Why text messages are limited to 160 characters

Credit: Lori Shepler / Los Angeles Times

Alone in a room in his home in Bonn, Germany, Friedhelm Hillebrand sat at his typewriter, tapping out random sentences and questions on a sheet of paper.

As he went along, Hillebrand counted the number of letters, numbers, punctuation marks and spaces on the page. Each blurb ran on for a line or two and nearly always clocked in under 160 characters.

That became Hillebrand's magic number -- and set the standard for one of today's most popular forms of digital communication: text messaging.

"This is perfectly sufficient," he recalled thinking during that epiphany of 1985, when he was 45 years old. "Perfectly sufficient."

The communications researcher and a dozen others had been laying out the plans to standardize a technology that would allow cellphones to transmit and display text messages.  Because of tight bandwidth constraints of the wireless networks at the time -- which were mostly used for car phones -- each message would have to be as short as possible.

Before his typewriter experiment, Hillebrand had an argument with a friend about whether 160 characters provided enough space to communicate most thoughts. "My friend said this was impossible for the mass market," Hillebrand said. "I was more optimistic."

His optimism was clearly on the mark. Text messaging has become the prevalent form of mobile communication worldwide. Americans are sending more text messages than making calls on their cellphones, according to a Nielsen Mobile report released last year.

U.S. mobile users sent an average of 357 texts per month in the second quarter of 2008 versus an average of 204 calls, the report said.

Texting has been a boon for telecoms. Giants Verizon Wireless and AT&T each charge 20 to 25 cents a message, or $20 for unlimited texts. Verizon has 86 million subscribers, while AT&T's wireless service has 78.2 million.

And Twitter, the fastest growing online social network, which is being adopted practically en masse by politicians, celebrities ...

... and news outlets, has its very DNA in text messaging. To avoid the need for splitting cellular text messages into multiple parts, the creators of Twitter capped the length of a tweet at 140 characters, keeping the extra 20 for the user's unique address.

Back in 1985, of course, the guys who invented Twitter were probably still playing with Matchbox cars.

Credit: Friedhelm Hillebrand

Hillebrand found new confidence after his rather unscientific investigations. As chairman of the nonvoice services committee within the Global System for Mobile Communications (GSM), a group that sets standards for the majority of the global mobile market, he pushed forward the group's plans in 1986. All cellular carriers and mobile phones, they decreed, must support the short messaging service (SMS).

Looking for a data pipeline that would fit these micro messages, Hillebrand came up with the idea to harness a secondary radio channel that already existed on mobile networks.

This smaller data lane had been used only to alert a cellphone about reception strength and to supply it with bits of information regarding incoming calls. Voice communication itself had taken place via a separate signal.

"We were looking to a cheap implementation," Hillebrand said on the phone from Bonn. "Most of the time, nothing happens on this control link. So, it was free capacity on the system."

Initially, Hillebrand's team could fit only 128 characters into that space, but that didn't seem like nearly enough. With a little tweaking and a decision to cut down the set of possible letters, numbers and symbols that the system could represent, they squeezed out room for another 32 characters.

Still, his committee wondered, would the 160-character maximum be enough space to prove a useful form of communication? Having zero market research, they based their initial assumptions on two "convincing arguments," Hillebrand said.

For one, they found that postcards often contained fewer than 150 characters.

Second, they analyzed a set of messages sent through Telex, a then-prevalent telegraphy network for business professionals. Despite not having a technical limitation, Hillebrand said, Telex transmissions were usually about the same length as postcards. 

Just look at your average e-mail today, he noted. Many can be summed up in the subject line, and the rest often contains just a line or two of text asking for a favor or updating about a particular project.

But length wasn't SMS's only limitation. "The input was cumbersome," Hillebrand said. With multiple letters being assigned to each number button on the keypad, finding a single correct letter could take three or four taps. Typing out a sentence or two was a painstaking task.

A GSM document outlining the definition of SMS. Credit: Friedhelm Hillebrand.

Later, software such as T9, which predicts words based on the first few letters typed by the user, QWERTY keyboards such as the BlackBerry's and touchscreen keyboards including the iPhone's made the process more palatable.

But even with these inconveniences, text messaging took off. Fast. Hillebrand never imagined how quickly and universally the technology would be adopted. What was originally devised as a portable paging system for craftsmen using their cars as a mobile office is now the preferred form of on-the-go communication for cellphone users of all ages.

"Nobody had foreseen how fast and quickly the young people would use this," Hillebrand said. He's still fascinated by stories of young couples breaking up via text message.

When he tells the story of his 160-character breakthrough, Hillebrand says, people assume he's rich. But he's not.

There are no text message royalties. He doesn't receive a couple of pennies each time someone sends a text, like songwriters do for radio airplay. Though "that would be nice," Hillebrand said.

Now Hillebrand lives in Bonn, managing Hillebrand & Partners, a technology patent consulting firm. He has written a book about the creation of GSM, a $255 hardcover tome.

