ppp connection unstable

[Stefan Ehmann]

I'm running user ppp for my Internet connection. It basically runs fine
but there is this quite annoying problem:

Sometimes packets stop going out through the tun0 interface (pppctl
shows
queued packets) but there are still packets incoming (obviously the
connection becomes unusable). The only remedy is to reconnect manually
(I'm doing this via pppctl)
or wait until this is done automatically when lqr is enabled.

When does this happen?
- many connections at the same time (e.g. running a file-sharing tool)
- heavy CPU load

A combination of the two factors usually result in the problem within
some
minutes.

When burning Cd's there's a similar problem. First the bandwidth goes
down
really low but pinging is still possible - sometimes i also get
disconnected. (But I could live with that problem since i don't burn
CD's
that often.)

My configuration:
I'm using FreeBSD CURRENT (but the same problem appeared using
4.8-RELEASE)

ISDN-Card: AVM Fritz!Card PCI (passive)

excerpt from kernel config
#AVM Fritz!Card
device ifpi

#ISDN Protocol Stack (mandatory)
device "i4bq921"
device "i4bq931"
device "i4b"

#ISDN Devices
device "i4btrc" 4
device "i4bctl"
device "i4brbch" 4
#device "i4btel" 2
#device "i4bipr" 4
#options IPR_VJ
#device "i4bisppp" 4

For ppp configuration I use isdnd.rc and ppp.conf.isdn from
/usr/share/examples/ppp/ (only telephone numbers and login information
changed)

I couldn't find the cause of this problem so far. My best guess would be
some kind of hardware incompatibility but there should be some remedy
since
it runs fine using windows.

Any help would be appreciated.