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-
-
-
-Leased line Mini HOWTO
-
-
-
-----
-
-!!!Leased line Mini HOWTO
-
-!!Rob van der Putten,
-rob@sput
.nlv2.1, 3 August 2000
-
-
-----
-''Configuring your modem and pppd to use a 2 wire twisted pair leased line.''
-----
-
-
-The most recent (beta) version of this HOWTO can be found at:
-http://www.sput.nl/software/leased-line/
-
-
-
-
-
-
-
-!!1. Introduction
-
-
-*1.1 Copyright and License
-
-*1.2 What is a leased line
-
-*1.3 Assumptions
-
-
-
-
-
-!!2. Modem
-
-
-*2.1 Modem Configuration
-
-*2.2 Test
-
-*2.3 Examples
-
-
-
-
-
-!!3. PPPD
-
-
-*3.1 Configuration
-
-*3.2 Scripts
-
-*3.3 Test
-
-----
-
-!!1. Introduction
-
-!!1.1 Copyright and License
-
-
-
-This document is distributed under the terms of the GNU Free Documentation License.
-You should have received a copy along with it. If not, it is available from
-http://www.fsf.org/licenses/fdl.html.
-
-!!1.2 What is a leased line
-
-
-
-Any fixed, that is permanent, point to point data communications link,
-which is leased from a telco or similar organisation.
-The leased line involves cables, such as twisted pair, coax or fiber optic,
-and may involve all sorts of other hardware such as (pupin) coils,
-transformers, amplifiers and regenerators.
-
-
-
-
-; __This document deals with:__:
-
-Configuring your modem and pppd to use a 2 wire twisted pair leased
-line.
-
-
-
-; __This document does __NOT__ deal with:__:
-
-SLIP, getting or installing pppd, synchronous data communication,
-baseband modems, xDSL.
-
-
-!!1.3 Assumptions
-
-
-
-You should already have a working pppd on your system.
-You also need Minicom or a similar program to configure your modems.
-----
-
-!!2. Modem
-
-
-A leased line is not connected to a telephone exchange and does not provide
-DC power, dial tone, busy tone or ring signal. This means that your modems
-are on their own and have to be able to deal with this situation.
-
-
-
-You should have 2 identical (including firmware version) __external__
-modems supporting both leased line and dumb mode. Make sure your modems can
-actually do this! Also make sure your modem is properly documented.
-You also need:
-
-
-*2 fully wired shielded RS232 cables. The shield should be connected to
-the connector shell (not pin 1) at both ends (not at one end).
-*
-
-*A RS232 test plug may be handy for test purposes.
-*
-
-*2 RJ11 cords, one for each end of the leased line.
-*
-
-*A basic understanding of `AT' commands.
-*
-
-
-!!2.1 Modem Configuration
-
-
-
-A note on modem configuration and init strings in general:
-Configure your modem software such as minicom or (m)getty to use the
-highest possible speed; 57600 bps for 14k4 and 115200 bps for 28k8 or
-faster modems.
-Lots of people use very long and complicated init strings, often starting
-with AT&F and containing lots of modem brand and -type specific
-commands. This however is needlessly complicated.
-Most programs feel happy with the same modem settings, so why not write
-these settings in the non volatile memory of all your modems, and only use
-`ATZ' as an init string in all your programs. This way you can swap or
-upgrade your modems without ever having to reconfigure any of your
-software.
-
-
-
-Most programs require you to use the following settings;
-
-
-*Fixed baud rate (no auto baud)
-*
-
-*Hardware bidirectional RTS-CTS flow control (no x-on/x-off)
-*
-
-*8 Bits, no parity, 1 stopbit
-*
-
-*The modem should produce the __TRUE__ DCD status (&C1)
-*
-
-*The modem should __NOT__ ignore the DTR status (&D2 or &D3)
-*
-
-Check this with AT&V or AT&Ix (consult your modem documentation)
-
-
-
-These settings are not necessarily the same as the default factory profile
-(&F), so starting an init string with AT&F is probably not a good
-idea in the first place. The smart thing to do is probably to use AT&F
-only when you have reason to believe that the modem setup stored in the non
-volatile memory is really screwed up.
-If you think you have found the right setup for your modems, write it to
-non volatile memory with AT&W and test it thoroughly with Z-modem file
-transfers of both ASCII text and binary files.
-Only if all of this works perfectly should you configure your modems for
-leased line.
-
-
-
-Find out how to put your modem into dumb mode and, more importantly, how to
-get it out of dumb mode; The modem can only be reconfigured when it is not
-in dumb mode.
-Make sure you actually configure your modems at the highest possible speed.
-Once in dumb mode it will ignore all `AT' commands and consequently will
-not adjust its speed to that of the COM port, but will use the speed at
-which it was configured instead (this speed is stored in a S-register by
-the AT&W command).
