The network topology consists of at least four layers. On top we've the TMS module of OpenWMS.org running within a z-nodes Terracotta cluster. All cluster nodes are communicating between each other and the underlying subsystem over RabbitMQ with AMQP. Messages that are exchanged between Layer N and N-1 are aligned to the OSIP (Open Systems Interchange Protocol) before they were translated into the binary transport protocol (AMQP). Layer N-1 is the so-called DaCo Data Multiplexing & Demultiplexing Layer that is responsible for collecting all status and control messages from lower layers and building higher level OSIP messages. Enhanced Raspberry Pi processors on this layer make it is possible to control basic material flow actions and take decision on state changes of underlying submodules. Processes running on these devices must be highly failure resistant and highly performant, thats why all control logic and messaging software is written in Erlang. The Arduino processor boards are responsible to control basic I/O flow control logic on layer N-2. Arduino offers a easy to learn programming language (based on Wiring) that fits perfect for that job. The communication between layer N-1 and N-2 happens via TCP/IP on Ethernet, whereas the protocol is not yet specified. Real hardware, like sensors and actuators, are connected to the software via the XBees on layer N-3. Each XBee has a couple of I/O ports that can be adapted to the hardware directly or indirectly and that is connected via RF to others (PAN) and to the controller of the PAN - an Arduino. An XBee talks to an Arduino controller via the standardized ZigBee protocol.