Both connect a business phone system to the public telephone network. A PRI does it over a digital telephone circuit with a set number of call channels. A SIP trunk does it over an IP connection, where the number of calls is a limit the carrier sets. That one difference shapes what you would notice as a customer: which port on your PBX the service plugs into, how you add capacity, and what the service depends on to stay up.
\n","summary":"A PRI connects a PBX to the public telephone network over a digital circuit with fixed call channels, 23 on a fully configured T1. A SIP trunk does the same job over an IP connection, with a simultaneous-call limit the carrier sets. The practical differences are the PBX interface, how capacity grows and what the service depends on.","publishedAt":"2026-06-21T15:01:32.764","verifiedAt":"2026-09-14T00:00:00","editorialStatus":"APPROVED","lastReviewedAt":"2026-10-10T03:37:25.503","nextReviewDueAt":"2026-12-14T00:00:00","templateVersion":"v2","aliases":["PRI vs SIP trunking","SIP trunk vs PRI","ISDN PRI vs SIP trunk","What is the difference between a PRI and a SIP trunk?","How does PRI differ from SIP trunking?","Should we replace our PRI with SIP trunking?","Is SIP trunking cheaper than PRI?","Does a PRI work during a power outage?","How many channels does a PRI have compared to a SIP trunk?"],"confidenceScore":84,"confidenceLabel":"High","canonicalUrl":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"contributorOrganizationProfile":null,"contributorPerson":null,"sections":[{"id":"1a337ab2-917e-4292-adec-4c59ea8387ed","sectionKey":"two_interfaces","sectionType":"markdown_section","heading":"Two ways to reach the same network","introMarkdown":"PRI stands for Primary Rate Interface. An interface, in this sense, is a defined way for a carrier's circuit to plug into a phone system. [Cisco's guide to configuring ISDN PRI](https://www.cisco.com/c/en/us/td/docs/ios/dial/configuration/guide/15_0s/dia_15_0s_book/dia_cfg_isdn_pri.pdf) gives the structure. On a T1 circuit, a PRI offers 23 B channels and one D channel. The B channels carry the calls, one call each, and the D channel carries the signaling that sets calls up and ends them. On an E1 circuit the figures are 30 B channels and one D.\n\nAtlantech Online sells both services, and its [comparison of SIP trunking and PRI](https://www.atlantech.net/blog/sip-trunking-vs-pri) describes the T1 version in the same terms. A PRI circuit there has 23 voice channels for 23 concurrent calls, and one data channel for call-related functions such as caller ID.\n\n[SIP trunking](https://www.answerstack.io/q/what-is-sip-trunking) is a service delivered over an IP connection. Your PBX and the carrier exchange SIP messages to set each call up, and the audio travels between them as a separate stream of packets, in the sequence we trace in [how SIP trunking works](https://www.answerstack.io/q/how-does-sip-trunking-work). The connection is not divided into fixed call channels ahead of time.\n\nIt is tempting to file one of these under old telephony and the other under digital. Both carry voice digitally, and both end at the same public network. The difference is in the handoff between the carrier and your PBX.","introHtml":"PRI stands for Primary Rate Interface. An interface, in this sense, is a defined way for a carrier's circuit to plug into a phone system. Cisco's guide to configuring ISDN PRI gives the structure. On a T1 circuit, a PRI offers 23 B channels and one D channel. The B channels carry the calls, one call each, and the D channel carries the signaling that sets calls up and ends them. On an E1 circuit the figures are 30 B channels and one D.
\nAtlantech Online sells both services, and its comparison of SIP trunking and PRI describes the T1 version in the same terms. A PRI circuit there has 23 voice channels for 23 concurrent calls, and one data channel for call-related functions such as caller ID.
\nSIP trunking is a service delivered over an IP connection. Your PBX and the carrier exchange SIP messages to set each call up, and the audio travels between them as a separate stream of packets, in the sequence we trace in how SIP trunking works. The connection is not divided into fixed call channels ahead of time.
