FSHost and FSHostSpy > Features

What happens between multiplayer updates?

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aladin456:
What happens between multiplayer updates?
as far as i am concerned ,in multi game,there are upates 4x per second,so does the FS automatically tween and calculate flight path between these two waypoints-updates?
what would happen if update was every 2 or 5 or 10 seconds? how would it look in the game?

Russell Gilbert:
Yes, when FS gets an update, it keeps the plane moving forward at the same speed, heading, altitude, pitch, bank, angle, etc. until it receives another update.  However, if it doesn't get another update within a few seconds, it jumps the plane back to the position of the last update, then moves it forward again, then jumps back, moves forward, and repeats this loop until it gets an update.

I thought the time it would wait for another update was about 10 seconds, but I did a couple of tests and found some interesting results...

I started up FSHost, then connected FS2002 and FS2004 to the server.  Then I put one plane (plane A) on autopilot, flying straight and level.  In the other plane (plane B), I switched to top-down view (Ctrl-S), then used Ctrl-Shift-T and Ctrl-Shift-F to jump near plane A, then let plane B just fly forward a few seconds while I watched the behavior of plane A (it helps if plane B is also on autopilot, or at least flying level also).

Keep in mind that since each plane was in a different version of FS, FSHost was forwarding the data between the two sessions at whatever rate was set on the Options / Session tab.  So by increasing the data forward rate, I could simulate what happens when FS doesn't receive an update quickly enough from another player.

What I found was that if the data forward rate was 1750ms or below (updates every 1.75 seconds), plane A moved forward very smoothly, with no problems.  But when I changed it to 2000ms, it jumped back to the last-known position, once between each update, just before the next update arrived (at maybe the 1.8 or 1.9 second mark).  Since there's a slight bit of delay in forwarding the data, I'm guessing the magic number is 2 seconds, not ten like I thought before.  And when I set it to anything higher than 2000ms, it was the same -- at about the 2 second mark, it would jump back to the last-known position and then fly forward for another 2 seconds, then jump back to the last-known position, repeating this loop until it received another update.

But the distressing part about all of this is that when it jumps back to the last-known position, it's not exactly the same position each time.  For example, when I had it set to 20,000ms (20 second updates), I could see that the first time it jumped back (at about 2 seconds), it jumped to near the last-known position, but a bit to the left of it and a bit behind it.  Then it flew forward for another 2 seconds or so.  At the next jump (4 seconds), it jumped back again, but this time it jumped slightly to the right, and a little further back than the last time.  Then it flew forward another 2 seconds or so.  At the next jump (6 seconds), it jumped back to the left a bit, and a little further back again.  It kept repeating this looping, jumping first left and back, then right and back, and each time was a little bit further back than the previous jump.

Now, let's remember that Squawkbox 2 (used with VATSIM, IVAO, etc.) only updates the planes once every five seconds!  No wonder the planes jump around so much in the sky!

And even in FSHost, remember that all planes within the same session (2002/2004) send all their data directly to each other -- it's not forwarded by FSHost.  So if one player is on an overloaded slow modem, or if he lives on the opposite side of the planet from you and his ping time is pretty horrible, it's possible that you might not get updates from him in time, which explains why we sometimes see planes jumping around for very slow players.

So there you have it -- keep your forward rates under 2000ms if you want to prevent planes from jumping around -- preferably even less, if you have the CPU and upload bandwidth to handle it.  I'd suggest not going below 250ms tho, since you'll just be flooding everyone with unneeded data.

Russell

aladin456:
cau tell me how to put jets on autopilot in local MP session>?

jonf:
The same way you do in a single player session. Set your heading, alt and speed then turn the autopilot on :)

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