Telecom Glossary

Each term links to this page directly by its name. For fuller explanations, see our insights.

A-Z termination

A voice termination service that can deliver calls to every international destination code.

A2P SMS

Application-to-person SMS: a message sent by software to a person, such as a one-time passcode or bank alert. Priced under separate A2P agreements by mobile operators.

ACD

Average call duration: the mean length of answered calls on a route. Unusually short ACD can indicate poor quality or false answer supervision.

AIT

Artificially inflated traffic, also called SMS pumping: fraudulent OTP or sign-up requests that generate messages to number ranges sharing revenue with the fraudster.

ASR

Answer-seizure ratio: the share of call attempts that are answered, used to measure voice route quality.

CDR

Call (or charging) detail record: the record of a call or message, used for billing and reconciliation between carriers.

CLI

Calling line identification: the caller's number as presented to the called party.

CPaaS

Communications platform as a service: a cloud platform that lets developers add SMS, voice and verification to their applications.

Diameter

The signaling protocol used between core network elements and roaming partners in 4G networks, replacing MAP over SS7.

DID

Direct inward dialling number: a phone number that routes inbound calls to a specific endpoint on a customer's network.

DLR

Delivery report or delivery receipt: the status message confirming whether an SMS reached the handset.

ESME

External short message entity: any system outside the mobile network, such as an aggregator or application, that sends or receives SMS through an SMSC.

FlashCall

A phone number verification method that places a short, unanswered call whose calling number carries the verification code.

Global Title (GT)

An address used in SS7 signaling to route messages between networks, identifying network elements such as HLRs, MSCs and SMSCs.

Grey route

A delivery path that carries commercial A2P SMS through connections priced for person-to-person traffic, so the receiving operator is not paid its A2P rate.

GTP

GPRS Tunnelling Protocol: the protocol that sets up and carries mobile data sessions, including data roaming between networks.

HLR, HSS, UDM

The subscriber databases of 2G/3G (HLR), 4G (HSS) and 5G (UDM) networks, which hold subscriber profiles and current location.

Honeypot (telecom)

Controlled trap numbers used to observe how SMS or calls reach a network, revealing grey routes and SIM box termination.

LCR

Least-cost routing: selecting a supplier for each call or message by destination, price and quality rules.

MAP

Mobile Application Part: the SS7 protocol layer used for mobile operations such as location updates and SMS delivery.

MT-ForwardSM

The MAP operation that delivers a mobile-terminated SMS to the network serving the recipient.

MVNO

Mobile virtual network operator: an operator that sells mobile services using another operator's radio network. Full MVNOs can run their own core elements, such as an SMSC.

OTP

One-time password: a short code sent to verify a user, usually by SMS or flash call.

P2P SMS

Person-to-person SMS: a message sent by one subscriber to another.

PDD

Post-dial delay: the time between dialling and hearing ringing, a measure of voice route quality.

SIGTRAN

A set of protocols that carries SS7 signaling over IP networks, for example M3UA over SCTP.

SIM box

A device holding many SIM cards that injects international calls or bulk SMS into a network as if they were local subscriber traffic.

SIP

Session Initiation Protocol: the signaling protocol used to set up voice calls over IP, including interconnects between carriers.

SMPP

Short Message Peer-to-Peer: the protocol ESMEs and SMSCs use to exchange SMS over TCP/IP.

SMPP gateway

A platform that accepts SMS from business customers over SMPP or HTTP and forwards them to upstream SMSCs, with account, routing and security controls.

SMS firewall

A network element that inspects inbound SMS and allows, blocks or re-routes messages to stop grey routes, spoofing and abuse.

SMS home routing

A configuration in which inbound SMS routing queries are answered by a network element that protects the subscriber's real identity and location.

SMSC

Short message service centre: the network element that stores and forwards SMS to handsets.

SRI-for-SM

SendRoutingInfoForSM: the MAP query a sending network uses to find where to deliver an SMS.

SS7

Signaling System No. 7: the signaling network used to set up calls, deliver SMS and support roaming between telephone networks.

STP

Signal transfer point: a router in the SS7 network that relays signaling messages between network elements and operators.

TON/NPI

Type of number and numbering plan indicator: SMPP fields that describe how a source or destination address is formatted, for example international E.164.

Voice origination

The wholesale service that delivers inbound calls dialled to a provider's numbers into the customer's network.

Voice termination

The wholesale service that delivers outbound calls to the destination network of the called party.