Following an early retirement that didn't take, Hillebrand is pondering his next project. Multimedia messaging could benefit from regulation, he said. With so many different cellphones taking photos, videos and audio in a variety of formats, you can never be sure whether your friend's phone will be able to display it.

But he's hoping to make a respectable salary for the work this time.

-- Mark Milian

Comments

[Ian Lamont]

Excellent interview. I always wondered about that, and am quite thankful that the limit wasn't set at just 80 or 100 characters -- it would make texting and tweeting a lot more challenging!

A related question, though: How do or did character sets based on non-Roman Alphabet character sets deal with this limit?

Ian Lamont
Managing Editor
The Industry Standard

[Angel]

There is a technical aspect of the GSM encoding that most people doesn't know: It's just 140 bytes. In most encodings (the way computers represent text as 0 and 1) one character of the english language can be seen as a byte, this is because the 8 bits of the byte are used to represent 256 numbers that are mapped to letters, since there is less than 127 characters (leters and symbols) in the english alphabet, the GSM encoding use only 7 bits (less than a byte!) to represent the letters, and taking adventaje of those bits left it finds the way to have 20 more characters than bytes.

[Tim Liao]

What holds us to this 160 character limit. Why can't we, let's say tweak it to 180 or 200 or 250?

[businessethos]

Interesting historical perspective-

many thanks!

@businessethos

[Katrin Verclas]

Great post! And amazing what can be done with 160 characters -- election monitoring to ensure fair and free elections, remote patient support in rural clinics in developing countries, and citizen reporting from crisis situations, to name just a few. There are no limits to human ingenuity in communications when it comes to the humble text message.

For non-Roman character sets - such as Arabic and Chinese, for example, the limit of characters for an SMS is lower. For an Arabic and Chinese speaker, there are only 70 characters available per SMS. There is actually some fascinating research that looks at 'code' and language switching between English (and the 160 characters available) and non-Roman languages, with English being the preferred language that allows texters to cram in more content.

Thanks for this!

Katrin Verclas
MobileActive.org

[Wonderwhy]

All this along with video, Internet, etc. And voice reproduction in these "phones" still suck, What a total scam.

[Kevin Holley]

If you look at GSM WP1 document 82/88 rev 1 (March 1988) you will see that the original length was restricted by base station experts to 250 characters and the demand from the requirements group was for a minimum of 100 characters. The proposal from the data group was 180 characters which was later reduced to 140 bytes with 7 bit coding making 160 characters.

Subsequent developments in the GSM standard allowed for longer messages by concatenating several short messages. Most modern handsets allow more than 160 characters by sending several component messages.

[Yuri]

Looks like there is competition on who invented the SMS and did not get royalties from it!

http://www.hs.fi/english/article/Finnish+inventions+-+going+cheap/1135220274722

[Mark Krenz]

I find it funny that the article states "What was originally devised as a portable paging system for craftsmen using their cars as a mobile office" because what I've seen is companies like Microsoft don't realize this. I'm a system administrator and need for SMS messages to wake me up, but Windows Mobile does not have a re-alert option for SMS messages. I don't understand why it doesn't because it allows you to re-alert for every other kind of event. But for SMS the option is greyed out. And its been this way for a few versions. WTF Microsoft?

Back when we actually used pagers, they would continue beeping every 2 minutes or so if you didn't check a message. This would eventually wake me up if I was sleeping. But now they just make a short and quite beep like every 15 minutes. Companies are forgetting who their original customers where.

[Gareth Wong]

Thanks for your comments above Kevin,

I think and look forward to Fred's post/comments to LA times re poetic license taken too far..

It is great to see success of probably one of the greatest 'standards like GSM/ETSI.. but its mightily weird at times when romantic stories pops up here and there..

We all forget one thing which is that :

1.) we need more coordination, rather than fragmentation of standards, look at 3G/4G..

2.) back to fundamentals/basics, which is as consumers/business, we might only need better service/products (even based on present technical standards) at a fair price..

Its interesting to review the previous stories (romantic or otherwise) regarding rise of iMode in Japan.

BR

@GarethWong

[Baconplus]

Great article, follow it up with "Why are text messages 20 cents a piece". Its a great money maker for the mobile carriers.

[Mike Chen]

Another question is how and why consumers allow the U.S. phone companies to get away with charging such a high rate for something that costs the companies nothing in bandwidth. The 20-25 cent charge for sending and receiving SMS messages is ten times or more higher than what phone companies in Europe charge for domestic SMS.

Since the SMS messages are carried on the secondary frequency that piggybacks on the signal sent to and from phones indicating phone status and doesn't significantly any extra resources for the phone companies, why do all they ALL charge more for that SMS message than a phone call -- which does use up much more bandwidth for that 1-minute call?

