Primary Rate Interface

<h2 id="isdn-service-types">ISDN service types</h2>
<p>The <a href="/facts/Integrated_Services_Digital_Network/zcV99rUb">Integrated Services Digital Network</a> (ISDN) prescribes two levels of service:<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
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<ul><li><a href="/facts/Basic_Rate_Interface/JAynT4Td">Basic Rate Interface</a> (BRI): one 16-kbit/s <a href="/facts/D_channel/MRGdbNlU">D channel</a> with two 64-kbit/s <a href="/facts/B_channel/1QoQqrcz">B channels</a>, intended for small enterprises and residential service.</li>
<li>Primary Rate Interface (PRI): one 64-kbit/s D channel with 23 (1.544 Mbit/s <a href="/facts/T-carrier/tCsEdK72">T1</a>, a.k.a. "23B + D") or 30 (2.048 Mbit/s <a href="/facts/E-carrier/h0MXcgXN">E1</a>, a.k.a. "30B + D") 64-kbit/s <a href="/facts/B_channel/1QoQqrcz">B channels</a>, intended for large organizations.</li></ul>
<p>Each B-channel carries data, voice, and other services. The D-channel carries control and signaling information. Larger connections are possible using PRI pairing. A dual T1-PRI could have 24 + 23 = 47 B-channels and 1 D-channel (often called "47B + D"), but more commonly has 46 B-channels and 2 D-channels thus providing a backup signaling channel. The concept applies to E1s as well and both can include more than 2 PRIs. When configuring multiple T1's as ISDN-PRI's, it's possible to use NFAS (non-facility associated signaling) to enable one or two D-channels to support additional B-channels on separate T1 circuits.
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<h2 id="application">Application</h2>
<p>The Primary Rate Interface channels are typically used by medium to large enterprises with digital <a href="/facts/Private_branch_exchange/eLWvlhzs">private branch exchange</a> (PBX) telephone systems to provide digital access to the <a href="/facts/Public_switched_telephone_network/eVrCTDU7">public switched telephone network</a> (PSTN). The B-channels may be used flexibly and reassigned when necessary to meet special needs such as video conferences.
</p><p>PRI channels and <a href="/facts/Direct_inward_dialing/jMetpsIg">direct inward dialing</a> are also common as a means of delivering inbound calls to <a href="/facts/Voice_over_IP/5QGBbXYg">voice over IP</a> gateways from the PSTN.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Non-Facility_Associated_Signalling/I9oMa6R2">Non-Facility Associated Signalling</a></li>
<li><a href="/facts/H_channel/yRwxBTwY">H channel</a></li>
<li><a href="/facts/I.431/ye0xwqpf">I.431</a></li>
<li><a href="/facts/Caller_ID_spoofing/VYmqWPh6">Caller ID spoofing</a></li></ul>

<ul><li> This article incorporates <a href="/facts/Copyright_status_of_works_by_the_federal_government_of_the_United_States/Q1jvr96g">public domain material</a> from <a href="https://web.archive.org/web/20220122224547/https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm"><i>Federal Standard 1037C</i></a>. <a href="/facts/General_Services_Administration/Np3opv9x">General Services Administration</a>. Archived from <a href="https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm">the original</a> on 2022-01-22.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Newton, Harry (15 January 2019). "Newton's Telecom Dictionary: The Official Dictionary of Telecommunications & the Internet". Telecom – via Google Books. <a href="https://books.google.com/books?id=0LyDQgAACAAJ&dq=newton's+telecom+dictionary+16th+edition" target="_blank">https://books.google.com/books?id=0LyDQgAACAAJ&dq=newton's+telecom+dictionary+16th+edition</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"I.412:ISDN user-network interfaces - Interface structures and access capabilities". www.itu.int. <a href="https://www.itu.int/rec/T-REC-I.412-198811-I/en" target="_blank">https://www.itu.int/rec/T-REC-I.412-198811-I/en</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"A Technical Coverage of Primary Rate Interface (PRI)". ISPFast. Retrieved 18 June 2015. <a href="http://ispfast.com/a-technical-coverage-of-primary-rate-interface-pri/" target="_blank">http://ispfast.com/a-technical-coverage-of-primary-rate-interface-pri/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
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Primary Rate Interface open-in-new

Primary Rate Interface