$Id: PROBLEMS-2.1.114,v 1.2 1999/07/01 18:00:25 he Exp $

Known problems observed when using X.25 on top of isdn with kernels
===================================================================

The X.25 PLP implementation was originally designed to be used on top
of a synchronous line (accessed via an X.25 network device driver)
or on top of lan (IEEE 802 LLC type 2). Furthermore, the X.25
implementation as well as the related isdn4linux extensions are labelled
as "EXPERIMENTAL" code in the kernel source tree. Thus, the X.25 protocol
sometimes doesn't behave as you would expect, in particular when used
on top of isdn.


Problems related to isdn drivers:
=================================

The isdnloop HL driver apparently has problems to re-establish a
connection that has been hung up from the outgoing device. You have to
unload the isdnloop driver after the faked isdn-connection is closed
and insmod it again. With the Hisax driver, this problem is not present.

When ifconfig'ing isdn network interfaces (with encap x25iface set) down,
"disconnect indication while unconfigured" messages might appear in
the syslog. This does not indicate any problem and can be ignored.

When establishing the first X.25 connection on a link, there is a
delay of some seconds until the link becomes established. This is only
a performance problem and harmless. Furthermore, this is fixed with
recent isdn4linux versions from the isdn4linux CVS tree. Kernel
2.2.10 still contains this outdated isdn4linux version.

Problems related to the X.25 PLP implementation:
================================================

isdn B channels are not closed automatically when the X.25 PLP
connection is closed. If you are lucky, your peer does it. eftd
and the eftp.sh shell script also try to close connection. But this
might sometime fail due to bugs. Thus, 
monitor your isdn connections while using X.25 on top of isdn4linux
(i.e. by watching syslog messages or by an isdn monitor program).
You can close the B channel connection by hand (using the
"isdnctrl hangup" command) or rely on the isdn network interface's
hangup timeout.