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fix: more accurate local time sync with server time #3206

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fix: more accurate local time sync with server time #3206

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24de284
get a more accurate local time by using half the RTT.
BenHamrick Aug 24, 2024
b9a9da8
update
NoelStephensUnity Jan 15, 2025
4945e3d
updarte
NoelStephensUnity Jan 15, 2025
07575a5
test
NoelStephensUnity Jan 16, 2025
a04a177
style
NoelStephensUnity Jan 16, 2025
5f12a96
style
NoelStephensUnity Jan 19, 2025
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2 changes: 2 additions & 0 deletions com.unity.netcode.gameobjects/CHANGELOG.md
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Expand Up @@ -18,6 +18,8 @@ Additional documentation and release notes are available at [Multiplayer Documen

### Changed

- Changed the `NetworkTimeSystem.Sync` method to use half RTT to calculate the desired local time offset as opposed to the full RTT. (#3206)

## [1.12.0] - 2024-11-19

### Added
Expand Down
4 changes: 3 additions & 1 deletion com.unity.netcode.gameobjects/Runtime/Timing/NetworkTimeSystem.cs
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Expand Up @@ -248,7 +248,9 @@ public void Sync(double serverTimeSec, double rttSec)
var timeDif = serverTimeSec - m_TimeSec;

m_DesiredServerTimeOffset = timeDif - ServerBufferSec;
m_DesiredLocalTimeOffset = timeDif + rttSec + LocalBufferSec;
// We adjust our desired local time offset to be half RTT since the delivery of
// the TimeSyncMessage should only take half of the RTT time (legacy was using 1 full RTT)
m_DesiredLocalTimeOffset = timeDif + (rttSec * 0.5d) + LocalBufferSec;
}
}
}
55 changes: 31 additions & 24 deletions com.unity.netcode.gameobjects/Tests/Editor/Timing/ClientNetworkTimeSystemTests.cs
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Expand Up @@ -18,15 +18,16 @@ public class ClientNetworkTimeSystemTests
public void StableRttTest()
{
double receivedServerTime = 2;

var timeSystem = new NetworkTimeSystem(0.05d, 0.05d, 0.1d);
var baseRtt = 0.1f;
var halfRtt = 0.05f;
var timeSystem = new NetworkTimeSystem(0.05d, 0.05d, baseRtt);
timeSystem.Reset(receivedServerTime, 0.15);
var tickSystem = new NetworkTickSystem(60, timeSystem.LocalTime, timeSystem.ServerTime);

Assert.True(timeSystem.LocalTime > 2);

var steps = TimingTestHelper.GetRandomTimeSteps(100f, 0.01f, 0.1f, 42);
var rttSteps = TimingTestHelper.GetRandomTimeSteps(1000f, 0.095f, 0.105f, 42); // 10ms jitter
var steps = TimingTestHelper.GetRandomTimeSteps(100f, 0.01f, baseRtt, 42);
var rttSteps = TimingTestHelper.GetRandomTimeSteps(1000f, baseRtt - 0.05f, baseRtt + 0.05f, 42); // 10ms jitter

// run for a while so that we reach regular RTT offset
TimingTestHelper.ApplySteps(timeSystem, tickSystem, steps, delegate (int step)
Expand All @@ -37,10 +38,11 @@ public void StableRttTest()
});

// check how we close we are to target time.
var expectedRtt = 0.1d;
var offsetToTarget = (timeSystem.LocalTime - timeSystem.ServerTime) - expectedRtt - timeSystem.ServerBufferSec - timeSystem.LocalBufferSec;
var offsetToTarget = (timeSystem.LocalTime - timeSystem.ServerTime) - halfRtt - timeSystem.ServerBufferSec - timeSystem.LocalBufferSec;
Debug.Log($"offset to target time after running for a while: {offsetToTarget}");
Assert.IsTrue(Math.Abs(offsetToTarget) < k_AcceptableRttOffset);

// server speedup/slowdowns should not be affected by RTT
Assert.True(Math.Abs(offsetToTarget) < k_AcceptableRttOffset, $"Expected offset time to be less than {k_AcceptableRttOffset}ms but it was {offsetToTarget}!");

// run again, test that we never need to speed up or slow down under stable RTT
TimingTestHelper.ApplySteps(timeSystem, tickSystem, steps, delegate (int step)
Expand All @@ -51,9 +53,10 @@ public void StableRttTest()
});

// check again to ensure we are still close to the target
var newOffsetToTarget = (timeSystem.LocalTime - timeSystem.ServerTime) - expectedRtt - timeSystem.ServerBufferSec - timeSystem.LocalBufferSec;
var newOffsetToTarget = (timeSystem.LocalTime - timeSystem.ServerTime) - halfRtt - timeSystem.ServerBufferSec - timeSystem.LocalBufferSec;
Debug.Log($"offset to target time after running longer: {newOffsetToTarget}");
Assert.IsTrue(Math.Abs(newOffsetToTarget) < k_AcceptableRttOffset);
// server speedup/slowdowns should not be affected by RTT
Assert.True(Math.Abs(offsetToTarget) < k_AcceptableRttOffset, $"Expected offset time to be less than {k_AcceptableRttOffset}ms but it was {offsetToTarget}!");

