I hope this is something really simple, but I'm now at a loss.
I'm connecting with a pcmcia modem in my laptop to my ISP via
PPP, and in general, everything works fine -- the connection can
stay up for days if I don't do anything substantial (e.g., if I
only read mail).  However, if I try and do any substantial data
downloads (such as cvs updating the pkgsrc tree), the modem
regularly hangs up, and I can't figure out why.  I've got the
pppd using debug and have looked at tcpdump output, and can't
find anything strange.  My only guess (and it's exactly that) is
that some control character is coming through and causing the
modem to hangup.  However, it may even be the case that the
provider is hanging up and I just don't know how to tell the
difference.  The only other information I have is that 1) this
doesn't happen under windows (with a different modem), so I don't
think the provider is hanging up; and 2)  the modem shows up as
follows:

pcmcia0 at pcic0 controller 0 socket 0
pcmcia0: CIS version PCMCIA 2.0 or 2.1
pcmcia0: CIS info: Simple Technology, Communicator, 001, STI-FAX DATA/FAX/VOICE/CELLPHONE
pcmcia0: Manufacturer code 0x14d, product 0x100
pcmcia0: function 0: serial port, ccr addr 200 mask 17
pcmcia0: function 0, config table entry 32: I/O card; irq mask 86bc; iomask a, iospace 3f8; audio
pcmcia0: function 0, config table entry 33: I/O card; irq mask 86bc; iomask a, iospace 2f8; io8 audio
pcmcia0: function 0, config table entry 34: I/O card; irq mask 86bc; iomask a, iospace 3e8; io8 audio
pcmcia0: function 0, config table entry 35: I/O card; irq mask 86bc; iomask a, iospace 2e8; io8 audio
pcmcia0: function 0, config table entry 48: I/O card; irq mask 86bc; iomask 3, iospace 0; io8 audio
com3 at pcmcia0 function 0 port 0x3e8-0x3ef: serial device
com3: ns16550a, working fifo

Any tips on how to fix this, where to look further to get more
information, or anything else, greatly appreciated.

Chris

PS, this is port I386, running current as of 7/14 (1.4F).