TAILIEUCHUNG - Lecture Data communications and networks: Chapter 3 - Forouzan 

One of the major functions of the physical layer is to move data in the form of electromagnetic signals across a transmission medium. Whether you are collecting numerical statistics from another computer, sending animated pictures from a design workstation, or causing a bell to ring at a distant control center, you are working with the transmission of data across network connections. Chapter 3 discusses the relationship between data, which are created by a device, and electromagnetic signals, which are transmitted over a medium. | Chapter 3 Data and Signals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. To be transmitted, data must be transformed to electromagnetic signals. Note 3. 3-1 ANALOG AND DIGITAL Data can be analog or digital. The term analog data refers to information that is continuous; digital data refers to information that has discrete states. Analog data take on continuous values. Digital data take on discrete values. Analog and Digital Data Analog and Digital Signals Periodic and Nonperiodic Signals Topics discussed in this section: 3. Note Data can be analog or digital. Analog data are continuous and take continuous values. Digital data have discrete states and take discrete values. 3. Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. Note 3. Figure Comparison of analog and digital signals 3. In data communications, we commonly use periodic analog signals and nonperiodic digital signals. Note 3. 3-2 PERIODIC ANALOG SIGNALS Periodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves. Sine Wave Wavelength Time and Frequency Domain Composite Signals Bandwidth Topics discussed in this section: 3. Figure A sine wave 3. We discuss a mathematical approach to sine waves in Appendix C. Note 3. The power in your house can be represented by a sine wave with a peak amplitude of 155 to 170 V. However, it is common knowledge that the voltage of the power in . homes is 110 to 120 V. This discrepancy is due to the fact that these are root mean square (rms) values. The signal is squared and then the average amplitude is calculated. The peak value is equal to 2½ × rms value. Example 3. Figure Two signals with the

• Quản trị mạng
• Data communications
• Lecture Data communications
• Physical layer
• Data link layer
• Digital Data
• Digital Signals
• Business data communications
• Network criteria
• Data communications system
• Data communications networks
• Media access control
• Network models
• Network standards
• Application layer
• Application architectures
• Digital transmission
• Network and transport layers
• Transport layers
• Local area networks
• Traditional ethernet
• Wireless local area networks
• Wireless LANs
• Backbone networks
• Backbone network architectures
• Circuit switched networks
• Wide area networks
• Network security
• Risk assessment
• Network design
• Traditional network design
• Network management
• Configuration management