patch-2.3.4 linux/Documentation/isdn/README.x25

• Lines: 267
• Date: Sun May 23 10:03:41 1999
• Orig file: v2.3.3/linux/Documentation/isdn/README.x25
• Orig date: Thu Jan 7 08:41:54 1999

diff -u --recursive --new-file v2.3.3/linux/Documentation/isdn/README.x25 linux/Documentation/isdn/README.x25
@@ -1,29 +1,24 @@
- 
-X25 support within isdn4linux
-
-
-This is experimental code and should be used with linux version 2.1.72.
-or later. Use it completely at your own risk.
-
+  
+X.25 support within isdn4linux
+==============================
 
+This is alpha/beta test code. Use it completely at your own risk.
 As new versions appear, the stuff described here might suddenly change
 or become invalid without notice.
 
 Keep in mind:
 
-You are using an experimental kernel (2.1.x series) with an experimental
-x25 protocol implementation and experimental x25-on-top-of-isdn extensions.
-Thus, be prepared to face problems related therefrom.
+You are using several new parts of the 2.2.x kernel series which
+have not been tested in a large scale. Therefore, you might encounter
+more bugs as usual.
 
-- If you connect to an x25 neighbour not operated by yourself, ASK the
+- If you connect to an X.25 neighbour not operated by yourself, ASK the
   other side first. Be prepared that bugs in the protocol implementation
-  might result in problems (even crashing the peer, however such ugly events
-  should only happen if your peer's protocol implementation has serious bugs).
+  might result in problems.
 
 - This implementation has never wiped out my whole hard disk yet. But as
-  this is experimental code, don't blame me if that happened to you. Take
-  appropriate actions (such as backing up important data) before
-  trying this code.
+  this is experimental code, don't blame me if that happened to you.
+  Backing up important data will never harm.
 
 - Monitor your isdn connections while using this software. This should
   prevent you from undesired phone bills in case of driver problems.
@@ -32,7 +27,7 @@
 
 
 How to configure the kernel
-
+===========================
  
 The ITU-T (former CCITT) X.25 network protocol layer has been implemented
 in the Linux source tree since version 2.1.16. The isdn subsystem might be 
@@ -48,32 +43,33 @@
 compilation. You currently also need to enable
 "Prompt for development and/or incomplete code/drivers" from the
 "Code maturity level options" menu. For the x25trace utility to work
-you also need to enable "Packet socket" (I recommend to choose "y",
-not "m" for testing) from the networking options.
+you also need to enable "Packet socket".
 
+For local testing it is also recommended to enable the isdnloop driver
+from the isdn subsystem's configuration menu.
 
-For testing you should also select the isdnloop driver from the
-isdn subsystem's configuration menu.
+For testing, it is recommended that all isdn drivers and the X.25 PLP
+protocol are compiled as loadable modules. Like this, you can recover
+from certain errors by simply unloading and reloading the modules.
 
 
 
 What's it for? How to use it?
+=============================
 
-
-X25 on top of isdn might be useful with two different scenarios:
+X.25 on top of isdn might be useful with two different scenarios:
 
 - You might want to access a public X.25 data network from your Linux box.
   You can use i4l if you were physically connected to the X.25 switch
-  by an ISDN line (leased line as well as dial up connection should work,
-  but connecting to x.25 network switches is currently untested. Testing
-  needs to be done by somebody with access to such a switch.) 
-
-- Or you might want to operate certain ISDN teleservices on 
-  your linux box. A lot of those teleservices run on top of the ISO-8208 
-  network layer protocol. ISO-8208 is essentially the same as ITU-T X.25.
+  by an ISDN line (leased line as well as dial up connection should work)
+
+- Or you might want to operate certain ISDN teleservices on your linux
+  box. A lot of those teleservices run on top of the ISO-8208
+  (DTE-DTE mode) network layer protocol. ISO-8208 is essentially the
+  same as ITU-T X.25.
 
-  Popular candidates of such teleservices are EUROFILE transfer or any
-  teleservice applying ITU-T recommendation T.90 (i.e., AFAIK, G4 Fax).
+  Popular candidates of such teleservices are EUROfile transfer or any
+  teleservice applying ITU-T recommendation T.90.
 
 To use the X.25 protocol on top of isdn, just create an isdn network
 interface as usual, configure your own and/or peer's ISDN numbers,
@@ -81,21 +77,18 @@
 
    isdnctrl encap <iface-name> x25iface.
 
-Once encap is set like this, the device can be used by the x25 packet layer.
+Once encap is set like this, the device can be used by the X.25 packet layer.
 
-All the stuff needed for x25 is implemented inside the isdn link
+All the stuff needed for X.25 is implemented inside the isdn link
 level (mainly isdn_net.c and some new source files). Thus, it should
-work with every existing HL driver. I was able to successfully open x25
+work with every existing HL driver. I was able to successfully open X.25
 connections on top of the isdnloop driver and the hisax driver.
 "x25iface"-encapsulation bypasses demand dialing. Dialing will be
-initiated when the upper (x25 packet) layer requests the lapb datalink to
-be established. But hangup timeout is still active. The connection
-will not automatically be re-established by the isdn_net module
-itself when new data arrives after the hangup timeout. But
-the x25 network code will re-establish the datalink connection
-(resulting in re-dialing and an x25 protocol reset) when new data is
-to be transmitted. (This currently does not work properly with the
-isdnloop driver, see "known problems" below)
+initiated when the upper (X.25 packet) layer requests the lapb datalink to
+be established. But hangup timeout is still active. Whenever a hangup
+occurs, all existing X.25 connections on that link will be cleared
+It is recommended to use sufficiently large hangup-timeouts for the
+isdn interfaces.
 
