Telecom glossary

A

# A2P SMS

Application-to-person SMS: a message sent by a software platform (e.g. an OTP service or a marketing tool) to an end-user's mobile handset, as opposed to person-to-person SMS sent between two human handsets.

C

# CLI

Calling Line Identification: the phone number presented to the called party when an outbound call is placed. Increasingly the regulator requires the CLI to be a number the originating party demonstrably controls.

D

# DID

Direct Inward Dialing. A publicly dialable phone number routed straight to the recipient's IP endpoint, instead of via a switchboard. Sold by country and area code.

E

# E.164

ITU-T standard format for international telephone numbers, written as a + sign followed by country code and subscriber number, with a maximum length of 15 digits.

# E.169 / UIFN

ITU-T E.169 defines the +800 international freephone (UIFN) range. A UIFN is a single freephone number that works across multiple originating countries.

# EECC

European Electronic Communications Code (Directive (EU) 2018/1972). The EU framework that governs end-user rights, numbering, emergency services and outbound CLI presentation.

# ENUM

RFC 6116 mapping from E.164 numbers to URIs in DNS. Used for inter-carrier and IP-based routing decisions; effectively a phone-book in DNS records.

F

# Freephone

A toll-free telephone number where the call cost is paid by the called party. Domestic ranges include 0800 and 1800; the international UIFN range (+800) is defined in ITU-T E.169.

G

# Geographic number

A phone number whose dialling code is tied to a specific city or region. Often referred to as a 'local number'. Contrast with non-geographic ranges like freephone or mobile.

H

# Honeypot

A form-input technique to detect automated bots: an invisible field that real users never fill in. Submissions where the honeypot field is non-empty are silently dropped without notifying anyone.

I

# Interconnect

The contractual and technical link between two telecommunications carriers that allows traffic to be exchanged between their networks. GlobalXess holds direct interconnects with the licensed carriers in the countries where we provision numbers.

# IRSF

International Revenue Share Fraud. A pattern where attackers route calls to expensive international destinations they own, profiting from termination revenue. Modern fraud detection catches the pattern in the first few minutes.

J

# Jitter

Variation in the inter-arrival time of voice packets. High jitter degrades call quality; networks compensate using a jitter buffer at the receiving end. Target on a carrier-grade route is under 30 ms.

K

# KYC

Know Your Customer: the regulatory obligation to verify the identity of the party purchasing telecom numbers. For business sign-ups GlobalXess validates the company against the relevant trade register before issuing portal credentials.

L

# LOA

Letter of Authorisation: the document a customer signs to authorise their new carrier to port a phone number away from the previous carrier. The losing carrier validates the LOA against current invoice details before releasing the number.

M

# Mobile number

A phone number from a range that is assigned to a mobile-network operator (MNO) by the local regulator. Can be SMS-capable depending on the operator and the regulator.

# MOS

Mean Opinion Score: a 1-to-5 voice-quality score, calculated either subjectively or by an algorithm such as PESQ or POLQA. A MOS above 4.0 is considered excellent; below 3.5 is degraded.

N

# Number portability

The regulatory right to move a phone number from one carrier to another while keeping the same digits. Implementation varies by country and number range; freephone portability is more restricted than geographic portability.

P

# Port-in

Moving an existing telephone number from another carrier to GlobalXess while keeping the same digits.

# PSTN

Public Switched Telephone Network. The legacy circuit-switched voice network; modern voice is increasingly carried over IP via SIP, with PSTN as the bridge to handsets that have not migrated yet.

R

# RTP / SRTP

Real-time Transport Protocol (RFC 3550) carries the actual voice media on a SIP call. SRTP (RFC 3711) is the encrypted variant used for confidential calls.

S

# SIP

Session Initiation Protocol (RFC 3261). The signalling protocol used to set up and tear down voice and video calls over IP.

# SIP trunk

A virtual replacement for the legacy PSTN trunk. Carries voice (and sometimes signalling extensions) over IP from the customer's PBX or session border controller.

# STIR/SHAKEN

A set of standards (RFC 8224 + RFC 8225 + ATIS-1000074) for cryptographically signing the originating CLI of a call so that the receiving network can verify the caller's number is one they actually control. Mandatory in the US since 2021; rolling out elsewhere.

T

# Two-way voice

A phone number that supports both inbound (DID) and outbound calls, with the number itself presented as the outbound CLI. Many freephone numbers are inbound-only by regulator decision.

W

# Wangiri

A short-duration ringback fraud pattern (Japanese for 'one-ring-and-cut'): the attacker calls victims briefly, hoping they call back to a premium-rate destination. Detection looks at sub-second call patterns at scale.