formances of the random access bus by exploiting the fact that the propaga- tion delay along the shared medium is very short in the case of a switch fabric because the entire network is enclosed into a single equipment. Carrier sense multiple access (CSMA) is one of these protocols that is extremely diffused for its application in Ethernet local area networks (LANs): we have informally introduced this protocol in Chapter 3 talking about Ethernet and now we want to analyze its work- ing and performances in a more detailed manner. One of the aspects that renders CSMA SO attractive for use in bus-based switches is that it is completely standardized [31] and widely used, SO that adopting it hides a low risk and assures the possibility to rely on large volume electronics components. A CSMA bus access point having a packet to transmit along the shared medium, instead of transmitting it as soon as possible, before transmission uses its receiving side to sense the activity along the shared medium (remember that the access point and the detection point corresponding to the nth input/output port are generally integrated together). If some signal is detected along the bus, the access points deduce that other access points are transmitting packets and do not transmit up to the first useful moment in which no signal (no carrier) is present in the bus. The intent of this procedure is to reduce the collision probability SO increasing the bus throughput. However, different from what seems as a superficial analysis, CSMA protocol does not completely avoid collisions, due to the presence of finite propagation delays along the bus. As a matter of fact, in the moment in which a certain access point senses the absence of carrier on the medium and starts to transmit it is possible that also another access point in a remote point of the bus is starting to transmit a packet whose leading edge is not yet arrived to the first access point. Thus, a newly generated packet in a CSMA bus is vulnerable to collision during the time needed to pr