A glossary of business phone terms.

Terms are grouped by topic, with an A–Z jump list for quick scanning. Formal definitions and US regulatory descriptions are cited to the source; ordinary industry terms are explained in plain language. A feature name alone does not tell you what a provider includes, so check the call flow and fallback behaviour.

Numbers and numbering

10-digit dialling (ten-digit dialing)

Dialling a full ten-digit NANP number, including the area code. Overlay areas require local ten-digit dialling; requirements elsewhere depend on the local dialing plan.14 The overlay guide explains when it becomes mandatory.

Area code overlay (overlay)

A way to add numbering capacity to a geographic area by assigning a new area code over the same region as an existing one. Because both codes serve the same area, callers may need to dial the area code for local calls; the exact dialing plan is area-specific.14 See how area code overlays work, with the groups in each state and province.

DID (direct inward dialling) (direct inward dial; direct dial-in)

A number that lets an outside caller reach a particular line, person, or destination through a phone system without first speaking to an operator. Providers use the term differently; it does not by itself guarantee a separate device or a particular routing feature.

LRN (location routing number) (location routing number)

The number that tells the network which switch now serves a ported number. ATIS defines it as "The ten-digit (NPA-NXX-XXXX) number assigned to a switch/POI used for routing in a permanent local number portability environment".26 When a number is ported, calls to it are routed on the NPA-NXX of the LRN instead of the dialled number's own; the LRN "is not a telephone number".27 See how a business call travels.

NANP (North American Numbering Plan)

The shared numbering plan used by the United States, Canada, and participating Caribbean countries and territories. NANP geographic numbers use a three-digit area code followed by a seven-digit local number.12

NPA (Numbering Plan Area) (area code)

The three-digit first part of a NANP number, commonly called its area code. The NANP format is NXX-NXX-XXXX.12 Every in-service geographic code is listed in the area-code reference.

NPAC (Number Portability Administration Center)

The database system that records which provider serves each ported number. iconectiv, the Local Number Portability Administrator for the United States, describes the US NPAC as "The largest system of databases of ported telephone numbers in the world", holding approximately 1 billion numbers.28 Canada has its own NPAC; a port completes when the new provider activates it there and the change is "broadcast to the telecommunications industry network".27

NXX (central office code) (prefix; exchange)

The middle three digits in a ten-digit NANP number, following the area code. NANPA describes it as the central office code, also called a prefix or exchange.13

SMS/800 TFN Registry (TFN Registry; SMS 800)

The database and tools used to manage toll-free number records. TFNRegistry is the current name for the toll-free number registry formerly known as the SMS/800 TFN Registry; authorised RespOrgs use it to search, reserve, and manage toll-free number records.15

Toll-free number (TFN)

A number in a toll-free numbering range, where the subscriber arranges for calls to be routed through the toll-free network. Its records are managed in the TFN Registry by a Responsible Organization (RespOrg).10 15

Auto Attendant can provide a local or toll-free business number; see local vs toll-free numbers. The seven codes are listed on the toll-free area codes page.

Vanity number (custom number)

A number selected because its letters or digit pattern are memorable or spell a word. Availability depends on the number type, provider inventory, and applicable number-allocation rules.

Virtual number (online number)

A number whose calls are routed through a service rather than being tied exclusively to one physical telephone line. The label is broad: ask which devices can ring, what happens when nobody answers, and whether the number can be ported.

Routing and menus

ACD (automatic call distributor)

Defined by the ATIS Telecom Glossary as "A device that distributes incoming calls to a specific group of terminals", which queues callers when everyone is busy: "If all terminals are busy, the incoming calls are held in a first-in-first-out queue until a terminal becomes available."1

The queue is the giveaway. An ACD is contact-centre equipment, built for a pool of interchangeable agents. Five tradespeople with different specialities are not a pool.

Auto attendant (automated attendant; virtual receptionist; phone tree)

The recorded menu that answers a business line and connects the caller according to the option they choose. Also called an automated attendant, virtual receptionist or phone tree; Google's documentation uses "automated attendant (auto attendant)".5

Unlike the other terms here it has no single standards-body definition — it is industry usage. The defining characteristic is that the caller makes the routing decision. See the full explainer.

