Chapter 8 OSI Physical layer

The OSI Physical layer makes available the means to transport across the network media the bits that make up a Data link layer frame. This layer allows a complete frame from the data link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are received by either an end device or an intermediate device. The physical media and associated connectors, a representation of bits on the media, encoding of data and control information, and transmitter and receiver circuitry on the network devices are required Physical layer elements for the delivery of frames across the local media. The purpose of the Physical layer is to create the electrical, optical, or microwave signal that represents the bits in each frame. These signals are then sent on the media one at a time. There are three basic forms of network media on which data is represented namely copper cable, fiber, wireless. The representation of the bits depends on the type of media. For copper cable media, the signals are patterns of electrical pulses. For fiber, the signals are patterns of light and for the wireless media the signals are pattern of radio transmissions. In addition, there are three elementary roles that physical layer take part, the physical components, data encoding, and signaling. The physical elements refer to the electronic hardware devices, media and connectors that transmit and carry signals to represent the bits. Encoding is a method of converting a stream of data bits into a predefined code. Signaling is the method of representing the bits into electrical, optical, or wireless signals that represent the 1’s and 0’s on the media. However, the speed of transfer of bits varies in type of media and it can be measured through bandwidth, throughput and goodput. The capacity of a medium to carry data is describe as bandwidth. Throughput is the measure of the transfer of bits across the media over a given period of time. On the other hand, goodput measures the transfer of usable data. The physical layer is concerned with network media and signaling. This layer produces the representation and groupings of bits as voltages, radio frequencies, or light pulses. The most commonly used media for data communication is cabling that uses copper wires to signal data and control bits between network devices. Nowadays, fiber optic cable is an alternative replacement for copper cables and somehow varies in speed, capacity and expense.