-
-
-
-Now configure your modem as follows;
-
-
-*Reset on DTR toggle (&D3, this is sometimes a S register). This
-setting is required by some ISP's!
-*
-
-*Leased line mode (&L1 or &L2, consult your modem documentation)
-*
-
-*The remote modem auto answer (S0=1), the local originate (S0=)
-*
-
-*Disable result codes (Q1, sometimes the dumb mode does this for you)
-*
-
-*Dumb mode (\D1 or %D1, this is sometimes a jumper)
-In dumb mode the modem will ignore all AT commands (sometimes you need
-to disable the ESC char as well).
-*
-
-Write the configuration to non-volatile memory (&W).
-
-!!2.2 Test
-
-
-
-Now connect the modems to 2 computers using the RS232 cables and connect
-the modems to each other using a RJ11 lead. Use a modem program such as
-Minicom (Linux), procom or telix (DOS) on both computers to test the
-modems.
-You should be able to type text from one computer to the other and vice
-versa. If the screen produces garbage check your COM port speed and other
-settings.
-Now disconnect and reconnect the RJ11 cord. Wait for the connection to
-reestablish itself. Disconnect and reconnect the RS232 cables, switch the
-modems on and off, stop and restart Minicom.
-The modems should always reconnect at the highest possible speed (some
-modems have speed indicator leds).
-Check whether the modems actually ignores the ESC (+++) character. If
-necessary disable the ESC character.
-
-
-
-If all of this works you may want to reconfigure your modems;
-Switch off the sound at the remote modem (M0) and put the local modem at
-low volume (L1).
-
-!!2.3 Examples
-
-
-!Hi-Tech
-
-
-This is a rather vague `no name clone modem'. Its config string is however
-typical and should work on most modems.
-
-
-
-
-; __Originate (local):__:
-
-ATL1&C1&D3&L2%D1&W&W1
-
-
-
-; __Answer (remote):__:
-
-ATM0L1&C1&D3&L2%D1S0=1&W&W1
-
-
-!Tornado FM 228 E
-
-
-This is what should work;
-
-
-
-
-; __Originate (local):__:
-
-ATB15L1Q1&C1&D3&L2&W&W1
-
-
-
-; __Answer (remote):__:
-
-ATM0B15M0Q1&C1&D3&L2S0=1&W&W1
-
-Move the dumb jumper from position 2-3 to 1-2.
-
-
-
-Due to a firmware bug, the modems will only connect after being hard reset
-(power off and on) while DTR is high. I designed a
-circuit
-which hard resets the modem on the low to high transition of DTR.
-The FreeBSD pppd however, isn't very happy about this. By combining the
-setting &D0 with a
-circuit
-which resets on the high to low transition instead, this problem can be
-avoided.
-
-!Tron DF
-
-
-The ESC char should be disabled by setting S2 > 127;
-
-
-
-
-; __Originate:__:
-
-ATL1&L1Q1&C1&D3S2=171\D1&W
-
-
-
-; __Answer:__:
-
-ATM0&L2Q1&C1&D3S0=1S2=171\D1&W
-
-
-!US Robotics Courier V-Everything
-
-
-The USR Sportster and USR Courier-I do not support leased line. You need
-the Courier V-everything version for this job.
-There is a webpage on the USR site `explaining' how to set-up your Courier
-for leased line. However, if you follow these instructions you will end up
-with a completely brain dead modem, which can not be controlled or
-monitored by your pppd.
-
-
-
-The USR Courier can be configured with dip switches, however you need to
-feed it the config string first.
-First make sure it uses the right factory profile. Unlike most other modems
-it has three; &F0, &F1 and &F2. The default, which is also the
-one you should use, is &F1. If you send it an AT&F, however it will
-load the factory profile &F0!
-For the reset on DTR toggle you set bit 0 of S register 13. This means you
-have to set S13 to 1. Furthermore you need set it to leased line mode with
-&L1;
-ATS13=1&L1&W
-The dip switches are all default except for the following:
-
-
-
-
-; __3__:
-
-OFF Disable result codes
-
-
-
-; __4__:
-
-ON Disable offline commands
-
-
-
-; __5__:
-
-ON For originate, OFF For answer
-
-
-
-; __8__:
-
-OFF Dumb mode
-
-----
-
-!!3. PPPD
-
-
-You need a pppd (Point to Point Protocol Daemon) and a reasonable knowledge
-of how it works. Consult the relevant RFC's or the
-Linux PPP HOWTO if necessary.
-Since you are not going to use a login procedure, you don't use (m)getty
-and you do not need a (fake) user associated with the pppd controlling your
-link. You are not going to dial so you don't need any chat scripts
-either.
-In fact, the modem circuit and configuration you have just build, are
-rather like a fully wired null modem cable. This means you have to
-configure your pppd the same way as you would with a null modem cable.
