Physical Layer notes of computer network, physical layer of Computer Network

Physical Layer notes of computer network, physical layer of Computer Network
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

• Category:
  • Single-Mode Optical Fiber
  • Multimode Optical FiberDisadvantage: optical pulse will cause distortion during transmission loss
• Advantages:
  • Large traffic volume
  • Low Transmission Loss
  • Good anti-lightning and electromagnetic interference capabilities
  • Small size, light quality
• Disadvantages:
  • Accurate connection with dedicated devices

Wireless Media

• 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
        • It is costly to use and maintain a large number of trunk stations.

Physical media type:

 

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:

Code Division Multiplexing CDM

• FunctionDifferent users use different code types that have been specially selected, so they will not interfere with each other.
• FeaturesThe signal sent by this system has a strong anti-interference capability, and its spectrum is similar to white noise, which is not easy to be detected by enemies. Each bit time is divided into m short intervals, called chip)

 

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

Questions about the computer network Physical Layer

The physical layer is mainly used for transmission and conversion of electrical signals. Regardless of the communication, both parties must eventually connect to each other through the transmission media. Different Media (coaxial cable, twisted pair wire, radio, etc) it has different features, so signal conversion is required. The main features of the physical layer include:
Electrical Characteristics: What signal is used to represent 1.0
Mechanical Characteristics: connector size, core number, core arrangement, connection root number, commonly used 25-core, 24, 37, 15
Features: functions of each pin of the connector
Specifications: Relationship between time series and operation process.
Both the physical layer and the data link layer belong to the media layer.

Q: What are the main tasks of the physical layer in the computer network?

The main function of the physical layer is to shield the differences between different hardware devices and transmission media, so that the data link layer on the upper layer only needs to consider services and protocols at the layer, rather than hardware devices and transmission media.