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1. Technology overview 1.1 LANChat - an UDP based network application 1.2 Auto-alive messages 1.3 Size of messages nad network usage 1.4 Data security 2. Network configuration examples 2.1 Simple Windows TCP/IP network (beginners !) 2.2 Segmented Local Area Networks with Linux routers 3. IP Forcer and solving IP problems

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1. Technology overview

1.1 LANChat Pro - an UDP-based network application

  LANChat Pro is a peer-to-peer application. It uses UDP protocol to communicate between stations. All LANChat Pro messages are always broadcast addressed (depending on your network mas it can be like 192.168.0.255 or anything). LANChat Pro ports are 16128 and 44145. LANChat broadcast messages go as far as routers allow broadcast messages to flow. Practically, every router has disabled this function and LANChat Pro works only in one segment of a network. There are several ways to help this problem. See routing and bridging section in this document.

1.2 Auto-alive messages

  Every LANChat Pro user sends one "alive" message every 5 seconds to keep other users informed about his presence. If there is no such message for 15 seconds LANChats signalize 'time out' of that user. Size of alive message is about 70 bytes.

1.3 Size of messages and network usage

  Size of LANChat messages is rather small: 70 bytes header plus data. Auto-alives sent every 5 seconds take minimal speed of your network. Every user requiers 70 bytes every 5 seconds, that's 14 bytes/second. 1000 users would take 14 000 bytes/second so the network usage is minimal.

1.4 Data security

  LANChat Pro messages are crypted using rather simple algorithm. Because Linux version of LANChat source is open to the public, original Windows LANChat uses two types of crypt - one to Linux users (you may find the algorithm in Linux LANChat source code) and another one to Windows users (no algorithm available). Chatting between Windows machines is more secure than between Linux or mixed machines. ...

2. Network configuration examples

2.1 Simple Windows TCP/IP network

  Typical Local Area Network should be addressed in the following format:
- IP address for each machine: 192.168.X.N, where:

X is your network's number (0-254) - please select any
N is each machine's number (1-254) - different for each station
So IP addresses of your machines may be e.g. 192.168.5.1, 192.168.5.2, 192.168.5.3 etc...

- network mask (filled automatically by Windows) 255.255.255.0
- network (not present in Win95/98 configuration) 192.168.X.0
- broadcast (not present in Win95/98 configuration) 192.168.X.255
  Installed components in your 'Network' sheet in Windows 95/98 Control Panel should have:
- network card (e.g. "NE2000 Compatibile" or your manufacturer's driver)
- TCP/IP protocol (with IP options set)
  Other components are not required to run LANChat, however it is recommended to install Microsoft Network Client and File Sharing.
  Here's a recepie for beginners: install Windows 95OSR2/98, install your network card using manufacturer's driver or Windows built-in driver, then add TCP/IP protocol (if Windows hadn't done it automatically), click Properties on it, then set IP address to 192.168.0.1 (on one machine) and 192.168.0.2 (on the second). Nothing more is required to run LANChat Pro. To test your setting try the utility 'ping' - write 'ping 192.168.0.2' on the machine with IP address (192.168.0.1), ping tries to find the specified address. That's the best method of testing TCP/IP networks.

2.2 Segmented Local Area Networks with Linux routers

  I will concentrate on a specific case: two networks connected with a server computer between with Linux operating systems (most popular for servers I think) and two network cards (one for each network). This router must have routing daemon installed, but that IS NOT ENOUGH to run LANChat, because routers do not pass broadcast messages (which LANChat Pro uses). All you have to do is launch a bridge daemon on this server (what will not affect router or anything). Click here for full documentation about installing bridge daemon in Linux (for now only Polish version of ths document is available, sorry).

3. IP Forcer and solving IP problems

  When using LANChat Pro all machines must have different last IP numbers. If two of your machines have equal last IP numbers (e.g. 192.168.0.5 and 193.169.2.5) IP Forcer can help you. It allows to override last IP number without any harm to your Windows Networking. The change is only visible to LANChat Pro. The changes made with IP Forcer (which can be found in your \add-ons directory) can be made using LANChat Pro Setup Dialog, but it's impossible to run LANChat Pro while a conflict occurs. If so, please override the last IP number to a value, which does not appear on the network (is unique).

(more advanced information coming soon...)

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End of LANChat Pro advanced documentation.

Piotr Kowalski