PRI — Primary Rate Interface
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PRI (Primary Rate Interface) is a legacy ISDN digital trunk that connects a business PBX to the public telephone network over a single T1 or E1 circuit, carrying multiple voice channels plus a separate signaling channel. In North America a T1-based PRI provides 23 bearer (B) channels for calls and one data (D) channel for call setup and signaling; in most of the world an E1-based PRI provides 30 B channels and one D channel.
More detail
PRI is a circuit-switched, TDM technology: each call occupies a fixed 64 kbps B channel for the duration of the call, with the D channel handling setup, teardown, and features like caller ID and direct inward dialing. It was the standard way enterprises connected a PBX to the PSTN before SIP trunking became common.
The main difference between PRI and SIP trunking is the physical interface and capacity model. PRI delivers a fixed number of concurrent calls over a dedicated T1/E1 line, while SIP trunking carries calls as packets over an internet connection and scales by adding concurrent-session capacity without new physical lines.
Organizations still use PRI where a dedicated, carrier-managed circuit is preferred for voice quality or where legacy PBX or fax equipment requires an ISDN handoff. Most modern cloud phone systems and CPaaS platforms connect to the same destinations through SIP trunking instead, with the softswitch handling the conversion to or from PRI where needed.
Sık sorulan sorular
- What does PRI stand for?
- PRI stands for Primary Rate Interface, the ISDN digital trunk standard that connects a PBX to the public telephone network over a T1 or E1 circuit.
- How many channels does a PRI have?
- A T1-based PRI in North America has 23 bearer (B) channels for voice or data calls plus one data (D) channel for signaling. An E1-based PRI in most other regions has 30 B channels and one D channel.
- What is the difference between PRI and SIP trunking?
- PRI is a dedicated TDM circuit with a fixed number of concurrent call channels, commonly delivered over T1 or E1 lines. SIP trunking sends calls as packets over an internet connection and can scale concurrent capacity without installing additional physical circuits.
See also
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