 number of transmission attempts reached? YES: Transmission abort flag TRUE. NO: Calculate and wait random backoff period based on number of collisions Transmission abort flag FALSE. Re-enter main procedure at label AAA. Telecommunication Networks This is in brief the description of the Ethernet CSMA protocol [29]. We will return on the CSMA protocol in much more detail in Chapter 7 dealing with time division dynamic switches; thus, the reader that is interested to go more in detail is encouraged to go there both for a longer discussion and for a detailed bibliography. On top of the simple bus LAN using CD-CSMA, several elements have been added to Ethernet to allow more complex LAN topologies to be managed: different Ethernet busses can be connected via bridges and hubs to extend the network and switches can be used to provide switching in more complex topologies [27]. It is out of the scope of this book that deals with the public network, to detail all the LAN-related Ethernet technologies. The only thing we have to add regarding the LAN-oriented Ethernet is to describe the working of an Ethernet switch, which will be the base for the development of important equipment that can be used in the public networks. Different Ethernet networks can be connected via bridges or hubs. When such connec- tion is done however, the bandwidth of the transmission medium continues to be shared among all the nodes of the network: thus, bridging and using hubs solve the problem of creating complex Ethernet topologies, but not the problem that by increasing the number of nodes the average bandwidth per node decreases. In order to solve this problem switches can be used. When two Ethernet networks are connected via a switch, it detects and memorizes the location of all the MAC addresses in one network or in the other. When an Ethernet frame arrives, the switches memorize it in an input queue, read the MAC address, and recognize the network it belongs to. Thus, it sends the frame to the correct output port [30]. It is evident that suc