Codan Modem Tips and Traps

I made plenty of mistakes during the course of this project—so you won't have to!

The mgetty and pppd configurations show the AT commands used to initialize the 9002 modems in our setup. You may be tempted to store these settings in non-volatile memory (AT&W) and then use a simple ATZ to initialize your modem here instead. I made this mistake myself, too, and spent several miserable and sweaty days banging around the insides of a Landcruiser paying for it. What happens is that Codan's proprietary comm software (imaginatively named 9102) writes its own settings to the modem, leaving you stuck with remote echo ON (R1)! Anytime after 9102 has run, the next time you try your PPP connection—or even a Kermit login—all traffic gets echoed back down the link, confusing both ends, without establishing any connection at all.

Here's another tip. When trouble-shooting your modem, setting and/or inspecting its configuration, the 9002 offers an online help screen with the AT? command. Browsing these screens may give the impression that the settings marked with an asterisk (*) are current. Well, they aren't. Use the undocumented A&V command to view the modem's current settings instead.

As for the PPP configuration, resist the temptation to use the defaultroute option on the link. I can assure you, you don't want any other traffic on the network trying to use this connection. The system in Kissidougou was up and running just fine, no problems—for only one week. Then I was hitching a ride back to Kissi—this time enjoying the reckless thrills of a small airplane to a dirt airstrip—just to find out why the mail stopped moving. Yes, I had the defaultroute option set, and in the meantime someone put a desktop on the network with a streaming audio application trying to connect to the Internet. It would be easier to suck sludge through a 300 mile long cocktail straw. Removing the defaultroute unplugged the link, and the mail has been flowing smoothly ever since.