high volumes in which Ethernet components are produced. Networks Fundamentals and Present Architectures If the Internet model is defined in a more operative and informal way with respect to the network models developed by the ITU-T, Ethernet in its LAN-oriented implementation can be considered extremely simple, although sufficiently rich to manage complex and extended private networks [27,28]. The core of Ethernet is constituted by the collision detection/carrier sense multiple access (CD-CSMA) protocol that manages the sharing between several clients of a com- mon transmission medium. Each Ethernet station in a local network is given a 48 bit MAC address and the access to a share medium, in the simplest case a bus. When the upper layer (e.g., the Internet layer of a TCP/IP LAN) wants to transmit a packet, the packet is sent to the IP-Ethernet adapta- tion and then enveloping it into the Ethernet frame that contains the MAC address of the destination machine. The Ethernet transmission procedure can be described as a simple algorithm that is based on the fact that each station can detect if the shared medium in a certain instant is idle and when it receives a frame it is able to send an acknowledgment at the sending station. The algorithm can be written as follows: Main Transmission Procedure-Carried Out by the Transmitting Node Frame ready for transmission, transmission abort flag FALSE. label AAA Is Transmission abort flag TRUE? YES: Abort transmission NO: Continue transmission procedure Is medium idle? NO, wait until it becomes ready wait the interframe gap period (9.6 us in 10Mbit/s Ethernet) and go ahead YES: Go ahead Start transmitting. Did a collision occur (i.e. no acknowledge from the receiving node)? YES: Go to collision detected procedure. NO: Reset retransmission counters end frame transmission. Collision Detection Procedure Continue transmission until minimum frame time is reached (jam signal) to ensure that all involved receivers detect the collision. Increment retransmission counter. Was the maximum