SMS glossary
The technical, legal and security concepts of the SMS, laid out simply. One sentence to grasp the essentials, one paragraph to go further.
Fundamentals
SMS
An SMS (Short Message Service) is a text message from the GSM standard capped at 160 characters, carried by the mobile network without ever revealing anything beyond the sender's number.
To go deeperMMS
An MMS (Multimedia Messaging Service) extends the SMS to carry photo, sound or video, freeing itself from the 160-character cap.
To go deeperRCS
RCS (Rich Communication Services) is the protocol meant to replace the SMS, with read receipts, a typing indicator and enriched messages.
To go deeperMVNO
An MVNO (Mobile Virtual Network Operator) is an operator that sells plans without owning any masts, by renting the network of an infrastructure operator.
To go deeperNumber portability
Number portability lets you change operator without losing your number, which makes the prefix useless for deducing the operator serving the line.
To go deeperRoaming
Roaming lets you use your mobile on a foreign or partner network, outside your own operator's network.
To go deeperTechnical aspects
GSM-7 alphabet
GSM-7 is the 7-bit character set used by default for SMS: it opens up 160 characters per message but omits some accented letters.
To go deeperUCS-2
UCS-2 is the 16-bit encoding triggered as soon as an SMS contains a character foreign to GSM-7: the capacity then drops to 70 characters per message.
To go deeperConcatenated SMS
A concatenated SMS is a long message chopped into several SMS that the phone reassembles, each segment carrying only 153 characters in GSM-7.
To go deeperSMS-C (operator's server)
The SMS-C is the operator's server that receives, holds then re-sends SMS as long as the recipient isn't reachable.
To go deeperDelivery report (DLR)
The delivery report, or DLR, is the notice returned by the network specifying whether an SMS has indeed reached the targeted phone.
To go deeperE.164 format
E.164 is the worldwide phone numbering standard: the number appears preceded by its country code, for example +33 for France.
To go deeperShort code
A short code fits in a few digits, reserved for services, and is used notably for opt-outs and reporting.
To go deeperAlphanumeric sender
An alphanumeric sender, or Sender ID, displays a brand name in place of a number as the sender of an SMS, within a limit of 11 characters.
To go deeperLegal framework
Opt-in
Opt-in is the prior, free and explicit consent a person gives to agree to receive commercial messages.
To go deeperOpt-out
Opt-out is the ability to leave a mailing list, embodied in SMS by the "STOP" notice.
To go deeperA2P SMS
An A2P SMS (Application-to-Person) is a message emitted automatically by a computer system to a mobile, as opposed to a text written by a human.
To go deeperSecurity
OTP code
An OTP code (One-Time Password) is a single-use, short-lived code, sent by SMS to validate a login or a payment.
To go deeperSmishing
Smishing is phishing carried out by SMS, seeking to extort personal or bank data by posing as a trusted organisation.
To go deeper33700 reporting (SMS spam)
33700 is the French service that lets you report an unwanted SMS free of charge by forwarding it to this short code.
To go deeper// Anonymous SMS · Hidden number · To France
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