I get terrible dialup ppp performance on a pinstrip toshiba satellite 4080xcdt laptop with a xircom eth/56k modem combo pcmcia card. Same works fine under windows. Using both Att business and uunet/msn as providers and also trying to switch of all compression on the line i get declining ppp performance, actually IP Performance after ppp finished on the dialup line. I get some packets through the first few seconds then go down to 100 bytes/second, then to nearly zero packets. Connect is at 31200 over an ISDN phone system that convers the modem signals (a quite usual setup). I get normal good performance when using the ethernet interface on the pcmcia combo card for network connections. I had to diable vj compression to stop a continuous flow of ConfReq / Rej packets, but that didnt help the main problem. On Alan Cox Suggestion I tried hdparm -u1 but that didnt help either.
Please verify this with a newer version of Red Hat Enterprise Linux or Fedora Core and reopen it against the new version if it still occurs. Closing as "not a bug" for now.