Now let's return to the earlier example of a travel agency to see how messaging facilities play a role in booking a vacation. Assume that the travel agent must reserve a flight, a hotel room, and a rental car. All of these reservations must succeed before the overall business transaction can be considered complete.

With a message queue manager such as WebSphere® MQ, the application can send several requests at once; it need not wait for a reply to one request before sending the next. A message is placed on each of three queues, serving the flight reservations application, the hotel reservations application, and the car rental application. Each application can then perform its respective task in parallel with the other two and place a reply message on the reply-to queue. The agent's application waits for these replies and produces a consolidated answer for the travel agent.

Designing the system in this way can improve the overall response time. Although the application might normally process the replies only when they have all been received, the program logic may also specify what to do when only a partial set of replies is received within a given period of time.

Figure 1. Parallel processing