Glossary

Voice fraud and call quality glossary

The terms carriers, contact centres and fraud teams use about scam calls, route fraud and call quality, each defined in a few sentences with its own link. Where TCXC Open Voice Shield measures or acts on the thing defined, the entry says so, and where it does not, as with IRSF, wangiri and voice cloning, the entry says that too.

ACD (average call duration): The average length of the answered calls on a route, in minutes: total conversation minutes divided by the number of answered calls. Carriers watch it beside ASR. A sudden rise in ACD on a route with no change in traffic can mean calls are being held open, which is one sign of false answer supervision.
ANI (automatic number identification): The calling party's number as the network carries it, the North American term for what most of the world calls CLI. Billing systems and call centres read ANI to identify the line a call came from, which is why a spoofed or rewritten ANI matters.
ASR (answer-seizure ratio): The share of call attempts on a route that were answered: answered calls divided by seized (attempted) calls, as a percentage. A low ASR points at a route that fails or rejects calls. In speech technology the same letters mean automatic speech recognition, the speech-to-text step that turns a call recording into a transcript.
CDR (call detail record): The record a switch writes for every call: the calling and called numbers, the start and answer times, the duration, the disconnect cause and the route it took. Billing, fraud management and route analytics are built on CDRs. A CDR describes the call but contains nothing of what was said.
CLI (calling line identification): The calling number presented with a call, shown to the person called as caller ID. On international and wholesale routes the CLI can be dropped, replaced or rewritten between carriers, which is why operators test whether it arrives intact.
CLI verification (CLI test): A test that places a call through a route to a number that reports the caller ID it received, to prove whether the CLI you sent arrived unchanged. TCXC Open Voice Shield runs CLI verification checks from the portal, the API or an AI agent, once or on a schedule.
FAS (false answer supervision): Route fraud in which the far end signals that a call was answered when no real conversation is taking place, so billing runs on a call that never connected or never carried a conversation. In the early-answer form the route answers while the callee is still ringing, so the caller pays for ringback. In the delayed-playback form the vendor answers legitimately, then swaps the callee leg for a recording to keep minutes running. TCXC Open Voice Shield measures the audio for ringback and busy tone after the answer and reads the callee channel of the transcript for the swap, and raises a route alert for either. See FAS detection.
IRSF (international revenue share fraud): Fraud in which calls are pumped to high-cost international numbers whose termination revenue the fraudster shares, often from a hacked PBX or compromised SIP credentials, and usually at night or over a weekend. It is caught by watching traffic patterns in CDRs, such as destinations, volumes and bursts of short calls. TCXC Open Voice Shield analyzes what is said on each call and does not detect IRSF by traffic pattern.
Jitter: Variation in the arrival time of the audio packets of a call, in milliseconds. A jitter buffer smooths it out at the cost of delay. When jitter exceeds what the buffer absorbs, packets arrive too late to play, and the listener hears the same gaps as packet loss.
MOS (mean opinion score): Voice quality on a scale of 1 (bad) to 5 (excellent), originally the average of listener ratings. On VoIP calls it is estimated instead, usually with the ITU-T G.107 E-model, which turns packet loss, jitter and delay into an R-factor and then a MOS. The estimate tops out around 4.4 to 4.5 for G.711. TCXC Open Voice Shield estimates MOS for each leg of every call it carries. See what is a good MOS score.
Packet loss: The share of a call's audio packets that never arrive. On a voice call, around 1 percent is audible as clipped words, and a few percent makes speech hard to follow. Loss is the largest single input to an estimated MOS.
PDD (post-dial delay): The time between sending a call and hearing the first sign of progress: ringback, a busy tone or an early-media announcement. In SIP it is usually measured from the INVITE to the first 180 Ringing or 183 Session Progress. A long PDD makes callers hang up before the call connects.
Robocall: A call placed automatically by an autodialer, often playing a prerecorded or artificial voice. Many robocalls are legal, such as appointment reminders and alerts. Unwanted telemarketing and scam robocalls are restricted in the United States by the TCPA and in Canada by the CRTC's Unsolicited Telecommunications Rules.
SBC (session border controller): A device or software that sits at the edge of a voice network and controls the SIP signalling and media that cross it: security, NAT traversal, header manipulation, codec handling and routing between carriers. An SBC can send calls to TCXC Open Voice Shield as one more next hop, the same way it reaches a carrier.
SIP trunk: A voice connection between a phone system or switch and a carrier that runs over IP using SIP, replacing physical phone lines. Calls on a SIP trunk carry their signalling in SIP and their audio in RTP, which is what lets an extra hop record and analyze them without anything installed on the phone system.
Smishing: Phishing by SMS text message: a text that impersonates a bank, a delivery company or an agency to get a click, a code or a payment. A scam often starts with a smishing text and moves to a vishing call. See vishing vs phishing vs smishing.
Caller ID spoofing: Presenting a calling number that the caller is not entitled to use, such as a bank's real number or a local number. In the United States the Truth in Caller ID Act makes spoofing illegal when it is done to defraud, cause harm or wrongfully obtain anything of value. STIR/SHAKEN was built to expose spoofed numbers on IP networks.
STIR/SHAKEN: The caller ID authentication framework used by carriers in the United States and Canada. The originating provider signs the calling number in a SIP Identity header with an attestation level: A (full) when it knows the customer and their right to the number, B (partial) when it knows the customer but not their right to the number, and C (gateway) when the call entered from elsewhere. The terminating provider verifies the signature. It proves who vouched for the number, not what the caller says. See STIR/SHAKEN vs call content analysis.
TCPA (Telephone Consumer Protection Act): The 1991 US federal law that restricts telemarketing calls, autodialed calls and calls using a prerecorded or artificial voice, and creates the National Do Not Call Registry. A person can sue for $500 per violation, up to $1,500 when the violation was willful or knowing. See TCPA compliance and what a TCPA violation costs.
Toll fraud: Unauthorized use of a phone system to place calls that the owner pays for, usually through a hacked PBX, a guessed SIP password or an exposed voicemail system. The calls typically go to premium or high-cost international numbers, which makes toll fraud the most common way IRSF is carried out.
Vishing: Voice phishing: a scam by phone call in which the caller impersonates someone trusted, such as a bank's fraud team, a government agency, IT support or the boss, to get money, a one-time code, a password or remote access. TCXC Open Voice Shield records, transcribes and scores calls block, review or allow, and blocks the next call from a flagged number. See what is vishing and anti-vishing.
Voice cloning: Synthesizing a specific person's voice from a sample of their speech, used in scams that impersonate a relative or an executive. Detecting a cloned voice from the audio needs voice biometrics or liveness analysis. TCXC Open Voice Shield does not do that: it reads what is said, and a cloned voice asking for a transfer or a code is judged on the request.
Wangiri: Japanese for one ring and cut: a fraud in which a call from an international premium-rate number rings a phone once and hangs up, so that the person calls back and pays a high per-minute rate, part of which goes to the fraudster. It is fought by blocking known number ranges and by warning subscribers, not by analyzing the short ring itself.

See the terms on a real call

Every call through the hop comes back with a verdict, a route alert when the far end is faked, and an estimated MOS for each leg.

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