Business hours schedule (open hours)

A timetable that determines which greeting or routing rules apply during stated opening hours. Check the time zone, treatment of holidays, and what happens at the exact opening and closing times.

Call flow (call path)

The sequence of decisions and destinations a call passes through, such as greeting, menu choice, ringing a team member, and voicemail if unanswered.

Call forwarding (conditional forwarding; unconditional forwarding)

Sending an incoming call to another number or destination. Unconditional forwarding redirects every call; conditional forwarding applies only under a rule such as busy, no answer, or unreachable. Provider behaviour and charges vary.

Call queue (queue)

A system that holds callers and connects them when a suitable person becomes available. Queue position, wait announcements, and callback options depend on the service. A ring group simply offers destinations to ring and does not necessarily hold a waiting caller.

Call screening

A feature that gives the recipient information or a prompt before they accept a call. It is separate from a menu that asks the caller to choose a department.

DTMF (dual-tone multi-frequency) (touch-tone)

The two-tones-per-key signalling that makes touch-tone dialling work, and therefore the input mechanism for every phone menu. Specified in ITU-T Recommendation Q.23, "Technical features of push-button telephone sets", published November 1988 and still formally in force.4

Its age is why a recorded menu works from any telephone on earth without an app.

Find me / follow me (find-me-follow-me)

A broad name for routing a call to one or more destinations according to a sequence or availability rule. It is not a single standard feature set; confirm whether ringing is simultaneous, sequential, or conditional.

Greeting (announcement)

The recorded message callers hear before or during routing. It may identify the business, explain available menu choices, or tell callers what to do after hours.

Holiday schedule (holiday hours)

A set of dates on which the normal business-hours call flow is replaced by a holiday greeting or alternate routing. Confirm the time zone and whether dates recur automatically.

Hunting, and hunt group (hunt group)

ATIS defines hunting, in telephony, as "pertaining to the operation of a selector or other similar device to find and establish a connection with an idle circuit of a chosen group."2 A hunt group is that chosen group: a set of phones tried in order until a free one is found.

"Ring group" is the modern synonym — Google's documentation says "Ring groups, also called hunt groups".6

IVR (interactive voice response) (voice menu)

A system that plays recorded or generated prompts and responds to caller input, commonly keypad presses or speech. An auto attendant is a simple kind of voice menu; IVR can also describe more complex self-service flows.

No-answer timeout (ring timeout)

The time a destination is allowed to ring before the call follows another rule, such as ringing a different person or going to voicemail.

Overflow (call overflow)

A fallback destination or action used when the first route is busy, unanswered, or unavailable. The term alone does not say whether callers wait in a queue.

Ring group (ring group)

A set of phones an option rings together, in sequence, or in rotation. The contemporary name for a hunt group, usually with more options than classic hunting. Auto Attendant does not ring phones together: each menu option rings up to three phones one after another. Designing your menu covers the patterns, and call queue vs ring group vs auto attendant compares them with queues.

Round robin (rotating ring)

A routing pattern that starts with a different recipient on successive calls, usually cycling through a list. Implementations differ on whether busy or unavailable recipients are skipped.

Sequential ring (serial ring)

A routing pattern that tries recipients one after another, typically moving to the next when the current phone is unanswered or unavailable. Confirm the ring duration and total time before the final fallback. Auto Attendant rings in this way: up to three phones per option, each for 10 to 60 seconds, then voicemail.

Simultaneous ring (ring all)

A routing pattern that makes several chosen phones ring at the same time. The first person to answer takes the call; check what happens if all recipients are busy or do not answer.

Speech-recognition IVR (speech IVR)

A voice menu that recognises spoken responses as input instead of, or alongside, keypad tones. Recognition accuracy depends on the caller's speech, background noise, prompt design, and supported vocabulary.

Sub-menu (nested menu)

A second menu reached from an option in the first menu. Each extra level adds another step before the caller reaches a person, so keep the choices clear and limited.

