Networked entities can be simulated either on a Game Client ("Client authority") or a Simulator ("Server-side authority"). Authority defines which Client or Simulator is allowed to make changes to the synced properties of an entity, and in general defines who "runs the gameplay code" for that entity.

To learn more about authority, check out this short video:

When an entity is created, the creator is assigned authority over the entity. Authority can be then transferred at any time between Clients – or even between Clients and Simulators, or between Simulators.

Regardless, only one Client or Simulator can be the authority over the entity at any given time.

Authority models

Distributed Client authority

Client authority is the easiest to set up initially, but it has some drawbacks:

  • Higher latency. Because both Clients have a non-zero ping to the Replication Server, the minimum latency for data replication and commands is the combined ping (Client 1 to Replication Server and Replication Server to Client 2).

  • Higher exposure to cheating. Because we trust Game Clients to simulate their own Entities, there is a risk that one such Client is tampered with and sends out unrealistic data.

In many cases, especially when not working on a competitive PvP game, these are not really issues and are a perfectly fine choice for the game developer.

Client authority does have a few advantages:

  • Easier to set up. No Client vs. Server logic separation in the code, no building and uploading of Simulation Servers, everything just works out of the box.

  • Cheaper. Depending on how optimized the Simulator code is, running a Simulator in the cloud will in most cases incur more costs than just running a Replication Server (which is comparatively very lean).

Server-side authority

Having one or several Simulators taking care of important world simulation tasks (like AI, player character state, score, health, etc.) is always a good idea for competitive PvP games. In this scenario, the Simulator has authority over key game elements, like a "game manager", a score-keeping object, and so on.

Running a Simulator in the cloud next to the Replication Server (with the ping between them being negligible) will also result in lower latency.

Server-side with Client input

A typical choice for competitive games, sometimes called "Server-authoritative". The entity is simulated on the Server, and the Client only sends inputs. To achieve smoother gameplay, the Client can predict the entity's state locally and then reconciliate once the Simulator has come back with a new state.

You can read more about how to achieve this in the section about Server-authoritative setup.

A cool possibility that coherence enables is to mix these modes, since authority is not tied to the match but rather a property of each CoherenceSync.

So for instance, you can have a game where some critical entities are server-side with client input for cheat prevention, while others are distributed among Clients. It's up to you!

Communicate with remote entities

Even if an entity is not currently being simulated locally (the Client does not have authority), we can still affect its state by sending a network command or even requesting a transfer of authority.

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