[plug] baud rates and modem dropouts

[Buddrige, David]

cheers - that's very handy - I'll give it a go tonight... (btw my phone
line from my modem to the wall socket goes from the spare bedroom, out
through the hallway and into the master bedroom on the other side of the
room... (and past my clock radio which is sitting near the phone jack on
the floor... might try moving it... and ensuring any other equipment is
reasonably far from it...

the phone line extension is about 8 meters...

thanks

David Buddrige
Software Engineer
MITS Ltd.
david.buddrige at mitswa.com.au

> -----Original Message-----
> From:	Matt Kemner [SMTP:zombie at networx.net.au]
> Sent:	Monday, November 23, 1998 9:08 AM
> To:	plug at linux.org.au
> Subject:	[plug] baud rates and modem dropouts
> 
> On Sun, 22 Nov 1998, David Buddrige wrote:
> 
> > I would assume that if the modem had been disconnected, then the
> light's
> > would all turn off... at present, it appears to remain connected,
> but the
> > ping's are no longer working.... I'm going to check out the
> suggestions
> > made by Christian...
> 
> I would say you're experiencing line noise of some sort.  Usually when
> a
> modem "hears" line noise, it will "retrain" down to a lower speed..
> Usually it will go from say 33.6 -> 28.8 -> 14.4 -> 9600 -> 4800 ->
> 2400
> -> 1200 -> 600 -> 300 -> dropout. (overly simplified - there are a few
> baud rates in between that it will use)  Most people that have line
> noise,
> have a lot of it, so their symptons are just that the modem drops out
> completely, because it has run through the speeds in fast succession..
> However, others have line noise at irregular intervals, and the modem
> cycles down to a speed below 1200, with the result being that it
> appears
> there is no connection between the two modems, but there is one that
> is
> very very slow. (read >20second ping times.)
> You may be experiencing the latter effect.  Since you've spoken to
> Telstra
> (and presumably your ISP) I assume you've checked the main causes of
> line
> noise, but just in case I'll list the main 2 culprits again.
> 
> 1. Disconnect ANY other equipment that's in parallel on your phone
> line
>    (especially Telstra Touchphones)
> 2. Make sure your phone line doesn't run past any electrical wires
> because
>    they can cause interference.
> 
> With the advent of 56k modems things are slightly different, because
> they
> don't just cycle down through the speeds, at regular intervals they
> will
> try to cycle back up through the speeds as well, to try and give you
> the
> fastest possible connection at all times.. However this can cause
> problems
> because often while the modem is retraining, if it gets some noise on
> the
> line, it may not be able to negotiate a speed and will drop out
> altogether.  To counter this you may want to choose a speed that your
> modem can happily attain every time (eg. 44k, 48k or even 50k if
> you're
> lucky) and force your modem to not connect to a higher speed than
> that.
> To do this on most modems you use the AT+MS init string.. Eg. to limit
> your modem to 44k, use AT+MS=56,1,300,44000
> 
> Anyway, enough of my ramblings :)
> 
>  - Matt