when to use synchronic and asynchronic messages in JMS?

You use synchronous messaging when the turnaround time is acceptably short enough (or important enough) that your clients can (or must) wait for the response to come back.

If the processing time required to produce the response is too long, or not important enough, or if the client would rather just check back for the response later, then it's possible to use asynchronous messaging.

http://stackoverflow.com/questions/4233116/when-to-use-synchronic-and-asynchronic-messages-in-jms