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How fast should a 28.8K modem be?

Posted on 1998-08-03
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Last Modified: 2012-05-04
Hi, anyone can explain to me, the relationship between 28.8k and the
actual download file speed. I dial up to the my company's intranet, and
download files, it shows about 3-3.4kByte/s. Is this because IP header
or what? Is there an equation to show the maxiam download speed given
the modem speed?
Thanks.
Shane
Thanks.
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Question by:xiaoxiangz
19 Comments
 
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Expert Comment

by:rmarotta
ID: 1122092
xiaoxiangz,
I can't help you with that ratio, but here is some modem speed information that you may find useful.

The following info was taken from the Modem FAQ here:

http://users.aimnet.com/~jnavas/modem/faq_e.htm#Windows95

**************************************************************
"The System Monitor accessory that comes with Windows 95 has a wealth of hidden features, among them the ability to display raw dial-up networking and/or modem throughput in real time. To get it working for dial-up networking (DUN):
 Install the Dial-Up Networking 1.2 Upgrade
 Start System Monitor; choose Edit | Add Item. Select "Dial-Up Adapter", then under Item select "Bytes Received/Second" and/or "Bytes Transmitted/Second", and click OK."
**************************************************************

If you need it, DUN1.2 is available for download here:

http://backoffice.microsoft.com/downtrial/moreinfo/win95pptp.asp

More info about getting System Monitor working is here:

http://support.microsoft.com/support/kb/articles/Q134/6/35.asp

Let me know if you need more, or if I can Post an answer for you.
Regards,
Ralph

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Expert Comment

by:TimCaturaHouser
ID: 1122093
You don't say if you have NT or Win 9.x  In either case, both versions of these OS's share this challange. I have pasted in the Q&A from the latest ntfaq (http://www.ntfaq.com) Without changing anything, the speed you are getting is typical of a 28.8


By default, NT will use a Maximum Transmission Unit (MTU) (packet size) over the path to a remote host of 576. Problems can arise if the data is sent over routes etc that cannot handle data of this size and the packets get fragmented.

The parameter EnablePMTUDiscovery set to 1 forces NT to discover the maximum MTU of all connections that are not on the local subnet. To change this perform the following:

Start the registry editor (regedit.exe)
Move to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
From the Edit menu select New-DWord value
Enter a name of EnablePMTUDiscovery and press enter
Double click on this new value and set to 1 then click OK
Close the registry editor and reboot the machine.
By discovering the Path MTU and limiting TCP segments to this size, TCP can eliminate fragmentation at routers along the path that connect networks with different MTUs. Fragmentation adversely affects TCP throughput and network congestion.

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Accepted Solution

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thresher_shark earned 60 total points
ID: 1122094
Actually, I can think of a ratio.  When a modem is giving its speed, in your case 28.8, it is saying that is how many bits-per-second it can send and recieve.  Since there are 8 bits in a byte, you take 28.8 and divide it by 8 which yields 3.6.  Due to internet congestion, slow servers, etc., the modem would rarely reach that maximum.  This is especially true with the new 56.6 modems.  They are really not that much faster than 28.8 (the fastest I've seen one go is 5kbps, a 30 - 40% increase).

So for the equation, take the modem speed (i.e. 28.8, 14.4, 56.6) and divide by 8 to get the maximum download speed in kb/sec.

You want to improve the overall speed of your modem and you have NT, I'd recommend that you follow TimCaturaHouser's suggestion.

Hope that answers your questions.
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Expert Comment

by:thresher_shark
ID: 1122095
In that last sentence of my answer, I meant to say the following:

If you want to improve the overall speed of your modem and you have Windows NT, I'd recommend that you follow TimCaturaHouser's suggestion.
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Expert Comment

by:thresher_shark
ID: 1122096
If you have any additional questions, feel free to ask.
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Expert Comment

by:rmarotta
ID: 1122097
I have one:

Why are you dividing a number that represents BAUD/p/s by 8 BITS?

BAUD does not equal BYTE nor is it a multiple.

If we extend this, we could divide apples by oranges.

Regards,
Ralph

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Expert Comment

by:rmarotta
ID: 1122098
Shane,
If the present proposed answer does not solve your problem, please select "reopen the question to other experts" from your list of options.
You do not have to accept any answer proposed to you until your problem has been solved to your satisfaction.
Regards
Ralph
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Expert Comment

by:thresher_shark
ID: 1122099
What in the world!?  Look:

baud (bôd) noun
Computer Science.
A unit of speed in data transmission usually equal to one bit per second.

