You can use direct and indirect links to interconnect service integration
buses so that all of the buses can exchange messages.
Service integration 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, one or more intermediate buses connected in a chain link
two buses.
Each bus must be able to get to every other bus to which it is connected,
using routing definitions. In this context, the bus you start with is referred
to as the local bus, and each of the buses to which it is connected is referred
to as a foreign bus. Information about how messages are routed from the local
bus to each foreign bus is stored in the local bus in a foreign bus definition's
routing definition. The routing definition indicates:
- Whether the link is direct or indirect.
- If the link is direct, the routing definition specifies 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.
- If the link is indirect, the routing definition specifies the next foreign
bus in the chain that leads to the routing definition's foreign bus.
Figure 1. Direct connection between two service integration
buses using a service integration bus linkBus 1 and Bus 2 are directly connected using a direct service integration
bus link.

Figure 2. Indirectly connecting two service integration buses,
using two direct service integration bus linksWhen connecting one bus to another bus via an intermediate bus or a chain
of buses, no new service integration bus links are required. Instead, each
foreign bus definition identifies a neighboring bus on route to the final
bus at the "next hop" in the chain. Each bus in the chain must know of the
next hop in the chain to reach the final bus. The local bus uses its foreign
bus definition to identify the next bus in the chain to the final bus, and
uses its direct service integration bus link to flow messages to that bus.
The intermediary bus then uses its locally defined foreign bus definition
to identify the next hop on to the final bus until the next hop bus is the
final bus.
To get indirectly from Bus 1 to Bus 3, your messages can be routed through
a link from Bus 1 to Bus 2, then through another link from Bus 2 to Bus 3.
In the foreign bus definitions of Bus 1, Bus 2 is identified as the next foreign
bus on route to Bus 3. Bus 2 then uses its locally defined foreign bus definition
to identify the next hop on to the final bus. In this case, Bus
3 is identified as a foreign bus connected indirectly via foreign bus Bus
2; Bus 3 is the final bus.

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, and to allow messages to flow between any
of the buses, the following items must be 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.
