Chapter 8 Physical Layer

                  The Open System Interconnectivity (OSI) model is a set of standard often follows in networking society for data communication. It is also called a reference model, because other networking models are being referenced to OSI model standard and structured. OSI model is composed of 7 layers and each layer conforms to a protocol that govern data communication over the network. One of the layers of OSI model is the physical layer, this layer provides a means of transmitting of bits across the network media that make up the data link layer frame. The basic work of the physical layer is to accepts a complete frame from the data link layer and encodes it as a sequence of signals that are transmitted onto the local media. The frame is the PDU of the data link layer it is composed of groups of bits and each bit represents a signal. The signal represented by the bit may vary according to the type of media being used by the network and the three basic forms of network media are the copper cable, fiber optic, and wireless media. Each media has different physical characteristics that significantly affect the process of delivering a data along the local media and it also represents  different kinds of signal, copper cable uses electrical signal, fiber optic uses also light wave signals and wireless medium uses radio frequency signal to represents a bit. When the physical layer encodes the bits into the signals for a particular medium for a successful delivery, but in order to recognize that particular passes through a media has successfully received by receiving device, there is a must to distinguish the end and the beginning of the next frame. The physical layer has three fundamental functions, the physical component, data encoding and signaling. Physical component is comprises of electronic devices, media and connectors that help to transmit and carry the signals to represent the bits. Physical component standard was being set or defined by some of the international organizations like the international Organization for Standardization(ISO), Institute  of Electronic and Electrical Engineers(IEEE) and American National Standards Institute . The second function of the physical layer is the data encoding , a method of converting stream of data bits into a predefined code, in order to create a predictable pattern of code to recognized by both the sender  and the receiver . The last is the signaling that uses binary bits the 0's and 1's on the media as a signal whether it is electrical pulses, light or wireless signals. 

               When studying the physical layer we need also to consider the speed and the data transfer and how it is being measured. Data transfer can be measured into three different ways, the bandwidth,throughput, and goodput. Each measured the capacity,speed and the usable data in transfering data. Cabling is an important factor to consider also in data communication for a successful,faster and less interference of data transmission. Cabling resolved the problems of external interferences like the electronic noise that corrupt and distort the data on the medium. Cabling can be Aa UTP, STP, and Coaxial cabling. All of these has different physical characteristics and features to cater different needs of organization. It plays an important role in the ohysical layer but it may also cause hazards if not properly configured and if not installed in a building correctly.