\nIt is tempting to file one of these under old telephony and the other under digital. Both carry voice digitally, and both end at the same public network. The difference is in the handoff between the carrier and your PBX.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":10},{"id":"3ca39b7f-da29-45f0-b6a0-9f96d76417ad","sectionKey":"comparison_table","sectionType":"table_section","heading":"The differences side by side","introMarkdown":null,"introHtml":null,"outroMarkdown":null,"outroHtml":null,"contentJson":{"rows":[{"cells":["What arrives at your site","A digital telephone circuit, such as a T1","Service over an IP connection"]},{"cells":["Where it connects","A PRI port on the PBX","The PBX's SIP trunk interface, across your data network"]},{"cells":["How calls are signaled","On the D channel","In SIP messages"]},{"cells":["How capacity is counted","B channels on the circuit, 23 on a fully configured T1","A simultaneous-call limit set by the carrier"]},{"cells":["What it shares","A circuit of its own","An IP connection your data may also use"]}],"columns":["What differs","PRI","SIP trunk"]},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":20},{"id":"fa85afbd-e808-4d0a-bfd0-ae42114abc34","sectionKey":"capacity_scaling","sectionType":"markdown_section","heading":"What happens when you need more calls","introMarkdown":"Suppose your office's busiest hour puts 26 outside calls in progress at once. One T1 PRI configured with 23 B channels has room for 23 of them and no channel for the other three. Covering them means more circuit capacity. A second full T1 PRI would add 23 channels to solve a shortfall of three, and what smaller increments a carrier will configure is a question for that carrier.\n\nOn a SIP trunk, the same shortfall is a change to a limit. Each call is a session the two ends agree on, and it holds no fixed time slot on a circuit. So a carrier that sells capacity by the call can set the trunk to 26. Atlantech's [April 2023 post on its SIP trunks](https://www.atlantech.net/blog/sip-trunking-business-phone-service) gives an example from one of its customers, a local government that adds capacity over its SIP trunks during weather events such as snowstorms and tropical storms. Atlantech's comparison draws the same contrast. It describes PRI capacity as bought in blocks, and SIP capacity as lines added for a month and removed when they are no longer needed.\n\nA higher limit at the carrier is one of several ceilings, because your PBX has a maximum of its own and so does your connection. Twilio's [trunking requirements](https://www.twilio.com/docs/sip-trunking) use a planning figure of 100 kbps for each simultaneous call on the G.711 codec, with overhead included. By that allowance, 26 calls need 2.6 Mbps available for voice. The figure to order is also a sizing decision. It comes from your busy-hour traffic and a margin you choose, as we work through in [how many simultaneous calls you need](https://www.answerstack.io/q/how-many-simultaneous-calls-do-i-need-or-get-on-a-sip-trunk), and it can come out above the highest count you have seen.","introHtml":"Suppose your office's busiest hour puts 26 outside calls in progress at once. One T1 PRI configured with 23 B channels has room for 23 of them and no channel for the other three. Covering them means more circuit capacity. A second full T1 PRI would add 23 channels to solve a shortfall of three, and what smaller increments a carrier will configure is a question for that carrier.
\nOn a SIP trunk, the same shortfall is a change to a limit. Each call is a session the two ends agree on, and it holds no fixed time slot on a circuit. So a carrier that sells capacity by the call can set the trunk to 26. Atlantech's April 2023 post on its SIP trunks gives an example from one of its customers, a local government that adds capacity over its SIP trunks during weather events such as snowstorms and tropical storms. Atlantech's comparison draws the same contrast. It describes PRI capacity as bought in blocks, and SIP capacity as lines added for a month and removed when they are no longer needed.
\nA higher limit at the carrier is one of several ceilings, because your PBX has a maximum of its own and so does your connection. Twilio's trunking requirements use a planning figure of 100 kbps for each simultaneous call on the G.711 codec, with overhead included. By that allowance, 26 calls need 2.6 Mbps available for voice. The figure to order is also a sizing decision. It comes from your busy-hour traffic and a margin you choose, as we work through in how many simultaneous calls you need, and it can come out above the highest count you have seen.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":30},{"id":"445046f2-e5c9-4253-a9b4-cafda67ce0c0","sectionKey":"pbx_compatibility","sectionType":"markdown_section","heading":"Your PBX decides which one you can use","introMarkdown":"A PBX connects to a carrier through whatever interface it was built or licensed with. A system with a PRI card expects a PRI, and a system with a SIP trunk interface expects SIP. Atlantech's [business phone page](https://www.atlantech.net/solutions/voice/phone) says it can deliver service to a customer's own PBX by SIP, PRI or analog, and the 2023 post explains the split. SIP trunks go to customers that already run a VoIP PBX, and PRI and analog lines go to customers with a legacy PBX. In that arrangement the choice follows the equipment you have.\n\nA gateway loosens that constraint. Sangoma [describes its digital gateways](https://sangoma.co.uk/voip-gateways/digital/) as devices that convert between PRI connections and VoIP connections, so a legacy phone system can use a SIP trunk. The PBX keeps seeing a PRI on its own port, and the gateway speaks SIP to the carrier. The PBX's PRI ports still set how many calls it can pass, so a gateway changes the carrier connection without lifting that ceiling. Whether your model can take this route is the question in using SIP trunking with an existing phone system.\n\nSome organizations keep both. Atlantech's comparison mentions educational institutions that move to unified communications and keep a few PRI lines for legacy intercom equipment and for some disaster recovery plans. The same comparison allows that keeping a working PRI can be the right choice for an organization that is not growing or changing its communications.","introHtml":"A PBX connects to a carrier through whatever interface it was built or licensed with. A system with a PRI card expects a PRI, and a system with a SIP trunk interface expects SIP. Atlantech's business phone page says it can deliver service to a customer's own PBX by SIP, PRI or analog, and the 2023 post explains the split. SIP trunks go to customers that already run a VoIP PBX, and PRI and analog lines go to customers with a legacy PBX. In that arrangement the choice follows the equipment you have.
