Unity Networking

Unity Networking and Multiplayer

Overview

Reference for implementing multiplayer systems and backend services in Unity. Covers the major networking frameworks, authority models, common multiplayer patterns, and Unity Gaming Services integration.

Networking Framework Comparison

Netcode for GameObjects (NGO)

Setup

1. Install via Package Manager: com.unity.netcode.gameobjects
2. Add NetworkManager to a scene GameObject
3. Select transport (Unity Transport is default)
4. Mark networked prefabs with NetworkObject component
5. Register prefabs in NetworkManager's prefab list

Core Components

RPCs (Remote Procedure Calls)

public class PlayerCombat : NetworkBehaviour
{
    NetworkVariable<int> _health = new(100,
        NetworkVariableReadPermission.Everyone,
        NetworkVariableWritePermission.Server);

    [ServerRpc]
    void AttackServerRpc(ulong targetId)
    {
        // Runs on server - validate and apply damage
        if (!IsServer) return;
        var target = NetworkManager.SpawnManager.SpawnedObjects[targetId];
        target.GetComponent<PlayerCombat>().TakeDamage(10);
    }

    [ClientRpc]
    void PlayHitEffectClientRpc(Vector3 position)
    {
        // Runs on all clients - visual feedback only
        Instantiate(hitVFX, position, Quaternion.identity);
    }

    void TakeDamage(int amount)
    {
        _health.Value -= amount;
        PlayHitEffectClientRpc(transform.position);
    }
}

NetworkVariable Permissions

// Server-writable (default) - authoritative state
NetworkVariable<int> score = new(0, writePerm: NetworkVariableWritePermission.Server);

// Owner-writable - client-authoritative (use sparingly)
NetworkVariable<Vector3> cursorPos = new(writePerm: NetworkVariableWritePermission.Owner);

Use OnValueChanged callback for UI reactions:

_health.OnValueChanged += (oldVal, newVal) => healthBar.value = newVal;

Authority Models

Server-Authoritative Flow

Client: Press "Attack" -> Send ServerRpc(targetId)
Server: Validate range/cooldown -> Apply damage -> Update NetworkVariable
Server: Send ClientRpc for VFX
All Clients: Play hit effect

Never trust client data. Validate positions, cooldowns, ammunition, and line-of-sight on the server.

Common Multiplayer Patterns

Lobby System

1. Player authenticates (UGS Auth / custom)
2. Player creates or joins lobby (UGS Lobby / custom)
3. Lobby fills -> host starts game
4. Relay allocation for NAT traversal (UGS Relay)
5. All players connect to relay
6. NetworkManager starts host/client

Spawn and Despawn

// Server-side spawning
var instance = Instantiate(prefab, spawnPoint, Quaternion.identity);
instance.GetComponent<NetworkObject>().SpawnWithOwnership(clientId);

// Server-side despawning
networkObject.Despawn(); // Removes from all clients

Scene Management

Use NetworkManager.SceneManager.LoadScene("GameScene", LoadSceneMode.Single) for synchronized scene loading. Only the server/host should call this.

REST API and WebSocket Integration

REST API (UnityWebRequest)

async Awaitable<T> GetAsync<T>(string url)
{
    using var request = UnityWebRequest.Get(url);
    request.SetRequestHeader("Authorization", $"Bearer {token}");
    await request.SendWebRequest();
    if (request.result != UnityWebRequest.Result.Success)
        throw new Exception(request.error);
    return JsonUtility.FromJson<T>(request.downloadHandler.text);
}

Use JsonUtility for simple types or Newtonsoft.Json (com.unity.nuget.newtonsoft-json) for complex serialization. Always use using with UnityWebRequest to prevent memory leaks.

WebSocket (NativeWebSocket / WebSocketSharp)

For real-time non-game communication (chat, notifications), use a WebSocket library. NativeWebSocket works across platforms including WebGL.

Unity Gaming Services (UGS)

Initialize UGS before using any service:

await UnityServices.InitializeAsync();
await AuthenticationService.Instance.SignInAnonymouslyAsync();

Firebase and PlayFab

Use Firebase for indie/mobile projects needing Realtime Database, Cloud Functions, and FCM push notifications. Use PlayFab for LiveOps-heavy games needing player segmentation, A/B testing, and automated rule processing. Both provide Unity SDKs via their respective download pages.

Additional Resources

Reference Files

• references/netcode-advanced.md -- Client prediction and reconciliation implementation, interest management, network LOD, bandwidth optimization, custom serialization, transport layer configuration
• references/backend-services.md -- Detailed UGS setup walkthroughs, Firebase/PlayFab integration patterns, REST API architecture, authentication flows, leaderboard and economy implementation