PRI and SIP trunking: What's the difference?

By Catherine Hensley
Updated: February 12, 2011

When managing business communications, it’s important to get the most out of your monetary investment in services and useful features. Telephone trunking, in which multiple phone conversations can be transported over long distances through a single line, is an efficient and financially sound option to consider for your company. The particular business needs of your organization will determine which system type you should invest in.

SIP Trunking

Most trunking systems have traditionally used “T1 lines” to connect between a company’s phone system and its telephone service provider. This is true for “SIP [Session Initiation Protocol] trunking,” which utilizes already installed IP-PBXs. T1 lines are the most readily available and cost-efficient types of telephone lines in use today. SIP trunking allows a business to connect with outside organizations in addition to its inter-office communications, all through a single SIP trunk line connected to a PSTN network. It most often uses the same Internet access used for data. The Internet telephone service provider supplies the SIP trunk line, and it eliminates the clunky bunches of physical phone wires once necessary with older telephone systems.

Because only three parts are needed to employ an SIP trunk line, this type of system is very cost-effective. The only requirements are:

  1. A provider offering Internet telephone or SIP-trunking service,
  2. A phone system that has a trunk side to enable SIP, and
  3. An “enterprise edge device” capable of understanding and working with SIP.

With just these three pieces, a business can increase its telecommunications reach, especially if there is an existing IP-PBX installed.


“PRI [Primary Rate Interface] trunking” is another option for transmitting many different voice and data communications amongst multiple locations. PRI, seen by many as an older alternative to the more modern SIP, is also based on the use of T1 lines, though telephone circuits not in place may need to be installed. Monthly rates and calling fees are often higher than with SIP, but PRI does allow the addition of large numbers of voicelines at once (i.e., 23 at a time, compared to only 1 SIP at a given time), an attractive option for large businesses. But traditional PRI does tend to cost many businesses more due to its older technology and equipment needs. It also does not include new popular features available with SIP, like IM-call screening and third-party interfacing.

The size of your business, the scope of its telecommunications needs, and budget flexibility should all factor in to a decision regarding whether to go with traditional PRI or new SIP trunking technology. No matter which you choose, both options will increase your company’s productivity and ability to interact internally and with outside clients.

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