Subject: Disconnection 2 - Setting Modem Speed
ART MATRIX - LIGHTLINK
PO 880 Ithaca, NY 14851-0880
(607) 277-0959 Voice
(607) 277-8913 Fax
(607) 277-5026 Modems
homer@lightlink.com E-mail
jes@lightlink.com E-mail
03/27/02 12:01pm
DISCONNECTION 2 - Setting Modem Speed
This is written for Windows 95/98 users, but the data applies to
all users.
Long time ago when ISP's were also modem jockeys, we learned a
trick to make modems get a stable connection when all else failed.
The basic problem is that line quality fluctuates, even across
periods of time as short as a few seconds, the quality can go up and
down, up and down. Or it can be basically good, then go splat for a
few moments then back to good again.
When modems dial up up they go through a speed negotiation phase
to see what speed they can support. That's all the moose honks you
hear when the modems dial in. Once they determine that they can hold
the line at a certain speed they complete the negotiation and give
control over to the user to start sending data.
However if the line quality is fluctuating, then the speed that a
modem finds acceptable one moment, may be a tad too high the next.
Usually modems will try to renegotiate the speed when too many erorrs
start to occur, you won't hear it like you did when they first signed
on, but for about 30 seconds the modem won't transmit data and what
its doing is the moose honk thing again silently trying to find a new
speed.
Sometimes by the time the negotiation is finished the line
quality is back where it was so the modem picks the same speed it did
the last time! Then the line qualities goes down for a moment and the
modem has to renegotiate all over again. Modems can get into a loop
where they are doing this over and over. To the end user it looks
like start, stop, start, stop, each cycle taking about 30 seconds.
However the modem is just as likely to hangup during these shenanigans
which results in a disconnect.
Many short session disconnects are caused by this very thing, the
modem signs on at 49,333, finds it can't support it, and hangsup a
minute later. A few more times the modem signs on at the same speed
and hangs up again a minute later. Then the modem signs on at 48,000
and gets a 'stable connection'.
There is another added complexity here in that modems not only
negotiate for speed but also for whether or not error correction will
be used. If a modem negotiates too high a speed and no error
correction, it is bound to hangup.
When it finally gets a good connection, nothing has really
changed except that the modem finally negotiated a speed that would
survive the ongoing ups and downs of line quality.
One quick and obvious answer to this is to set the modem so that
it HAS to sign on at 48,000 say, that bypasses the negotiation phase
and makes for stable connections until the line quality drops even
lower if it does, which it may not.
(We also want to force the use of error correction with the
'required to connect' setting in Windows 95/98, this was covered in
Disconnection 1 - Settings)
Each modem has different ways of setting these things, so we
became very good at walking off with people's modem manuals. We used
to offer a house call in exchange for their manual!
Of course all these manuals are obsolete by now, but present day
modems still have those settings and most can probably be set to fix
the speed at something that will be stable for you.
The way you play this game, is you sign on normally and find out
what speed your modem is signed on at from the dialup icon in the
lower right, say 49,333. Then if you get disconnected, you set the
modem to use 48,000 instead. If it still disconnects, you try the
next speed down. Usually the modem will stabilize quickly at one or
two notches down, if it doesn't, then something else is very wrong
with your situation.
Historically the USR modems had the following settings for fixing
the speed. If you have something other than a USR modem, you will
probably have to visit your modem's web page, look at the
documentation and find the proper commands for your modem. If you are
brave enough to do this, certainly let us know what you find out.
Over time we will be doing this ourselves on all the major modems that
our users are using.
ISA modems are the ones that fit in the bigger black slots, ISA
stands for Industry Standard Architecture. PCI modems are the ones
that fit in the smaller white slots of the mother board. PCI stands
for Personal Computer Interface, or Peripheral Connect Interface or
some such (you'd think I would know).
USR ISA MODEMS USR PCI MODEMS
&N10 19,200 &N17 28,000
&N11 21,600 &N18 29,333
&N12 24,000 &N19 30,666
&N13 26,400 &N20 32,000
&N14 28,800 &N21 33,333
&N15 31,200 &N22 34,666
&N16 33,600 &N23 36,000
&N17 33,333 &N24 37,333
&N18 37,333 &N25 38,666
&N19 41,333 &N26 40,000
&N20 42,666 &N27 41,333
&N21 44,000 &N28 42,666
&N22 45,333 &N29 44,000
&N23 46,666 &N30 45,333
&N24 48,000 &N31 46,666
&N25 49,333 &N32 48,000
&N26 50,666 &N33 49,333
&N27 52,000 &N34 50,666
&N28 53,333 &N35 52,000
&N29 54,666 &N36 53,333
&N30 56,000 &N37 54,666
&N31 57,333 &N38 56,000
To set your USR modem for a particular speed, goto My Computer ->
Dialup Networking, put the mouse on the Lightlink icon, hit the RIGHT
button once, and then hit on Properties with the left button. Make
sure you have a USR modem of some kind, if you don't, these particular
codes probably won't work. We will try to find codes for other modems
and get back to you in a while.
If you aren't having problems with chronic disconnects, you don't
need to worry about any of this, and are best off leaving your
settings alone.
Go to CONFIGURE -> CONNECTION -> ADVANCED and in Extra Settings
add the following onto the end of whatever is there:
&Nx where x is the number you have chosen from above.
Most people should have something like
S10=20 &Nx
The S10=20 tells the modem to tolerate 2 seconds of carrier loss
before hanging up, that should suffice to weather most harsh static
and line noise.
If the modem won't sign on at all, or still disconnects lower the
value of 'x' until it is stable. If it still doesn't work, take the
setting out.
Homer