Random Facts: Why SMS Is Only 160 Characters

from the that's-a-bit-refreshing dept

The LA Times has tracked down the reasoning for why SMS text messaging is limited to 160 characters. Basically, one guy working on the project figured that was plenty after typing a bunch of sentences out and noticing that most were less than 160 characters. There was no serious additional research done on it. It just sorta stuck once implemented. In an age where so many things are user-tested to death, it's kind of nice to know this was almost an accident of history, based on the reasoning of one guy.


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  1.  
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    dieselmcfadden, May 4th, 2009 @ 5:06pm

    or it could be because the out-of-band signaling channel could fit 160 characters of effectively "free" bandwidth to the cell towers and no more....

     

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  2.  
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    Anonymous Coward, May 4th, 2009 @ 5:19pm

    it must be true

    If the LA times reported it then it must be true. Google- LA Times- correcting the correction correction of the correcting the correction correction.

    Not making that up....but they may have.

     

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  3.  
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    Anonymous Coward, May 4th, 2009 @ 5:24pm

    Shhhh, don't let word word get out.

    Musn't let people know that by using the out of band signaling channel, SMS cost the providers almost nothing.

    Better that they believe some knuckle head couldn't string more than 160 coherent characters together. :D

     

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  4.  
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    Mike (profile), May 4th, 2009 @ 5:28pm

    Re:

    or it could be because the out-of-band signaling channel could fit 160 characters of effectively "free" bandwidth to the cell towers and no more....

    The article notes that they could originally only fit 128 characters, and they knew that wasn't enough... so they had to work to get it up to 160.

     

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  5.  
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    Anonymous Coward, May 4th, 2009 @ 5:29pm

    Hmm

    It's also the most expensive method to transmit information. I read somewhere that at 10-cents a text, it weighed in at about $1,300 a megabyte, making the $17/megabyte cost to receive pictures from the Hubble Telescope a real bargain.

    But yes, SMS used excess signaling capacity in the BCCH if I recall, and for the most part, all the result of a series of mistakes, but adopted from the bottom-up instead of top-down.

    In it's infancy before T9 prediction technology, it was seen as too difficult for the older folks, but adopted very quickly by the younger ones.

     

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  6.  
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    Zaven (profile), May 4th, 2009 @ 5:40pm

    Like a lot of things in the news paper, I'm pretty sure this story is not entirely true. The real reason is because there are 160 bytes left in the messages that get sent to towers to determine signal strength.

     

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  7.  
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    Lawrence D'Oliveiro, May 4th, 2009 @ 5:58pm

    Data Efficiency

    Note that 160 bytes is equivalent to 80 Unicode characters. In an ideographic script (e.g. Chinese, Japanese) that’s about 80 words, which is way more than you can manage with an alphabetic script. So the East Asians get to say more in each txt than anybody else does. :)

    Why don’t they include some compression in the text encoding? English text only has an information content of about 1.2 bits per character. You know why people leave vowels out of their txts? They’re basically making up for the lack of compression. But why not let the computers do the work for us?

     

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  8.  
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    mobiGeek, May 4th, 2009 @ 5:59pm

    In an age where so many things are user-tested to death

    I don't know what fancy-pants technologies you are using...

    Or is it that your definition of "user-tested" radically different from most high-tech companies I have to deal with?

     

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  9.  
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    Mike (profile), May 4th, 2009 @ 6:27pm

    Re:

    Or is it that your definition of "user-tested" radically different from most high-tech companies I have to deal with?

    Heh. Fair enough... I think I was thinking of recent stories about user-testing coming out of Google and Yahoo.

     

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  10.  
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    Anonymous Coward, May 4th, 2009 @ 6:31pm

    Re: Data Efficiency

    So are you saying that the kids who leave out vowels are all infringers of Huffman or LZW compression algorithms too?

    Bad kids! Go to your room :-P

     

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  11.  
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    Jim Gaudet (profile), May 4th, 2009 @ 6:34pm

    Who needs bete testing

    To come up with a great idea....

     

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  12.  
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    John, May 5th, 2009 @ 4:51am

    DWN WTH VWLS!

     

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  13.  
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    Anonymous Coward, May 5th, 2009 @ 6:43am

    Re:

    O I OOA

     

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  14.  
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    Anonymous Coward, May 5th, 2009 @ 7:07am

    Re:

    U OU

     

    reply to this | link to this | view in thread ]

  15.  
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    Derek Kerton (profile), May 5th, 2009 @ 7:26am

    Re: Data Efficiency

    People leave out letters for three reasons:

    1) manual compression, as you said
    2) entering each character historically can require a triple-tap, so each skipped character saves more than one keystroke. That's a big speed improvement.
    3) overall space is limited, both the 160 limit, and the size of the screen for composing and reading. Shorter fits better.

