VROC: Virtual Racers' Online Connection

Bandwidth Settings Recommendations

In earlier VROC versions, we recommended use of a core.ini file to race online. The host can now control communications settings to best advantage by checking "Use recommended bandwidth." Using these recommendations is likely to allow more players to join the race, and will reduce disconnects and other unpleasant phenomona.

Specifically, we send command line arguments that set the following:

net_mdm_client_send_every = 3
net_mdm_client_send_size = 84 
net_mdm_server_send_every = 3 
net_mdm_server_send_size = 84 
disable_modem = 1

This creates the same effect as do equivalent core.ini settings, and in fact overrides (but does not overwrite) core.ini in this respect. For your convenience, we also disable the modem poll at startup, which speeds up loading of the game.

According to the information on the wonderfully informative web site of Bart Westra, this will give the following bandwidth requirements:

Client: upload 9.9Kb/s, download 13.2Kb/s
Server (3 clients): upload 39.8Kb/s, download 25.9Kb/s
Server (5 clients): upload 66.2Kb/s, download 43.2Kb/s
Server (8 clients): upload 106.1Kb/s, download 69.1Kb/s
Server (12 clients): upload 159.0Kb/s, download 103.7Kb/s
Server (16 clients): upload 212.0Kb/s, download 138.2Kb/s

This suggests that a 64kb ISDN modem should be able to handle 4 clients reliably, and that a 112 or 128kb ISDN modem should be able to handle 8 clients reliably. Cable and xDSL will depend on the available upload speed; anything over about 270kb should be able to handle a full field of 20 players.

Clearly, it's pushing it to try to host three clients on an analog modem, since even 56kb analog modems have a maximum of 33.6kb upload.

Of course, these numbers are theoretical and each host must establish their own practical maximum through experience.

Why use bandwidth settings?

Reducing the bandwidth reduces the load on the serial port. If your CPU cannot keep up with the data coming into and going out of the serial port, important information is lost. If too much information is lost, the sim decides that the connection quality is too poor for racing, and disconnects.

Besides checking out Bart's site, the more technically inclined may click here to download a zip file containing several core.ini files and a ReadMe file with a detailed explanation of core.ini parameters. See also Eagle Woman's GPL Online FAQ for more information about bandwidth, core.ini, and other online racing topics.