How much info could you send on a "Klax"? (Pratchett-verse)

[Crossroads Inc.]

In the new TV Movie "Going Postal" a large part of the plot revolves around a Semaphore like machine called the "Klax" In earlier books it was described as being able to send simple messages and encoded information.

By "Going Postal" it had been fleshed out and expanded upon, we are told it can send complex information, even "Pictures" even pictures in Color!

The basic system, as describe in Going Postal, is a 4x4 grid of lights and shutters. 16 shutters in all that turn on and off. It seems a perfect set up for using Binary. On for "1" and off for "0" But since I doubt the Pratchett-verse has Binary in the same way we do, I am curious what other forms you could use to send information? How fast? Could you indeed send something as complicated as a picture using a 4x4 grid?

Using a Binary "like" system I imagine you could send "16bits" of information per shutter flash, or you could use a different code for larger items and use each configuration as a different symbol. So:
*0**
****
****
****

Could be "Hello" all in one shutter flash for instance.

I know there are a good deal of computer programers on the bored, and I am curious what real programers might make of such a system.

[Mayabird]

It's "clacks," you barely literate moron. People could theoretically send as much as they could pay for, with the note that the bigger and more complex the information being sent (color pictures, etc) the longer it would take to encode, transmit, and decode the message and thus the more expensive that would be.

[Simon_Jester]

Oh, come on, Maya.

It's pretty clear that he's asking what the bandwidth of the klacks is, on a per-frame basis. He may not be fully aware that this is what he's asking, but it is.

[Crossroads Inc.]

Oh, come on, Maya.

It's pretty clear that he's asking what the bandwidth of the klacks is, on a per-frame basis. He may not be fully aware that this is what he's asking, but it is.

Thank you Simon, although I do apologize for getting "clacks" wrong, I have the audio books, bur haven't physically read it in a while.
But yes, mostly want I am curious about is just how long, or how fast you could send information using a "16bit" system, or if there are other ways of sending it.

[Simon_Jester]

The best you're going to get is two bytes (16 bits) per "frame," where a frame is defined as the amount of time the clacks towers spend flashing one message.

That's not enough to send more than very tiny pictures, VERY slowly, unless you have an incredibly good encryption scheme or can somehow send hundreds of frames per second. Which the clacks can't, because they rely on operators with brains made out of meat and not silicon.

[Dave]

It's pretty clear that he's asking what the bandwidth of the klacks is, on a per-frame basis.

Of course, the technically proper term is throughput, (bandwidth referring to a range of frequencies.)

But to get back on track, the theoretical throughput would be 16bits * frames per unit time.
So, for example, if your human operator can read 2 frames per second, you get 16 bits * 2 = 32 bits per second. If you have a computer operator that can read 2 million frames per second, you get 16 bits * 2 000 000 = 32 million bits per second, or ~3.81 MBps.

This is with no error correction, no overhead, or anything else, just raw transfer speed.

Yes, it is possible to transfer more information using special encodings, such as the one you mentioned
(0100 0000 0000 000 representing "Hello",for example), but that limits you to the 'language" that you use.

With sixteen lights, and assuming that they only have two states, you can have a maximum of 216 possible permutations of the lights, which works out to be 65 536 combinations. Given that there are upwards of 100 000 words in the English language, you may lose part of your message.

Notice that you have increased your transmission speed (whole English words per frame versus sixteen ones and zeros per frame) at the expense of content. But now I'm just rambling.

Now, if the lights had more states than just on/off, you have more possible permutations of the lights to play with and thus can send more information in a single "frame".

[Crossroads Inc.]

Now, if the lights had more states than just on/off, you have more possible permutations of the lights to play with and thus can send more information in a single "frame".

Toward the end of "Going Postal" an engineer was talking about using special chemicals in a glass vial that could go form "On" and "Off" and also "Red" and "Blue" depending on how they are turned, up, down right, or left. so you could go from two states to four, thought that was more "in theory" and was just being experimented with.

As for posting speed. At 32bits per second, how long would it take to send an average 100 word message?

