I set up a new machine yesterday with kernel 2.4.17-pre8, usb-uhci and acm
drivers (non modular). The machine is a Dell machine, Celeron 600 with Intel
PIIX4 providing USB interfaces. There is a brand-new 3Com/USR ISDN Pro TA
attached.

I set up a ppp connection, and am able to connect once out of every five or
six times. Once I connect, data transfers are fast and reliable (no dropped
data, no retransmissions apparent). However, when I can't connect, the
symptoms are very weird. The ifup process starts pppd, which then calls
"wvdial" to actually dial the modem and make the connection. Watching the
logs, I can see wvdial initialize the modem, send the dial command, and then
wait for CONNECT from the modem. The modem connects, but wvdial doesn't
report the connection, and never passes control back to pppd.

After the connection has been up for 15-20 seconds, the other end hangs up
because my end never talked to it :-) When this happens, wvdial reports
_ONE_ incoming buffer full of data, with all the PPP negotiation attempts
from the other end, then another buffer with NO CARRIER.

This does not happen every connection attempt, most of them. Just for grins,
I changed to using the serial connection instead of USB, and it worked
perfectly. This leads me to believe that this is somehow related to the ACM
driver, or the way that the wvdial program is reading the data from the ACM
device. I haven't yet looked at the wvdial source, but I will do so.

Has anyone else had a problem like this? It appears that data is coming in,
even with pauses between the packets, but they aren't getting passed up the
chain to wvdial until something more severe happens, like a control line
change (in this case, the "carrier" being dropped).


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