WCF
Message Exchange Patterns
- Request/Response (default)
- OneWay - [OperationContract(IsOneWay=true)]
- Duplex - [ServiceContract(CallbackContract=typeof(x)] and the client will have a long running session. Not good at interop or scaling. Service implemntations must have [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant or Multiple)]
WCF Topics
And...
See also .Net 1 remoting and webservices