Foreign buses

You can configure a service integration bus to connect to, and exchange messages with, other messaging networks. To do this, you configure a foreign bus connection, which represents either another service integration bus, or a WebSphere® MQ queue manager or (for WebSphere MQ for z/OS®) queue-sharing group, that the existing service integration bus can exchange messages with. In this way, you can extend the network of buses that can exchange messages.

When an application connects to a service integration bus, that bus is its local bus. A foreign bus is any other bus that has a link to the local bus. When the foreign bus is a service integration bus, it can be in the same cell as the local bus, or in a different cell.

To exchange messages between two buses, you configure a foreign bus connection from the local bus to the second bus. The foreign bus connection is associated with the local bus, and identifies the second bus as a foreign bus.

If the second bus is another service integration bus, you then configure a foreign bus connection from the second bus to the first bus. The foreign bus connection is associated with the second bus, and identifies the first bus as a foreign bus relative to the second bus. If the second bus is in a different cell from the first bus, you use the administrative console for the second cell to configure this foreign bus connection.

A foreign bus connection can be direct or indirect. For a direct foreign bus connection, messages route directly through a link between the local bus and the foreign bus. For an indirect foreign bus connection, messages route indirectly through one or more intermediate buses.

A foreign bus connection contains a routing definition, also known as a virtual link, which indicates the type of physical link:

In the following figure, for an application that is connected to Bus 1, messages that are routed to Bus 2 use a direct foreign bus connection. Messages that are routed to Bus 3 use an indirect foreign bus connection and use Bus 2 as an intermediate bus.

Figure 1. Linking service integration buses.
Three service integration buses are connected through a service integration bus link on a messaging engine in each bus.

When you configure a foreign bus connection, the service integration bus link or WebSphere MQ link, as appropriate, is created automatically. If required, you can view or amend this link.

The following restrictions apply when you configure a foreign bus connection:
When you configure a bus, you can select the Configuration reload enabled option so that if the configuration properties of any foreign bus connections are changed later, the changes are updated automatically. The time when these changes take effect varies, depending on the properties that are changed:

You can define an explicit destination on a foreign bus that an application can send messages to. You can also configure default properties for use by messages that are 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.

Messages flowing to or from a foreign bus that cannot be processed successfully are rerouted to the system exception destination of the messaging engine that owns the link to the foreign bus, possibly disrupting message order. Common reasons for rerouting messages to the exception destination are that the target destination is unknown by the foreign bus, or that the foreign bus has not granted the sending bus access to the target destination.

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, you must map topic space names on a local bus 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 to the foreign bus, an equivalent topic space mapping is required by the foreign bus.

You administer topic space mappings when you create a foreign bus connection, or through the routing properties for a foreign bus connection. Topic space names for the local bus are mapped to topic space names that are defined on the foreign bus. It is common for these two names to match. Note that mapping two topic spaces implies that the topics in them are the same.

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Last updated: Oct 21, 2010 10:04:34 PM CDT
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