\nA gateway loosens that constraint. Sangoma describes its digital gateways as devices that convert between PRI connections and VoIP connections, so a legacy phone system can use a SIP trunk. The PBX keeps seeing a PRI on its own port, and the gateway speaks SIP to the carrier. The PBX's PRI ports still set how many calls it can pass, so a gateway changes the carrier connection without lifting that ceiling. Whether your model can take this route is the question in using SIP trunking with an existing phone system.
\nSome organizations keep both. Atlantech's comparison mentions educational institutions that move to unified communications and keep a few PRI lines for legacy intercom equipment and for some disaster recovery plans. The same comparison allows that keeping a working PRI can be the right choice for an organization that is not growing or changing its communications.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":40},{"id":"b5a278bf-4117-4144-9d9a-21636858a9ae","sectionKey":"beyond_the_name","sectionType":"markdown_section","heading":"What the name does not tell you","introMarkdown":"Neither name settles reliability. A PRI has a circuit to itself, and Atlantech lists as a PRI advantage that it \"does not rely on data bandwidth to support voice calls.\" A SIP trunk shares an IP connection unless you give it one of its own. Calls can degrade when that connection is congested, and they stop when it is down. But the same comparison points out that a PRI customer loses phone service when part of the circuit's own infrastructure is damaged, and it names weather, vandalism and aging cable among the causes. On the question of which is more reliable, its own answer is \"It depends.\" The useful comparison is between the specific circuit and the specific connection you would be relying on.\n\nNeither name settles security either. Atlantech disputes the common belief that PRI is the more secure of the two, and notes that copper cabling can be intercepted. It also says that voice run over the public internet without adequate network security can be exposed. In both cases the protection comes from how the service is built and run.\n\nCost depends on the quote more than on the interface. Atlantech's phone page describes its pricing as tailored to the customer and prints no rate for either connection. A fair comparison therefore needs two quotes built on the same inputs: the same number of simultaneous calls, the same phone numbers and the same calling. On the SIP side, count what the trunk adds to what you already pay for. That may be extra capacity on your data connection, and a gateway if the PBX needs one.\n\nHow long a PRI will stay on offer also sits outside the name. Atlantech wrote in 2023 that PRI and analog lines \"continue to dwindle,\" while its phone page still lists PRI delivery today. If you plan to keep a PRI-based PBX for years, ask the carrier how long it will supply and support the circuit.","introHtml":"Neither name settles reliability. A PRI has a circuit to itself, and Atlantech lists as a PRI advantage that it "does not rely on data bandwidth to support voice calls." A SIP trunk shares an IP connection unless you give it one of its own. Calls can degrade when that connection is congested, and they stop when it is down. But the same comparison points out that a PRI customer loses phone service when part of the circuit's own infrastructure is damaged, and it names weather, vandalism and aging cable among the causes. On the question of which is more reliable, its own answer is "It depends." The useful comparison is between the specific circuit and the specific connection you would be relying on.
\nNeither name settles security either. Atlantech disputes the common belief that PRI is the more secure of the two, and notes that copper cabling can be intercepted. It also says that voice run over the public internet without adequate network security can be exposed. In both cases the protection comes from how the service is built and run.
\nCost depends on the quote more than on the interface. Atlantech's phone page describes its pricing as tailored to the customer and prints no rate for either connection. A fair comparison therefore needs two quotes built on the same inputs: the same number of simultaneous calls, the same phone numbers and the same calling. On the SIP side, count what the trunk adds to what you already pay for. That may be extra capacity on your data connection, and a gateway if the PBX needs one.
\nHow long a PRI will stay on offer also sits outside the name. Atlantech wrote in 2023 that PRI and analog lines "continue to dwindle," while its phone page still lists PRI delivery today. If you plan to keep a PRI-based PBX for years, ask the carrier how long it will supply and support the circuit.
