LinuxSA Mailing list archives

  From: Rick Marshall <rjm@herzfeld.com.au>
  To  : Alan Kennington <akenning@dog.topology.org>
  Date: Thu, 04 Mar 1999 00:48:07 +1100

Re: Modem Problems

Alan Kennington wrote:

> Rick,
>
> I agree that noise could be triggering the modem problems,
> but it's unlikely to be the reason it stays around.
>
> The nature of the problem is that the line is perfect for
> about 2 to 30 days, and then it goes wrong until the modem is
> reset. I kept it in the pathological state for
> about 8 hours last time, logging every single packet.
> And when I re-start pppd, the problem goes away for
> many more days.
>
> It's unlikely that the noise would just stop when I
> restart pppd.

Correct (trivially) but i fthe modem has tracked down to a slow baud
rate to cope with the line then resetting will provide a magic fix.

> Also, the link from the cisco router to me
> is digital except for the last leg to my house.
> I.e. the next time I dial, only the digital lines
> are different, not the analogue stretch, which is the only
> bit that could reasonably have noise.
>
> It just might be that there are 33.6 k modems out there that
> do not have matching state machines, in which case
> the sync seeking algorithm may be faulty in some way.
>

I suspect this to be the case. Or more importantly they sometimes miss a
protocol frequency.....

I get bizarre things like dial in, modem answers, can't get its protocol
right, hangs up. Dial again straight away and all is well.....

I have a ppp link that should stay up full time, but every now and then
it drops out and can take several goes to get back up - 5 or six
sometimes. One day it took an hour (don't even start to think about the
phone bill). Once it got up it stayed up for a week. ?!**#?!

What would be really nice is for Telstra to accept modem grade service
rather than voice grade as their minimum standard. Modems still don't
have the noise filtering nearly as good as the brain.

Rick

>
> Strangely, the problem has tended to happen after I ahve been
> passing a lot of traffic onthe link.
> Last time it was when the yahoo robot or spider was browsing my
> site at the same time at the googlebot
> (http://www.google.com).
> this seems to indicate that there could be some
> buffer overflow condition which triggers the
> modem on one side to go into an unusual state from which it
> cannot extricate itself.
>
> The telstra engineer told me if I turned off
> compression, it shoudl be fine.
> But I turned off compression (%c0 or somehting), and
> I still get 5 kBytes/sec on a 33.6 kbit/sec modem,
> which is impossible.
> I just wonder if MS windOS users get this problem too,
> or if maybe their machines never stay up long enough
> to see the problem.
>
> Maybe I should put the problem to a different e-mail list.
> Does anyone know of a newsgroup or something where
> the world's modem experts congregate?
>
> Regards,
> Alan Kennington.

--
mailto:rjm@herzfeld.com.au <=>  RICK MARSHALL  <=> http://www.herzfeld.com/isl
   International Software Laboratories Pty Limited - Australia, New Zealand
     Footwear: Retail Management, Point of Sale, Wholesale, Manufacturing
    (-: All in Linux :-)   (-: On the Web :-)   (-: All in UNIBASE 5GL :-)



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