Porting

CSR (customer service record)

An account record used in number-porting workflows to confirm details such as the account name, service address, and numbers on the account. The information must match the current provider's record closely enough for its validation process.

FOC (firm order commitment)

The confirmation a losing carrier returns against a port request, committing to a date. It follows the LSR. Industry process terminology rather than a defined regulatory term.

Letter of authorization (LOA) (porting LOA)

A document authorising a gaining provider to submit a request to transfer a number. The required signer and information depend on the account and provider; an LOA does not itself guarantee that a port will be accepted.

LNP (local number portability) (number portability)

The right to keep your number when changing providers. In the US the intervals are set by 47 CFR § 52.35: one business day for a simple wireline-to-wireline or simple intermodal port, four business days for a non-simple one.3 See porting your existing number.

LSR (local service request)

The order a gaining carrier submits to start a port. The rule attaches real consequences to its timing: "An accurate and complete Local Service Request (LSR) must be received by the current service provider between 8 a.m. and 1 p.m. local time", and anything later counts as received the next business day.3

Port-out fraud (unauthorised port)

The porting form of the same attack: the criminal asks another provider to port the victim's number away, so the number leaves the carrier altogether. The FCC's 2023 order requires wireless providers to authenticate a customer "before redirecting a customer's phone number to a new device or provider" and to notify customers of port-out requests, but several of its paragraphs were "delayed indefinitely".30 A port-out PIN or number lock is the defence a customer can turn on. See port-out fraud and SIM swaps.

Port-out freeze (number lock)

A lock some carriers apply to an account to prevent unauthorised transfers. It is an anti-fraud measure and only the account holder can lift it — and it is a common cause of a rejected port. See port-out fraud and SIM swaps.

Port-out PIN (transfer PIN; number transfer PIN)

A security code some providers require before releasing a number for transfer. It is account-specific and may differ from the phone's device unlock code or account password. See port-out fraud and SIM swaps.

Porting rejection (port rejection)

A response that a number-transfer request cannot proceed as submitted. Common reasons include mismatched account details, an account security lock, an inactive number, or a number that is not eligible for that kind of transfer. The current provider's stated reason determines the correction.

RespOrg (Responsible Organization) (Responsible Organization)

For toll-free numbers, "The entity chosen by a toll free subscriber to manage and administer the appropriate records in the toll free Service Management System for the toll free subscriber."10 Moving a toll-free number means changing RespOrg, which is not an ordinary port. See local vs toll-free.

SIM swap (SIM swap fraud; SIM change fraud)

A fraud in which a criminal persuades a mobile carrier to move the victim's number onto a SIM the criminal controls, so calls, texts and sign-in codes go to them. The FCC describes SIM swap and port-out fraud as practices bad actors use "to take control of consumers' cell phone accounts" without "ever gaining physical control of a consumer's phone".30 The resulting rule, 47 CFR § 64.2010(h), covers mobile (CMRS) providers only, and its text says compliance "will not be required until this paragraph is removed or contains a compliance date".29 See port-out fraud and SIM swaps.

Simple port

The class of port that gets the one-business-day interval. Notably, the term is not defined anywhere in the Code of Federal Regulations — it appears in the operative text of §§ 52.35 and 52.36 but in no definitional paragraph.

The nearest authoritative description is the FCC's consumer guidance: simple ports "generally do not involve more than one line or more complex adjustments to telephone switching equipment".11

Voicemail and messaging

Ring-no-answer (RNA)

A call that rings a destination but is not answered before the system's timeout. The configured fallback might be another recipient, a general voicemail box, or a disconnect message.

Transcription (voicemail transcription)

A text rendering of speech recorded in a voicemail. Automated transcripts can omit or misrecognise words; listen to the recording when the exact wording matters.

Visual voicemail

A phone interface that lists voicemail messages and may let the user play or manage them without calling a voicemail access number. It is distinct from a voicemail transcript delivered by email.

