 time slot, in a small service time Ts T, where no transmis- sion is possible, each access point senses the shared medium and, if no carrier is detected, starts a transmission with probability p. If two or more stations attempt to access the bus in the same slot, in the successive slot collision is detected by all the access points and any ongoing transmission is immediately stopped. At the beginning of an available time slot (i.e., a time slot where no transmission is ongo- ing) the probability that one station begins a successful transmission is equal to the prob- ability Ps that no other station starts to transmit in the same time slot. It writes, with the usual notations, = = Np(1-p)(N-1) (7.18) Generally, collisions can occur; thus, the number J of time slots waited by a packet at an input queue head before a successful transmission is a random variable; and since succes- sive transmission attempts in different time slots are independent, it is a geometrically distributed random variable. This means that we can write (7.19) The total time I elapsing from the completion of the transmission of a packet and the completion of the transmission of the following packet is also a random variable. The aver- age of I can be written as (7.20) Telecommunication Networks summing up the geometrical series and simplifying it is obtained (7.21) Finally, the throughput is given by (7.22) In Equation 7.22, the role of the ratio between the round trip and the packet length at the bus bit rate is clearly evidenced. We know that the efficiency given by Equation 7.22 is maximized if the denominator is minimized. For a given ratio 2+/ts, it is verified if the term Np(1 - p)(N-1) is maximum, thus for p= 1/N, obtaining (7.23) and for large values of N the equation for the throughput further simplifies as (7.24) It is to be noticed that when applying Equation 7.23 to a switch fabric implemented with today's available technology, assuming that the input queues are sufficiently long to avoid congestion for the impossibility of acceptin