the modem conection dies and i get a message like this in the /var/log/messages file:

Jan 13 10:23:58 localhost kernel: serial8250: too much work for irq5

i've found similar error messages posted on various sites but no solutions. the odd
thing is that the modem is not a uart 8250 it's a 16550A as shown by setserial:

/dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 5

this setup worked perfectly for 18 months on redhat v9 but since i've upgraded to fedora core 3 i've been having this problem a little bit too frequently. it's happening almost daily now and is getting really annoying.