\n","outroMarkdown":null,"outroHtml":null,"contentJson":{},"configJson":{},"noteMarkdown":null,"noteHtml":null,"sortOrder":50}],"citations":[{"title":"ITU-T Recommendation I.412 (11/88): ISDN user-network interfaces - Interface structures and access capabilities","url":"https://www.itu.int/rec/T-REC-I.412/en","excerpt":"4.1.2.2 At the 1544 kbit/s primary rate the interface structure is 23 B + D. 4.1.2.3 At the 2048 kbit/s primary rate the interface structure is 30 B + D. ... the 64 kbit/s capacity of the D-channel may or may not be used to provide an additional B-channel, depending on the situation; e.g., 24 B for a 1544 kbit/s interface.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Approved November 1988, status In force. Clause 3.1.1 puts the B channel at 64 kbit/s. Clause 4.1.2.1 puts the D channel of a primary rate structure at 64 kbit/s; 4.1.2.2 sets 23B+D at the 1544 kbit/s primary rate; 4.1.2.3 sets 30B+D at 2048 kbit/s; 4.1.2.4 allows the unactivated D channel capacity ","domain":"itu.int","publisherName":"International Telecommunication Union (ITU-T)"},{"title":"ITU-T Recommendation I.431 (03/93): Primary rate user-network interface - Layer 1 specification","url":"https://www.itu.int/rec/T-REC-I.431/en","excerpt":"8.1 Provision of power. The provision of power to the NT via the user network interface using a separate pair of wires from those used for signal transmission, is optional. 8.2.1 Power Available from the TE. The power available (from the TE) at the NT shall be a minimum of 7 watts.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Approved March 1993, status In force. Clause 1.1 scopes it to user-network interfaces at 1544 and 2048 kbit/s for the channel arrangements defined in I.412. Clause 2.1 states the primary rate access supports only a point-to-point configuration and refers electrical characteristics to G.703. Clause 8","domain":"itu.int","publisherName":"International Telecommunication Union (ITU-T)"},{"title":"ITU-T Recommendation G.703 (04/16): Physical/electrical characteristics of hierarchical digital interfaces","url":"https://www.itu.int/rec/T-REC-G.703/en","excerpt":"Physical/electrical characteristics of hierarchical digital interfaces. Status: In force.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Latest approval April 2016 with Amendment 1 of May 2021, status In force. Named by I.431 clause 2.1 as the source of the electrical characteristics of the primary rate interface, which establishes that the PRI physical layer is a hierarchical digital interface specification rather than anything spec","domain":"itu.int","publisherName":"International Telecommunication Union (ITU-T)"},{"title":"ITU-T Recommendation Q.931 (05/98): ISDN user-network interface layer 3 specification for basic call control","url":"https://www.itu.int/rec/T-REC-Q.931/en","excerpt":"ISDN user-network interface layer 3 specification for basic call control. Status: In force.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Approved May 1998, status In force, also numbered I.451. Establishes that ISDN call setup and clearing use a defined layer 3 protocol, which on a primary rate interface is carried on the D channel, and is therefore not SIP.","domain":"itu.int","publisherName":"International Telecommunication Union (ITU-T)"},{"title":"RFC 3261: SIP: Session Initiation Protocol","url":"https://datatracker.ietf.org/doc/html/rfc3261","excerpt":"This document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Defines SIP as an application-layer control (signaling) protocol for creating, modifying and terminating sessions including internet telephone calls. The specification contains no channel count, line rate or concurrency limit, which is the basis for saying that SIP trunk channels are a commercial un","domain":"datatracker.ietf.org","publisherName":"IETF"},{"title":"RFC 3550: RTP: A Transport Protocol for Real-Time Applications","url":"https://datatracker.ietf.org/doc/html/rfc3550","excerpt":"RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of-service for real-time services.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Establishes that the media of a SIP call travels separately from the signaling, as RTP over multicast or unicast network services, and that RTP does not reserve resources or guarantee quality of service.","domain":"datatracker.ietf.org","publisherName":"IETF"},{"title":"47 CFR 9.3 Definitions","url":"https://www.ecfr.gov/current/title-47/section-9.3","excerpt":"An interconnected Voice over Internet Protocol (VoIP) service is a service that: (i) Enables real-time, two-way voice communications; (ii) Requires a broadband connection from the user's location; (iii) Requires internet protocol-compatible customer premises equipment (CPE); and (iv) Permits users generally to receive calls that originate on the public switched telephone network and to terminate calls to the public switched telephone network.