You want a Web method to perform a long task, and you don’t want to force the client to wait while the Web service code executes.
Create a one-way Web method by applying the SoapDocumentMethod or SoapRpcMethod attribute and setting the OneWay property to True.
With one-way Web methods, the client sends a request message, and the server responds immediately to indicate that the method began processing. This behavior has the following consequences:
The client doesn’t need to wait while the Web method code executes.
The Web method can’t return any information to the client, either through a return value or a ByRef parameter.
If the Web method throws an unhandled exception, it won’t be propagated back ...