Voicemail to email (voicemail by email)

A notification that sends voicemail information to an email inbox, often with an audio recording and sometimes a transcript. Consider who can access the mailbox and whether forwarding exposes the recording to others.

Whisper message (call whisper)

A short prompt played to the recipient before the caller is connected, often indicating which menu option or line the call came through.

Regulation and emergency calling

911 and emergency calling (9-1-1)

Emergency calling rules for interconnected VoIP and multi-line systems involve service capability, routing, callback, and location information. Which obligations apply depends on the service and deployment; see emergency calling. The terms below describe parts of that framework.8

Copper retirement (copper sunset)

A carrier taking its copper phone lines out of service. The FCC's network-change rules define it 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".33 The FCC's consumer guidance says providers "will retire aging copper-line networks used to provide voice services in areas where modern fiber, satellite, and wireless services are available as a replacement".32 See copper retirement and the POTS sunset.

CPNI (customer proprietary network information)

Information about a customer's telecommunications service use, such as numbers called and call timing. Federal law and FCC rules impose privacy duties on covered carriers and interconnected VoIP providers; a product's use of the term does not establish its regulatory classification.18

Dispatchable location

A US regulatory term: under RAY BAUM'S Act, "the street address of the calling party, and additional information such as room number, floor number, or similar information necessary to adequately identify the location".7 The FCC's deadlines for providing it differ by device category8 — see emergency calling.

E911 (enhanced 911) (enhanced 9-1-1)

Emergency telephone service that can provide information such as the caller's number or location to emergency services, depending on the system and jurisdiction. It is not a guarantee that every internet calling setup sends an accurate dispatchable location; see emergency calling.8

ESInet (Emergency Services IP network)

The IP network that carries emergency calls to answering points under NG911. FCC rules define it as "An Internet Protocol (IP)-based network that is managed or operated by a 911 Authority or its agents or vendors and that is used for emergency services communications, including Next Generation 911."37 See the NG911 transition.

Interconnected VoIP service

A US regulatory category, defined at 47 CFR § 9.3 as a service that enables "real-time, two-way voice communications", requires a broadband connection and IP-compatible customer premises equipment, and "Permits users generally to receive calls that originate on the public switched telephone network and to terminate calls to the public switched telephone network."8

Falling inside it brings substantial 911 obligations. Classification is fact-specific; we make no claim about our own status, for the reasons set out on emergency calling.

Kari's Law

A US federal law requiring covered multi-line telephone systems to allow users to dial 911 directly, without first entering an outside-line prefix, and to provide notifications to a central location when a 911 call is made. Coverage and implementation details are set by the statute and FCC rules.20

MLTS (multi-line telephone system)

A US regulatory category defined at 47 CFR § 9.3 as "A system comprised of common control units, telephone sets, control hardware and software and adjunct systems, including network and premises based systems, such as Centrex and VoIP, as well as PBX, Hybrid, and Key Telephone Systems".8

It is broader than people expect, explicitly covering network-based and VoIP systems and non-profit and government deployments. Systems inside it carry Kari's Law and dispatchable-location obligations.

NG911 (Next Generation 911) (NG9-1-1)

The move of 911 from legacy circuit-switched trunks to IP networks. FCC rules define NG911 as "An Internet Protocol-based system" that, among other things, is secure, uses commonly accepted standards and "Enables emergency communications centers to receive, process, and analyze all types of 911 requests for emergency assistance".37 Originating service providers, a defined group that includes interconnected VoIP providers, deliver 911 traffic in IP format at an "NG911 Delivery Point" designated by the 911 authority.37 See the NG911 transition.

PIDF-LO (location object) (Presence Information Data Format Location Object)

The IETF format for carrying a caller's location over the internet. RFC 4119 (December 2005) defines a location object that "extends the Presence Information Data Format (PIDF)" and can hold geographic coordinates or a civic address.38 RFC 6442 defines how SIP carries that location with a call, including "location-based routing, where SIP intermediaries make routing decisions based upon the location".68 See the NG911 transition.

