A service integration bus provides a scope within which you can configure resources for mediation modules and interaction endpoints deployed in WebSphere ESB.
When abbreviating references about an enterprise service bus, we use the term ESB. When abbreviating references about a service integration bus, we use the term bus.
For WebSphere ESB, a bus enables message routing between endpoints with specific quality of interaction service and can temporarily persist messages if required. You can configure a variety of quality of service from secure, assured delivery (where messages are guaranteed not to get lost and are transported securely) to best-effort (where messages might get lost in case of a system failure). Endpoint implementers choose their desired quality of service by declaring the annotations on SCA module exports and imports. If a quality of service is unspecified, WebSphere ESB applies its defaults.
When you install WebSphere ESB, an SCA.SYSTEM bus is created for you to deploy SCA modules. If the configuration of this bus is not adequate for your SCA modules, or you want service integration buses for other uses, you can choose between a variety of bus environments including a multiple-server bus, several single-server buses that use different servers, and buses linked to WebSphere MQ.
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. 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 might be interconnected to form complex networks. An enterprise might deploy multiple buses for organizational reasons; for example, an enterprise with several autonomous departments might want to have separately-administered buses in each location.