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High speed modems can sometimes connect
to HiWAAY at speeds far greater than most phone lines can support. This is
mainly because of noise in the phone lines and telco equipment. Most modems
can be set to connect only at a speed or range of speeds. The common symptom
is to see very slow transfer rates with constant disconnects. This can occur
at anytime due to the nature of an ever-changing telephone network. Your
telco is constantly changing their equipment configurations as well, which
can also result in changes to your telephone connection quality. But just a
tiny change either way will simply fool you modem into training to a speed
the line will not actually support and the retrain yoyo problems begin. The
problem has become more pronounced with 56K technology modems, which seem to
exhibit the characteristic of negotiating too high a connect speed. Limiting
you modem connect speed may be helpful if you experience variability in your
CONNECT rates, and only want to connect on your higher speed connections, or
if your modem is connecting at too high a speed. There are many modems on
the market which are very aggressive on connect speeds. Many disconnect
and/or low throughput problems can be solved by forcing the modem to connect
at a slower speed.
Slowing down your modem is not the same as adjusting your port speed. The
port speed is just the speed your modem connects to your computer. What you
want to do is make to modem connect at a slower speed to HiWAAY. To do this
you have to send an AT command to the modem.
If your modem brand is not listed here then try one of the commands for the
modems that are. Other sources for this information should be found in the
modem's documentation and can also often be found online at the
manufacturers web site.
We've included the commands to force your modem to connect at speeds from
19,200 to 28,800. We suggest that you start at 24,000. If that works you can
up the speed to 26,400 and try again. If it doesn't, then try drooping the
speed to 21,600. What you're looking for is the speed that your modem will
connect to HiWAAY without being troubled by line noise.
3Com/US Robotics Modems V.90
These commands sets connect speeds. &N sets the highest speed at which your
modem will connect.
&N # where # is the maximum speed you want.
For example: &N18 would limited the maximum connection rate to
29,333.
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21,600bps &N11
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24,000bps &N12
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26,400bps &N13
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28,800bps &N14
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31,200bps &N15
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33,600bps &N16
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28,000bps &N17
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29,333bps &N18
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30,666bps &N19
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32,000bps &N20
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33,333bps &N21
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34,666bps &N22
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36,000bps &N23
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37,333bps &N24
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38,666bps &N25
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40,000bps &N26
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41,333bps &N27
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42,666bps &N28
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44,000bps &N29
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45,333bps &N30
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46,666bps &N31
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48,000bps &N32
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49,333bps &N33
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50,666bps &N34
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Lucent V.90 Modems
The Lucent LT Win Modem (Apollo/Mars) with V.90 firmware does not have the
same flexibility for connect speed options as 3Com and Rockwell. It will
either do autorate (default), or you can specify a single 56k speed to (try
to) connect with:
AT-V90=# where # represents the desired connection rate.
For example: AT-V90=6 would limited the maximum connection rate to
33,333bps.
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Disable V.90 -V90=0
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28,000bps -V90=2
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29,333bps -V90=3
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30,666bps -V90=4
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32,000bps -V90=5
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33,333bps -V90=6
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34,666bps -V90=7
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36,000bps -V90=8
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37,333bps -V90=9
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38,666bps -V90=10
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40,000bps -V90=11
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41,333bps -V90=12
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42,666bps -V90=13
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44,000bps -V90=14
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45,333bps -V90=15
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46,666bps -V90=16
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48,000bps -V90=17
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49,333bps -V90=18
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50,666bps -V90=19
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52,000bps -V90=20
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The following commands are implemented on
both the Lucent Apollo/Mars (LT Win Modem) and Venus modems, so try them if
the ones above do not work:
S38=# where # represents the desired connection rate.
For example: S38=6 would limited the maximum connection rate to
40,000bps.
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Disable Flex S38=0
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32,000bps S38=2
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34,000bps S38=3
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36,000bps S38=4
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38,000bps S38=5
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40,000bps S38=6
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42,000bps S38=7
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44,000bps S38=8
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46,000bps S38=9
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48,000bps S38=10
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50,000bps S38=11
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52,000bps S38=12
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Motorola SM56 V.90 Modems
SM56 Modems are K56Flex and V.90 capable.