 
 In order to set up a conforming protocol stack you also need to
@@ -114,104 +107,64 @@
    isdnctrl l2_prot <iface-name> x25dce
 
 However, x25dte or x25dce is currently not supported by any real HL
-level driver. The main difference between x75 and x25dte/dce is that
+level driver. The main difference between x75i and x25dte/dce is that
 x25d[tc]e uses fixed lap_b addresses. With x75i, the side which
 initiates the isdn connection uses the DTE's lap_b address while the
-called side used the DCE's lap_b address. Thus, l2_prot x75i will
-probably work if you access a public x25 network as long as the
-corresponding isdn connection is set up by you. However, I've never
-tested this.
-
-
+called side used the DCE's lap_b address. Thus, l2_prot x75i might
+probably work if you access a public X.25 network as long as the
+corresponding isdn connection is set up by you. At least one test
+was successful to connect via isdn4linux to an X.25 switch using this
+trick. At the switch side, a terminal adapter X.21 was used to connect
+it to the isdn.
 
-How to use the test installation?
 
+How to set up a test installation?
+==================================
 
-To test x25 on top of isdn, you need to get
+To test X.25 on top of isdn, you need to get
 
-- a patched version of the "isdnctrl" program that supports setting the new
-  x25 specific parameters.
+- a recent version of the "isdnctrl" program that supports setting the new
+  X.25 specific parameters.
 
-- the x25-utils-2.1.x package from ftp.pspt.fi/pub/ham/linux/ax25
-  or any mirror site (i.e. ftp://ftp.gwdg.de/pub/linux/misc/ax25/).
+- the x25-utils-2.X package from 
+  ftp://ftp.hes.iki.fi/pub/ham/linux/ax25/x25utils-*
+  (don't confuse the x25-utils with the ax25-utils)
 
-- a kernel patch that enhances isdn4linux to provide x25 network
-  interface support. (This file is part of that kernel patch).
-
-- an application that uses linux AF_X25 sockets program. 
+- an application program that uses linux PF_X25 sockets (some are
+  contained in the x25-util package).
 
 Before compiling the user level utilities make sure that the compiler/
-preprocessor will fetch the proper (patched) kernel header files. Either make
-/usr/include/linux a symbolic link pointing to your developer kernel's
-include/linux directory or set the appropriate compiler flags.
-
-It is recommended that all isdn drivers and the x25 PLP protocol 
-are compiled as loadable modules. Like this, you can recover
-from certain errors by simply unloading and reloading the modules.
+preprocessor will fetch the proper kernel header files of this kernel
+source tree. Either make /usr/include/linux a symbolic link pointing to 
+this kernel's include/linux directory or set the appropriate compiler flags.
 
 When all drivers and interfaces are loaded and configured you need to
-ifconfig the network interfaces up and add x25-routes to them. Use
+ifconfig the network interfaces up and add X.25-routes to them. Use
 the usual ifconfig tool.
 
 ifconfig <iface-name> up
 
 But a special x25route tool (distributed with the x25-util package)
-is needed to set up x25 routes. I.e. 
+is needed to set up X.25 routes. I.e. 
 
 x25route add 01 <iface-name>
 
-will cause all x.25 connections to the destination x.25-address
+will cause all x.25 connections to the destination X.25-address
 "01" to be routed to your created isdn network interface.
 
-
-There are currently no real x25 applications available. However, for
+There are currently no real X.25 applications available. However, for
 tests, the x25-utils package contains a modified version of telnet
-and telnetd that uses x25 sockets instead of tcp/ip sockets. Use
-this for your first tests. Furthermore, there is an x25.echod and a client
-named "eftp" (which contains some experimental code to download files
-from a remote eft server using the EUROfile transfer protocol).
-It available at ftp://ftp.hamburg.pop.de/pub/LOCAL/linux/i4l-eft/eftp4linux-*
+and telnetd that uses X.25 sockets instead of tcp/ip sockets. You can
+use those for your first tests. Furthermore, you might check
+ftp://ftp.hamburg.pop.de/pub/LOCAL/linux/i4l-eft/ which contains some
+alpha-test implementation ("eftp4linux") of the EUROfile transfer
+protocol.
+
+The scripts distributed with the eftp4linux test releases might also
+provide useful examples for setting up X.25 on top of isdn.
 
 The x25-utility package also contains an x25trace tool that can be
-used to monitor x25 packets received by the network interfaces.
+used to monitor X.25 packets received by the network interfaces.
 The /proc/net/x25* files also contain useful information. 
 
-The eftp4linux test release also contains an "ix25test" script that can
-be used for testing x25 on top of isdn4linux. Edit
-this script according to your local needs and then call it as
-
-ix25test start
-
-This will set up a sample configuration using the isdnloop and hisax
-driver and create some isdn network interfaces.
-It is recommended that all other isdn drivers and the
-x25 module are unloaded before calling this script.
-
-
-
-Known problems and deficiencies:
-
-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.
-
-Sometimes the x25 module cannot be unloaded (decrementation of its use
-count seems to get lost occasionally).
-
-Using the x25 based telnet and telnetd programm to establish connection
-from your own to your own computer repeatedly sometimes totally locked
-up my system. However, this kernel patch also modifies
-net/x25/af_x25.c to include a workaround. With this workaround
-enabled, my system is stable. (If you want to disable the
-workaround, just undefine ISDN_X25_FIXES in af_x25.c).
-
-The latter problem could be reproduced by using hisax as well as the
-isdnloop driver. It seems that it is not caused by the isdn code.
-Somehow, the inode of a socket is freed while a process still refers
-the socket's wait queue. This causes problems when the process tries to
-remove itself from the wait queue (referred by the dangling
-sock->sleep pointer) before returning from a select() system call.
-
 - Henner
-