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3D Spotlight : Tweaking : Tweaking your modem

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.


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.


MTU, TTL & others

Go into the Registry guide for more detailed information on setting your TTL, MTU values & such. If you dont 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 ISPs 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 Dont 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 Id set my MTU to 1500 as higher values give me the fragment message.

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