Telecom Glossary

Short, plain-English definitions for the terms used across RateCenters.com. This glossary is educational and general in nature — not a technical standard.

Rate Center: A defined telecom area used to determine local calling boundaries and how phone numbers are grouped for rating and numbering purposes.
Area Code (NPA): The three-digit numbering plan area at the start of a North American phone number, covering a broad geographic region.
NPA: Numbering Plan Area — the formal term for what is commonly called an area code.
NXX: The three-digit central office code that follows the area code in a phone number, historically tied to a specific switch.
NPA-NXX: The combined six-digit prefix (area code + central office code) that identifies a specific block of telephone numbers.
Local Calling Area: The set of rate centers considered "local" to a given phone number for calling and billing purposes.
Wire Center: A physical telecom facility where local loops and switching equipment connect, related to but distinct from a rate center.
LERG: A term commonly used for industry routing and numbering reference data that maps number prefixes to rate centers and carrier ownership.
Local Number Portability (LNP): The ability to keep an existing phone number when switching carriers or service providers.
VoIP: Voice over Internet Protocol — technology that carries voice calls over internet connections rather than traditional phone lines.
SIP Trunking: A method of connecting a business phone system to the public telephone network using SIP over an internet connection.
DID Number: Direct Inward Dialing — a phone number that routes directly to a specific line or extension without a shared trunk line.
Local Presence Number: A phone number with a local area code and rate center used so a business appears local to a specific area.
Toll-Free Number: A phone number that can be called without cost to the caller, with usage charges typically billed to the number's owner.
Carrier: A company that provides telecommunications network services, such as voice calling, over its own or leased infrastructure.
CLEC: Competitive Local Exchange Carrier — a telecom company that competes with an established local carrier in a given market.
ILEC: Incumbent Local Exchange Carrier — the historically established local telephone company in a given market.
CPaaS: Communications Platform as a Service — a cloud platform that lets developers add calling, messaging, or video into applications.
Number Pooling: A numbering administration practice where number blocks are allocated in smaller increments to reduce waste of available numbers.