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Phone System Glossary — VoIP Terms in Plain Language
Plain-language definitions for the terms you'll meet in Signal and in any modern business phone system. Each entry is self-contained.
Auto attendant — the recorded menu that answers a number and routes callers by keypress ("press 1 for scheduling"). Also called a virtual receptionist; in enterprise contexts, an IVR.
BLF (Busy Lamp Field) — a phone button that shows live status of another extension (idle/ringing/busy) and doubles as one-touch call, transfer, or pickup.
CNAM — the caller ID name database record. Receiving carriers look up and display it; updates propagate on their schedule.
DID (Direct Inward Dial) — a public 10-digit phone number. "DID" and "phone number" are used interchangeably.
E911 — enhanced 911: emergency calls carry the registered street address of the phone's location so dispatch knows where to go.
Extension — an internal identity (3–4 digits) representing a person or role; rings one or more devices.
Hunt group / ring group / call group — one target that rings several extensions, together or in sequence. Signal's term: call group.
LNP / porting — moving your existing numbers between carriers. Numbers keep working at the old carrier until the port completes.
MAC address — a device's 12-character hardware identifier; how a desk phone is recognized by provisioning.
PoE (Power over Ethernet) — power delivered through the network cable, eliminating phone power adapters.
QoS (Quality of Service) — network settings that prioritize voice packets over bulk traffic; the cure for choppy calls on busy links.
Registration — a device's authenticated, periodically-refreshed connection to the platform; a registered device can make and receive calls.
SIP — Session Initiation Protocol, the signaling standard VoIP systems use to set up and tear down calls.
SRTP — encrypted voice media.
Softphone — a phone as software: Signal's web and mobile apps, or third-party SIP clients.
Toll fraud — theft of service by placing premium-rate calls on stolen credentials; mitigated by per-extension international-dialing controls.
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Last reviewed August 6, 2026. Still stuck? Contact Signal Support from your portal — include what you expected, what happened instead, and one example phone number or extension.