A service integration bus is a group of one or more application servers or server clusters in a WebSphere® Application Server cell that cooperate to provide asynchronous messaging services. The application servers or server clusters in a bus are known as bus members. WebSphere MQ servers can also be bus members so that messages can be written to, and read from, WebSphere MQ queues.
Usually, a cell requires only one bus, but a cell can contain any number of buses. The server component that enables a bus to send and receive messages is a messaging engine.
Different service integration buses can, if required, be connected. This allows applications that use one bus (the local bus) to send messages to destinations in another bus (a foreign bus). Note, though, that applications cannot receive messages from destinations in a foreign bus.
An application can connect to more than one bus. For example, although an application cannot receive messages from destinations in a foreign bus, if the application connects to that bus, the bus becomes a local bus and then the application can receive messages.
For example, in the following diagram, the application can send messages to destination A and destination B, but it cannot receive messages from destination B.
In the following diagram, the application can send messages to, and receive messages from, destination A and destination B.
A service integration bus comprises a SIB Service, which is available on each application server in the WebSphere Application Server environment. By default, the SIB Service is disabled. This means that when a server starts it does not have any messaging capability. The SIB Service is automatically enabled when you add the server to a service integration bus. You can choose to disable the service again by configuring the server.
A service integration bus supports asynchronous messaging; that is, sending messages asynchronously. Asynchronous messaging is possible regardless of whether the consuming application is running or not, or if the destination is available or not. Point-to-point and publish/subscribe messaging are also supported.
After an application has connected to the bus, the bus behaves as a single logical entity and the connected application does not need to be aware of the bus topology. In many cases, connecting to the bus and defining bus resources is handled by an application programming interface (API) abstraction, for example the administered JMS connection factory and JMS destination objects.
The service integration bus is sometimes referred to as the messaging bus if it is used to provide the messaging system for JMS applications using the default messaging provide.
Many scenarios require a simple bus topology; perhaps, for example, a single server. By adding multiple servers to a single bus, you can increase the number of connection points for applications to use. By adding server clusters as members of a bus, you can increase scalability and achieve high availability. Servers, however, do not have to be bus members to connect to a bus. In more complex bus topologies, multiple buses are configured, and can be interconnected to form complex networks. An enterprise might deploy multiple interconnected buses for organizational reasons. For example, an enterprise with several autonomous departments might want to have separately administered buses in each location.