If cell companies priced SMS much closer to their relative cost and more people used them in the U.S., the load on the voice/data network would be reduced considerably and they would have much fewer problems with bandwidth. They would have to temporarily sacrifice the huge revenue they get from the windfall that consumers pay them for what costs the companies nothing -- but that might balance out somewhat in reducing the costs needed to upgrade their bandwidth capacity to keep up with ever-increasing voice and data traffic.

Or maybe not. Maybe they've done their calculation and figured out consumers here are more than willing to dish out an extra $10 per month or more for SMS, and this is just free money for the phone companies and none are willing to kill this golden goose.

[Aaron]

The perception that SMS is free for the company in question is incorrect. What started out as "free bandwidth" is in fact not infinite.

I know for certain that mobile networks have had to reallocate bandwidth from the voice channel path and put it into the paging channel in almost any medium or higher density service area.

SMS is also quite a bit more chatty on the SS7 network than other things, it's not exactly a 120 byte packet that is fired off and forgotten about.

Does it cost the carrier .20US to send or receive? Not really, tho I think it has more to do with the US market's fixation on ARPU (Average Revenue per User) .. they REALLY want you to reliably pay $xx.xx per month and not deal with the billing if it means more consistant revenue over the course of the mobile contract. Which is of course pound foolish because revenue is revenue and who cares if it comes in pennies at a time.

[Joe]

"

What holds us to this 160 character limit. Why can't we, let's say tweak it to 180 or 200 or 250?

Posted by: Tim Liao "

Tim,

Instead of asking for more characters to state your message, practice creating messages that use fewer words. More is said with less.

Joe

[Chua]

Perhaps there is a slang and downward trend? Twitter brought the magic number down by 20 to 140. Who know next time it'll be a hundred. Till then, I can afford to type like this.

[Mike]

Um..., no.

GSM is a protocol to coordinate signals from cellphones to cell towers. The towers and phones need to keep in contact so that the towers know that the cell phone is connected and so that they can control where and when the cellphone should switch to a new tower. The control protocol called for a "packet" of data to be sent from the tower to the phone. That packet carried some data, but not nearly enough data to fill the packet.

SMS messages simply fill the remaining bytes in the packets that GSM phones use to coordinate with the network. After the coordination protocol and some SMS headers are counted, there are 140 bytes remaining in the packet. With some simple packing techniques, those 140 bytes can be used to encode 160 7-bit characters, and THIS is why SMS messages are limited to 160 characters. The fact that you can communicate many ideas and sentences in 160 characters is what makes SMS useful.

[Gianluca]

Great article that proves how text messaging has been gold for mobile carriers so far. Sending a text message involves using a pre-existing channel of the communication between phone and cell towers, how can be possible that text messaging rates grew so much in the past years ? (look at the U.S. market for example).

My guess is that text messaging reached a point to evolve (plus be cheaper!) and that's what I found at btexty. If you are interested give it a try: www.btexty.com

[Paul]

Text Messaging: Never have so many paid so much for so little.

[Dr. Singh]

I think the approach they used was suboptimal.

Two ideas I'm sure others have looked at:
5 bits, = 32 char combo. But, use some of those as "function" key to change to different char set, for like numbers and punctuations and capital lettters. This gives you max 224 char but capital letters and numbers and uncommon punctuation takes two blocks, so prog has to count bytes for user. Divides evenly into 1120 bit GSM message block

2nd idea. Some words like "the" "lol" and ";-)" can be encoded as single char. Although youth have already done this already and probably better:
I h8 u 4 cht. brk. 2 bad 4 u.

[JN]

How about some useful reporting on the topic: Why is SMS so freaking expensive???

AT&T examples:
(1500 SMS) / $15.00 * (140 bytes / 1 SMS) = 14 KB / $1.00
(450 Voice Minutes) / $39.99 * (4.75Kbit / 1 second) * (60 seconds / 1minute) * (1 KB / 8Kb) = 400 KB / $1.00

And this is a very conservative approximation - the 450 minutes includes the cost of service, where the 1500 SMS is added to an existing service. The figure 4.75Kb/sec is the absolute worst coding rate for AMR-NB - all cell providers use higher coding rates to improve voice quality.

What gives? Investigative journalism??

[Koko]

160 characters is not enough!

[Peter]

In this day and age, it is ridiculous to think we are still constrained by some archaic and arbitrary considerations made with antique equipment. (oops did I exceed 160)

[Copper]

The end result is just more text messages . . when one of just the right length would have been more efficient.Memory shouldn't be a constraint anymore. Sending of long messages could be done on a bandwidth as available basis

[Phil]

JN,
As pointed out in the article, SMS is probably cell phone companies' most lucrative product. It uses otherwise unused bandwidth and they can charge an arm and a leg for them.

[Pete Ashton]

The New York Times ran a piece last year about the price of text messages given that, as other have noted, they cost the carriers nothing to transmit. I was surprised it wasn't followed up.

http://www.nytimes.com/2008/12/28/business/28digi.html?_r=1&partner=rss&emc=rss&pagewanted=all