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Current text retrieved through the eCFR renderer API because the eCFR HTML is JavaScript rendered. Sets the four-part test for interconnected VoIP service and separately defines common carrier, which is the category a PRI provider falls in.","domain":"ecfr.gov","publisherName":"Office of the Federal Register (eCFR)"},{"title":"47 CFR 9.11: E911 Service (interconnected VoIP)","url":"https://www.ecfr.gov/current/title-47/section-9.11","excerpt":"(a) [Reserved] ... Each interconnected VoIP service provider shall specifically advise every subscriber, both new and existing, prominently and in plain language, of the circumstances under which E911 service may not be available ... broadband connection failure, loss of electrical power, and delays that may occur in making a dispatchable location available.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Current text retrieved through the eCFR renderer API. Paragraph (a) reads [Reserved]; the source note records the amendment at 91 FR 1403, January 14, 2026. Paragraph (b) carries the operative duties: transmit all 911 calls with ANI and location, automated dispatchable location for fixed interconnec","domain":"ecfr.gov","publisherName":"Electronic Code of Federal Regulations (National Archives / GPO)"},{"title":"47 CFR 9.4, Obligation to transmit 911 calls","url":"https://www.ecfr.gov/current/title-47/section-9.4","excerpt":"All telecommunications carriers shall transmit all 911 calls to a PSAP, to a designated statewide default answering point, or to an appropriate local emergency authority as set forth in Sec. 9.5.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Current text retrieved through the eCFR renderer API. The one-sentence rule that places the 911 transmission duty on telecommunications carriers, which is the regulatory frame for PRI voice as distinct from the interconnected VoIP frame in 9.11.","domain":"ecfr.gov","publisherName":"Electronic Code of Federal Regulations (eCFR), Office of the Federal Register"},{"title":"47 CFR 9.16: General obligations, direct 911 dialing, notification, and dispatchable location","url":"https://www.ecfr.gov/current/title-47/section-9.16","excerpt":"A person engaged in the business of installing, managing, or operating multi-line telephone systems may not install, manage, or operate for use in the United States such a system, unless such system is configured such that a user may directly initiate a call to 911 from any station equipped with dialing facilities, without dialing any additional digit, code, prefix, or post-fix, including any trunk-access code such as the digit 9.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Current text retrieved through the eCFR renderer API. Paragraph (b) places direct 911 dialing without a trunk-access digit, MLTS notification and dispatchable location duties on the person installing, managing or operating a multi-line telephone system, with compliance dates of January 6, 2021 for o","domain":"ecfr.gov","publisherName":"Electronic Code of Federal Regulations (National Archives / GPO)"},{"title":"Delete, Delete, Delete (FCC direct final rule), 91 FR 1400","url":"https://www.federalregister.gov/documents/2026/01/14/2026-00612/delete-delete-delete","excerpt":"The Direct Final Rule would repeal approximately 21 rule provisions and rule parts ... that plainly no longer serve the public interest because they have sunset by operation of law; govern an expired event; regulate an obsolete technology; are no longer used in practice by the FCC or licensees; or are otherwise duplicative, outdated, or unnecessary.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"GN Docket No. 25-133, FCC 25-80, published January 14, 2026 at 91 FR 1400 to 1404, effective March 16, 2026. Repeals roughly 21 rule provisions that have sunset, govern an expired event, regulate an obsolete technology or are otherwise outdated. This is the instrument that removed and reserved 47 CF","domain":"federalregister.gov","publisherName":"Federal Register / Federal Communications Commission"},{"title":"47 CFR 51.325, Notice of network changes: Public notice requirement","url":"https://www.ecfr.gov/current/title-47/section-51.325","excerpt":"(3) Will result in a copper retirement, which is defined for purposes of this subpart as: (i) The removal or disabling of copper loops, subloops, or the feeder portion of such loops or subloops; or (ii) The replacement of such loops with fiber-to-the-home loops or fiber-to-the-curb loops.