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
• Network connection options

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#

Players can create and join sessions using different network connection types and configuration options.

Types of network#

The following network connections types are available:

• 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.

Configurable network options#

You can override the default network options of your sessions, including both direct and relay-based networking.
If you do not specify network options when calling the WithRelayNetwork(),WithDirectNetwork() or WithDistributedAuthorityNetwork() methods, the Session system automatically applies its default settings to configure the requested network type. For details about default values and behaviors for these methods, refer to Class SessionOptionsExtensions.

DirectNetworkOptions#

Configure direct network connections with DirectNetworkOptions. Use these options with WithDirectNetwork() when setting a SessionOption to override the default behavior. The following settings are available:

• ListenIp: The IPv4 or IPv6 address to listen for incoming connections.
• PublishIp: The IPv4 or IPv6 address to publish for other clients to connect to.
• Port: The port number used for both listening and publishing endpoints.

RelayNetworkOptions#

Configure relay protocol-based network connections with RelayNetworkOptions. Use with the WithRelayNetwork() or WithDistributedAuthorityNetwork() when setting SessionOption to override the default behavior.

The following settings are available:

• Protocol: The network protocol that the Relay connection uses.
• Region: Forces a specific Relay region to be used, and skips auto-selection from QoS results.
• PreserveRegion: If enabled, saves the relay region to session properties, and reuses it in case of host migration.

The following Relay protocols are supported:

• User Datagram Protocol (UDP)
• Datagram Transport Layer Security (DTLS)
• Secure websocket (WSS)

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 Task 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.

Example: Creating a session with a client-hosted solution with overridden default relay options#

The following example demonstrates how to create a session using a Unity client-hosted solution with overridden options provided to the relay allocation:

// When the region is specified, it forces the use of a specific Relay region, and skips QoS auto-selection.
async Task StartSessionAsHost(string region = null) 
{   
    var options = new SessionOptions
    {
      MaxPlayers = 2
    }.WithRelayNetwork(new RelayNetworkOptions(RelayProtocol.Default, region, true)); // 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}");
}

The points from Example: Creating a session with a client-hosted solution also apply to this example, along with the following information:

• The RelayNetworkOptions class configures the session to start the relay connection using the platform-suggested Default protocol using the provided region parameter. If PreserveRegion is set to true, the newly-elected host won't change the relay allocation region in the event of a host migration. If set to false, the region might change.
• If the region is not passed as a parameter, the default null value triggers a QoS query to determine the most optimal region for the relay allocation. For the list of available regions, refer to Relay locations and regions.

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());