Chapter 9 Ethernet

                Ethernet as it is being introduced is the predominant LAN technology used today in the world, because of its great impact to the overall performance of a network. According to the history, it was Robert Metcalfe and his co worker at XEROX who developed this technology and they have dedicated many years of their lives for about 30 years of developing this ethernet technology. The OSI model upper layers function protocols were being defined and maintained by the International Engineering Task Force (IEFT), while the functional of the lower layers ,specifically the Data Link Layer  and the Physical Layer were maintained by many international organizations. Here the ethernet is being comprised of the standards at these lower layers. In 1980 the standards of ethernet were first established, and these standards work at the Data Link lower layer and Physical layer.

                The Data Link Layer is further subdivided into two sublayers, the logical link layer and the Media Access Control layer. The ethernet standard 802.3 works at the lower layer of the Data Link layer and to the Physical layer for addressing scheme and recognizing bit stream or a frame, but this has limitations and there comes the logical link layer that resolve these limitations. Logical Link layer connects or communicates to the upper layers of the OSI model. This media access control has many features, it use for frame delimiting and error detection and for managing collisions on a shared media. MAC uses the CSMA/CD method on a shared media where traffic is heavy and collision percentage is high. If ever collision occurs at the media CSMA/CD detects the collision and then prompts the node to retransmit the frame that failed. MAC address also plays a role on the network, every node connected to a network should have MAC address, it is used To determine the destination node of the frame in a network. The ARP or the Address Resolution Protocol help to address the issue of IPv4 addresses. ARP table stores the IPv4 addresses and MAC address and match these addresses in order to send the frame to the end devices. Ethernet LAN technology offers ethernet hubs to cater number of hosts connected to them on a LAN, but these two have different characteristics and features. Hubs and switches have the same function. Hub is an intermediary device where in multiple nodes can be connected to it in a shared media environment. Designated bandwidth in a hub-based ethernet network is being divided to number of nodes in that particular network segment, since the frame from other network will be receive by the hub port it will then send it to all the nodes causing traffic and occasionally a collision. As the number of nodes increases in a hub-based network the bandwidth will decrease and at the same time the throughput also decreases. The switch based. Ethernet network addressed those issues, switch manages a segment of the network to be collision free environment. Its port in the switch has its own designated bandwidth, thus it increases throughput.