rec.autos.simulators

I need your help with my GPL network utility called GPLProxy. You have probably
never heard of it as it was released in a beta version this year. Simply put,
the Java Application acts as an intermediate step between a client and a server,
and records all of the network traffic (UDP packets) from the server to the
client. This allows the application to retransmit the packets to a number of
other clients who are tricked into believing the application is a genuine
server. The effect is that a (theoretically limitless) number of other GPL
clients can see exactly the same as the original one without being able to
interact with the real server. The application can handle different latencies
and some other stuff quite well, and it is fairly good at doing what it is
supposed to do.

However, due to the nature of my method, retransmitting server packets, all of
"viewers" receive their data with a delay equal to the delay between their
connection to the GPLProxy and the connection of the real client. Eg. if they
connect 10 mins. later, they will see everything 10 mins. after it really
happened.

I know that somehow the network code is very robust and by testing I can see
that if I skip a number of packets, the client will carry on as if nothing had
happened which would be just fine except for one little detail: A lot of
driver/car/race information is lost! I have figured out that somehow the GPL
code transmits race data (eg. lap times, names, standings, etc) instead of car
data at various fixed(?) intervals. I think that by sending just these special
packets and otherwise skipping ahead, I would be able to make my application
"Live-ish", but I have been unable to identify these packets with my packet
sniffer.

Now my question to you, Mr. Cassidy, is whether you would be willing to share
with me a bit of information on how to identify the race information packets? If
you are unable or unwilling to do so, I would understand and just carry on with
my tedious packet analysis. If you should decide to reply by email, I promise
you to keep your address confidential.

Some more background on GPLProxy can be found here:
http://www.racesimcentral.net/

Sincerely yours,
Jens H. Kruuse

jens.h (at) kruuse.dk

Edward

--
Scott B. Husted
PA-Scott
http://www.Husted.cc

And frankly - with the N4 / N4 '02 engine - it wouldnt take very long to
make a Cart sim either - infact it's more of a car and track update than a
whole new game

They ahve the licence - they have the gfx, phys and 'netplay engines - if
they dont work on a Cart sim between now and doing YET ANOTHER ***Y
SPAZCAR SIM then either Papy or Sierra need to get SHOT

Doug

...

The packets are so-called reliable packets (retransmitted when it
looks the client didn't get them). Perhaps they can be discovered by
looking for similar packets, esp. in bad network conditions, since the
resent ones will look the same.
On the other hand, in a nice network library, other (less important)
message will often piggyback on the UDP message, as more than one
message is generally sent in one packet. Although even there you'd
probably see the more important data in the front of the packet.

In my sim for example, multiple smaller messages are packed into 1
packet, and then sent. So reliable and unreliable message may be
mixed, and it would be quite hard to pick them out without knowing the
size of each message inside the packet.

One thing to option for might be to make every packet a reliable one
(maybe even turning it into TCP/IP, yugh).

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/