Ethernet

                This is the 9^th chapter of Cisco Networking Academy (CCNA) Exploration Network Fundamental Course. As stated, Ethernet is defined by Data Link layer and Physical layer protocols which are the 1^st and 2^nd layers of the OSI model.

                Robert Metcalfe and his workers designed the 1^st LAN at Xerox more than 30 years ago. The 1^st LAN was the original version of Ethernet. This Ethernet was released as an open standard. In 1985, IEEE published standards for LANs = 802. The logical topology of Ethernet is a multi-access bus. It was designed to accommodate multiple computers that were interconnected on a shared bus topology. The Ethernet usually adapted optical fiber media. It also uses UTP copper cables to interconnect network devices via intermediary devices such as hubs and switches.

                The Ethernet standard which is 802.3 operates in the lower 2 layers of the OSI model: the Data Link layer and the physical layer. The Data Link layer consists of sub layers: Media Access Control (MAC) – lower sub layer, and Logical Link Control (LLC) – upper sub layer. The MAC is a unique identifier that was created to assist in determining the source and destination address with in an Ethernet network. All devices connected to an Ethernet LAN have MAC addressed interfaces. For Ethernet, the IEEE 802.2 standard describes the LLC sub layer functions while the 802.3 standard describes the MAC sub layer and Physical layer functions. The Ethernet MAC has 2 primary responsibilities: Data encapsulation and MAC. The data encapsulation has primary functions of frame delimiting, addressing, and error detection.

             The early versions of Ethernet are: Thicknet (10BASE5) – used a thick coaxial that allowed for cabling distances of up to 500 meters before the signal required a repeater; and Thinnet (10BASE2) – used a thin coaxial cable that was smaller in diameter and more flexible than Thicknet and allowed for cabling distances of 185 meters.

             Four data rates currently defined for operation over optical fiber and twisted-pair cables: (1) 10Mbps -> for 10BASE-T Ethernet and have a bit time of 100ns; (2) 100Mbps -> for fast Ethernet and have a bit time of 10ns; (3) 1000Mbps or 1Gbps -> for gigabit Ethernet and have a bit time of 1ns; and (4) 10Gbps -> for 10 Gigabit Ethernet and have a bit time of .1ns. With 10Gbps Ethernet, flexible, efficient, reliable, relatively low cost end-to-end Ethernet networks become possible.

               The difference of using hub and switches in the network: Some related issues using hub are scalability, latency, network failure, and collisions. In 10BASE-T networks, typically the central point of the network segment was a hub. Three primary reasons for the increase of throughput using switch: dedicated bandwidth to each port, collision-free environment, and full-duplex operation. He The switches enhanced LAN performance and it can control the flow of data by isolating each port and sending a frame only to its proper destination (if the destination is known), rather than send every frame to every device. Three reasons for still using hubs: availability, economics, and requirements.

               

Important keywords:

1.)    CSMA/CD -> Carrier Sense Multiple Access w/ Collision Detection.

     -> manage the problems that result when multiple devices attempt to communicate over a           shared physical medium.

2.)    Collision -> the frames from each device impact and are damage when they meet in the physical media.

3.)    Alohanet -> a digital radio network designed to transmit information over a shared radio frequency between the Hawaiian Islands.

4.)    Half-duplex communication -> a connection of sharing the media where only one station could successfully transmit a t a time.

5.)    Full-duplex communication -> having a connection that can carry both transmitted and received signals at the same time.

6.)    Jamming signal -> used to notify the other devices of a collision, so that they will invoke a backoff algorithm.

7.)    Backoff algorithm -> causes all devices to stop transmitting for a random amount of time, which allows the collision signals to subside.

8.)  Slot time -> the time that a transmitting station waits before attempting to retransmit following a collision.