PSAP (Public Safety Answering Point) (public safety answering point)

The emergency communications centre that receives 911 calls and routes or dispatches them to the appropriate emergency response. The name and organisation of PSAPs vary by location.8 See the NG911 transition.

RAY BAUM'S Act

A US law that includes requirements concerning dispatchable location for emergency calls from multi-line telephone systems. FCC rules specify how those requirements apply by device and system category; the phrase is not a blanket certification for a phone service.22 8

Reassigned Numbers Database (RND)

An FCC-established database that lets callers check whether a number was permanently disconnected after a date on which the caller obtained consent, helping identify numbers that may have been reassigned. It is relevant to certain calling rules, not a general number-ownership directory.21

RTT (real-time text) (real-time text)

Text sent as it is typed, so the other person sees the message form during the conversation. FCC rules define it as "text communications that are transmitted over Internet Protocol (IP) networks immediately as they are created, e.g., on a character-by-character basis", use RFC 4103 as the reference format, and provide for gateways to older TTY devices.39 RFC 4103 carries the text in RTP packets.40 See the NG911 transition.

Section 214 discontinuance (discontinuance of service)

The US approval a carrier needs before ending a service. Section 214(a) of the Communications Act says "No carrier shall discontinue, reduce, or impair service to a community, or part of a community" without first obtaining an FCC certificate.34 For these rules "carrier" includes interconnected VoIP providers,35 and 47 CFR § 63.71 requires written notice to each affected customer explaining how to object.36 The eCFR flags an amendment to § 63.71 published on 1 October 2026.36 See copper retirement and the POTS sunset.

Simple port interval

Under 47 CFR § 52.35, the interval for a simple wireline-to-wireline or simple intermodal port is one business day; a non-simple port has a four-business-day interval. The rule defines intervals and request timing, not a guarantee that every port completes on that schedule.3

TCPA (Telephone Consumer Protection Act)

A US federal law governing certain calls and texts, with restrictions that depend on the technology, number called, message purpose, consent, and applicable exceptions. The statute and FCC rules should be checked for the specific campaign; this glossary is not legal advice.16

VoIP and carriers

B2BUA (back-to-back user agent) (back-to-back user agent)

A SIP element that answers the incoming call leg and places a new outgoing one, so it stays in the middle of the call. RFC 3261 defines it as an entity that "receives a request and processes it as a user agent server (UAS)" and then "acts as a user agent client (UAC) and generates requests"; "Unlike a proxy server, it maintains dialog state".55 RFC 7092 gives IP PBXs, session border controllers and application servers as examples.54 See the open-source SIP servers compared.

Codec (coder-decoder)

Software or hardware that encodes and decodes audio for transmission. Codecs trade off bandwidth, processing, and sound quality; both ends of a call need compatible handling. Common examples are G.711 and Opus.

G.711 (PCMU; PCMA; mu-law; A-law)

The ITU-T Recommendation "Pulse code modulation (PCM) of voice frequencies", first published in 1988 and still in force.49 In RTP it is carried as PCMU (mu-law) or PCMA (A-law), at eight bits per sample.50 See codec.

Jitter (packet delay variation)

Variation in the time packets take to arrive. High jitter can make real-time audio uneven or choppy, especially when a device or network cannot buffer the variation.

Latency (delay)

The time audio takes to travel between speakers. Long delays make conversation feel less natural and can cause people to talk over one another.

MOS (mean opinion score)

A score used to summarise perceived voice quality, traditionally based on listener ratings and sometimes estimated from network measurements. A single MOS figure depends on the method and conditions used; ask how it was measured.

Opus (Opus codec)

An open audio codec defined in RFC 6716 (September 2012) for interactive uses "including Voice over IP, videoconferencing, in-game chat, and even live, distributed music performances". It "scales from low bitrate narrowband speech at 6 kbit/s to very high quality stereo music at 510 kbit/s".51 See codec.

Packet loss

Audio packets that fail to reach their destination. Lost packets can create gaps, distortion, or reduced intelligibility in an internet voice call.

