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.