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"Current text retrieved through the eCFR renderer API. Paragraph (a)(3) defines copper retirement as the removal or disabling of copper loops, subloops or the feeder portion of them, or their replacement with fiber-to-the-home or fiber-to-the-curb loops. Establishes that copper retirement is a physic","domain":"ecfr.gov","publisherName":"Electronic Code of Federal Regulations (eCFR), Office of the Federal Register"},{"title":"Reducing Barriers to Network Improvements and Service Changes, Report and Order (FCC 26-19), 91 FR 20913","url":"https://www.federalregister.gov/documents/2026/04/20/2026-07622/reducing-barriers-to-network-improvements-and-service-changes","excerpt":"the Commission adopted a Report and Order that reduces regulatory barriers and costs that hinder the transition from outdated legacy networks and services to next-generation, Internet Protocol (IP)-based infrastructure ... This rule is effective May 20, 2026.","quoteText":null,"sourceRole":"INDEPENDENT","verifiedAt":"2026-09-15T00:00:00","supportsText":"WC Docket Nos. 25-208 and 25-209, FCC 26-19, published April 20, 2026 at 91 FR 20913, effective May 20, 2026 except for seven instructions whose effective date is delayed indefinitely. Reduces filing barriers to retiring legacy networks while retaining section 214(a) discontinuance authorization and","domain":"federalregister.gov","publisherName":"Federal Communications Commission, via the Federal Register"},{"title":"AT&T Inc., Form 8-K Exhibit 99.1, Fourth-Quarter and Full-Year 2025 earnings release","url":"https://www.sec.gov/Archives/edgar/data/732717/000073271726000047/t-4q2025exhibit991.htm","excerpt":"The Company's consolidated financial outlook assumes sustained declines in service revenues within its Legacy segment as it makes progress against its objective of powering-down its energy-intensive copper-based network across the large majority of its footprint by the end of 2029 and upgrading customers to advanced connectivity services powered by 5G and fiber.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"Filed January 28, 2026, accession 0000732717-26-000047. AT&T's own statement of its copper plan, framed as an assumption in its consolidated financial outlook covering the large majority of its footprint by the end of 2029, with Legacy service revenue expected to decline more than 20 percent in 2026","domain":"sec.gov","publisherName":"AT&T Inc., filed with the U.S. Securities and Exchange Commission"},{"title":"Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI), CenturyLink wholesale product catalog","url":"https://www.centurylink.com/wholesale/pcat/isdnpri.html","excerpt":"CenturyLink Resale - Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI) service is grandfathered effective July 1, 2026 and is no longer available as a new service effective in all CenturyLink states. ... The basic service consists of 23 B Channels and a D Channel with a transmission rate of 1.544 Megabits per second (Mbps).","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"Carrier's own product catalog, page last updated May 4, 2026. States that CenturyLink Resale ISDN PRI is grandfathered effective July 1, 2026 and no longer available as a new service in all CenturyLink states. Also corroborates the 23B+D structure at 1.544 Mbps on a DS1 facility and records that ava","domain":"centurylink.com","publisherName":"CenturyLink (Lumen Technologies)"},{"title":"ISDN PRI, AT&T GTA Direct services catalog","url":"https://www.attgtadirect.com/isdn-pri/","excerpt":"Pricing provided for a flat-rate PRI includes: T1 local channel, voice/data interface, and 23 B Channels. Telephone numbers are charged separately based on quantity required. ... Long distance services are not included and will be charged separately. ... You can use one D channel to control multiple ISDN PRI lines, freeing the 24th channel on additional ISDN PRI circuits to increase capacity.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"AT&T's published rate card for the Georgia state contract, page dated December 11, 2020 and read September 15, 2026. PRI-ISDN 1.5Mbps at $649.59 monthly with $0.00 non-recurring, DID telephone number $0.21 monthly, calling name delivery $102.50 per PRI. Regulatory fees EUCL/ARC $52.55 per PRI, feder","domain":"attgtadirect.com","publisherName":"AT&T (Georgia Technology Authority GTA Direct contract)"},{"title":"SIP Trunking Pricing","url":"https://www.sip.us/pricing/","excerpt":"$24.95 per channel per/month ... $19.99 per channel per month ... Includes local and long distance calls to the US48 states and Canada (excluding NWT) at no additional charge. ... Excludes any local, state or federal taxes and/or fees.