Why Text Messages Are Limited To 160 Characters

The LA Times has a story about Friedhelm Hillebrand, one of the communications researchers behind efforts to standardize various cell phone technologies. In particular, he worked out the 160 character limit for text messages. "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 ... 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. ... 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.

Comments

Re:no, its because 160

[Anonymous Coward]

it also happens to be precisely 2 lines of text on a good old 80 character wide terminal.

Re:no, its because 160

[SgtPepperKSU]

is the bastard offspring of the union of the hexdecimal and the decimal, literally 0xF*10

fixed that for you

Are you joking?
0x10*10...

Re:Why text messages instead of email?

[Sockatume]

The account's set up with your phone number, uses the same user identifier, travels with the phone number, and there's a billing infrastructure for it. Meanwhile the vast majority of phone users don't even have packet data plans. It's operator inertia, basically.

Re:no, its because 160

[jellomizer]

80 characters (bytes) just happened to be how many punched you can normally fit on a standard punch card.

Re:SMS vs email

[Rob Kaper]

Differences:

- SMS is available: it's built-in, e-mail is not present on every phone and relies on a third-party service provider plus settings

- SMS is faster: because there is no GPRS/TCP/IP/SMTP/IMAP/POP connection and transfer overhead

- SMS is clean: no risk of having to retrieve large attachements, hardly any spam due to sender costs

- SMS is cheaper: most plans offer a sufficient amount of free messages a month for most users, e-mail requires an additional GPRS data plan

YMMV but SMS is not as bad as some people claim.

Getting 160 chars in 128 bits.

[pavon]

For those that were wondering how they got 160 characters into 128 bytes (6.4 bits/char), they didn't. The increased the length of the frame to 140 bytes, which is is 160 characters using a 7 bits/char. Curiosity forced me to look this up, expecting to find some snazzy compacting algorithm for a non power-of-two alphabet.

Re:Getting 160 chars in 128 bits.

[evanbd]

There are some straightforward compaction algorithms for non power-of-two sizes. The simplest approach is to take n symbols in your alphabet, treat it as an n-digit number base b (the number of different symbols), and convert that to base two. You'll use at most ceiling(n * log2(b)) bits.

You can be more sophisticated by using a compression algorithm of some sort (Huffman with a standardized dictionary, for a simple example). Anything that does better than the above n * log2(b) will produce a variable length output, though, which means that while you could usually fit more than 160 characters into 140 bytes, sometimes the limit would be lower (since rare characters take more bits to encode).

Re:SMS vs email

[Dan East]

Here's what's ridiculous. I have a Blackberry, and do not have an SMS plan with my carrier, thus each text costs me 25 cents to send. Receiving SMS is free and unlimited. I have an unlimited data plan for Blackberry, so I simply send emails using the carrier email SMS gateways for "free". The only downside is that the recipient cannot directly reply to my message. Here's the stupid part. The amount of bandwidth, processing, and inter-service gateways my emails have to pass through must require at least 100 times the resources of sending an actual SMS. The final kicker is that even if I keep my actual message under 160 chars, they are usually broken up into more than one SMS message because of the header attached by the SMS gateway that contains my email address, etc.

BINGO!

[wonkavader]

And a full-screen terminal (3270, etc.) is really just 25 punch cards. You press "Enter" and they get submitted. Your batch processes and the system returns you 25 punch cards which your smart 3270 punch card reader/editor displays for you.

Punch cards are based on the civil-war-era dollar bill because there were already machine to count and stack dollar bills.

Punch cards were IBM's most profitable product ever until the introduction of the IBM PC.

Re:BINGO!

[OlRickDawson]

http://en.wikipedia.org/wiki/Punched_card Punch cards predate the computer, because they were used in loom machines to generate paterns. The punch cards were later used for statistical purposes. IBM was already selling statistical machines that used the punch cards before the computer. The reason that IBM was able to grab the market instead of Univac, is because IBM's computers was compatible with the punch cards that the corporations already had.

Silly me.

[hrimhari]

Here I was, in my dumb ignorance caused by blind experience on the field, thinking that the limit was actually caused by the magic 255 number less protocol overhead (result: 140) plus 7-bit encoding compression (result: 160).

Re:I'll Be Damned

[nomorecwrd]

Actually, SMS is like a "stowaway" of a signal your cell must receive from time to time.
So the "real" cost of a SMS is 0.000000.

This is a broadly known fact.

Years ago, here in Chile anyway, SMS where free of charge.
Now is pure profit. (about 8ct/SMS at current exchange)