Not able to understand your question .. may there is a typo error there ...
Web Services can be synchronous or asynchronous.
Synchronous WS follows normal request - response model where client makes a request to Server and then waits till Server return response back in Client.
Asynchronous WS do not follow normal request - response model. Here, client makes a request to Server and then continue to work on next work. After a while , Server response back to Client with it's Response.
Asynchronous WS can use polling or callback mechanism to receive response back from Server.
You might think that this Asynchronous Web service closely similar to JMS Queues. Difference is Asynchronous Web service deals more with Transport layer (how messages are transport from Client to serve and vice-versa) where JMS system is full fledged messaging system which manages messages are application layer of TCP IP.
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