Chapter 9 Ethernet

Chapter 9

This chapter focuses the different layers of OSI and TCP/IP and hoe they support networks to communicate. The functional protocol and services for the TCP/IP protocol suite in the upper layer is maintain  by the internet engineering task force. The Ethernet operates across the two layers of OSI model the physical layer and the data link layer. The Ethernet is now the predominant LAN technology in the world. Ethernet at layer 1 involves signals, bit streams that travel on the media physical components that put signals on media and various topologies. The Ethernet at layer two connects to the upper layers via logical link control and uses addressing schemes to identify devices. Ethernet separates the function of the data link layer into two distinct sub layers the logical link control sub layer and the media access control sub layer. The logical link control sub layer handles the communication between the upper layers and the networking software and the lower layer typically the hardware. The media access control sub layer is the lower Ethernet sub layer of the data link layer. MAC is implemented by hardware typically in the computer network. Media Access Control  controls the placement of the frames on the media and the removal of frames from the media. Logical topology of the Ethernet is a multi-access bus. This means that all nodes in the network segment receive all frames transmitted by any node on that segment. Ethernet specifies and implements encoding schemes that enables the frame bits to be carried as signals across media. Ethernet technology was first established in 1970 with the program called ALOHANET a digital radio network design to transmit information over a shared radio frequency between the Hawaiian Islands. The first version of  Ethernet  incorporated a media access method known as carrier sense multiple access with collision and detection. It manages the problems that result when multiple devices attempt to communicate over a shared physical medium. The early version of Ethernet uses coaxial cable to connect computers in a bus topology. The Ethernet frame size gas an standard of minimum frame size as 64 bytes and the maximum as 1518 bytes in 1998 it was extended its maximum allowable frame size to 1522. The frame size was increase to accommodate the virtual local area network. The MAC address was created to assist determining the source and destination address within your computer.

physical layer chapter 8

The purpose of the physical layer is to create electrical, optical and microwave signals  that represent bit in each frame. The physical layer produces the representation and groupings of bits as voltage, radio frequencies or light pulses. This discusses the different kind of media that is use by the different kind of network. The three basic forms of media networks are copper , fiber optics and wireless media. Copper media use copper wire to send signal data and control the bits between network devices. Fiber optics uses glasses or plastic fibers to guide light impulses to send the data from source to destination. Wireless media carries an  electromagnetic signals at radio and microwave frequencies that represent binary digits. Wireless media can will differ from its location to get a great signal to send data.

There are fundamental functions of physical layer one of this is its physical components, data encoding and signaling. Data encoding is the method of converting the data bits into codes the codes are group into bits to provide common pattern that can be recognize by both the sender and the receiver. Signaling it generate electrical, optical or wireless signals that represent 1 or 0. All data from the human network will become binary which are transported individually across the physical layer. The physical layer received data to the transmitted signals and converted back to bits. The bits are check to start of frame and end of frame bit patterns to determine that the complete frame has been receive. Some method may use one attribute of signal to represent a single 0 and use another attribute of signal to represent a single 1. The Manchester encoding indicates 0 by high to low voltage transition in the middle of the bit time. For 1 there is a low to high voltage transition in the middle of the bit time. The signaling method must be compatible with the standard so that the reciever can detect signals and decode them. In NRZ (Non Return to Zero) a low voltage represent 0 and a high voltage represent 1.

Signaling patterns is one way to provide frame detection to begin each frame with pattern or signals representing bits that the physical layer recognize denoting the beginning of the frame. The data transfer can be measured in three ways Bandwidth, throughput, and  goodput. Bandwidth is the capacity of a medium to carry data. It measure the amount of information that can be flow from one place to another in the given amount of time. Throughput is the measure of the transfer of bits  across the media in a given amount of time. The last is the goodput is the measure of the usable data transferred over the given period of time.