Updated on September 18, 2000 by Thomas
McGuire - Page 2/10
In the Extra
settings field I suggest entering the following Init
string into the space provided (NOTE
- The strings below is intended 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.
US Robotics Courier owners with a 25Mhz clock (not on
earlier models) should use this AT%G1&K3S15=2S11=38S27=16S0=0
Here is an explanation of each string setting, as
taken from the modem manual.
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.
Disables MNP5 compression (which often adds latency to
This sets the duration & spacing, in ms, for tone
dialling (You can increase/decrease this value as you wish
by changing the 38).
Disables MNP 2-4 compression.
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
with your experiences using this string, or if you have a
TTL & DefaultRcvWindow
First a few definitions;
Maximum Transmission Unit.
This specifies the maximum transmission unit size of a
packet. A packet larger than the MTU size will be fragmented
into smaller packets. Using the (Maximum) MTU your ISP
allows can result in less fragmentation of packets.
Time To Live.
This sets the number of hops a packet is allowed to pass
between "you" & it's destination.
DefaultRcvWindow. This sets the size of the TCP send & receives
windows, which is the amount of data that can be accepted in
a single transaction.
setting your MTU you must find it. To
start with you should set your MTU to a high
value. This way the following procedure will be accurate,
i.e. If you MTU is currently 576 then the procedure won't
find an MTU an larger than 576. Basically skip to the Setting
MTU/TTL/RWIN section & set your MTU
to 1500 or greater.
on Start, Programs,
Accessories, MS-DOS prompt
once connected to the Internet. Type in ping
–f –l xxxx www.yourisp.com. Replace www.yourisp.com
with whatever address your ISP’s is (Or the IP address).
Replace xxxx with
numeric values until you get the message Packet
needs to be fragmented by DF set. Use whatever the largest
value is before
that error message & add 28
to it to find your MTU.
Sets a Don’t
Fragment flag in packet.
xxxx. This sends a buffer
ping –f –l 1472
+ 28 = 1500. As a result I’d set my MTU to 1500 as higher values return the fragment message.
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