[Parallax]

I may be mistaken but I seem to recall that the Clacks Tower system had developed it's own shorthand code for use in messages and had developed increasingly sophisticated systems which made sending larger amounts of information possible.
Exactly how much is never stated in the novels but, apparently, they can handle images - though it is stated to be expensive to do so.

[Simon_Jester]

Of course, the technically proper term is throughput, (bandwidth referring to a range of frequencies.)

Sorry. Duly noted.

With sixteen lights, and assuming that they only have two states, you can have a maximum of 216 possible permutations of the lights, which works out to be 65 536 combinations. Given that there are upwards of 100 000 words in the English language, you may lose part of your message.

Well, you can always have a code group that means "I am about to spell out this word" and use an alphanumeric code to transmit words that you don't have a code group for.

That works for alphabetic signal flags.

Now, if the lights had more states than just on/off, you have more possible permutations of the lights to play with and thus can send more information in a single "frame".

At night you can possibly use colored lights and improve throughput that way. You get, say, four permutations (light off/red light/yellow light/green light) in place of two, per bit. That could... wow. If you could control each light independently, that gives you 4^16 = roughly four billion combinations. Though setup is going to be more laborious.

[Dave]

Toward the end of "Going Postal" an engineer was talking about using special chemicals in a glass vial that could go form "On" and "Off" and also "Red" and "Blue" depending on how they are turned, up, down right, or left. so you could go from two states to four, thought that was more "in theory" and was just being experimented with.

So then, I believe that would raise the number of possible combinations to 416, or over 4 billion.

As for posting speed. At 32bits per second, how long would it take to send an average 100 word message?

Hmm... I'm going to use part of your post to get a feel for this one...

Code: Select all

Toward the end of "Going Postal" an engineer was talking about using special chemicals in a glass vial that could go form "On" and "Off" and also "Red" and "Blue" depending on how they are turned, up, down right, or left.  so you could go from two states to four, thought that was more "in theory" and was just being experimented with.

As for posting speed. At 32bits per second,  how long would it take to send an average 100 word message?

The above text contains 82 words, or 432 characters, including spaces, punctuation, paragraph marks and so on. I'm using it to get a feel for the average content of a message, which is not just words (and how long is the average word?). Does that make sense?

Assuming:
(1) We are sending the above 82 word message
(2) We use 8 bits to account for each character, as in ASCII, a common computer text encoding method.

We get 432 characters * 8 bits/character = 3456 bits
3456 bits / 32 bits per second = 108 seconds, for the above paragraph, with no error correction.

Of course, the technically proper term is throughput, (bandwidth referring to a range of frequencies.)

Sorry. Duly noted.

No one actually uses it correctly anyways.

[Simon_Jester]

Given the Ankh-Morpork cultural attitude to spelling, there probably isn't any error correction.

[PeZook]

Given the Ankh-Morpork cultural attitude to spelling, there probably isn't any error correction.

Also, spaces can be just cut out and replaced later. Punctuation also isn't necessary: telegrams did without any for more than a century, you just need to write your messages a specific way.

Most clack messages are probably going to look less like a well-written paragraph and more like "Cott sale p 82 pp", which is gibberish to most, but for a merchant's office will be perfectly understandable.

The clack towers seem about as limited as the telegraph, though sending pictures is a capability no telegraph station ever had as far as I know.

[Twigler]

I'd image that for sending images, someone would translate the image into a type of embroidery pattern of black and white squares. Then all the clacks operator had to have is a start and end code for images and then the image would be sent in little 4x4 blocks of black and white pixels.

BTW the clacks were actually used in real, a Swedish inventor called Edelcrantz set up a similar system with ten lights. The towers were about 10km apart and not really used for commercial goals, more for official messages. I've seen a reconstructed model of it once in Sweden and thought right away that this must be what Pratchett based his clacks on.

The below PDF goes into details concerning the protocols used, control characters, and similarities with network protocols. Interesting read.
http://spinroot.com/gerard/pdf/geheim95.pdf
Sadly nothing about speed.

[Molyneux]

I believe the books implied there were significantly more than sixteen lights - that's the impression I got, anyway. They don't seem to have any trouble sending through quite complex messages in a fairly short time.

