You can use direct and indirect links to connect service integration
buses together so that all of the buses can exchange messages.
Buses can be linked directly or indirectly. In the case of a direct connection,
two buses are connected directly by a single service integration bus link.
In the case of an indirect connection, there are one or more intermediate
buses connected in a chain of links between the two buses. For example, to
get indirectly from Bus A to Bus C, your messages might be routed through
a link from Bus A to Bus B, then through another link from Bus B to Bus C.
Each bus needs to know how to get to every other bus to which it is connected.
In this context, the bus in question is referred to as the local bus, and
each of the buses to which it is connected is referred to as a foreign bus.
Routing information from the local bus to each foreign bus is
stored in the local bus in a routing definition, also known as a virtual link.
The routing definition indicates:
- The type of physical link - either a service integration bus link from
a messaging engine in the local bus to a messaging engine in the foreign bus,
or a WebSphere MQ link from a messaging
engine in the local bus to a WebSphere MQ gateway queue manager.
- Whether the link is direct or indirect. If the link is indirect, the routing
definition also specifies the next bus in the chain that leads to the foreign
bus.
For more information about foreign buses, see
Foreign buses.
The following diagram shows an existing network of three buses, Bus 1,
Bus 2 and Bus 3, to which a new bus, Bus n, is to be added. Bus n will be
connected directly to Bus 1, and indirectly to Buses 2 and 3.

To add Bus n to the network, the following items are created:
In Bus n:
- A foreign bus representing Bus 1, with a direct routing definition.
- Foreign buses representing Buses 2 and 3, with an indirect routing definition
specifying the foreign bus that represents Bus 1 as the next bus in route.
- A service integration bus link from the
messaging engine hosting the routing definition from this bus to Bus 1, to
a messaging engine in Bus 1.
In Bus 1:
- A foreign bus representing Bus n, with a direct routing definition.
- A service integration bus link from the
messaging engine hosting the routing definition from this bus to Bus n, to
a messaging engine in Bus n. The name of the service integration bus link must
match the name of the service integration bus link created
in Bus n.
In Bus 2:
- A foreign bus representing Bus n, with an indirect routing definition
specifying the foreign bus that represents Bus 1 as the next bus in route.
In Bus 3:
- A foreign bus representing Bus n, with an indirect routing definition
specifying the foreign bus that represents Bus 2 as the next bus in route.
The following diagram illustrates the network after adding Bus n.
