tailieunhanh - Lecture Business data communications: Chapter 7 - Behrouz A. Forouzan

Chapter 7 - Transmission media. In this chapter we discuss different kinds of transmission media, their use, and their advantages and disadvantages. After reading this chapter, the reader should: Understand the difference between guided and unguided media, be familiar with twisted-pair cable and the rationale for twisting, be familiar with shielded twisted-pair cable and the rationale for shielding, be familiar with coaxial cable, understand how the air (or vacuum) can be a transmission medium for signals. | Chapter 7 Transmission Media Understand the difference between guided and unguided media. Be familiar with twisted-pair cable and the rationale for twisting. Be familiar with shielded twisted-pair cable and the rationale for shielding. Be familiar with coaxial cable. After reading this chapter, the reader should be able to: OBJECTIVES Understand how the air (or vacuum) can be a transmission medium for signals. GUIDED MEDIA Figure 7-1 Categories of guided media Figure 7-2 Twisted-pair cable A twisted pair consists of two conductors each surrounded by an insulating material. Note: Technical Focus: Why Twisted-Pair Cable Reduces Noise Interference from devices such as a motor can create unequal noise over two parallel lines. The line that is closer to the device receives more interference than the one that is farther. If however, the wires are twisted around each other at regular intervals, each wire is closer to the noise source for half of the time and farther for the other . | Chapter 7 Transmission Media Understand the difference between guided and unguided media. Be familiar with twisted-pair cable and the rationale for twisting. Be familiar with shielded twisted-pair cable and the rationale for shielding. Be familiar with coaxial cable. After reading this chapter, the reader should be able to: OBJECTIVES Understand how the air (or vacuum) can be a transmission medium for signals. GUIDED MEDIA Figure 7-1 Categories of guided media Figure 7-2 Twisted-pair cable A twisted pair consists of two conductors each surrounded by an insulating material. Note: Technical Focus: Why Twisted-Pair Cable Reduces Noise Interference from devices such as a motor can create unequal noise over two parallel lines. The line that is closer to the device receives more interference than the one that is farther. If however, the wires are twisted around each other at regular intervals, each wire is closer to the noise source for half of the time and farther for the other half. Both receive the same amount of noise. The noise from two wires cancel each other out at the receiver. Technical Focus: Categories of Twisted-Pair Cables Category 1: The basic cabling used for voice Category 2: Suitable for voice and data up to 4 Mbps Category 3: Suitable for data up to 10 Mbps Category 4: Suitable for data up to 16 Mbps Category 5: Suitable for data up to 100 Mbps Business Focus: Use of UDP in Telephone Network In the early days of the telephone network, the local loop, the two wires that connect a residence to the telephone office, was made of two parallel wires. The telephone companies later changed the local loop to a pair of twisted-pair wires, which is less prone to noise than the previous parallel wires. Figure 7-3 Shielded twisted-pair cable Technical Focus: Shielding and Lightning We can be immune from lightning in a desert if we are sur- rounded by a metallic cover (inside a car, for example). The reason is that electromagnetic energy (lightning) can .