SMS glossary
The technical, regulatory and security concepts behind SMS, defined simply. One sentence to understand, one paragraph to go further.
The basics
SMS
SMS (Short Message Service) is the text messaging service of the GSM standard, limited to 160 characters per message.
In detailMMS
MMS (Multimedia Messaging Service) is the extension of SMS that carries images, audio or video, with no 160-character limit.
In detailRCS
RCS (Rich Communication Services) is the messaging protocol meant to succeed SMS, with read receipts, typing indicators and rich content.
In detailMVNO
An MVNO (Mobile Virtual Network Operator) is a mobile operator that sells plans without owning a network, renting one from an infrastructure operator.
In detailNumber portability
Number portability lets someone change operator while keeping their phone number, which makes the prefix useless for guessing the operator.
In detailRoaming
Roaming is the ability to use a phone on a foreign or partner network, outside your own operator's network.
In detailTechnical
GSM-7 alphabet
GSM-7 is the 7-bit alphabet used by default for SMS: it allows 160 characters per message but does not contain every accented character.
In detailUCS-2
UCS-2 is the 16-bit encoding used when an SMS contains characters missing from GSM-7: capacity then drops to 70 characters per message.
In detailConcatenated SMS
A concatenated SMS is a long message split into several SMS reassembled by the handset, each segment holding only 153 characters in GSM-7.
In detailSMS-C (message centre)
The SMS-C is the operator's server that receives, stores and forwards SMS until the recipient can be reached.
In detailDelivery report (DLR)
A delivery report, or DLR, is the notification returned by the network stating whether an SMS was delivered to the recipient's handset.
In detailE.164 format
E.164 is the international telephone numbering standard: a number is written with its country code, for example +33 for France.
In detailShort code
A short code is a number of only a few digits, reserved for services and used in particular for opt-outs and spam reporting.
In detailSender ID
A sender ID lets a brand name appear as the sender of an SMS instead of a number, within a limit of 11 characters.
In detailRegulation
Opt-in
Opt-in is the prior, freely given and explicit consent of a person to receive commercial messages.
In detailOpt-out
Opt-out is the ability to unsubscribe from a mailing list, expressed in SMS by the word "STOP".
In detailA2P SMS
An A2P (Application-to-Person) SMS is a message sent automatically by a computer system to a phone, as opposed to one written by a person.
In detailSecurity
OTP code
An OTP (One-Time Password) is a single-use, short-lived code sent by SMS to validate a login or a transaction.
In detailSmishing
Smishing is a phishing attempt carried out by SMS, aiming to obtain personal or banking data by impersonating a trusted organisation.
In detailReporting to 33700
33700 is the French service for reporting an unwanted SMS free of charge, by forwarding it to that short code.
In detailSend your SMS for free
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