Excerpted from The American Heritage® Dictionary of the English Language, Third Edition  © 1996 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution in accordance with the Copyright Law of the United States. All rights reserved.

I left the copywrite information in the definition so you can see where it came from and how up to date it is.

That is exactly what one baud is, one bit per second.  To convert to kb/sec, you divide by 8.  Now please, xiaoxiangz, disregard rmarotta's comment.  As you can see, my answer is correct.

Thank you.
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Expert Comment

by:thresher_shark
ID: 1122100
What in the world!?  Look:

baud (bôd) noun
Computer Science.
A unit of speed in data transmission usually equal to one bit per second.

Excerpted from The American Heritage® Dictionary of the English Language, Third Edition  © 1996 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution in accordance with the Copyright Law of the United States. All rights reserved.

I left the copywrite information in the definition so you can see where it came from and how up to date it is.

That is exactly what one baud is, one bit per second.  To convert to kb/sec, you divide by 8.  Now please, xiaoxiangz, disregard rmarotta's comment.  As you can see, my answer is correct.

Thank you.
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Expert Comment

by:thresher_shark
ID: 1122101
Also, rmarotta, did you notice how closely the 3.6 coincided with the 3.3 - 3.4 that xiaoxiangz mentioned?  Also, when they say how fast a modem goes, have you ever seen it expressed like 28,800 bps?  bps stands for bits-per-second.  So you can take 28,800 divided by 8, and you get how many BYTES per second the modem is capable of sending.
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Expert Comment

by:thresher_shark
ID: 1122102
In the future, rmarotta, please don't be so haste in making people's answers look bad, you should consider doing some research on the person's answer before immediately disregarding it as being incorrect.

If you can show me information that would lead me to believe that my answer is wrong, I would like to hear it, because to the best of my knowledge the answer is correct.

Thank you.
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Expert Comment

by:rmarotta
ID: 1122103
thresher_shark,
Don't get so excited......
There may be something wrong with my math, but using your definition, I can't see how you can convert kb/sec by dividing by 8!
I think you are trying to say that a BYTE is equal to an 8-bit word. (And that a BYTE is equal to BAUD)
Not necessarily true.

BTW: the term BAUD came into use long before bits & bytes, during the days of Teletype. (see if you can look that up!)

Shane I appologize for taking up so much of your space here.

Regards to all,
Ralph

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Expert Comment

by:rmarotta
ID: 1122104
Try this link:
http://www.pcwebopedia.com/baud.htm
Regards
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Expert Comment

by:rmarotta
ID: 1122105
Shane,
In my original post, (before we got side-tracked) I asked you to let me know if you needed more.  I still have more......
Your answer will probably be found here:

http://www.well.com/user/rdp/bitsbau.html

Give the points to thresher_shark.
Regards,
Ralph

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Expert Comment

by:thresher_shark
ID: 1122106
I just noticed something, in my answer I stated it wrong.

"When a modem is giving its speed, in your case 28.8, it is saying that is how many bits-per-second it can send and recieve."

It should really be "kilobytes-per-second" right?  Now-a-days, it seems modem manufacturers say their modem is capable of, for example, 56.6kbps which is kilo-BITS-per-second.  Then, to solve the problem of how many kilo-BYTES-per-second it could send and recieve, you would divide by 8, right?

Oh, hehe, also:
--
Teletype

Teletype (tel'e-tìp`) noun
The Teletype Corporation, developer of the teletypewriter and various other printers used with computers and communications systems. See also teletypewriter.
--

Sorry for getting little upset :-)
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Expert Comment

by:thresher_shark
ID: 1122107
Ahh... There needs to be an option to go back and modify comments and questions...

First sentence third paragraph should be:
It should really be "kilo-BITS-per-second" right?

Sorry for making so many mistakes :-(
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Author Comment

by:xiaoxiangz
ID: 1122108
Thank you for so many comments. I really appreciate it.
Now I understand.
Thanks.
Shane
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Expert Comment

by:thresher_shark
ID: 1122109
Glad I could be of help.  Again, I'd like to appologize to rmarotta for being so, well, rude.

Thanks for the 'A'! :-)
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Expert Comment

by:rmarotta
ID: 1122110
No apology needed.
Regards,
Ralph

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