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"Provider's published price list read September 15, 2026. SIP channels at $24.95 per channel per month month-to-month and $19.99 per channel per month on yearly plans, no setup fee, each channel including unlimited outbound calling to the US48 and Canada and unlimited inbound to your local numbers. U","domain":"sip.us","publisherName":"SIP.US"},{"title":"Elastic SIP Trunking Pricing","url":"https://www.twilio.com/en-us/sip-trunking/pricing","excerpt":"48 States (Zone 1): $0.0100 / min ... Local origination: $0.0034 / min ... Unlimited Call Concurrency: Included ... No contracts and no channel limits.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"Provider's published price list read September 15, 2026. United States termination to the 48 states at $0.0100 per minute, local origination at $0.0034 per minute, toll-free termination from $0.0011 per minute and toll-free origination at $0.0130 per minute, local phone numbers $1.1500 per month and","domain":"twilio.com","publisherName":"Twilio"},{"title":"Flowroute pricing details","url":"https://www.flowroute.com/pricing/","excerpt":"Outbound rate (US lower 48 & Canada) beginning at $0.00833/minute ... Domestic Inbound rate starting at $0.005/minute ... no limit on simultaneous calls.","quoteText":null,"sourceRole":"PRIMARY","verifiedAt":"2026-09-15T00:00:00","supportsText":"Provider's published price list read September 15, 2026. Outbound for the US lower 48 and Canada from $0.00833 per minute, domestic inbound from $0.005 per minute, toll-free inbound $0.00975 per minute, DID $1.00 per number, mandatory E911 association charged per phone number, and no limit on simult","domain":"flowroute.com","publisherName":"Flowroute"}],"revisions":[{"revisedAt":"2026-07-18T15:01:32.764+00:00","versionLabel":"Originally published","note":"","reviewedBy":null}],"relatedAnswers":[{"id":"77b3581e-fb3d-43da-aefa-a3ebd533d57d","slug":"how-many-simultaneous-calls-do-i-need-or-get-on-a-sip-trunk","question":"How many simultaneous calls do I need or get on a SIP trunk?","publishedAt":"2026-07-18T15:16:53.422","confidenceScore":82,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"sip-trunking","label":"SIP Trunking","description":"SIP trunking for business voice: how it works, channels, bandwidth, and PBX connectivity.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"To size a SIP trunk, measure the calls in your busiest hour, convert that traffic to call paths with a blocking target, then check the result against the provider's plan, your equipment and your connection. What you get is the lowest of those limits.","url":"/q/how-many-simultaneous-calls-do-i-need-or-get-on-a-sip-trunk"},{"id":"bc3ff0a8-b843-46c0-a953-41aa557e1110","slug":"what-is-the-difference-between-sip-trunking-and-cloud-pbx","question":"What is the difference between SIP trunking and cloud PBX?","publishedAt":"2026-07-18T15:01:34.706","confidenceScore":84,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"sip-trunking","label":"SIP Trunking","description":"SIP trunking for business voice: how it works, channels, bandwidth, and PBX connectivity.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"SIP trunking connects a phone system you run to the public telephone network. A cloud PBX is the phone system itself, run by a provider and billed per user.","url":"/q/what-is-the-difference-between-sip-trunking-and-cloud-pbx"},{"id":"97ab21fb-1842-45fa-90d8-e34e67a64794","slug":"what-is-the-difference-between-sip-trunking-and-voip","question":"What is the difference between SIP trunking and VoIP?","publishedAt":"2026-07-18T15:01:30.724","confidenceScore":86,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"sip-trunking","label":"SIP Trunking","description":"SIP trunking for business voice: how it works, channels, bandwidth, and PBX connectivity.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"VoIP is a technology category: voice carried over data networks with internet protocols. SIP trunking is one carrier service built on it, connecting a phone system you run to the public telephone network. A SIP trunk is VoIP. The real choice appears when VoIP means a hosted phone service, and it turns on who runs the phone system.","url":"/q/what-is-the-difference-between-sip-trunking-and-voip"},{"id":"fa8568a0-bdf2-4a59-945f-3ebb2492ff83","slug":"how-does-sip-trunking-work","question":"How does SIP trunking work?","publishedAt":"2026-07-18T15:01:28.862","confidenceScore":92,"confidenceLabel":"High","industry":{"id":"ff619d7c-d7d7-485e-a05a-53fba07f33ed","slug":"telecommunications","label":"Telecommunications","description":"Business voice, fiber, UCaaS, and network services"},"topic":{"slug":"sip-trunking","label":"SIP Trunking","description":"SIP trunking for business voice: how it works, channels, bandwidth, and