// difference between first and second offset should be minimal
var dif = offsetToTarget - newOffsetToTarget;
Expand All @@ -67,13 +70,14 @@ public void StableRttTest()
public void RttCatchupSlowdownTest()
{
double receivedServerTime = 2;

var timeSystem = new NetworkTimeSystem(0.05d, 0.05d, 0.1d);
var baseRtt = 0.1f;
var halfRtt = 0.05f;
var timeSystem = new NetworkTimeSystem(0.05d, 0.05d, baseRtt);
timeSystem.Reset(receivedServerTime, 0.15);
var tickSystem = new NetworkTickSystem(60, timeSystem.LocalTime, timeSystem.ServerTime);

var steps = TimingTestHelper.GetRandomTimeSteps(100f, 0.01f, 0.1f, 42);
var rttSteps = TimingTestHelper.GetRandomTimeSteps(1000f, 0.095f, 0.105f, 42); // 10ms jitter
var steps = TimingTestHelper.GetRandomTimeSteps(100f, 0.01f, baseRtt, 42);
var rttSteps = TimingTestHelper.GetRandomTimeSteps(1000f, baseRtt - 0.05f, baseRtt + 0.05f, 42); // 10ms jitter

// run for a while so that we reach regular RTT offset
TimingTestHelper.ApplySteps(timeSystem, tickSystem, steps, delegate (int step)
Expand Down Expand Up @@ -102,11 +106,14 @@ public void RttCatchupSlowdownTest()

// speed up of 0.1f expected
Debug.Log($"Total local speed up time catch up: {totalLocalSpeedUpTime}");
Assert.True(Math.Abs(totalLocalSpeedUpTime - 0.1) < k_AcceptableRttOffset);
Assert.True(Math.Abs(totalServerSpeedUpTime) < k_AcceptableRttOffset); // server speedup/slowdowns should not be affected by RTT
var expectedSpeedUpTime = Math.Abs(totalLocalSpeedUpTime - halfRtt);
var expectedServerSpeedUpTime = Math.Abs(totalServerSpeedUpTime);
Assert.True(expectedSpeedUpTime < k_AcceptableRttOffset, $"Expected local speed up time to be less than {k_AcceptableRttOffset}ms but it was {expectedSpeedUpTime}!");
// server speedup/slowdowns should not be affected by RTT
Assert.True(Math.Abs(totalServerSpeedUpTime) < k_AcceptableRttOffset, $"Expected server speed up time to be less than {k_AcceptableRttOffset}ms but it was {expectedServerSpeedUpTime}!");


// run again with RTT ~100ms and see whether we slow down by -0.1f
// run again with RTT ~100ms and see whether we slow down by -halfRtt
unscaledLocalTime = timeSystem.LocalTime;
unscaledServerTime = timeSystem.ServerTime;

Expand All @@ -121,13 +128,13 @@ public void RttCatchupSlowdownTest()

totalLocalSpeedUpTime = timeSystem.LocalTime - unscaledLocalTime;
totalServerSpeedUpTime = timeSystem.ServerTime - unscaledServerTime;

// slow down of 0.1f expected
// slow down of half halfRtt expected
Debug.Log($"Total local speed up time slow down: {totalLocalSpeedUpTime}");
Assert.True(Math.Abs(totalLocalSpeedUpTime + 0.1) < k_AcceptableRttOffset);
Assert.True(Math.Abs(totalServerSpeedUpTime) < k_AcceptableRttOffset); // server speedup/slowdowns should not be affected by RTT


expectedSpeedUpTime = Math.Abs(totalLocalSpeedUpTime + halfRtt);
expectedServerSpeedUpTime = Math.Abs(totalServerSpeedUpTime);
Assert.True(expectedSpeedUpTime < k_AcceptableRttOffset, $"Expected local speed up time to be less than {k_AcceptableRttOffset}ms but it was {expectedSpeedUpTime}!");
// server speedup/slowdowns should not be affected by RTT
Assert.True(Math.Abs(totalServerSpeedUpTime) < k_AcceptableRttOffset, $"Expected server speed up time to be less than {k_AcceptableRttOffset}ms but it was {expectedServerSpeedUpTime}!");
}

/// <summary>
Expand Down Expand Up @@ -172,8 +179,8 @@ public void ResetTest()
receivedServerTime += steps[step];
timeSystem.Sync(receivedServerTime, rttSteps2[step]);

// after hard reset time should stay close to rtt
var expectedRtt = 0.5d;
// after hard reset time should stay close to half rtt
var expectedRtt = 0.25d;
Assert.IsTrue(Math.Abs((timeSystem.LocalTime - timeSystem.ServerTime) - expectedRtt - timeSystem.ServerBufferSec - timeSystem.LocalBufferSec) < k_AcceptableRttOffset);

});
Expand Down
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