Which modem are you using? At least, the default Ubuntu/GNOME distribution is working fine with an older US Robotics 56k modem.

It's an Actiontec 56k external modem.

Have you already tried Ubuntu with GNOME on that machine?
 
If you prefer a lightweight desktop, there are also Xfce4 packages available for Fedora Core 5. You find these packages in the Fedora Extras repository.

Try running:
wvdialconf /etc/wvdial.conf
as root in terminal.
 
"This will identify the port your modem is on, establish an initialization string for your modem and save the results in the /etc/wvdial.conf directory."
 
Then edit /etc/wvdial.conf to reflect your settings.

Thanks. With the wvdial command I was able to get a sustained connection. However, like pon it didn't allow a browser or apt-get to function. Below is the output... sorry that it's a bit long. The termination signal near the end was to disconnect after I found it wan't working (it's not an errror). Any ideas where to go from here?
 
atagar@pc1:~$ sudo wvdialconf /etc/wvdial.conf
Editing `/etc/wvdial.conf'.
 
Scanning your serial ports for a modem.
 
ttyS0<*1>: ATQ0 V1 E1 -- OK
ttyS0<*1>: ATQ0 V1 E1 Z -- OK
ttyS0<*1>: ATQ0 V1 E1 S0=0 -- OK
ttyS0<*1>: ATQ0 V1 E1 S0=0 &C1 -- OK
ttyS0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 -- OK
ttyS0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK
ttyS0<*1>: Modem Identifier: ATI -- 56K External Modem Venus V.92 Serial s02.08.16iA06 V2 V92cap Mercury
ttyS0<*1>: Speed 4800: AT -- OK
ttyS0<*1>: Speed 9600: AT -- OK
ttyS0<*1>: Speed 19200: AT -- OK
ttyS0<*1>: Speed 38400: AT -- OK
ttyS0<*1>: Speed 57600: AT -- OK
ttyS0<*1>: Speed 115200: AT -- OK
ttyS0<*1>: Max speed is 115200; that should be safe.
ttyS0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK
ttyS1<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud
ttyS1<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 115200 baud
ttyS1<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up.
Modem Port Scan<*1>: S2 S3 S4 S5 S6 S7 S8 S9
Modem Port Scan<*1>: S10 S11 S12 S13 S14 S15 S16 S17
Modem Port Scan<*1>: S18 S19 S20 S21 S22 S23 S24 S25
Modem Port Scan<*1>: S26 S27 S28 S29 S30 S31 S32 S33
Modem Port Scan<*1>: S34 S35 S36 S37 S38 S39 S40 S41
Modem Port Scan<*1>: S42 S43 S44 S45 S46 S47
 
Found a modem on /dev/ttyS0.
Modem configuration written to /etc/wvdial.conf.
ttyS0<Info>: Speed 115200; init "ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0"
------------------------------
atagar@pc1:~$ sudo vim /etc/wvdial.conf
 
[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = Analog Modem
Baud = 115200
New PPPD = yes
Modem = /dev/ttyS0
ISDN = 0
Phone = 4951000
Password = password
Username = guest
------------------------------
atagar@pc1:~$ sudo wvdial
--> WvDial: Internet dialer version 1.55
--> Initializing modem.
--> Sending: ATZ
ATZ
OK
--> Sending: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
OK
--> Modem initialized.
--> Sending: ATDT4951000
--> Waiting for carrier.
ATDT4951000
CONNECT 45333 V42bis
--> Carrier detected. Waiting for prompt.
CVX Access Switch.
Access is restricted to authorized users only.
login:
--> Looks like a login prompt.
--> Sending: guest
guest
password:
--> Looks like a password prompt.
--> Sending: (password)
Exiting shell, and starting PPP session.
~[7f]}#@!}!}!} }8}!}$}%\}"}&} }*} } }%}&}0}&>T}'}"}(}"n}#~~[7f]}#@!}!}"} }8}!}$}%\}"}&} }*} } }%}&}0}&>T}'}"}(}"$[11]~
--> PPP negotiation detected.
--> Starting pppd at Wed Aug 16 14:11:58 2006
--> Pid of pppd: 5216
--> Using interface ppp0
--> pppd: ??[05][08]
--> pppd: ??[05][08]
--> pppd: ??[05][08]
--> pppd: ??[05][08]
--> local IP address 64.40.63.246
--> pppd: ??[05][08]
--> remote IP address 64.40.40.6
--> pppd: ??[05][08]
--> primary DNS address 64.40.40.53
--> pppd: ??[05][08]
--> secondary DNS address 66.54.140.10
--> pppd: ??[05][08]
Caught signal 2: Attempting to exit gracefully...
--> Terminating on signal 15
--> pppd: ??[05][08]
--> Connect time 2.7 minutes.
--> pppd: ??[05][08]
--> pppd: ??[05][08]
--> Disconnecting at Wed Aug 16 14:14:36 2006
 

Check that
Auto DNS is set to yes in /etc/wvdial.conf and it is not commented out.
 
Auto DNS = yes
 
Save and then redial.
 