     

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  16.  
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    dspntd, May 5th, 2009 @ 7:27am

    Re:

    DMN U TRLLS!

     

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  17.  
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    Derek Kerton (profile), May 5th, 2009 @ 8:28am

    Glamorous Story, But Not Quite True

    This LA Times article is missing critical information. SMS was not designed so deliberately by one man. It was mostly an accident of the technical specs of a GSM cellular network.

    The specs defined the size of packets that were to be sent from the network, over the SS7 signaling network, and then wirelessly over the control channel from a tower to the phones connected to it. The tower needs to communicate with the phones to get their ID, check their credentials, tell them when to switch to another tower, tell them if they have a voicemail waiting, tell them to ring, accept their dialing call requests, etc. These are all "control" events.

    Voice calls take place on TWO separate radio channels, one for voice in and one for voice out, and the radio is only activated to do this when needed. This saves on bandwidth and on battery. The control channel, on the other hand, is more or less always on. Phones use this channel to set up the calls and activate the voice channel. THIS is the original purpose of this channel in the GSM standard, and the size and length of control instruction packets was defined around these tasks.

    So later on, some people decided to "tack on" the ability to send a message inside this same channel. It WAS smart, and it does make sense. They simply looked at the packet size they had available, and made the best of it. This made it into the GSM standard, and since GSM is a rigid standard, all the terminal vendors built handsets that complied.

    It was a great "invention", but it was invention by committee, not one guy (and more than one guy claims credit). That's how the GSM Association works. Also, it was not as "free form" as the LA Times would have you believe - some guy typing messages out to see how long they were, and deciding on 160 characters. Maybe it's true that he did that as well, but if so, he did it just to test whether 160 would be adequate. The SMS specs were already constrained to 140 bytes by the real priority technical specs, and the SMS function was just a "nice to have" add in.

    You see, the network control signals were sent between tower and handset in a packet that included header information plus about 140 bytes of payload. If you wanted to piggyback on this existing channel, you had 140 bytes to work with - no matter what your typewriter experiment concluded.

    Hillebrand, or someone, then took the 140 byte limit (1 byte = 8 bits = 1 character), and figured an easy way to use a reduced character set of 7 bits each to squeeze 160 characters out of the constraint (140 * 8 / 7 = 160)

    Therefore, an SMS message isn't limited to 160 characters because of some dude's typewriter experiment. It is limited because the signaling channel's standard packet size payload was 140 bytes. It's a less glamorous reality.

     

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  18.  
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    Get a Life..., May 5th, 2009 @ 9:26am

    Texting is stupid.

    Just call them. I don't text, so I don't really care what the limit is!

     

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  19.  
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    mp3, May 6th, 2009 @ 6:18am

    I so prefer call than type text, for me more intresting sendig big data via music

     

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  20.  
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    another mike, May 6th, 2009 @ 12:21pm

    twitter?

    Where does Twitter's 140 character limit come from then? I'd have thought they'd set up a system where you could submit your microblog by SMS message. It would have synchronized more with existing communication technology.

     

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  21.  
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    porno izle, Jun 25th, 2009 @ 8:46am

    Re:

    Note that 160 bytes is equivalent to 80 Unicode characters. In an ideographic script (e.g. Chinese, Japanese) that’s about 80 words, which is way more than you can manage with an alphabetic script. So the East Asians get to say more in each txt than anybody else does. :D (Y)porno izle,sikiş izle

     

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  22.  
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    Allan Masri (profile), Sep 8th, 2009 @ 11:47am

    Re: Data Efficiency

    So the East Asians get to say more in each txt than anybody else does.

    Uh...no, there is not a one-to-one ratio between words and characters in Asian languages. More like one-to-two in Chinese, but Japanese is even less condensed since it uses many particles and spells out many words using syllabaries. Irrelevant, I admit, but amusing.

     

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  23.  
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    Chris, Jan 31st, 2012 @ 11:20am

    SMS is modeled after the postcard you morons....160 characters is the magic number because that's how many was determined would fit on a damn postcard

     

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  24.  
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    Chris, Jan 31st, 2012 @ 11:21am

    SMS is modeled after the postcard you morons....160 characters is the magic number because that's how many was determined would fit on a damn postcard

     

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  25.  
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    STDog, Dec 9th, 2012 @ 3:42pm

    Re: twitter?

    140 characters for the message, 20 characters for the userID.

     

    reply to this | link to this | view in thread ]


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