Networked entities can be simulated either on a Game Client ("Client authority") or a Simulation Server ("Server authority"). Authority defines which Client or Simulation Server is allowed to make changes to an Entity. An Entity is any networked GameObject.
When an Entity is created, the creator is assigned authority over the Entity and that authority can be transferred between Clients and Simulators, but only one Client or Simulator can be the authority over the Entity at at time.
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).
Having one or several Simulators taking care of the important World simulation tasks (like AI, player character state, score, health, etc.) is always a good idea for competitive PvP games.
Running a Simulator in the cloud next to the Replication Server (with the ping between them being negligible) will also result in lower latency.