A foreign bus is a representation of another service integration bus, or a WebSphere MQ queue manager, with which an existing service integration bus, or a WebSphere MQ queue manger, can exchange messages. The purpose of a foreign bus is to extend the network of buses that can exchange messages.
A foreign bus is a property of a service integration bus or a WebSphere MQ queue manager. A foreign bus, and the service integration bus it represents, can exist in separate network cells or within the same cell. A foreign bus that represents a WebSphere MQ queue manger can exist in a separate WebSphere MQ network, or within the same WebSphere MQ network as the queue manager. The existing service integration bus or WebSphere MQ queue manager is referred to as the local bus.
In the following figure, Figure 1, buses 1 and 2 are linked directly, and buses 1 and 3 are linked indirectly through bus 2.
You can define an explicit destination on a foreign bus, to which an application can send messages. You can also configure default properties for use by messages sent to destinations on a foreign bus when there is no explicit foreign destination definition, and the application does not explicitly provide values for the properties. An application cannot receive messages from a foreign destination; it can only consume messages from a destination on the bus to which it is connected.
An application subscribing to a local topic space can receive messages published to a topic on a foreign bus. To allow publish/subscribe messaging between buses, topic space names on a local bus must be mapped to topic space names on a foreign bus.
A topic space mapping allows subscribers on the local topic space to receive messages published in the foreign topic space. For publications to flow from the local topic space into the foreign bus, an equivalent topic space mapping is required by the foreign bus.
Topic space mapping is administered through the routing properties for a foreign bus. Topic space names for the local bus are mapped to topic space names defined on the foreign bus. It is common for these two names to match. Note that mapping two topic spaces implies that the topics within them are "the same".