VoIP Glossary: 60 Terms Explained

Telecom has its own language. This glossary defines 60 terms that come up when evaluating carriers, configuring phone systems, or running call center operations. Each definition is written for operators, not engineers — practical meaning over technical precision. For deeper coverage of specific topics, links to our detailed guides are included where available.

SIPNEX is an FCC-licensed carrier providing SIP trunking for call centers and dialer operations. This glossary reflects the terminology our customers encounter daily.

A

A2P (Application-to-Person) — Business messages sent by software to individual consumers. Requires 10DLC registration for standard phone numbers. Contrast with P2P (Person-to-Person) messages between individuals.

ACD (Automatic Call Distribution) — System that routes incoming calls to available agents based on rules (skills, queue priority, longest-idle). In VICIdial, handled by in-group configuration.

AHT (Average Handle Time) — Average total time per call: talk time plus wrap-up time. Key agent efficiency metric. See call center metrics.

AMD (Answering Machine Detection) — Dialer feature that analyzes audio to determine if a human or machine answered. Accuracy depends on codec choice — G.711 is best.

ASR (Answer-Seizure Ratio) — Percentage of call attempts resulting in any answer (human, machine, or voicemail). Measures network completion. See telecom acronyms.

ATDS (Automatic Telephone Dialing System) — Legal classification under TCPA determining consent requirements. See auto dialer laws.

Attestation — The level of verification a carrier provides when signing a call via STIR/SHAKEN. A-level = fully verified. B-level = partially verified. C-level = gateway only.

B

Bandwidth (network) — The data capacity of your internet connection, measured in Mbps. Each G.711 VoIP call uses approximately 85 kbps. See VoIP quality guide.

BYE — The SIP message that terminates a call. Either party can send BYE to hang up.

C

CDR (Call Detail Record) — Data record for every call containing timestamps, duration, numbers, and disposition. Essential for billing, compliance, and performance analysis.

CID (Caller ID) — The phone number displayed to the called party. Set in the SIP From header. See caller ID reputation.

CNAM (Calling Name) — The 15-character name displayed alongside the CID number. Stored in LIDB databases. See CNAM guide.

Codec — Coder-decoder: converts voice to digital data and back. Common VoIP codecs: G.711, G.729, Opus.

CPaaS (Communications Platform as a Service) — API-based communications platform (Twilio, Telnyx). Contrast with carrier-direct SIP trunking. See VoIP buyer’s guide.

CPS (Calls Per Second) — Rate at which your system initiates new call attempts. Limited by carrier capacity, server processing, and bandwidth.

D

DID (Direct Inward Dial) — A phone number that routes directly to a specific endpoint. See DID guide.

DNC (Do Not Call) — The National DNC Registry plus company-specific and state lists. Must scrub every 31 days. See TCPA guide.

DTMF (Dual-Tone Multi-Frequency) — Touch-tone signals from phone keys. Transmitted via RFC 2833 (recommended), SIP INFO, or in-band audio in SIP.

E

E.164 — International phone number format: + country code + subscriber number. For US: +1XXXXXXXXXX. See E.164 guide.

E911 (Enhanced 911) — VoIP emergency calling service that provides location information to 911 dispatchers. Required for VoIP providers serving end users.

F

FCC (Federal Communications Commission) — US federal agency regulating telecommunications. Issues carrier licenses, enforces TCPA, mandates STIR/SHAKEN.

FOC (Firm Order Commitment) — The confirmed date for a number port to complete. Set during the LNP process.

FreePBX — Open-source PBX web interface built on Asterisk. Provides GUI management for call routing, trunks, extensions. See PBX guide.

G

G.711 — Uncompressed voice codec at 64 kbps. Highest quality (MOS 4.4). Standard for call centers.

G.729 — Compressed voice codec at 8 kbps. Good quality (MOS 3.9). Used when bandwidth is limited. See codec comparison.

H

Hosted PBX — Cloud-managed phone system (RingCentral, Zoom Phone). Provider handles all infrastructure. See hosted PBX vs SIP trunking.

I

INVITE — The SIP message that initiates a call. Contains called number, caller ID, and codec preferences.

IVR (Interactive Voice Response) — Automated phone menu (“Press 1 for sales, 2 for support”). Configured in PBX dial plan or VICIdial in-group settings.

J

Jitter — Variation in packet arrival timing. Causes choppy audio when excessive. Target: under 30ms. See VoIP quality.

