High-Level Networking

High-level networking layer supports creating fully-featured multiplayer games. It features:

  • High-level networking abstraction and implementation
    • Singleton service (1 per running game)
    • Configuration from game settings
    • Ability to adjust configs at runtime (eg. server ip/port)
  • Allows creating multiplayer games easily
    • Shooters
    • Strategy
    • Coop
    • Competitive
  • Can be integrated into an existing game project
  • Not enabled/user by default
    • Reduce bloat in the engine from this feature
  • Synchronizes game objects across the network
    • Game session state
    • Players data
    • Scene objects
      • Actors
      • Scripts
      • SubObjects
  • Provides automatic data replication
    • Ability to prioritize objects to synchronize
    • Synchronize objects placed on a map (already on the level)
    • Synchronize objects spawned on a map
      • Synchronized object/prefab spawning
      • Authoritative or weak
  • Remote procedure call (RPC)
    • Ability to invoke gameplay method on server or remote clients
    • Automatic arguments serialization
    • Customizable NetworkChannelType
  • Build on top of the existing low-level networking
    • Offers the ability to swap INetworkDriver backend
    • Cross-platform networking
  • Supports cross-play
  • Client-Server connection only (clients cannot communicate directly)
  • Scales up to 100 players
  • Provides network profiler
    • Analyze data transfer usage per-frame

In this section

Scripting integration

If you want to use automatic objects network replication or RPCs codegen, then modify your game code module build scripts by adding Network tag to it - it wil trigger additional processing and code generation to optimize networking.

// Game.Build.cs

public override void Setup(BuildOptions options)
{
    base.Setup(options);

    Tags["Network"] = string.Empty;
    options.PublicDependencies.Add("Networking");
}

Network Manager

The main manager of high-level networking system is NetworkManager which provides API such as StartServer()/StartClient()/StartHost()/Stop(). It creates NetworkManager.Peer to run as a server or client.

Clients

Network Manager running as server or host receives new client connections which can be validated/rejected with NetworkManager.ClientConnecting event. For example, game client can send version, player info or local game files checksum to perform server-side verification for competitive multiplayer gaming.

After performing initial handshake with a new client it's added to NetworkManager.Clients list and NetworkManager.ClientConnected event is being called (as opposted to NetworkManager.ClientDisconnected event upon connection end or timeout). Network state can be checked with State property (NetworkConnectionState enum) and responsed to changes on NetworkManager.StateChanged event.

Each client has own unique uint32 ClientId used to identify it within a network session. Network manager in mode Server or Host always uses NetworkManager.ServerClientId = 0 to distinguish from other peers.

Extending network objects

To extend networking for more custom case you can use INetworkObject interfaces on networked objects:

  • INetworkObject - allows to extend networked objects lifetime with custom events called on certain points during it's lifetime (eg. spawn/despawn or during replication).
  • INetworkSerializable - allows to override default replication logic by using custom serialize/deserialize methods that send object state over network using NetworkStream object.

Profiling and debugging

To analyze network transfer use Network tab in Profiler window in Editor. To quickly profile networking with lag simulation (eg. due to bad network ocnnection) you can use NetworkLagDriver (set it in Network Settings) which can delay network messages sending to fake the lag between server and client.

To access objects replication logs use:

NetworkReplicator.EnableLog = true;