Reference
SMS and SMPP glossary
32 terms you meet when you buy, sell or run A2P SMS traffic, explained in plain words.
32 termsUpdated 26 October 2026
- A2P SMS
- Application-to-person messaging: messages sent by a business system to people, such as codes, alerts and marketing.
- Aggregator
- A company that buys SMS delivery from many suppliers and sells it to many customers, usually over SMPP and HTTP.
- Bind
- An authenticated SMPP session. A transmitter bind sends, a receiver bind receives, a transceiver bind does both.
- Concatenated SMS
- A long message split into parts with a header (UDH) so the handset can join them again. Each part is billed as a segment.
- Data coding
- The data_coding field that says how the text is encoded, for example GSM-7 or UCS-2 (Unicode).
- deliver_sm
- The SMPP command used to send a message or a delivery receipt from the SMSC to the ESME.
- DLR
- Delivery receipt or delivery report: the message that tells the sender the final state of an SMS.
- ESME
- External Short Message Entity: an application that connects to an SMSC or gateway over SMPP.
- esm_class
- An SMPP field that describes the message type, for example a delivery receipt or a message with a UDH.
- GSM-7
- The default 7-bit SMS alphabet: 160 characters in one SMS, 153 per part in a long message.
- HLR lookup
- A query to the home location register, or a service built on it, to check that a number exists and which network serves it.
- Least-cost routing (LCR)
- Choosing, for each destination, the cheapest supplier that meets the quality you require.
- MCC/MNC
- Mobile country code and mobile network code: together they identify a mobile network.
- MNP
- Mobile number portability: a number can move to another network, so routing by prefix alone can be wrong.
- MO
- Mobile-originated: a message sent by a phone, for example a reply to a virtual number.
- MT
- Mobile-terminated: a message delivered to a phone.
- OTP
- One-time password: a short code sent by SMS to verify a login or a payment.
- PDU
- Protocol data unit: one SMPP command or response on the wire, such as submit_sm or submit_sm_resp.
- Segment
- One SMS part. Long or Unicode messages use several segments and are usually billed per segment.
- Sender ID
- The name or number shown as the sender. Many countries require alphanumeric sender IDs to be registered.
- SMPP
- Short Message Peer-to-Peer: the standard protocol for exchanging SMS between applications, gateways and SMSCs.
- SMSC
- Short Message Service Centre: the network element that stores and forwards SMS.
- SMS firewall
- A filter that blocks unwanted or fraudulent SMS traffic by sender, content, origin or destination.
- SS7
- Signalling System No. 7: the signalling network used by mobile operators, also to deliver SMS.
- submit_sm
- The SMPP command an ESME uses to send a message.
- System ID
- The username of an SMPP account, sent in the bind request with the password.
- TLV
- Tag-length-value: an optional SMPP parameter added to a PDU.
- TON/NPI
- Type of number and numbering plan indicator: they say how an address is written, for example international or alphanumeric.
- TPS
- Transactions per second: the rate at which messages are sent or accepted.
- UCS-2
- The 16-bit encoding used for Unicode SMS: 70 characters in one SMS, 67 per part in a long message.
- UDH
- User data header: the header at the start of a message part, used for concatenation.
- Validity period
- How long the network keeps trying to deliver a message before it expires.
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