L

Latency — Time for a packet to travel from source to destination. One-way target: under 150ms for voice. See VoIP quality.

LIDB (Line Information Database) — Database storing CNAM records. Queried by terminating carriers to display caller name.

LNP (Local Number Portability) — FCC-mandated right to port phone numbers between carriers. See number porting.

LOA (Letter of Authorization) — Document authorizing a carrier to port your phone numbers. Required for LNP.

M

MOS (Mean Opinion Score) — Voice quality score from 1 (unintelligible) to 5 (excellent). Target: 4.0+ for call centers. See VoIP quality.

MMS (Multimedia Messaging Service) — Text messaging with images, video, and audio support. See SMS vs MMS.

N

NANPA (North American Numbering Plan Administration) — Organization managing area code and number block assignments for US, Canada, and Caribbean nations.

NAT (Network Address Translation) — Router process translating private IPs to public IPs. Causes one-way audio in VoIP if not configured correctly. See VICIdial setup.

NPA-NXX — First 6 digits of a US phone number (area code + exchange). Used for routing and geographic identification.

O

Opus — Modern adaptive codec (6-128 kbps). Exceeds G.711 quality at high bitrates. Increasingly supported but not yet universal.

P

Packet Loss — Percentage of voice packets that never arrive. Target: under 1%. Causes audio gaps. See VoIP quality.

PBX (Private Branch Exchange) — Business phone system handling internal switching and external connectivity. See PBX guide.

PDD (Post-Dial Delay) — Time between sending a call and the recipient’s phone ringing. Target: under 3 seconds. See telecom acronyms.

POTS (Plain Old Telephone Service) — Traditional analog landline service over copper pairs. Being decommissioned. See VoIP vs landline.

PRI (Primary Rate Interface) — Legacy voice delivery: 23 channels over T1 line. Being sunset. See SIP vs PRI.

PSTN (Public Switched Telephone Network) — The global telephone network connecting callers worldwide.

Q

QoS (Quality of Service) — Router-level traffic prioritization for voice packets. Essential on shared internet connections. See VoIP quality.

R

RespOrg (Responsible Organization) — Entity authorized to manage toll-free number routing. See toll-free guide.

RMD (Robocall Mitigation Database) — FCC database where carriers file compliance certifications. Non-filers may have traffic blocked. See RMD guide.

RTP (Real-time Transport Protocol) — Protocol carrying actual voice audio during calls. See RTP guide.

S

SDP (Session Description Protocol) — Protocol in SIP messages describing media session parameters (codecs, IPs, ports).

SIP (Session Initiation Protocol) — Signaling protocol for setting up, managing, and ending voice calls over IP. See SIP guide.

SIP Trunk — Logical connection between your PBX and a carrier via SIP protocol for PSTN access. See SIP trunking guide.

SMS (Short Message Service) — Text messaging limited to 160 characters per segment. See SMS vs MMS.

SP-KI (Service Provider Key Identifier) — The STIR/SHAKEN certificate held by carriers for signing calls. See STIR/SHAKEN technical guide.

SRTP (Secure RTP) — Encrypted version of RTP for secure voice transmission. See VoIP security.

STIR/SHAKEN — Cryptographic caller ID verification framework. See STIR/SHAKEN guide.

T

TCPA (Telephone Consumer Protection Act) — Federal law governing autodialed calls, texts, and consent requirements. See TCPA guide.

TLS (Transport Layer Security) — Encryption for SIP signaling. Prevents eavesdropping on call setup. See VoIP security.

TSR (Telemarketing Sales Rule) — FTC regulation requiring caller identification and prohibiting certain practices. See compliance guide.

U

UCaaS (Unified Communications as a Service) — Bundled cloud phone + video + chat platform (RingCentral, Zoom Phone). See VoIP buyer’s guide.

UDP (User Datagram Protocol) — Network protocol used by RTP for voice. Sends packets without delivery guarantees for minimum latency. See RTP guide.

V

VICIdial — Open-source predictive dialer built on Asterisk. The standard platform for outbound call centers. See VICIdial carrier.

VoIP (Voice over Internet Protocol) — The broad category of voice communication over IP networks. SIP is the dominant protocol within VoIP. See SIP vs VoIP.

W

WebRTC (Web Real-Time Communication) — Browser-based real-time voice/video protocol. Enables calling from web pages without plugins.

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SIPNEX provides the carrier infrastructure behind the acronyms — SIP trunking, DIDs, STIR/SHAKEN, and support that speaks the language. Get started or see our rates.