Physical Layer notes for computer networks

Physical Layer notes for computer networks
Physical Layer directory

Purpose
Indicates that there are three basic forms of Data Network Media
Three basic functions
Four features
Several Basic Concepts about signals
Channel multiplexing
Width Access Technology
Signal bit for Media

Purpose

Creates an electrical signal, optical signal, or microwave signal to represent the bit in each frame.

Indicates that there are three basic forms of Data Network Media Copper cable

• Coaxial Cable
  • Advantages:
    • Good anti-interference capability, widely used for transmitting high-speed data
    • Twisted Pair wires
      • Communication distance:
        • Dozens of kilometers
        • Composition:
          
          Optical Cable
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            • Short-Wave Communication
              • The communication quality of short-wave channels is poor, but it mainly depends on the reflection of the electron.
              • Microwave Communication
                • Features:
                  • In space, it is mainly linear propagation.
                  • Category:
                    • Satellite Communication
                      • Advantages:
                        • Communication bandwidth
                        • Large communication capacity
                        • The received interference is small, and the transmission quality is high.
                        • Stable Communication
                        • Disadvantages:
                          • The adjacent stations must be directly connected without obstacles.
                          • Affected by bad weather
                          • Poor concealment and confidentiality compared with Cable Communication
                          • It is costly to use and maintain a large number of trunk stations.
                          • Large propagation latency
                          • Features:
                            • Long communication distance
                            • Ground Microwave Relay Communication
                              • Advantages:
                                • Communication bandwidth
                                • Large communication capacity
                                • The received interference is small, and the transmission quality is high.
                                • Stable Communication
                                • Disadvantages:
                                  • The adjacent stations must be directly connected without obstacles.
                                  • Affected by bad weather
                                  • Poor concealment and confidentiality compared with Cable Communication
                                  • Types of physical media that consume a large amount of use and maintenance for a large number of relay stations:
                                    Three basic functions

                                    Physical Components

                                    Data Encoding

                                    Signal

                                    Four features

                                    Mechanical PropertiesIndicates the shape and size of the connector used for the interface, the number and arrangement of leads, and the fixing and locking devices.

                                    Electrical PropertiesIndicates the range of voltage that appears on each line of the interface cable.

                                    FeaturesIndicates the significance of the voltage of an electric flat on a line.

                                    Process FeaturesSpecify the sequence of events that may occur for different functions

                                    Several Basic Concepts about signals

                                    TicketThere can be only one direction of communication without interaction in the opposite direction.

                                    Half DuplexBoth parties can send messages, but cannot send messages simultaneously (of course, they cannot receive messages at the same time)

                                    Full DuplexBoth parties can send and receive information simultaneously.

                                    Channel multiplexing

                                    OFDM

                                    • After a user allocates a certain frequency band, the user occupies this frequency band from start to end during communication.
                                    • All users of Frequency Division Multiplexing occupy different bandwidth resources at the same time (note that the "Bandwidth" here is the frequency bandwidth rather than the data transmission rate)

                                      TDM

                                      • DefinitionDivides the time into long time-division multiplexing frames (TDM frames) such as segment ). Each time division multiplexing user occupies a fixed serial number of time slots in each TDM Frame
                                      • FunctionAll users use the same band width at different times
                                      • DisadvantagesThis will cause a waste of line resources.

                                        WDM

                                        Optical Frequency Division Multiplexing Technology:

                                        The signal sent by the system has a strong anti-interference capability. Its spectrum is similar to white noise and is not easy to be detected by enemies. Each bit time is divided into m short intervals, which are called chips)

                                        Width Access Technology

                                        XDSL technology

                                        Category:

                                        • • ADSL(Asypolicric Digital Subscriber Line) Asymmetric Digital user Line
                                          • HDSL(High speed DSL) High speed digital user line
                                          • SDSL(Single-line DSL) Peer digital user line
                                          • VDSL(Very high speed DSL) extremely high-speed digital user line
                                          • RADSL(Rate-Adaptive DSL) Rate Adaptive

                                            Fiber-optic coaxial hybrid network

                                            Developed a residential broadband access network based on CATV of cable TV network
                                            

                                            FTTx Technology

                                            Fiber-to-xx broadband access network solution for residents

                                            Signal bit for Media

                                            Communication is transmitted one by one through physical media in the form of binary numbers

                                            You can change the signal to represent the signal on the media using one or more of the following features:

                                            • Amplitude
                                            • Frequency
                                            • Phase