Chapter 8- Physical Layer

Physical layer is the first layer in the OSI model; it is a layer protocol that organizes data from the source for transmission to its destination. A layer that holds and manage how being placed on the communication media Since network understands binary digit only, physical layer is the one that encode the binary digit so that it can represent to the data link layer frames into signal to transmit and receive those signals across the physical media. Physical layer is the one responsible for crossing the bits put into the frame of the data link layer by the network media. It provides the bits for the data link layer who encodes to transform into signals for transmission onto the local media. It may receive by the end device or an intermediate device. This layer uses different communication media to connect devices in order to transmit data from one network to the other. Some of those media are copper, fiber and wireless. The type of signal which represented by bits depends on what type of media being used. For copper cable, the signals are pattern of electrical pulses. For fiber, the signals are patterns of light and for wireless, the signals are patterns of radio transmissions. Standard of physical layer specify signals, connectors and cabling requirements. Fundamental functions of physical layers vary the physical component, data encoding and signaling. When we say physical components, it refers to the electronic devices, media and connectors that transmit and take the signals to represent the bits. Encoding is the process of converting the data bits into the code that are understandable by the network in order to recognized properly by the receiver and avoid media error detection. There are different methods in encoding like Manchester encoding in which the bits are represented as voltage transitions. There are also encoding by grouping the bits. After encoding, the signaling will generate to actively transmit the data into its destination. There are also different method in signaling depends on how does this method being used in transmitting the data in the network. Data transfer can be measures in three ways: Bandwidth, Throughput and Goodput. When we say bandwidth, it measures the data that can flow from one place to another in a given amount of time. Throughput is the measure of the measure of the transfer of bits across the media over a given period of time. Goodput is the measure of usable data transferred over a given period of time, and is therefore the measure that is of most interest to network users.