Asynchronous Call
Application can make a call to the Webservice and then continue to do whatever it wants to do.When the service is ready it will notify the application. Application can use BEGIN and END method to make asynchronous call to the web method. We can use EITHER a WaitHandle or a DELEGATE object when making asynchronous call.The WaitHandle CLASS share RESOURCES between several objects. It provides several methods which will wait for the resources to become AVAILABLE. The easiest and most powerful way to implement an asynchronous call is using a delegate object. A delegate object wraps up a callback function. The idea is to pass a method in the invocation of the web method. When the webmethod has finished it will call this callback function to process the result.

Synchronous Call
Application has to wait until has completed.

Asynchronous Call
Application can make a call to the Webservice and then continue to do whatever it wants to do.When the service is ready it will notify the application. Application can use BEGIN and END method to make asynchronous call to the web method. We can use either a WaitHandle or a Delegate object when making asynchronous call.The WaitHandle class share resources between several objects. It provides several methods which will wait for the resources to become available. The easiest and most powerful way to implement an asynchronous call is using a delegate object. A delegate object wraps up a callback function. The idea is to pass a method in the invocation of the web method. When the webmethod has finished it will call this callback function to process the result.

Synchronous Call
Application has to wait until has completed.