%B# where # represents the desired connection rate.
For example: %B=21 would limited the maximum connection rate to
36,000bps.
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9,600bps %B6
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14,400bps %B9
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16,800bps %B11
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19,200bps %B12
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21,600bps %B13
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24,000bps %B14
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26,400bps %B15
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28,800bps %B16
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31,200bps %B17
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29,333bps %B35
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30,666bps %B36
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33,600bps %B18
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33,333bps %B37
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34,666bps %B38
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37,333bps %B39
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38,666bps %B40
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41,333bps %B41
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42,666bps %B42
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45,333bps %B43
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46,666bps %B44
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49,333bps %B45
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50,666bps %B46
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Rockwell Conexant V.90 Modems
These initialization strings are sometimes the most difficult to drill down,
it may take a little trial and error in order to find the one that works for
you.
The command format is:
>+MS=
[,[][,[][,[][,[][,[]]]]]]
Newer chipsets have another variation of
the above command with an extra field at the end of above which I believe is
maximum upstream rate except for HCF and Soft56 modems where the command
format is:
+MS=,,,,,
You can determine the format of the +MS
command for your modem with the command:AT +MS=? which
returns all possible values for each field. The command AT +MS?
will return the current settings for each field.
To limit the Rockwell-chipset (Conexant chipset) modem to a minimum of
44,000bps and a maximum of 52k, the following string would be entered in
extra settings: +MS=,,44000,52000 (non HCF)
+MS=,,,,44000,52000 (HCF) Note: If you place any
commands after the +MS= command, you must terminate the +MS
portion with a semicolon - ie: +MS=12,0;s10=7
The preferred modulation can be selected by placing the following parameter
before the first comma:
|
Modem |
V.90 |
K56Flex |
V.34 (no 56K) |
|
Rockwell/Conexant (non HCF) |
12 |
56 |
11 |
|
Rockwell/Conexant (HCF) |
V90 |
K56 |
V34 |
+MS=12,,44000,52000 (non
HCF) - V.90 is preferred, connect min 44k, max 52k
+MS=V90,,,,44000,52000 (HCF) -
+MS=V90,,,,44000,52000(HCF) - V.90 is preferred, connect min 44k,
max 52k.
The default for automode - the second parameter - is 1
which will allow other than the selected modulation; to force V.90 in the
prior example:
+MS=12,0,44000,52000 (non HCF) - V.90 is required, connect
min 44k, max 52k
+MS=V90,0,,,44000,52000 (HCF) - V.90 is required, connect
min 44k, max 52k.
Below are the initialization strings to disable the various protocols when
using different modems. Sometimes it is necessary to disable a V.90 protocol
if the KFlex protocol performs better.
|
Modem |
Disable x2 |
Disable v.42 |
Disable V.90 |
Disable V.90 & x2 |
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Sportster/USR |
S32=34 |
S15=128 |
S32=66 |
S32=98 |
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Courier |
S58=1 |
S27=32 |
S58=32 |
S58=33 |
|
|
Disable KFlex |
Disable V90 |
Disable V90 & Flex |
Disable v.42 |
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Rockwell Dual |
+MS=12 |
+MS=56 |
+MS=11 |
& Q6 |
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Rockwell HCF & Soft56 |
+MS=V90,0 |
+MS=K56,0 |
+MS=V34 |
+ES=1,0,1; |
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Lucent LT |
s38=0 |
-v90=0 |
2 |
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Lucent Venus |
s109=2 |
s109=0 |
s38=0 |
2 |
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PCTel HSP |
n0s37=14 |
n0s37=13 |
n0s37=12 |
* |
|
Motorola SM56 |
*MM15
-or- *MM14 |
*MM13 |
*MM12 |
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NOTE: If you're not sure
which chipset is in your modem then try sending it the ATI3
command (Some modems might require ATI5 instead.). If
you're lucky your modem will tell you what chipset is hidden inside it. If
you're unlucky then you'll get a cryptic number returned that identifies the
chipset but is not decipherable by mere humans. You'll have to result to
looking in your modem's manual (gasp!) or calling the modem's manufacturer
and asking.
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