Howto:Set up a FGCom server

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For running a FGCom server you need Asterisk and depending on the amount of users much bandwith and CPU power. Because of puting pilots and Air Traffic Controllers in a VoIP conference the server-admin has to assure that there is enough network and CPU power to avoid drop-outs of the voice stream.

Pre-requirements

Install Asterisk on top of your favorite distribution. Please refer to installation manuals (e.g. Asterisk-Guru) that you can find on the net. You do not need H.323 or SIP because the fgcom client uses IAX2 as VoIP signaling protocol. Only if you think about connecting external VoIP applications to FGCom you should consider to activate H.323 or SIP (but this is not the scope of this small howto).

Notice: You need to install the zaptel driver modules - even if you won't use any hardware for telecom interfacing. You need the ztdummy kernel module for the asterisk conference application MeetMe() because it simulates a hardware clock needed by this application. Further development of FGCOM might use app_conference which don't needs any timing device.

For now we want to use /etc/asterisk as the base configuration directory.

Setting up the radio frequencies

The radio frequencies are "simple" Conferences and realized due to the Asterisk application MeetMe().

Part 1: General configuration

First you have to set up the general configuration of the system. Put the following at the top of your "extensions.conf" file:

 [general]
 static=yes
 writeprotect=yes
 ;
 [globals]
 ;
 [macro-com]
 exten => s,1,Answer()
 exten => s,n,MeetMe(${MACRO_EXTEN},qd)
 exten => s,n,Hangup()
 ;
 [macro-echo]
 exten => s,1,Answer()
 exten => s,n,Echo()
 exten => s,n,Hangup()
 ;
 [guest]
 ; ATC-Help
 exten => 01-ZZZZ-911.000,1,Macro(com)
 exten => 012525252591100,1,Dial(Local/01-ZZZZ-911.000)
 exten => 01-ZZZZ-910.000,1,Macro(echo)
 exten => 012525252591000,1,Dial(Local/01-ZZZZ-910.000)
 ;
 [default]
 include => guest
 ;
 ; Code:
 ; 01 - FlightGear
 ; 02 - Microsoft Flight-Simulator
 ; 03 - ...
 ;
 ; Air2Air
 exten => 01-ZZZZ-123.450,1,Macro(com)
 exten => 012525252512345,1,Dial(Local/01-ZZZZ-123.450)
 exten => 01-ZZZZ-122.750,1,Macro(com)
 exten => 012525252512275,1,Dial(Local/01-ZZZZ-122.750)

Part 2: Adding your favorite (all?) frequencies

For this you have simply to create an extension for every touple of airport/frequency in extensions.conf. The following is an example for Berlin Tempelhof Airport (EDDI). The information comes from the file "apt.dat.gz" of your FlightGear installation.

 ; EDDI ATIS 126.020 - Berlin Tempelhof
 exten => 01-EDDI-126.020,1,Macro(com)
 exten => 010403030812602,1,Dial(Local/01-EDDI-126.020)
 ;
 ; EDDI BERLIN DEP 120.620 - Berlin Tempelhof
 exten => 01-EDDI-120.620,1,Macro(com)
 exten => 010403030812062,1,Dial(Local/01-EDDI-120.620)
 ;
 ; EDDI BERLIN DIRECTOR 121.120 - Berlin Tempelhof
 exten => 01-EDDI-121.120,1,Macro(com)
 exten => 010403030812112,1,Dial(Local/01-EDDI-121.120)
 ;
 ; EDDI BERLIN ARR 126.420 - Berlin Tempelhof
 exten => 01-EDDI-126.420,1,Macro(com)
 exten => 010403030812642,1,Dial(Local/01-EDDI-126.420)
 ;
 ; EDDI GND 121.950 - Berlin Tempelhof
 exten => 01-EDDI-121.950,1,Macro(com)
 exten => 010403030812195,1,Dial(Local/01-EDDI-121.950)
 ;
 ; EDDI TWR 119.570 - Berlin Tempelhof
 exten => 01-EDDI-119.570,1,Macro(com)
 exten => 010403030811957,1,Dial(Local/01-EDDI-119.570)
 ;
 ; EDDI BERLIN DIRECTOR 136.100 - Berlin Tempelhof
 exten => 01-EDDI-136.100,1,Macro(com)
 exten => 010403030813610,1,Dial(Local/01-EDDI-136.100)
 ;
 ; EDDI TWR 118.100 - Berlin Tempelhof
 exten => 01-EDDI-118.100,1,Macro(com)
 exten => 010403030811810,1,Dial(Local/01-EDDI-118.100)
 ;
 ; EDDI BERLIN DEP 119.500 - Berlin Tempelhof
 exten => 01-EDDI-119.500,1,Macro(com)
 exten => 010403030811950,1,Dial(Local/01-EDDI-119.500)
 ;
 ; EDDI BERLIN ARR 119.620 - Berlin Tempelhof
 exten => 01-EDDI-119.620,1,Macro(com)
 exten => 010403030811962,1,Dial(Local/01-EDDI-119.620)

What does the above mean? There are two lines (three with the comment) for each frequency: The first one sets up an extension named "01-EDDI-119.500". Yes, for VoIP you can use textual extensions but be careful if you want to setup your Asterisk-Server with POTS (=Plain old telephone service). Therefor you need the second line which is the same as above but without dashes and the letters in the decimal representation of the ASCII Code. The second line does only a "rewrite" of the numerical representation to the textual one.

For setting up all airports you can write your own simple script. But this maybe also not needed in further versions of FGCOM.

After editing the extensions.conf file you have to reload the extensions file (e.g. "asterisk -rx extensions reload").

You can add further nice goodies to your extensions.conf: MorseCode() for morsing the code of the VOR (MorseCode() will only work in Asterisk >= 1.4), Recording of metar data and playing this recording back when using the frequency of the metar information, ...

Setting up user accounts

The user accounts are located in the file iax.conf (and perhaps also in sip.conf, but this is not necessary). The top of the file should look like this:

 [general]
 bandwith=low
 disallow=lpc10
 jitterbuffer=yes
 forcejitterbuffer=no
 tos=lowdelay
 autokill=yes
 disallow=all
 allow=alaw
 allow=gsm
 allow=ilbc
 allow=g726
 allow=ulaw
 language=en
 maxauthreq=10
 context=guest
 ;
 [guest]
 type=user
 username=guest
 context=guest
 qualify=yes
 callerid=Guest IAX User
 host=dynamic
 ;

You may want to disallow more codecs or want to allow additional codecs (such as speex). But have in mind that the internal mixing of the conferences are done in "ulaw". But "ulaw" needs about 80 kBit/s because it does no compression. So you have to think about what's better for you: less bandwidth (per user) and more CPU usage or more bandwidth (per user) and less CPU usage... you should also consider the "sound" of some codecs may not have the 'real radio sound'.

For each user you have to add a bunch of lines to your iax.conf file:

 [<USERNAME>]
 type=user
 username=<USERNAME>
 secret=<PASSWORD>
 context=default
 host=dynamic
 nat=yes
 notransfer=yes

You just have to fill in the <USERNAME> and <PASSWORD>. After each change you have to reload the configuration (e.g. "asterisk -rx reload chan_iax2.so"). Perhaps you want to write scripts for automatic configuration and so on. But be warned: Further versions of fgcom may use the multiplayer servers for getting usernames and position data and you have to change your scripts.

Problems?

If you have problems you can contact me via email at "dcoredump AT gmail.com".