WebSphere WebSphere Application Server Network Deployment, Version 6.1.x Operating Systems: AIX, HP-UX, i5/OS, Linux, Solaris, Windows, z/OS

Foreign buses

You can configure a bus to connect to, and exchange messages with, other messaging networks. To do this, you must configure a foreign bus. A foreign bus is a representation of another service integration bus, or a WebSphere MQ queue manager, with which an existing service integration bus can exchange messages. The purpose of a foreign bus is to extend the network of buses that can exchange messages.

A foreign bus encapsulates information related to the remote messaging network, such as the type of the foreign bus and whether messaging applications are allowed to send messages to the foreign bus. A foreign bus is associated with a service integration bus. The bus with which the foreign bus is associated is known as the local bus. The foreign bus represents another service integration bus, either in the same cell as the local bus or in a different cell, or it represents a WebSphere MQ queue manager. From the local bus, every other bus is regarded as a foreign bus, even if it is a bus in the same cell.

Messages are routed to a foreign bus either directly through a link between the local bus and the foreign bus, or indirectly through one or more intermediate buses. Regardless of where the buses exist, if one is foreign to the other, it requires a foreign bus link. For example, if a cell contains more than one bus, each bus within it is regarded as foreign to each other bus. The link is defined in a routing definition, also known as a virtual link. The type of routing definition for a foreign bus indicates the type of physical link:

In the following figure, buses 1 and 2 are linked directly, and buses 1 and 3 are linked indirectly through bus 2.

Figure 1. Linking service integration buses. Three service integration buses connected through a service integration bus link on a messaging engine in each of the buses.
Before you create and configure a foreign bus link, you must create a foreign bus. The following restrictions apply to creating a foreign bus:

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.

Messages flowing to or from a foreign bus that cannot be successfully processed are re-routed to the system exception destination of the messaging engine that owns the foreign bus link, possibly disrupting message order. Common reasons for re-routing 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 into the foreign bus, an equivalent topic space mapping is required by the foreign bus.

You administer topic space mappings 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.

Related concepts
Message ordering
Related tasks
Connecting buses
Connecting buses directly
Extending the bus network
Configuring foreign bus definitions
Adding a foreign bus
Configuring the properties of a foreign bus
Listing the foreign buses
Removing a foreign bus
Configuring destination defaults for a foreign bus
Creating a routing definition
Modifying a routing definition
Removing a routing definition
Configuring service integration bus links
Creating a foreign bus destination
Securing access to a foreign bus
Planning a bus topology
Planning a multiple-bus topology
Planning a topology that includes WebSphere MQ

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Timestamp icon Last updated: 26 February 2009
http://publib.boulder.ibm.com/infocenter/wasinfo/v6r1/index.jsp?topic=/com.ibm.websphere.pmc.nd.multiplatform.doc/concepts/cjj0030_.html

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