SessionMode Enumeration
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SessionMode Enumeration


Specifies the values available to indicate the support for reliable sessions that a contract requires or supports.

Namespace:   System.ServiceModel
Assembly:  System.ServiceModel (in System.ServiceModel.dll)

public enum SessionMode

Member nameDescription

Specifies that the contract supports sessions if the incoming binding supports them.


Specifies that the contract never supports bindings that initiate sessions.


Specifies that the contract requires a sessionful binding. An exception is thrown if the binding is not configured to support session.

Use the SessionMode enumeration with the ServiceContractAttribute.SessionMode property to require, allow, or prohibit bindings to use sessions between endpoints that connect to or support the service contract. A session is a way of correlating a set of messages exchanged between two or more endpoints. For more information about sessions, see Using Sessions.

If your service supports sessions, you can then use the ServiceBehaviorAttribute.InstanceContextMode property to specify the relationship between instances of your service contract implementation and the channel session.

For example, if the SessionMode property is set to SessionMode.Allowed and the ServiceBehaviorAttribute.InstanceContextMode property is set to InstanceContextMode.PerSession, a client can use a binding that supports reliable sessions to make repeated calls to the same service object.

Because a session is a channel-level concept that the application model uses, there is an interaction between the SessionMode enumeration in a contract and the ServiceBehaviorAttribute.InstanceContextMode property, which controls the association between channels and specific service objects.

The following table shows the result of an incoming channel either supporting reliable sessions or not supporting reliable sessions given a service's combination of the values of the ServiceContractAttribute.SessionMode property and the ServiceBehaviorAttribute.InstanceContextMode property.

InstanceContextMode Value







  • Behavior with sessionful channel: An exception is thrown.

  • Behavior with sessionless channel: An System.ServiceModel.InstanceContext for each created singleton or for the user-specified singleton.

The following code example shows how to use the SessionModeproperty of the ServiceContractAttribute to specify that the IMyService service contract requires bindings that support session state.

using System;
using System.Collections.Generic;
using System.ServiceModel;
using System.Threading;

namespace Microsoft.WCF.Documentation
    Name = "SampleDuplexHello",
    Namespace = "http://microsoft.wcf.documentation",
    CallbackContract = typeof(IHelloCallbackContract),
    SessionMode = SessionMode.Required
  public interface IDuplexHello
    [OperationContract(IsOneWay = true)]
    void Hello(string greeting);

  public interface IHelloCallbackContract
    [OperationContract(IsOneWay = true)]
    void Reply(string responseToGreeting);

  public class DuplexHello : IDuplexHello

    public DuplexHello()
      Console.WriteLine("Service object created: " + this.GetHashCode().ToString());

      Console.WriteLine("Service object destroyed: " + this.GetHashCode().ToString());

    public void Hello(string greeting)
      Console.WriteLine("Caller sent: " + greeting);
      Console.WriteLine("Session ID: " + OperationContext.Current.SessionId);
      Console.WriteLine("Waiting two seconds before returning call.");
      // Put a slight delay to demonstrate asynchronous behavior on client.
      IHelloCallbackContract callerProxy
        = OperationContext.Current.GetCallbackChannel<IHelloCallbackContract>();
      string response = "Service object " + this.GetHashCode().ToString() + " received: " + greeting;
      Console.WriteLine("Sending back: " + response);

.NET Framework
Available since 3.0
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