[Vendetta]

That's not enough to send more than very tiny pictures, VERY slowly, unless you have an incredibly good encryption scheme or can somehow send hundreds of frames per second. Which the clacks can't, because they rely on operators with brains made out of meat and not silicon.

Except for the gargoyles.

[Eframepilot]

That's not enough to send more than very tiny pictures, VERY slowly, unless you have an incredibly good encryption scheme or can somehow send hundreds of frames per second. Which the clacks can't, because they rely on operators with brains made out of meat and not silicon.

Except for the gargoyles.

And the trolls. Though I don't remember if any trolls have become clacks operators yet.

[Molyneux]

That's not enough to send more than very tiny pictures, VERY slowly, unless you have an incredibly good encryption scheme or can somehow send hundreds of frames per second. Which the clacks can't, because they rely on operators with brains made out of meat and not silicon.

Except for the gargoyles.

And the trolls. Though I don't remember if any trolls have become clacks operators yet.

Gargoyles are a subspecies of troll, so...kinda.
I don't think any of the base-type trolls have been mentioned, though.

[Simon_Jester]

The clack towers seem about as limited as the telegraph, though sending pictures is a capability no telegraph station ever had as far as I know.

Really, that's mostly because it didn't occur to them, and because no one was willing to pay for it. You could replicate dot-matrix type pictures over the telegraph; it would just be ridiculously expensive.

[Glass Pearl Player]

Assuming:
(1) We are sending the above 82 word message
(2) We use 8 bits to account for each character, as in ASCII, a common computer text encoding method.
We get 432 characters * 8 bits/character = 3456 bits

Switching to some sort of Baudod encoding gives us 5 bits per character, for 2160 bits total, in about 70 seconds.
Then again, the clacks being operated with profit in mind, there would be some brainpower applied to cut that down even further (at least for the usual messages).

[PeZook]

Really, that's mostly because it didn't occur to them, and because no one was willing to pay for it. You could replicate dot-matrix type pictures over the telegraph; it would just be ridiculously expensive.

Yeah, I should've added they couldn't do it cheaply enough for it to be profittable. In Pratchett's books, newspapers use clacks to send pictures all the time, so it can't be very difficult or expensive.

[wautd]

In the new TV Movie "Going Postal"

There's a new movie? Why was I not informed? Was it any good?

[Crossroads Inc.]

In the new TV Movie "Going Postal"

There's a new movie? Why was I not informed? Was it any good?

http://bbs.stardestroyer.net/viewtopic. ... 2&t=141499

TRailer and now review thread, evidently not too good though.

[Minischoles]

They definitely can send pictures, in Monstrous Regiment (a couple of books before Going Postal) reporters were able to send pictures back through the clacks system, and they could even send pictures during Going Postal - the book they use has illustrations in it, and it's stated the hard part isn't so much the actual sending, but the encoding it first (I think they state it'll take 'hours' to do the entire book) So while there might not be much call for it, and it probably got priced out by Reacher Gilt and co, they very definitely can send pictures fast enough to make the next days news.

[Bounty]

I'm reading Unseen Academicals and it mentions a clacks-transmitted photograph:

The definition wasn't too bad at all. The technique of translating the clacks semaphore signal into a black-and-white picture was quite well advanced these days. Even so, his people in Ankh-Morpork must have thought this particularly interesting to merit the expense of the bandwith required.

So it seems as if

1) there's some sort of compression being used, since the original photographs were up-close, colour, high-res-for-Discworld Imp pictures
2) clacks technology is still rapidly advancing as of the last book
3) it's still very expensive to send data that isn't just words

[Molyneux]

I'm reading Unseen Academicals and it mentions a clacks-transmitted photograph:

The definition wasn't too bad at all. The technique of translating the clacks semaphore signal into a black-and-white picture was quite well advanced these days. Even so, his people in Ankh-Morpork must have thought this particularly interesting to merit the expense of the bandwith required.

So it seems as if

1) there's some sort of compression being used, since the original photographs were up-close, colour, high-res-for-Discworld Imp pictures
2) clacks technology is still rapidly advancing as of the last book
3) it's still very expensive to send data that isn't just words

Sounds vaguely reminiscent of the Internet about, oh, fifteen years ago to me.