# Thread: The great connection speed mystery

1. ## The great connection speed mystery

Can someone please explain to me why my 56K modem seems to have a maximum (sustained) download speed of about 7 kbps, surely when I dial my ISP and get a 46.6 kbps speed I should be able to download at something comparable to the connection speed??

(Have always wondered how they worked out the speeds of modems)

Cheers

Liam
http://www.chatf1.net.nz
http://www.desktop.net.nz

2. ## Re: The great connection speed mystery

You connected at 46.6Kbps (Kilobits per second). That is what you originally connected to the ISP at, once connected that figure means nothing and it was always just a rough guess anyway.

You're downloading at 7KBps (KiloBytes per second). There are 8bits in a byte then there is a start/stop bit and other bits for parity.

So

46.6/8 = 5.825 KBps.

So I'd say that you're going along quite nicely there.

3. ## Re: The great connection speed mystery

It's not a mystery. It's magic. The telephone line has a rated speed of about 3200 baud. With various incantations, and spells (correctly spelt) it is possible to get 56000 bits/sec download, and 33600 bits/sec upstream. Using 10 bits/byte (because of the start and stop bits used in asynchronous communications) that gives you a theoretical rate of 5600 bytes/sec download. If your line is not perfect and noise-free, the modems negotiate a lower rate.

That is for "binary"/"uncompressible" data being transferred. Many files can be compressed and this is done transparently in the modems. So your average transfer rate will be higher than the theoretical rate, but it will be reduced by the overhead of the protocol being used. That is, the addresses etc contained in the TCP/IP header of each packet.

About all you can say is that sometimes you get faster transfers than at other times. Sometimes it's slower.

But remember that there is a difference between a bit and a byte (or octet). The abbreviations are bit="b", byte="B". Also "m" = milli, "M" = mega. The difference is a factor of a thousand million People seem to always mix them up. I am amused when I hear of a 90 milliwatt power station. The abbreviation for "kilo" (one thousand or sometimes 2^10, the "binary k") is "k". "K" is the kelvin temperature unit.

4. ## Re: The great connection speed mystery

Also there is compression that happens which is why you can get 7KBps and greater download speeds.

I really hate the way that there is no standard to the whole B=Byte, b=bit thing. Some people must get ripped off by things like that.

It's one of my pet hates is the way that happens. Also happens with harddrives some manufacturers use these "Metric" measurements instead.

5. ## Re: The great connection speed mystery

There is a standard. It's called the SI. (Systeme Internationale). People are ignorant. My other peeve is dimensions. Some newspapers use kmh for km/h. There is a difference. They could use "kph" as " mph" was used for mi/hr.

6. ## Re: The great connection speed mystery

Even worse Graham, is that some car dealers dont know how many kilo-metres ( note the pronunciation, it is NOT ..lometres) their cars have done. Some ads miss out the thousands, so the cars have apparently only done 56km, or 95km for example.

7. ## Re: The great connection speed mystery

Incidently whilst we're on pronunciation, what is the difference between a micrometer and a micrometre?
One is a measing instrument, the other (micro-metre) is a micron or 0.001mm. Then of course in Germany a metre is spelt meter

8. ## Re: The great connection speed mystery

> what is the difference between a micrometer and a micrometre?
> One is a measing instrument, the other (micro-metre)
> is a micron or 0.001mm.

I got tripped up on this one recently. I thought I would change the spelling of micrometer to micrometre believing this was more correct!!!

BTW, micron is the common usage name instead of micro-metre.

9. ## Re: The great connection speed mystery

I can't spell 'measuring' now! Micrometer, a handheld instrument, eg made by Moore & Wright, Browne & Sharpe, Mitutoyo etc. One psychological reason that Europeans eg the Germans or Swiss thought (or think) they could work more accurately than the British is that their micrometers are graduated in 0.001mm divisions, whereas Imperial micrometers are graduated in 0.001 inches, some 2-1/2 times larger.

10. ## Re: The great connection speed mystery

I use a Ernst Leitz Wetzlar micrometer (definitely not hand held!) as I measure objects from 2 microns upwards. The micrometer is as old as the hills but you can't beat the German accuracy and quality (at least not cheaply).

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