Primary Rate Interface

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What Does Primary Rate Interface Mean?

Primary Rate Interface (PRI) is a telecommunications interface standard primarily used in Integrated Services Digital Networks (ISDNs) and is basically a service provided for larger enterprise users. PRI lines are a high-capacity service carried on T1 or E1 trunk lines, depending on the country, between the telecommunications provider’s central service station and the customers’ end.


Techopedia Explains Primary Rate Interface

The T1 trunk line used in a PRI service is divided into 24 channels of 64 Kbps capacity each. Twenty-three of these channels are called bearer channels (B channels), equivalent to having 23 telephone lines, whereas the 24th channel is called a delta channel (D channel), which is used to carry control signals and information like caller ID and information services. In contrast, an E1 trunk line has 32 channels, 30 of which are used as B channels and 2 as D channels. T1 is used by countries such as the USA, Canada and Japan, whereas most European countries use E1 lines.

Advantages of PRI lines:

  • Consolidated installation and billing — Compared to getting 30 individual telephone lines and having all of them terminated end-to-end and installed, a single PRI line saves both time and money.
  • More reliable — PRI lines are digital, so they have better clarity than analog trunk lines and are also easier to troubleshoot.
  • More secure — Unlike analog lines, they cannot be simply tapped into in order to listen to conversations.
  • Faster calls — Calls are established quicker than with analog lines.
  • Flexible — One or multiple channels can be used for voice or data for a larger bandwidth.

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Margaret Rouse
Senior Editor
Margaret Rouse
Senior Editor

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.