Gateway Function
The cluster provides a connection between bus systems. This allows different bus networks to transfer information between them. The cluster "translates" this information and distributes it to the required network. For example, the D-bus does not connect directly to all modules on the E46. Any modules on the K-bus are diagnosed via the pathway created by the cluster. The path is as follows - D-bus > cluster > K-bus > component.
Signals are also shared via the gateway as well as commands. An example of this would be the cruise control system. The MFL control module, which control cruise control switches, sends a command to the DME system. The DME systems is responsible for engine speed control. The command for "accelerate" for example, is sent to the DME via the gateway (cluster) to the CAN-Bus.