PBX (private branch exchange)

ATIS gives three definitions, including "A subscriber-owned telecommunications exchange that usually includes access to the public switched network" and "A private telephone switchboard that provides on-premises dial service".9

Historically a physical box; now usually software. The auto attendant was traditionally a feature inside one.

POTS (plain old telephone service) (plain old telephone service; copper line)

Basic voice calling over a traditional phone line. ATIS defines it narrowly as "A call that requires nothing more than basic call handling";31 in everyday use it means the analogue line delivered over copper. The FCC reports that 5% of US households still have "legacy copper telephone service".32 See copper retirement and the POTS sunset.

PSTN (public switched telephone network)

The traditional public telephone network, including the interconnected network of carrier switches and transmission systems. The term also appears in regulatory definitions that describe calls originating from or terminating to the PSTN.8

RFC 4733 (telephone-event) (RFC 2833; out-of-band DTMF)

The IETF standard for sending keypad presses as named events inside the RTP stream instead of as audio tones. RFC 4733 (December 2006) "describes how to carry dual-tone multifrequency (DTMF) signalling, other tone signals, and telephony events in RTP packets", obsoletes RFC 2833 and registers the media type "audio/telephone-event".52 See DTMF and the Asterisk auto attendant dialplan.

RTP (Real-time Transport Protocol) (RTCP)

The protocol that carries the audio of a VoIP call in packets, separately from the SIP signalling. RFC 3550 (July 2003) describes "end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data", and notes that RTP "does not guarantee quality-of-service"; its companion protocol RTCP monitors delivery.47 See how a business call travels.

SBC (session border controller) (session border controller)

A SIP device at a network edge. RFC 5853 notes the term "is not standardized or defined anywhere"; SBCs "usually sit between two service provider networks in a peering environment, or between an access network and a backbone network", and provide "perimeter defense (access control, topology hiding, and denial-of-service prevention and detection)", NAT traversal and protocol repair, and media and quality-of-service management.53 RFC 7092 lists SBCs as a kind of B2BUA.54

SDP (Session Description Protocol) (offer/answer)

The text block inside a SIP message that describes a call's media, including the media formats (codecs) and the transport port to send audio to. RFC 8866 (January 2021) defines SDP "for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation".45 In SIP one side offers an SDP and the other answers with its own, the offer/answer model of RFC 3264.46 See how a business call travels.

SIP (Session Initiation Protocol)

A signalling protocol used to establish, manage, and end multimedia communication sessions, including many internet voice calls. RFC 3261 (June 2002) describes it as "an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants".55 SIP handles session signalling; the audio travels separately over RTP, described by SDP. See how a business call travels.

SIP proxy (proxy server)

RFC 3261: "An intermediary entity that acts as both a server and a client for the purpose of making requests on behalf of other clients." Its main job is routing, ensuring "a request is sent to another entity 'closer' to the targeted user", and it can enforce policy; it rewrites parts of the request "if necessary" before forwarding it.55 Unlike a B2BUA it does not start a new call. See Kamailio and OpenSIPS.

SIP registrar (registrar; REGISTER)

RFC 3261: "a server that accepts REGISTER requests and places the information it receives in those requests into the location service for the domain it handles." Registration "allows users to upload their current locations for use by proxy servers", which is how a desk phone or softphone tells the server where to send its incoming calls.55

SIP trunk (SIP trunking)

A carrier connection that uses SIP signalling to connect a phone system to a provider's network. Capacity, geographic coverage, emergency calling, and charges depend on the contract and service design.

SRTP (Secure RTP)

An encrypted form of RTP. RFC 3711 (March 2004) defines it as "a profile of the Real-time Transport Protocol (RTP), which can provide confidentiality, message authentication, and replay protection to the RTP traffic" and to RTCP.48 It protects the audio only; securing the SIP signalling is a separate setting.

Caller ID and spam labelling

Call attestation (A/B/C) (STIR/SHAKEN attestation)

A provider's assertion in STIR/SHAKEN about its knowledge of the caller and the caller's right to use the number. A means the provider knows the customer and has verified the number; B means it knows the customer but not the number's right of use; C means the call entered the IP network from elsewhere and the provider lacks a relationship with the caller. Attestation is not a rating of whether a call is wanted or safe.17 See STIR/SHAKEN call authentication.

