> ## Documentation Index
> Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Telecom glossary

> Glossary of telecom and VoIP terminology including ACD, ANI, CDR, DID, MOS, SIP trunking, E911, and other carrier-grade voice acronyms.

| Term          | Definition                                                                                                              |
| ------------- | ----------------------------------------------------------------------------------------------------------------------- |
| ACD           | Average Call Duration — Mean time a call lasts.                                                                         |
| ANI           | Automatic Number Identification — Identifies the caller’s number.                                                       |
| ASR           | Answer-Seizure Ratio — Ratio of answered to attempted calls.                                                            |
| B2BUA         | Back-to-Back User Agent — VoIP architecture for media and signaling control.                                            |
| CDR           | Call Detail Record — Metadata generated for a telecom transaction.                                                      |
| CLD           | Calling Line Destination — Identifies the called party’s number in a VoIP call setup.                                   |
| CLI           | Calling Line Identification — Displays the caller’s phone number.                                                       |
| CNAM          | Caller Name — Displays the name associated with the caller’s number.                                                    |
| CPE           | Customer Premises Equipment — Devices installed at a customer’s location.                                               |
| CPaaS         | Communications Platform as a Service — Telecom services offered via cloud.                                              |
| Codec         | Audio compression methods (G.711, G.729, Opus) used in VoIP.                                                            |
| DID           | Direct Inward Dialing — Allows external callers to reach an internal extension.                                         |
| DNIS          | Dialed Number Identification Service — Identifies the number dialed by the caller, used for routing inbound VoIP calls. |
| DS0/DS1/DS3   | Digital Signal Levels — T-carrier transmission system levels (e.g., DS1 = T1 line).                                     |
| DTLS          | Datagram TLS — Used in WebRTC encryption.                                                                               |
| DTMF          | Dual Tone Multi-Frequency — Signals used for dialing and input (touch-tone).                                            |
| E.164         | Numbering Format — International telephone numbering standard.                                                          |
| E911          | Enhanced 911 — Provides caller location info to emergency services.                                                     |
| ENUM          | Telephone Number Mapping — Converts phone numbers to Internet addresses.                                                |
| FAS           | False Answer Supervision — Fraudulent call charge without real connection.                                              |
| ICE           | Interactive Connectivity Establishment — Helps with NAT traversal in VoIP.                                              |
| IVR           | Interactive Voice Response — Automated telephony system for user interaction.                                           |
| Jitter        | Variation in packet arrival time that can affect voice quality.                                                         |
| Jitter Buffer | Helps to smooth audio variations in VoIP packets.                                                                       |
| LATA          | Local Access and Transport Area — Geographic area for call routing.                                                     |
| LEC           | Local Exchange Carrier — Provides local phone service.                                                                  |
| LNP           | Local Number Portability — Keep phone numbers when changing providers.                                                  |
| Latency       | Delay between sending and receiving data.                                                                               |
| MOS           | Mean Opinion Score — Subjective quality rating of voice (1–5).                                                          |
| NPA-NXX       | Numbering format: NPA = area code; NXX = central office code.                                                           |
| PBX           | Private Branch Exchange — Internal phone switching system in organizations.                                             |
| PDD           | Post Dial Delay — Time from call initiation to ringing.                                                                 |
| POTS          | Plain Old Telephone Service — Basic analog phone service.                                                               |
| PRI           | Primary Rate Interface — ISDN line with multiple voice/data channels.                                                   |
| PSTN          | Public Switched Telephone Network — Traditional circuit-switched network.                                               |
| QoS           | Quality of Service — Measures reliability and performance of telecom service.                                           |
| RTP           | Real-Time Transport Protocol — Used for transmitting audio/video streams.                                               |
| Rate Center   | A geographic area used to determine local vs. long-distance calls.                                                      |
| SBC           | Session Border Controller — Secures and manages VoIP traffic.                                                           |
| SDC           | Short Duration Calling — Often used in VoIP fraud detection and SIP trunk analysis.                                     |
| SHAKEN/STIR   | Caller ID verification to prevent spoofing.                                                                             |
| SIP           | Session Initiation Protocol — Initiates and manages VoIP calls.                                                         |
| SIP Proxy     | A SIP server that routes and forwards SIP requests, enforcing policy and facilitating call setup.                       |
| SIP Trunk     | Virtual VoIP trunk line — Replaces traditional PRI.                                                                     |
| SIPS          | SIP over TLS — Secure VoIP signaling.                                                                                   |
| SRTP          | Secure RTP — Encrypts RTP media streams.                                                                                |
| STUN/TURN     | Servers to support NAT traversal in real-time communications.                                                           |
| T.38          | Protocol for Fax over IP (FoIP).                                                                                        |
| TLS           | Transport Layer Security — Encrypts communications over IP.                                                             |
| UCaaS         | Unified Communications as a Service — Integrated voice, video, messaging.                                               |
| VoIP          | Voice over Internet Protocol — Sends voice over IP networks.                                                            |
| WebRTC        | Web Real-Time Communication — Browser-based real-time media exchange.                                                   |