Dropout Prevention Guide - Advanced Modem Configuration

The following information focuses on modem initialisation strings (or "init strings" for short). A modem initialisation string is simply a group of commands that are sent to the modem to change the way in which it connects and behaves whilst connected. It is relatively simple to insert an init string.

Directions are as follows:

Windows 95/98/Me/NT4:

Go to the Start menu and choose Settings, then click on Control Panel
Double-click on Modems
Click on your modem in the list, then click Properties
Click on the Connection tab across the top
Click on the Advanced button down the bottom
Under "Extra Settings" down the bottom, enter the string you want to try
Click OK, then OK again, then Close

Windows 2000/XP:

Go to the Start menu and choose Settings, then click on Control Panel
Double-click on Phone and Modem Options
Click on the Modems tab
Click on your modem in the list, then click Properties
Click on the Advanced tab across the top
Under "Extra Settings", enter the string you want to try
Click OK, then OK again

MacOS:

Unfortunately, it is not possible to enter an init string on a Mac. Provided that you have the correct connection script installed, your connection should be fine. You may find it worth checking to see if your modem manufacturer has a different version of their script available that may cater for any problems that you are having. For example, iMac owners should go to the Apple web site and download the iMac v.34 only script.

Once you have entered the string, you only need to reconnect for the change to take effect. If you find that you get an error such as "No response from modem" or an Error 630, this means that you have either entered the string incorrectly, or that particular string does not work with your modem. Take the string out, or put a different one in, then reset the modem. For an external modem, you do this by turning it off for about 10 seconds, then back on. For an internal modem, you need to restart your computer.

The following table shows you the most common characters that are used for initialisation strings and how to type them for those who are not very familiar with their use.

Char Name How to type it

& Ampersand Shift and 7

% Percentage sign Shift and 5

* Asterisk Shift and 8

- Minus sign next to 0 on the top row of your keyboard

= Equals sign next to the minus key

+ Plus sign Shift and =

, Comma next to M

\ Backslash usually next to or under Backspace

Some points to note:
Be careful not to confuse commas and fullstops. Fullstops are not generally used in init strings and will probably cause your modem to stop responding.

Make sure that you type the entire string all in the same case, either upper or lower. For example, at&f%c0 will work, AT&F%C0 will work, but At&F%c0 will not. (You will find it easiest to just use lowercase the whole time to be on the safe side!)

If you find a string that works well for you, but want to try another one listed here, just add it on the end. For example, if you have at&f and want to try changing the signal strength, you'd just add the command on the end like so: at&fs91=11.

Basic Strings

The first string to try is at&f, which resets the modem to factory defaults. This should work on basically every modem on the market. If it does not - you might like to get your modem checked by the manufacturer. Also try at&f&c1&d2%c0 and at&f%c0%e2, which should also work on most modems.

Signal strength

This specifies how loud the modem's signal is when it sends it over the phone line. By default, most modems have this set to 10, which is fine for the majority of lines, however, it sometimes helps to tweak it a little. This is done by entering the command s91=x where x is the strength you want to use. The maximum is 17, so try this first. Other settings you might like to try are 9 and 11. These two settings are worth a try on any modem, but are particularly known to help when using Netcomm Roadster and Banksia WaveSP series modems.

Data compression

Modems by default will compress data during the connection to help increase speeds. This can, however, cause problems with the connection, so it is recommended that you turn it off. To do this, add %c0 to your string. (Just check that this is not already set!)

Error Control

Most modems have a feature called error control, which helps the modem detect data that is corrupted in transmission and have it resent. This is usually a good thing, however on some bad lines it can cause so much data to be resent that the connection slows to a crawl. On most modems, this is set with the \n command. Try a lower level of error control with \n1, or turning it off completely with \n0. Note that this can cause some instability with your connection, but if it is better than before then go with it.

Flow control

Most modems have a flow control feature which helps make sure that the modem is not overflowed with data at any point in the connection. This is usually controlled by the modem itself, but in some cases it help to let your operating system handle it. To do this, add the command &k4 to your init string. This is known to work well on some internal modems, particularly HSP and Motorola SM56 modems.

Retraining

During the call, your modem will retrain. This means that it adjusts the speed of the connection up or down depending on the quality of the connection. When this happens the connection stops transmitting data for a short while - anywhere up to 30 seconds. What can happen in some situations is that so much retraining happens that the connection dies or goes very slowly. Some modems seem to have retraining disabled by default, so you might have to play around with this one a bit. The settings are: %e2 which is for full retraining (use this if possible), %e1 for fall back only and %e0 to disable it altogether (avoid if possible).

Restricting the connection speed

If nothing else helps the stability of your connection, it may be necessary to simply lower the connection speed of your modem to suit your conditions. This may mean just a slight drop back in speed, or in the more extreme case, it may be necessary to restrict the speed severely to achieve a stable connection. The way in which this is done will depend on your modem type. The chart below will allow you to find the correct string for your modem.
Select your brand of modem, or the chipset your modem has on the left hand side. (To find out what chipset your modem has, check your modem manual or contact your modem manufacturer.) Select the speed you wish to try on the right hand side. Note: This should be lower than the speed you normally connect at. For example, if you get dropouts at 48000, try 46000. If you modem or chipset is not in this list, you will need to check your modem manual or contact your modem manufacturer to see which commands change the connection speeds on your modem.

Chipset or Brand:	Speed:

Your init string is:

You may find that you need to experiment before you find a speed that suits your conditions. Try stepping down in lots of 4000 until you find a stable speed. To fine-tune the best speed for you, gradually step up through each higher speed until you encounter problems again. Select with the highest speed that allows you a stable connection. This may need to be adjusted slightly from time to time. For example, line conditions are often worse in the winter due to the moisture and bad weather, so a lower speed may be necessary for a few months in order to cope with this.

If you find that you need to restrict to a speed lower than 28800 to get a stable connection, it is most likely that you either have a serious line fault, or a faulty modem. Usually, it is the latter. You may like to borrow a modem from a friend to see if your connection problems disappear. If they do not, you may need to get back to your telephone company and have them take a closer look at your line.

Finally, it may be possible that you have one of those rare problems that is not covered by this guide. Please do not hesitate to contact us at support@alphalink.com.au or on 1300 137 425. Our technicians have a lot of experience in dealing with dropout problems and other related issues. They will be only too happy to help.