Modem keeps disconnecting

Posted on 1998-05-04
Last Modified: 2011-09-20
I have been trying to get my plug n play card to work correctly with linux for a while now.  I can can actually dial my ISP or some BBS board successfully.  The problem is that I cannot stay connected for no longer than a couple of minutes before I am disconnected, and returned an error 'No Carrier'.  If I am quick enough to get a file to download, I will stay connected until the file is completely downloaded, then I'm disconnected.  I assumed then that the CPU provides the plug n play card with some continuous signal to ensure online connection via Win95, which I also have
installed on my system.  I then went and bought a cheap 33.6 modem card to test this assumption.  The result, actually turned out to be the same.  That is when I am disconnected, I recieved the error 'No Carrier'.  This isn't a real easy problem to solve, and would expect a detailed answer that would explain what the problem is; how it can be solved; and if it can't be solved what are the alternatives.  Also is there a way that I could "fake" the modem into thinking that it has a signal in order to stay connected.  I am thinking to do this, I probably would need to write a device driver, something I would like to not do if possible.

As for checking noise on the telephone line, it is about as clean as it is going to get.  I also disable call waiting when I dial out, so call waiting is not the cause either.  Also, I cannot find any interrupt conflicts that may be causing this problem, so I suspect that this isn't the problem either.

I need all the help that I can get on this matter to solve this problem.
Question by:shipley
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Author Comment

ID: 1584257
Edited text of question

Accepted Solution

natmak earned 100 total points
ID: 1584258
use a kernel compiler with the serial driver intergrated (not in a module)


Expert Comment

ID: 1584259
Some questions:

a) What chipset is your modem?
b) What chipset does your ISP use for their modems?

Call your telco and ask them to do a silence test. If you're in the UK get a NETCOM account and do their modem-info test to give you a graph of attenuation.

Try writing S10=254 to the modem as part of the init.

If it's a PnPray problem, you could try running isapnptools (search Altavista for that). But if a "cheap modem" gives the same result then you're looking at a line problem. Move all your modem cables away from power sources. Disconnect any other telephony devices on the line.  

Run irqtune to increase the IRQ priority (this made a lot of differnce for me a while ago with RH 3.3.3).

Finally, after all that, get an engineer from the telco to check your line.

Author Comment

ID: 1584260
I tried adding S10=254 to init string, but the modem reported an error.  As for irqtune, I cannot locate it on my linux system.  My modem is a 336F by Best Data (Smart One Series).  What else can I try to get my modem working properly.

Expert Comment

ID: 1584261
You could try forcing a V.FC connect - +MS=74 off the top of my head - check out the manual. If this holds the line, then you're looking at line noise in the high range which upsets V34.

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