Modem speed doesn't match thruput speed

[f117nighthawk]

When I checked my connection speed at http://www.numion.com/YourSpeed/Checkup.php it gave me the following info about my connection.

Throughput Modem speed
2642 Bps 24 kbps

My question is, why is my thruput at 26 k, but my modem speed only at 24 k? Aren't the 2 the same? TIA.

[Ricardo Dávidow]

The explanation for this is on a link at that same page:

Translation between "Throughput" and "Comparable Modem Speed" is done by assuming 9 bits per byte. Most modems use 9 bits to transmit a byte (8 bits, no parity,1 stop bit). The "kilo" in "kilobit per second" stands for 1000, not 1024 as is customary
when describing memory and harddisk size.

So, you have 2642 bytes/second. Multiplying by 9, you have 23778 bits/second. Dividing by 1000, you get 23.778 kbits/second, which rounded gives you 24 Kbits/second.
If you like it more, you can also say, 2642 bytes/second, divided by 1024, equals 2.58 Kbytes/second.
Quite confusing, isn't?


http://www.animation-station.com/anigifs/anim1341.gif


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Those are my principles. If you don't like them I have others.

Groucho Marx

[Ricardo Dávidow]

On the other hand, if you have 23778 bits/second, you may divide by 8, and say you have 2972.25 bytes/second. Then, dividing by 1024, it gives you 2.90 Kbytes/second.
Which way is the proper one?
I am not sure.


http://www.animation-station.com/anigifs/anim1341.gif

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Those are my principles. If you don't like them I have others.

Groucho Marx

[Ricardo Dávidow]

Hi,

Thinking this over, I realized that by focusing on calculations, I have not properly addressed your main question.
You are asking why your Throughput does not match your Modem Speed.

[list=1]
They are given in different measuring units. Throughput is in bytes/second, while Modem Speed is in Kbits/second.

1 byte = 8 bits ; 1 Kbyte (Kilobyte) = 1024 bytes ; 1 Kbit (Kilobit) = 1000 bits.

Throughput measures the amount of actual data (characters) transmitted. Here it is assumed that to transmit 1 character (1 byte) modems need to transmit 9 bits.

Modem Speed measures the quantity of bits transmitted. So Modem Speed is higher than Throughput.

On my previous posts I proposed two ways of calculation, and wondered which was the right one. Now I realize that both are right, because they calculate different things.

The first one, 2642 bytes/second divided by 1024 bytes per Kbyte, which equals 2.58 Kbytes/second, calculates Throughput.

The second one, 2642 bytes per second * 9 bits per byte = 23778 bits per second, calculates modem speed. To express it in bytes per second, I divided it by 8 bits per byte. This gives 2972.25 bytes/second. To express it in Kbytes per second, I divided it by 1024 bits per byte. This gives 2.90 Kbytes/second of modem speed.
[/list=a]

Let me know if this has helped you.


http://www.animation-station.com/anigifs/anim1341.gif

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Those are my principles. If you don't like them I have others.

Groucho Marx

[f117nighthawk]

Thx for the 411. Yeah, it helped me realize that computer measurements are too confusing to think about. Thx again. http://discussions.virtualdr.com/smile.gif

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The Velociraptor (http://www.anandtech.com/mysystemrig.html?rigid=12654)