If your telephone line requires pulse dialing (instead of the default touch-tone dialing), you may need to change the modem dialup command from "ATDT" (="ATtantion Dial Touchtone") to "ATDP" (="ATtantion Dial Pulse"). These commands work with any standard Hayes-compatible modem.
For some combinations of hardware on your computer, one may need to set up the modem on ttyS2 or ttyS3 (instead of the typical ttyS1, while ttyS0 is typically taken by mouse) because of interrupt conflict, e.g., with a network card. This can be achieved by setting the modem hardware (jumpers on your modem may need to be removed or repositioned, you have to look into the modem manual for specifics) and placing in the file /etc/rc.d/rc.local a line like this:
setserial /dev/ttyS3 irq 3
The standard PC settings for serial ports are:
port address of i/o port irq
/dev/ttyS1 0x03f8 4
/dev/ttyS1 0x02f8 3
/dev/ttyS2 0x03e8 4
/dev/ttyS3 0x02e8 3
I may use other, non-standard combinations or irq and i/o addresses to avoid conflicts with other hardware I might have. See man setserial for good a overview. Modem with unacceptable setup of irq and input-output address will not dial.
If your modem dials correctly and you are able to connect, but your authentication fails, perhaps your Internet Service Provider (ISP) uses a different authentication protocol. Call them and ask what authentication protocol they use. Or try "pap", "terminal-based" or "chap" (in your kppp setup) until you find the one which works with your ISP. "Terminal-based" always works for me if I only remember the password correctly.
In one instance, I had a problem with the reliability of establishing a connection (the error would pop up saying something like: "time-out for the pppd startup", and the connection would establish only once every few trials). The problem was solved by changing the "flow control" option (in the kppp "setup" under "device") from "CRTSCTS" to XON/XOFF. (Still CRTSCTS is the recommended flow control method in most cases.) In another case, opposite happened: communications was painfully slow because I did not set "flow control" to "hardware".
Random disconnects (after some time of correct connection) can have many causes. (1) They may be caused by "glitchy" drops of "data terminal ready" (DTR) signal or "carrier" signal. e.g., due to a noisy line. Most modems respond to that by hanging up. To change this default behaviour, you may need to add to your "modem initialization string" something like S10=50 . This sets the duration of DTR loss (in 0.01 s) after which hangup is executed (check your modem manual, "US Robotics" modems may need something like S25=200). (2) Call-waiting feature on your phone line may disconnect you when somebody tries to call you. (3) Old phone cables and dirty or corroded phone plugs or sockets are a common source of problems. Check the connections, replace the cables. Run the cables further away from sources of great electrical noise. (4) Too high modem speed for your village long and noisy phone cables. Drop the modem speed (or move to a city). (5) Many ISPs will diconnect you after some period of inactivity (30 min?).
If you keep having problems setting up ppp, you may want to try minicom to see if you can get your modem working from there. minicom is something like PROCOMM for Linux. It should be present on your system if you chose to install it during your RedHat initial setup. Here is a post from a newsgroup comp.os.linux.help which explains how to start ppp manually using minicom (edited for space):
From: mark <balthazaar@one.net.au> Subject: Re: pppd problem with kppp
BachuZ wrote:
>>Also, for an experiment, try using minicom to connect to your ISP, start ppp manually ... this can prove buggy scripts. >how would u do that?
Easy!! If your ISP doesn't allow a manual logon then you might be in trouble. Every ISP I've ever used does allow this, so.. 1. Start minicom. 2. dial your ISP. 3. Log in. 4. After your ISP
