Question Synchronize IBufferElementData or any other array of data

Hey YuriyVotintsev!

Simply add the [GhostField] attribute to the field(s) of the IBufferElementData, and replication will be handled (assuming it's a ghost etc).

Ensure you have the ghost type set to Interpolated, high importance, and static optimized.

However, we don't recommend sending data over 1kb in this fashion. It's worth seeing how well it compresses (via the NetDbg tool) to ensure you're not filling up (or fragmenting) your snapshots with this data.

If possible, prefer to send large data outside NetCode (i.e. traditional socket TCP communication), prebake it, or calculate it deterministically via fixed point math and a seed.

Cheers!

 

GhostField data is stored in unreliable snapshots. At around 1kb of (assumed entirely uncompressed) data, you'll start to fragment these unreliable snapshots. This means that each client needs to receive 2+ unreliable UDP packets just to receive that 1 piece of data. I.e. If a client drops EITHER of those packets, they'll drop the entire snapshot.

Thus, the problem gets exponentially worse as the packet size increases.

RPCs are also not entirely suitable (even though RPCs are sent reliably), as fragmentation again triggers multiple packets, and multiple packets being sent to every client can trigger the reliable pipeline send queue (in the Unity Transport Package) to fill up, and throw.

Thus: NetCode (and the Transport it's built on) are simply not designed for "large data". It's significantly better to set that data as a compressed blob via your matchmaking/matchfinding TCP / WebSocket service.

If you absolutely must send a lot of data via netcode, try to batch that large data into small chunks, then filter those chunks based on Relevancy (and importance), and replicate those chunks as GhostFields.

Out of curiosity: Would you mind replying with more details about the size of your data, and a screenshot of the NetDbg screen showing the per-client overhead with this approach? Feel free to DM if there is sensitive data (or not send at all, of course).

 

Ah fair. Two more nuances, done with my own testing:

• The way Snapshots work is that they'll resend a chunk of ghosts (to a specific client) until that client acks a snapshot with those ghosts in them. Thus, you will almost certainly send the same data multiple times, to every client, before each of them replies with an ack. The quantity of resends depends on Importance, Relevancy, GhostCount, and Ping. This is true even with static optimize enabled.
  
  In my own test, the server sent the 1kb of data (compressed into 400bytes) IBufferElementData to the client 14 times before the client acked it.
  
  
• The IBufferElementData serializers do delta-compress (via Huffman encoding) every 4byte stride, so naïve compression could be okay. As mentioned, in my test it was about 40% of the original size.
  
  Thus, I also highly recommend you aggressively quantize your float data to make this better.
  
  You may be able to use some assumptions about VRIK data to improve this, but it's tricky.
  
  RPCs may therefore be more appropriate (although you cannot use the NetDbg tool to visualize RPC overhead).

 

I don't know the details, but if you are using the buffer to store the current state of the bones (for a given tick) and the bones transforms are calculated/update as part of the prediction loop, then things should work.

the client is ahead of the server, so lets say 2/3 tick (server frame 10, client frame 13).
When the client received data from frame 11 (rollback 2 tick) it will start re-predicting up to the next tick, tick 14.

When he receive the data from the server, the state of the buffer is restore to the tick 11. Unless there is a system that calculate the bones position inside the GhostPredictionGroup, you will constantly see this back and forward.

 

How did you configure the character ghost??

I suppose that, because it is the player character I presume (just presume) you setup it as OwnerPredicted. In such a case, the ghost is predicted and that is pretty obvious why the buffer data go back in time.

Are you seeing the character position moving back and forth or are the bones that get completely wrong?
Also, because the character is moving again forward, what system is responsible to move the character? Who is handling the input (if any)?

If the entity is interpolated, the character bones you are using should be the one at InterpolatiomTick (so old of about at least 2 ticks plus some extra to compensate for jitter if present).
The InterpolationTick never goes back in time (in normal circumstances) so the behaviour would be odd.

 

It looks like the server is trying to send too many ghosts in a single packet.
Now would be a very good time to add "Distance Based Importance Scaling".

Which would work beautifully with tweaks to the `GhostSendSystemData`. See the 0.8.0 changelog entry: Added parameters to control how much data the server serializes based on CPU time in addition to bandwidth. The parameters are MinSendImportance, MinDistanceScaledSendImportance, MaxSendChunks and MaxSendEntities.

So, I'd try some combination of things (assuming the base "Importance" of the Phantom ghost is 1):

• `MaxSendEntities` to 20-100, reducing the issue you have now.
• `MinSendImportance` to ~10 (so a ghost is only replicated in every tenth snapshot, by default).
• Edit2: `NetworkStreamSnapshotTargetSize` should be used to force a desired snapshot size, which will help enforce a specific KBPS target for server send (egress), and client ingress (receive).

 

Just adding: My earlier comment about `NetworkStreamSnapshotTargetSize` was wrong (now corrected). You can add `NetworkStreamSnapshotTargetSize` to each connection entity (on the server) to force that connections snapshot to be a given size.

Example: 416 bytes * 60hz = 200kbit/s. For reference, most AAA shooters these days tend to be around 50 to 200kbit/s.

Important context is that this 416 bytes value:

• Does not affect RPCs, commands, or control messages.
• Does include UTP header overhead, nor UDP header overhead.
• I.e. It's only payload bytes.

 

For completeness, answers continue here: https://forum.unity.com/threads/how-to-setup-distance-based-importance-scale.1372326/