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SMS glossary: A2P, SMPP, DLR, MNP and more, in one or two lines
The words you meet when you send SMS from software, explained in one or two lines each.
Terms
| Term | Meaning |
|---|---|
| A2P | Application-to-person: messages sent by software (codes, alerts, marketing) to people. |
| P2P | Person-to-person messaging between two phones; most networks treat bulk traffic disguised as P2P as fraud. |
| Alphanumeric sender ID | A sender name of up to 11 letters and digits instead of a number. Some countries require it to be registered; replies are not possible. |
| Bind | An authenticated SMPP session: transmitter (send), receiver (receive) or transceiver (both). |
| Concatenated SMS | A long text split into parts (153 GSM-7 or 67 UCS-2 characters each) that the phone joins again; each part is billed. |
| DLR (delivery receipt) | The report a network sends back with the final state of a message: delivered, undelivered, expired… |
| E.164 | The international number format: country code plus national number, up to 15 digits (e.g. +573001234567). |
| Encoding (GSM-7 / UCS-2) | GSM-7 fits 160 characters per SMS; any character outside it (emoji, many accents, non-Latin scripts) switches the message to UCS-2 with 70. |
| ESME | External Short Message Entity: in SMPP, the client application that connects to the gateway. |
| Flash SMS | A message shown directly on the screen and not stored by default (class 0). |
| HLR / MNP lookup | A query that tells whether a number is valid and which network it belongs to today, including ported numbers. |
| LCR (least-cost routing) | Choosing, per destination network, the supplier route with the best price for the required quality. |
| Long code / short code | A normal phone number used to send (long code) or a short number of 3–6 digits approved per country (short code). |
| MO / MT | Mobile-originated (a message sent by a phone, e.g. a reply) and mobile-terminated (a message sent to a phone). |
| MCC / MNC | Mobile country code and mobile network code: together they identify a network (e.g. 732-101). |
| Opt-out | A recipient's request to stop receiving messages (e.g. replying STOP); senders must honour it. |
| OTP | One-time password: a short code sent to verify a phone number or a login. |
| SMPP | Short Message Peer-to-Peer: the binary TCP protocol (version 3.4 in practice) used between applications and SMS gateways for high volume. |
| SMSC | Short Message Service Centre: the network element that stores and forwards SMS to phones. |
| SMS pumping (AIT) | Artificially inflated traffic: bots trigger messages (often OTPs) to numbers whose operator shares the revenue with the fraudster. |
| Throughput (TPS) | Messages per second an account or bind may send; going faster returns ESME_RTHROTTLED. |
| TON / NPI | Type of number and numbering plan indicator of an SMPP address (e.g. TON 1 / NPI 1 for an international number, TON 5 for alphanumeric). |
| UDH | User data header: bytes at the start of a message that carry concatenation or port information. |
| Validity period | How long the network keeps trying to deliver a message before it expires. |
| Webhook | An HTTP call the platform makes to your server when something happens (a status change, a reply). |
Frequently asked questions
Why is my 100-character message billed as two SMS?
It probably contains a character outside GSM-7 (an emoji or certain accents), so it is sent as UCS-2, where one SMS holds 70 characters.
Is SMPP better than an HTTP API?
SMPP keeps a connection open and suits sustained high volume; an HTTP API is simpler to integrate. Many platforms offer both with the same routes and prices.
Read more
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