Why does a text message have exactly 160 characters?
Question by Trainday | 2012-08-06 at 21:41
I was wondering for a long time, why a text message on the mobile phone has actually just exactly 160 characters. Who came up with this and why exactly this limitation?
160 characters for one SMS are already quite short and sound, at least at a first glance, rather arbitrary. Or has it a special reason?
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Presumably, someone has analyzed, how long such a message should be, so that on the one hand, it can provide enough information and on the other hand, it is also not too long. Perhaps, people have analyzed different notes or the like, to get the ideal length, but I also do not know it exactly.
2012-08-07 at 15:11
That makes no sense. Then, it would be a better idea to make the length of a SMS unlimited, because in an unlimited SMS, really each message possible would fit.
In the same way, nobody says, that the field for the bank account number in a referral has to have a specific length, just because that is the average length of an account number - even though, there are also long account numbers.
Es sagt ja auch niemand, dass das Feld für die Kontonummer auf einer Überweisung auf eine bestimmte Länge begrenzt ist, nur weil dir durchschnittliche Kontonummer diese Länge hat - und das obwohl es längere Kontonummern gibt.
Or, imagine if e-mails would be limited to a certain length!
2012-08-09 at 19:36
In fact, the length is not limited just like that by chance, it has a technical background.
To put it in simple words: the SMS transmission has to run somehow over a communication or broadcast channel in the mobile network. There are certain standards, defining how big such a transmitted packet can be. Each package contains on the one hand the so-called user data, and on the other hand information such as the addressee, the used encoding, the character set and the like.
In the case of the text message, the available package size for the user data (payload) is precisely so big, that it comes to our familiar 160 characters. Specifically, this is exactly a size of 1120 bit.
Incidentally, an SMS can be transmitted in different character encodings. The normal 160 characters correspond to the 7-bit encoding (7x160 bits = 1120 bits), with an 8-bit encoding, only 140 characters are possible (8x140 bit) and with a 16-bit encoding, only 70 characters (16x70 bit). Depending on the encoding, different amounts of storage per single character are used. For example, if special characters or foreign letters must be transferred, the text message has to use more storage space per character as if a limited character set is used.
Naturally, with very long text messages, the data does not fit in one packet. Here, the long SMS will then be sent in parts and the phone of the recipient has to put the parts together. When the mobile phone of the recipient does not support this feature, the text message will also arrive separately.
Who wants to know it in detail, is welcome to search for the terms MAP (Moblie Application Part) and Signaling System 7. These are systems which are used in the transmission.
2012-08-10 at 16:45
Well explained. Another short addition: The channel used for the text message was actually put in place only for occasional other information such as information on the network strength and the like. Since this channel was actually rarely used at that time, the text message could use it and was immediately available and feasible on all networks.
Thus, the text message is emerged as a kind of peripheral product and for this reason, once it was absolutely free. Only later after some time, money was taken for an SMS.
2012-08-12 at 19:27