Caller ID (calling number)

Information presented to a recipient to identify the calling line, commonly a telephone number and sometimes a name. The displayed number can be authenticated, withheld, mislabelled, or spoofed; the display alone does not prove who is calling.17

CNAM (caller name) (caller ID name)

A caller-name value associated with a telephone number and displayed by some networks or devices. Name display can depend on carrier databases and device behaviour, and can be stale or inaccurate.17 See who sees your business name when you call.

Number reputation (call reputation)

A broad industry term for how a carrier or analytics service classifies a calling number based on its own data and policies. It is not a single shared score, and different services may show different labels.

PASSporT (Personal Assertion Token) (PASSporT)

The signed token that STIR/SHAKEN attaches to a call. RFC 8225 (February 2018) defines it as a token "that cryptographically verifies an originating identity or, more generally, a URI or telephone number representing the originator".24 The SHAKEN extension in RFC 8588 adds the attestation level, "a specific set of levels of confidence in the correctness of the originating identity", and an origination identifier.25 See STIR/SHAKEN call authentication.

Rich Call Data (RCD) (RCD)

Signed information about the caller that travels with a call beyond the number itself, such as a display name. IETF RFC 9795 (July 2025) extends the STIR PASSporT token so that "rich metadata about a call and caller" can be "signed and integrity protected, transmitted, and subsequently rendered to the called party".23 The RFC defines the format; it does not by itself make a network or handset display anything. See who sees your business name when you call.

Robocall Mitigation Database (RMD)

An FCC database where voice service providers file certifications about STIR/SHAKEN implementation or robocall mitigation plans. Its entries describe provider filings; inclusion is not an FCC endorsement of a particular provider or a guarantee about a specific call.19 See STIR/SHAKEN call authentication.

Spam likely label (spam label; scam likely)

A warning some carriers or caller-ID apps attach to a number or call based on their own analytics and policies. Labels can differ between networks and do not by themselves establish whether an individual call is fraudulent. See why a business number may show as spam likely.

STIR/SHAKEN

A set of technical standards and protocols for IP networks that allows authenticated information about a call to travel with it. Providers use it to help deter number spoofing; it does not certify that a caller's purpose is legitimate or that a recipient should answer.17 The signed token it uses is a PASSporT. See STIR/SHAKEN call authentication.

Business texting

A2P 10DLC (10DLC; 10-digit long code)

"10DLC stands for 10-digit long code", an ordinary local number; A2P (application-to-person) 10DLC is, in Twilio's words, "the standard that carriers have implemented in the US" for business texting from those numbers, and anyone texting the US from a 10DLC number through an application "must register".41 The Campaign Registry describes it as a channel "in which Brands and Campaign Service Providers (CSPs) are verified prior to being allowed to send messages".42 See business texting and 10DLC.

Short code (common short code)

A five- or six-digit number leased for high-volume business texting in the US. Short codes "are administered by the Common Short Code Administration (CSCA), an LLC governed by CTIA, the wireless trade association, on behalf of U.S. wireless carriers"; the registry lists a lease rate of $1,000 a month for a code you choose yourself.44 See business texting and 10DLC.

The Campaign Registry (TCR) (TCR)

The industry registry where 10DLC brands and campaigns are recorded. It describes itself as "the backbone support for the 10DLC messaging ecosystem"; registrations are made by Campaign Service Providers (CSPs) through its portal or APIs, and messages flow once the sender gives its connectivity partner the resulting Campaign ID.42 A business normally registers through its texting provider, not with TCR directly. See business texting and 10DLC.

Toll-free verification (toll-free message verification)

The review a toll-free number must pass before it can send text messages in the US and Canada. Twilio's documentation states that "As of January 31, 2024, messages sent from any unverified (Restricted or Pending) Toll-Free phone numbers (TFPN) are blocked."43 It is separate from 10DLC registration, which covers local numbers. See business texting and 10DLC.

