DATACOM

Physical Layer

Chapter 8

                                Chapter eight is all about the Physical Layer. The purpose of the physical layer is to create the electrical, optical, or microwave signal that represents the bits in each frame. The signals are sent on the media one at a time. The physical layer also retrieve the individuals signals from the media, it can restore to their bit representations and pass the bits of data link layer as complete frame. There are three basic forms of network media which is copper cable, fiber and wireless. Copper cable media is the signals are patterns of electrical pulse. Fiber is the signals are patterns of light. And for the wireless media, is the signals are patterns of radio transmission. The physical layer consists of hardware, developed by engineers in the form of electronic circuitry, media and connectors. It is appropriate that the standards governing this hardware are defined by the relevant electrical and communications engineering organizations. As we saw in a previous chapter, the services and protocols in the TCR/IP suite are defined by the Internet Engineering Task Force (IETF) in RFCs. Physical buyer technologies are defined by organizations such as: ISO, IEEE, ANSI, ITV, EIA/TIA, FCC, and Physical Layer Technologies and Hardware. There are three Fundamental functions of the physical Components Data encoding and signaling. Encoding is a method of converting a stream into code: Signaling method used into a compatible standard so that the receiver can detect the signals. Data transfer can be measured in three ways: Bandwidth, Throughput, Goodput. Band width is typically measured in kilobits per second or megabits per second. Throughput is the measure of the transfer of bits across the media over a given period of time. Good put is the measure of usable data transferred over a given period of time. The physical layer is concerned with network media and signaling. This layer produces the representation and groupings of bits as voltages, radio frequencies of light pulses. Unshielded twisted-pair (UTP) cabling is used in Ethernet LANs; consist of four pairs of color-coded wires that have been twisted together. The UTP cabling commonly found in workplaces, schools, and homes conforms to the standards established jointly by the Telecommunication Industry Association (TIA) and the Electronics Industries Alliance (EIA).