the IT staff, and could significantly reduce the cost of telephone service. It also supports mobile employees and helps drive increases in revenue when used to support a unified communications strategy.

What is PRI trunking?

Communications technology has evolved a lot over the last 40 years, but PRI systems are still an option. PRI has been around since the 80s and works well for many companies. The physical copper wires in your building deliver this traditional voice service. It doesn’t rely on data bandwidth to host calls, which is why it was historically touted as providing a higher quality of service. 

Each PRI line can simultaneously support 23 separate communications (voice, data, or video) at the same time. It is unlikely that all 23 lines will be active at once, and with that in mind, businesses usually have a ratio of users to PRI. When an organization adds new users, they have to be mindful of their PRI limits. Adding a new PRI trunk can be expensive and cumbersome, with a company waiting weeks to add another communications line.

With all the drawbacks and considerations, PRI trunking is often a good option for companies that don’t have access to fiber-optic internet connectivity or enough bandwidth to support IP-hosted phones. 

Do I need PRI, SIP, or IP trunking?

The decision on the type of communications service often comes down to the availability of onsite resources. A SIP trunk would provide the dial tone and the ability to deliver multimedia services, but your organization would still need to manage its communications. A VoIP service, over an IP trunk, would provide the complete service. 

Here are a few things to consider when making decisions about phone service:

IP trunking 

In IP trunking, voice transmissions are considered data, and they are communicated over data connections. This is in contrast to traditional plain old telephone service (POTS) lines that transmit voice through electrical-based signals. IP trunking is an alternative to a private branch exchange (PBX) system, rather than an alternative to SIP trunking.

The benefits of IP trunking include:

  • Measurable cost savings
  • Excellent scalability to add and remove lines
  • Sophisticated multimedia communications
  • Mobility

Potential drawbacks of IP trunking include:

  • There must be sufficient data connectivity to ensure the quality of service
  • Power outages could affect handsets
  • Public internet connectivity can affect the ability of IP trunking to work effectively

SIP trunking 

SIP trunking is a standard approach for handling the transmission of multimedia communications. As an alternative to PBX phone systems, SIP trunking is a way to support VoIP telephony with services hosted either on-site and managed by the IT team, or in a cloud server with a monthly subscription. 

The benefits of including SIP trunking in a communications service subscription include:

  • SIP can support a variety of media types
  • SIP integrates with other platforms easily because it is an open standard
  • SIP supports multimedia data transmission, with multiple transmissions occurring simultaneously

The potential drawbacks of SIP trunking include:

  • It can be challenging to find a skilled SIP specialist
  • While SIP is considered open standard, there are some exceptions with its features

Organizations that want to drive cost savings and improvements in productivity and mobile connectivity should consider all the relevant options. While IP trunking and SIP trunking are not competing technologies, they are each an important consideration for updating communications.

Still not sure what communication service makes sense, BlackPoint IT Services is one of the only technology services providers to offer a full suite of solutions. Your phone system should provide seamless connectivity and ensured uptime, no matter how many devices are in use or how widely dispersed those devices are from your physical business location. Contact us to learn more about options for your phone system.

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