Session creation#

Configure session options and choose network connection types to add multiplayer support to your project.

To start a multiplayer game, the host must create a session that other players join to participate in the game. This page outlines what you must include in your script to create a session. Consider the following factors when you create a session:

• Session options properties
• Network connection types

using Unity.Services.Multiplayer;

The CreateOrJoinSessionAsync method#

Use the CreateOrJoinSessionAsync method to do the following:

• Join an existing session with the given ID.
• Create a session if the ID doesn't exist.

This approach ensures that only one session is created when multiple clients attempt to join the same session, often referred to as race conditions.

var session = await MultiplayerService.Instance.CreateOrJoinSessionAsync(sessionId, options)

Session options properties#

The session options determine various properties of your session, such as the maximum number of players, or whether the session is password protected.

Refer to Class SessionOptions for a full list of options.

Network connection types#

Players can join sessions using different network connection types:

• Direct network connection.
• Client-hosted solutions by Unity, using Relay or Distributed Authority. This practice is recommended for peer-to-peer games played over the internet.

Refer to Class SessionOptions > Methods for more information.

Example: Creating a session with a client-hosted solution#

The following example demonstrates how to create a session using a Unity client-hosted solution:

async void StartSessionAsHost()
{
    var options = new SessionOptions
    {
      MaxPlayers = 2
    }.WithRelayNetwork(); // or WithDistributedAuthorityNetwork() to use Distributed Authority instead of Relay
    var session = await MultiplayerService.Instance.CreateSessionAsync(options);
    Debug.Log($"Session {session.Id} created! Join code: {session.Code}");
}

In this code:

• The variable MaxPlayers sets the maximum number of players allowed in the session, including the host. In this example, the maximum number of players is two.
• The variable options of class SessionOptions can determine other session options, such as the session’s name, and whether it is password protected.
• The use of WithRelayNetwork() (or WithDistributedAuthorityNetwork()) configures the session to use Relay (or Distributed Authority) networking rather than direct connections (in other words, with a fixed IP address and port). This is the recommended best practice for peer-to-peer connectivity over the Internet. Refer to Relay or [Distributed Authority].
• The line var session = await MultiplayerService.Instance.CreateSessionAsync(options); creates the session, and makes the player the host.
• The final line, Debug.Log($"Session {session.Id} created! Join code: {session.Code}");, displays the session ID and join code in the console of the Unity Editor. The host would then share this join code with the other players. Alternatively, you could create a variable to get the join code, as in var joinCode = session.Code; and use that variable instead.

Using a custom network handler#

Advanced users can specify a custom network handler by implementing INetworkHandler, which overrides the default integration with Netcode for Game Objects and Netcode for Entities.

var options = new SessionOptions { MaxPlayers = 2 }
        .WithRelayNetwork()
        .WithNetworkHandler(new CustomEntitiesNetworkHandler());