of such a working is provided by the switch fabric of a router working in a datagram network. In this case, the switch fabric works generally in tandem with a set of queues that can be located at the fabric input, at the fabric output, or in both the configurations. In the most general case of queues both at input and output, every time a packet arrives at an input, it is stored into a queue and its address is read. The processor identifies the output destination port, the switch fabric is configured to connect the input to the output, and the packet is transmitted at the output queue. After that, another packet is considered requir- ing another connection and SO on. The semi-static and the dynamic switch fabrics require different controllers [7,8]. In the semi-static case, the controller has the role of performing actions dictated by the overall connection setup procedure and to manage the hardware of the switch. In the dynamic case, the controller, on top of the switch management and on the route finding inside the switch, has to manage conflicts arising when packets from different inputs either have to be sent to the same output or require the use of the same internal resource. This structure is represented schematically in Figure 7.2. In this case, generally, either the controller runs two different processes or two differ- ent dedicated hardwares exist: one of them is the switch fabric manager; the other is the so-called arbiter. The manager performs all the configuration operations on the switch fabric, while the arbiter performs conflicts solution on the ground of a suitable solution strategy [9]. Normally, the arbiter works on the ground of the priorities that are assigned to the input requests by an external entity: for example, by the request remote origin on the ground of its quality of service level. Telecommunication Networks Arbiter Manager FIGURE 7.2 Block scheme of a dynamic space diversity switch with a switch fabric manager and a contention and queue policy arbiter. Input queues Output queues Ho