The commands are of the form:

--multiplay=in | out,Hz,destination address,destination port
--callsign=a_unique_name


Below are some examples of startup commands that demonstrate the use of the 
multiplayer facilities.

For two players on a local network or across the internet:
----------------------------------------------------------
Player1:
--multiplay=out,10,192.168.0.3,5500 --multiplay=in,10,192.168.0.2,5501 
--callsign=player1

Player2:
--multiplay=out,10,192.168.0.2,5501 --multiplay=in,10,192.168.0.3,5500 
--callsign=player2


For multiple players on a local network:
----------------------------------------
Player1:
--multiplay=out,10,255.255.255.255,5500 
--multiplay=in,10,255.255.255.255,5500 --callsign=player1

Playern:
--multiplay=out,10,255.255.255.255,5500 
--multiplay=in,10,255.255.255.255,5500 --callsign=playern

Note that the callsign is used to identify each player in a multiplayer game 
so the callsigns must be unique. The multiplayer code ignores packets that 
are sent back to itself, as would occur with broadcasting when the rx and tx 
ports are the same.


Multiple players sending to a single player:
--------------------------------------------
Player1:
--multiplay=out,10,192.168.0.2,5500 --callsign=player1

Player2:
--multiplay=out,10,192.168.0.2,5500 --callsign=player2

Player3:
--multiplay=out,10,192.168.0.2,5500 --callsign=player3

Player4 (rx only):
--multiplay=in,10,192.168.0.2,5500 --callsign=player4

This demonstrates that it is possible to have multiple instances of 
Flightgear that send to a single instance that displays all the traffic. This 
is the sort of implementation that we are considering for use as a tower 
visual simulator.


For use with a server (when one is created):
--------------------------------------------
Player1:
--multiplay=out,10,serveraddress,6000 --multiplay=in,10,myaddress,5500 
--callsign=player1

Player2:
--multiplay=out,10,serveraddress,6000 --multiplay=in,10,myaddress,5501 
--callsign=player2

Playern:
--multiplay=out,10,serveraddress,6000 --multiplay=in,10,myaddress,5502 
--callsign=playern

The server would simply act as a packet forwarding mechanism. When it 
receives a packet, it sends it to all other active players.