Tweaking
your modem
Last
Updated on March 28, 2000 by Thomas
McGuire - Page 2/8
Init
strings
In
the Extra settings field I suggest entering the
following Init string into the space provided (NOTE: The
strings below are for 3com/US Robotics modems, do NOT
use it on non-3Com/USR modems, refer to your modem manual
for appropriate strings). You can find modem Init strings
for other brand modems at 56k.com.
You should try to reference it with the appropriate version
of the ones recommended below.
AT&F1&K3S15=2S11=38S27=16S0=0
US
Robotics Courier owners with a 25Mhz clock (not on earlier
models) should use this AT%G1&F1&K3S15=2S11=38S27=16S0=0
Explanation
of settings
Here
is an explanation of each string setting, as taken from my
modem manual.
AT%G1
enables
a higher DTE rate of 230400. This may not work with all
modems, unless they have a 25Hz clock speed, or fast serial
port connection. Refer to your manual if unsure.
&F1
loads a read-only factory configuration (in this case)
Hardware flow control template. (NOTE – Winmodem
users should set this to &F0).
&K3
disables MNP5 compression (which often added latency to
connections).
S15=2
disables retrains.
S11=38
set the duration & spacing, in ms, for tone dialling
(You can increase/decrease this value as you wish).
S27=16
disables MNP 2-4 compression.
S0=0
disables Auto-answer.
Users
of Diamond Supra modems might want to try the
following Init string. This string however needs some
testing. It is similar to the 3COM/USR string above. Email
me with your experiences using this string, or if
you have a better one.
AT&F&K3W2
MTU,
TTL & others
Go
into the Registry
guide for more detailed information on setting
your TTL, MTU values & such. If you don’t want to
manually edit the registry you can use a program to do so,
such as iSpeed or TweakDUN. If you choose to use them
instead, follow the instructions below & enter in the
appropriate information into the program(s).
MTU
- To find your MTU you must first set the MTU to 1500. Restart your PC
then open an MS-DOS prompt once connected to the Internet.
Type in ping
–f –l xxxx www.yourisp.com. Replace yourisp
with whatever address your ISP’s is. Replace xxxx
with number values until you get the message Packet needs to be fragmented by DF set. Use whatever the largest
value is before the error message & add 28
to it to find your MTU. –f means Set Don’t
Fragment flag in packet. –l xxxx means Send
buffer size xxxx.
E.g.
ping –f –l 1472 www.iol.ie
1472
+ 28 = 1500. As a
result I’d set my MTU to 1500
as higher values give me the fragment message.
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