Or you could try to add your ISP's dns servers to
/etc/resolv.conf
 

Code:

nameserver 64.40.40.53nameserver 66.54.140.10

Wilhelmus, looking at the output of wvdial;
 
--> Carrier detected. Waiting for prompt.
CVX Access Switch.
Access is restricted to authorized users only.
login:
--> Looks like a login prompt.
--> Sending: guest
guest
password:
--> Looks like a password prompt.
--> Sending: (password)
 
Can this mean that the user name and password is not set, so this is why he is getting a disconnect? Or is this set in a script?
 
I have not done dialup in quite a while, so tell me if I am wrong.

I'm fairly certain this is a set part of the script. When trying to connect there were several failed attempts where it said different things. wvdial seems to be very good at giving verbose output and specifying if anything goes wrong. -Damian

I've made several changes and had mixed success (trying wvdial after each step). A friend of mine pointed out DialupModemHowto. It suggested adding 'replacedefaultroute' to the end of /etc/ppp/options. I also added both the DNS changes suggested by Wilhelmus. None of these seemed to change the output of the wvdial command, nor did it make the connection work.
 
However, when I tried pon again I got a connection that allowed me to access web pages. Before breaking out the champaign I tried Synaptic to get firestarter and the modem lights component. However, Synaptic failed to connect to the repositories. I also closed Synaptic and tried 'sudo apt-get update' which failed to download anything. After a few minutes the browser connection stopped working as well. I'm about to go on a trip for the weekend so it looks like any further tweaks will need to wait until later. Cest la vi.

I've decided to switch to Ubuntu to see if it solves the problem. I haven't spotted many cries for help from the diminishing modem using community so whatever's going wrong is probably a subtle issue with Xubuntu. Thanks, though for all the help.

I just switched to Ubuntu and it has the exact same problem. I determined that the point at which the pon command started partly working was when adding the DNS entries to /etc/resolv.conf. However, it still only allows a brief connection (and doesn't allow Synaptic or apt-get to work at all). Any ideas would be appreciated. -Damian

Have you tried:
 
System->Administration->Networking.
 
Select Modem connection and it's Properties.
Tick Enable Connection, enter all required information on General tab. Select Modem tab. Click Autodetect.
On Options tab, select all checkboxes. Click OK.
Try to Activate the connection...
 

That's the first thing I tried. It didn't work.

Can you post the exact model number of the Actiontec modem, located on the back/underneath ID panel of the modem?

I'm not quite sure what all the numbers mean. It says:
US: LNQM508BEX560LKA (it repeats EX56OLKA higher up)
Below the barcode: NS2520009335
Hope it helps.

Take a look at this previous post.
 
Looks like you are not alone. I will have to see what chipset is in this modem. The chipset is not listed on the Actiontec webpage, but note, it has no support for Linux, according to Actiontec.
 
However, the Puppy Linux Wiki shows it as working, but gives no details.
 
Wait a minute...I looked farther down.
 
Is this modem connected via serial or USB?

The modem has a serial connection. Again, this modem works under Fedora 4 and 5, so it seems like the problem mentioned in the post probably wasn't a mechanical issue.
 
What does "adduser <user name> dip" do? Is this something I should try? I searched the man page for adduser and couldn't figure out what the 'dip' is for.

I've been testing to what extent the connection works and doesn't... and its a bit odd.
 
Of roughly seven dial attempts with wvdial two were successful (able to load a web page). The first allowed me to go to any site for about a minute. After this I could make google searches and access a gmail account. However, any trying to access any search result would time out.
 
The second attempt again allowed me to travel to web pages for around a minute. However, "ping 4.2.2.2" and "dig www.google.com" both failed. After this I couldn't access any web pages.
 
The gateway seems to be correct (ppp0 when connnected), and the DNS addresses in /etc/ppp/resolv.conf are definitely being set by the ISP (and since it works in Windows, I guess they're valid addresses).

Let's take a step back and see what you should be doing. To establish a connection, if the modem is supported, all you should need to connect via pon and poff, is the username for your ISP, your password and the name of the device that the modem is connected to.
 
Did you read the Ubuntu wiki page on this, located here?
 
Look at the section under pppconfig & pon/poff.
 
Read that section. You should be choosing the options listed. There should not be any other options listed for the modem connection, except those mentioned.
 
Also, look under the section Configuring the dialup connection to your provider.

Yes, I did read most of the Ubuntu wiki. I tried the adduser command and my user already belongs to both the dip and dialout groups. Connections through pon and the network gui both die out after the handshake. The wvdial, however, is the one having mixed success (working for a few seconds).
 
I think that I may have found the issue. I checked the DNS addresses with "cat /etc/resolv.conf" immediately after connecting (when it's working) and got the DNS addresses listed by my provider. A few seconds later (when I can't access web pages, but it's still connected) I checked again and found them replaced by 192.168.123.254.
 
I'm not a network spe[censored]t, but isn't the 192 a home ip address range? Perhapse the network is trying to but in on the modem session, messing with the config file...
 
I tried manually changing the /etc/resolv.conf but it switched back to the 192 address after a few seconds. Also the route command had two default listings, one ppp0 and the other ethernet (though I only spotted this issue once).
 
Thus, I'm wondering if there's a way to set the DNS and keep it from being tweaked. Would chmod be a good idea? While I'd like to give Ubuntu a try, if this doesn't start working soon I'm throwing in the towl and going back to Fedora.