As for the Service Bus, the Windows Azure middleware solving the EAI (Enterprise application integration), here is the second way to do the messaging using Brokered Messaging. Clarifying what Brokered Messaging means.
The Brokered Messaging is a durable, asynchronous messaging that has several ways to achieve this like the “Queues”, the “Topics and Subscriptions”, in a way that the senders and the receivers don’t have to be online when the message is send to receive it.
Starting first with the Queues, this way of communication can be used to make the connection between two points, it is totally like the Point-to-Point messaging. For the queues, it is like any normal queue data structure, or like the Windows Azure Queue storage (all the predefined .net functions) the first message sent is the first is to be received by the receiver (FIFO). This feature also works If you do have several receivers of the message through the Service bus.
Our Next Brokered Messaging way is the Topics and the Subscriptions, for the users, they can subscribe to a specific topic and after that can easily get all the messages sent through the service bus related to the subscribed topic.