PBX connectivity.","schemaKind":null},"contributor":{"id":"ec39deab-44fe-48d8-9029-fefe993ab85a","slug":"answer-stack","displayName":"AnswerStack","websiteUrl":null},"snippet":"A SIP trunk links your PBX to a carrier over an IP network. SIP messages such as INVITE, 180 Ringing, 200 OK, ACK and BYE set up and end each call, and the audio travels separately as RTP packets. The carrier passes calls to and from other networks, and call capacity is a limit rather than a count of physical lines.","url":"/q/how-does-sip-trunking-work"}],"contributorStats":{"verifiedAnswers":149,"openDisputes":0},"schemaJson":{"@context":"https://schema.org","@type":"Question","name":"What is the difference between SIP trunking and PRI?","text":"What is the difference between SIP trunking and PRI?","url":"https://www.answerstack.io/q/what-is-the-difference-between-sip-trunking-and-pri","answerCount":1,"datePublished":"2026-06-21T15:01:32.764","about":[{"@type":"Thing","name":"SIP Trunking"},{"@type":"Thing","name":"Telecommunications"}],"acceptedAnswer":{"@type":"Answer","text":"Both connect a business phone system to the public telephone network. A PRI does it over a digital telephone circuit with a set number of call channels. A SIP trunk does it over an IP connection, where the number of calls is a limit the carrier sets. That one difference shapes what you would notice as a customer: which port on your PBX the service plugs into, how you add capacity, and what the service depends on to stay up.","url":"https://www.answerstack.io/q/what-is-the-difference-between-sip-trunking-and-pri","upvoteCount":0,"datePublished":"2026-06-21T15:01:32.764","dateModified":"2026-09-14T00:00:00","citation":[{"@type":"CreativeWork","name":"ITU-T Recommendation I.412 (11/88): ISDN user-network interfaces - Interface structures and access capabilities","url":"https://www.itu.int/rec/T-REC-I.412/en"},{"@type":"CreativeWork","name":"ITU-T Recommendation I.431 (03/93): Primary rate user-network interface - Layer 1 specification","url":"https://www.itu.int/rec/T-REC-I.431/en"},{"@type":"CreativeWork","name":"ITU-T Recommendation G.703 (04/16): Physical/electrical characteristics of hierarchical digital interfaces","url":"https://www.itu.int/rec/T-REC-G.703/en"},{"@type":"CreativeWork","name":"ITU-T Recommendation Q.931 (05/98): ISDN user-network interface layer 3 specification for basic call control","url":"https://www.itu.int/rec/T-REC-Q.931/en"},{"@type":"CreativeWork","name":"RFC 3261: SIP: Session Initiation Protocol","url":"https://datatracker.ietf.org/doc/html/rfc3261"},{"@type":"CreativeWork","name":"RFC 3550: RTP: A Transport Protocol for Real-Time Applications","url":"https://datatracker.ietf.org/doc/html/rfc3550"},{"@type":"CreativeWork","name":"47 CFR 9.3 Definitions","url":"https://www.ecfr.gov/current/title-47/section-9.3"},{"@type":"CreativeWork","name":"47 CFR 9.11: E911 Service (interconnected VoIP)","url":"https://www.ecfr.gov/current/title-47/section-9.11"},{"@type":"CreativeWork","name":"47 CFR 9.4, Obligation to transmit 911 calls","url":"https://www.ecfr.gov/current/title-47/section-9.4"},{"@type":"CreativeWork","name":"47 CFR 9.16: General obligations, direct 911 dialing, notification, and dispatchable location","url":"https://www.ecfr.gov/current/title-47/section-9.16"},{"@type":"CreativeWork","name":"Delete, Delete, Delete (FCC direct final rule), 91 FR 1400","url":"https://www.federalregister.gov/documents/2026/01/14/2026-00612/delete-delete-delete"},{"@type":"CreativeWork","name":"47 CFR 51.325, Notice of network changes: Public notice requirement","url":"https://www.ecfr.gov/current/title-47/section-51.325"},{"@type":"CreativeWork","name":"Reducing Barriers to Network Improvements and Service Changes, Report and Order (FCC 26-19), 91 FR 20913","url":"https://www.federalregister.gov/documents/2026/04/20/2026-07622/reducing-barriers-to-network-improvements-and-service-changes"},{"@type":"CreativeWork","name":"AT&T Inc., Form 8-K Exhibit 99.1, Fourth-Quarter and Full-Year 2025 earnings release","url":"https://www.sec.gov/Archives/edgar/data/732717/000073271726000047/t-4q2025exhibit991.htm"},{"@type":"CreativeWork","name":"Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI), CenturyLink wholesale product catalog","url":"https://www.centurylink.com/wholesale/pcat/isdnpri.html"},{"@type":"CreativeWork","name":"ISDN PRI, AT&T GTA Direct services catalog","url":"https://www.attgtadirect.com/isdn-pri/"},{"@type":"CreativeWork","name":"SIP Trunking Pricing","url":"https://www.sip.us/pricing/"},{"@type":"CreativeWork","name":"Elastic SIP Trunking Pricing","url":"https://www.twilio.com/en-us/sip-trunking/pricing"},{"@type":"CreativeWork","name":"Flowroute pricing details","url":"https://www.flowroute.com/pricing/"}]}}}