-
-
-
-For a reliable link, your setup should meet the following criteria;
-
-
-*Shortly after booting your system, pppd should raise the DTR signal in
-your RS232 port, wait for DCD to go up, and negotiate the link.
-*
-
-*If the remote system is down, pppd should wait until it is up again.
-*
-
-*If the link is up and then goes down, pppd should reset the modem
-(it does this by dropping and then raising DTR), and then try to
-reconnect.
-*
-
-*If the quality of the link deteriorates too much, pppd should reset
-the modem and then reestablish the link.
-*
-
-*If the process controlling the link, that is the pppd, dies, a watchdog
-should restart the pppd.
-*
-
-
-!!3.1 Configuration
-
-
-
-Suppose the modem is connected to COM2, the local IP address is `Loc_Ip'
-and the remote IP address is `Rem_Ip'. We want to use 576 as our MTU.
-The /etc/ppp/options.ttyS1 would now be:
-
-
-crtscts
-mru 576
-mtu 576
-passive
-Loc_Ip:Rem_Ip
--chap
-modem
-#noauth
--pap
-persist
-
-
-Stuff like `asyncmap ', `lock', `modem' and `-detach' are probably already in
-/etc/ppp/options. If not, add them to your
-/etc/ppp/options.ttyS1.
-So, if the local system is 192.168.1.1 and the remote system is 10.1.1.1,
-then /etc/ppp/options.ttyS1 on the local system would be:
-
-
-crtscts
-mru 576
-mtu 576
-passive
-192.168.1.1:10.1.1.1
--chap
-modem
-#noauth
--pap
-persist
-
-
-The options.ttyS1 on the remote system would be:
-
-
-crtscts
-mru 576
-mtu 576
-passive
-10.1.1.1:192.168.1.1
--chap
-modem
-#noauth
--pap
-persist
-
-
-The passive option limits the number of (re)connection attempts.
-The persist option will keep pppd alive in case of a disconnect or when it
-can't connect in the first place.
-If you telnet a lot while doing filetransfers (FTP or webbrowsing) at the
-same time, you might want to use a smaller MTU and MRU such as 296. This
-will make the remote system more responsive.
-If you don't care much about telnetting during FTP, you could set the MTU
-and MRU to 1500.
-Keep in mind though, that UDP cannot be fragmented. Speakfreely for instance
-uses 512 byte UDP packets. So the minimum MTU for speakfreely is 552 bytes.
-The noauth option may be necessary with some newer distributions.
-
-!!3.2 Scripts
-
-
-!Starting the pppd and keeping it alive
-
-
-You could start the pppd form a boot (rc) script. However, if you do this,
-and the pppd dies, you are without a link.
-A more stable solution, is to start the pppd from /etc/inittab;
-
-
-s1:23:respawn:/usr/sbin/pppd /dev/ttyS1 115200
-
-
-This way, the pppd will be restarted if it dies.
-Make sure you have a `-detach' option (nodetach on newer systems) though,
-otherwise inittab will start numerous instances of pppd, will complaining
-about `respawning too fast'.
-
-
-Note: Some older systems will not accept the speed `115200'. In this case
-you will have to set the speed to 38400 en set the `spd_vhi' flag with
-setserial.
-Some systems expect you to use a `cua' instead of `ttyS' device.
-
-!Setting the routes
-
-
-The default route can be set with the defaultroute option or with the
-/etc/ppp/ip-up script;
-
-
-#!/bin/bash
-case $2 in
-/dev/ttyS1)
-/sbin/route add -net ...0 gw Rem_Ip netmask ...
-;;
-esac
-
-
-Ip-up can also be used to sync your clock using netdate.
-
-
-
-Of course the route set in ip-up is not necessarily the default route.
-Your ip-up sets the route to the remote network while the ip-up script on
-the remote system sets the route to your network. If your network is
-192.168.1.0 and your ppp interface 192.168.1.1, the ip-up script on the
-remote machine looks like this;
-
-
-#!/bin/bash
-case $2 in
-/dev/ttyS1)
-/sbin/route add -net 192.168.1.0 gw 192.168.1.1 netmask 255.255.255.
-;;
-esac
-
-
-The `case $2' and `/dev/ttyS1)' bits are there in case you use more than
-one ppp link. Ip-up will run each time a link comes up, but only the part
-between `/dev/ttySx)' and `;;' will be executed, setting the right route
-for the right ttyS.
-You can find more about routing in the
-Linux Networking HOWTO section on routing.
-
-!!3.3 Test
-
-
-
-Test the whole thing just like the modem test.
-If it works, get on your bike and bring the remote modem to the remote side
-of your link.
-If it doesn't work, one of the things you should check is the COM port
-speed;
-Apparently, a common mistake is to configure the modems with Minicom using
-one speed and then configure the pppd to use an other. This will __NOT__
-work! You have to use the same speed all of the time!
-
-
-
-----
+Describe [HowToLeasedLine] here
.