Developer platforms

AGI (Asterisk Gateway Interface) (FastAGI)

Asterisk describes AGI as "analogous to CGI in Apache": it "provides an interface between the Asterisk dialplan and an external program that wants to manipulate a channel in the dialplan". It is synchronous, so each action blocks until it completes.64

ARI (Asterisk REST Interface) (Stasis)

An interface for writing your own call-handling application on top of Asterisk. It has three parts: "A RESTful interface that a client uses to control resources in Asterisk", "A WebSocket that conveys events in JSON about the resources in Asterisk to the client", and "The Stasis dialplan application that hands over control of a channel from Asterisk to the client".63 See Asterisk architecture and PJSIP.

Dialplan (extensions.conf)

In Asterisk, the program that decides what happens to each call: "essentially a scripting language specific to Asterisk", kept in extensions.conf.58 It is organised into contexts, extensions and numbered priorities; "An extension is simply a named set of actions", performed in priority order when that extension is dialled.59 See an auto attendant in the Asterisk dialplan.

PJSIP (Asterisk) (res_pjsip; chan_pjsip; pjsip.conf)

Asterisk's SIP stack: the chan_pjsip channel driver and the res_pjsip modules, introduced with Asterisk 12 and built on the pjproject library, configured in pjsip.conf.56 The older chan_sip driver was deprecated in Asterisk 17 and removed in Asterisk 21.57 See Asterisk architecture and PJSIP.

TwiML (Twilio Markup Language)

Twilio's XML instruction format: "a set of instructions you can use to tell Twilio what to do when you receive an incoming call or SMS". When a call arrives, Twilio requests the URL configured on the number and follows the TwiML it gets back, with verbs such as Say, Gather and Dial.60 See build an IVR on Twilio.

Webhook (callback URL)

An HTTP request a platform sends to your application when something happens, such as an incoming call. In Twilio's words, after certain events "Twilio sends an HTTP request to a webhook URL you provided"; the request "is called a webhook or callback".61 Twilio signs each request with an X-Twilio-Signature header, and the application should check it before responding.62 See build an IVR on Twilio.

Canadian privacy and anti-spam law

CASL (Canada's anti-spam legislation) (S.C. 2010, c. 23)

The usual name for the federal statute S.C. 2010, c. 23. Section 6 prohibits sending "a commercial electronic message" to an electronic address unless the recipient "has consented to receiving it, whether the consent is express or implied" and the message identifies the sender and how to contact them. Section 6(8) excludes "an interactive two-way voice communication between individuals" and "a voice recording sent to a telephone account", so it reaches business texts and email, not ordinary calls.65 See business texting and 10DLC.

Law 25 (Quebec private-sector privacy act) (Act respecting the protection of personal information in the private sector; CQLR c. P-39.1)

The usual name for the 2021 amending statute (S.Q. 2021, c. 25) that amended Quebec's Act respecting the protection of personal information in the private sector (CQLR c. P-39.1); the section histories cite "2021, c. 25". The Act covers personal information a person "collects, holds, uses or communicates to third persons in the course of carrying on an enterprise". Under s. 3.1 the person with the highest authority in the enterprise is the person in charge of protecting personal information unless the function is delegated in writing, and that person's title and contact information must be published on the enterprise's website (or made available by other appropriate means if it has none); under s. 3.5 an incident that "presents a risk of serious injury" must be reported promptly to the Commission d'accès à l'information.67 See our privacy notice for Canadian residents.

PIPEDA (Personal Information Protection and Electronic Documents Act)

Canada's federal private-sector privacy law, the Personal Information Protection and Electronic Documents Act (S.C. 2000, c. 5). Part 1 "applies to every organization in respect of personal information that ... the organization collects, uses or discloses in the course of commercial activities".66 Quebec has its own private-sector act (see Law 25). See our privacy notice for Canadian residents.

Sources

Primary sources are used for regulatory, numbering-plan, and toll-free registry claims. Industry terms without a formal definition are described as usage rather than regulation.