This is the 19th day of my participation in the August Wenwen Challenge.More challenges in August

Overview of Computer Networks

The origin of the computer

  • The world’s first computer was created in 1946 at the University of California, Sydney, USA
  • In order to solve the missile trajectory calculation speed (instead of manual)
  • In fact, the German military used computers for missile trajectory calculations in 1938
  • Almost all inventions of man are used first to strike at his fellow men, and later to benefit them

Six stages in the development of computers and computer networks

< 1 > batch

  • Program cards, multiple people take turns using a computer

<2> Time-sharing system

  • A host serves multiple terminals at a time sharing time (using UNIX OS)

<3> Communication between computers

  • Computers communicate directly with each other

<4> The generation of computer networks

  • Many large American companies have launched their own lans. Such as: Ethernet, token network

<5> The popularity of the Internet

<6> Internet age

Currently, a typical network OS is used

  1. UNIX
  2. Windows
  3. Mac OS
  4. Novell

Computer network architecture

A five-tier protocol architecture

< 1 > the physical layer

  • Establish, manage, and release physical connections between network nodes using transport media for communication
  • Realize the transparent transmission of bitstream and provide data transmission service for data link layer
  • The data transfer unit at the physical layer is the bit

<2> Data link layer

  • On the basis of the services provided by the physical layer, the data link layer is in

Establish a data link connection between communicating entities

  • The transmission unit of the data link layer is “data frame”
  • Error control and flow control methods are used to turn error-free physical lines into error-free data links

< 3 > network layer

  • The routing algorithm is used to select the most appropriate path for the packet to pass through the communication subnet
  • Create logical links for data transmission between nodes, realize congestion control, network interconnection and other functions
  • A transport unit is a packet

< 4 > transport layer

  • Provide users with reliable end-to-end services
  • Handles packet errors, packet ordering, and other critical transport issues
  • As a key layer in computer communication system, the transmission layer shields the details of data communication from the lower layer

< 5 > the application layer

  • Network services are provided for the application
  • The application layer needs to identify and ensure the availability of communication partners, enabling synchronization between applications that work together
  • Establish control mechanisms to correct transmission errors and ensure data integrity

Entities, protocols, services, and service access points

< 1 > entity (entity)

  • Represents any hardware or software process that can send or receive information
  • Entities at the same layer on different machines are called peer entities.

< 2 > agreement

  • Is a set of rules that control the communication between two peer entities at a business line. That is, the protocol is horizontal
  • Under the control of the protocol, communication between two peer entities enables this layer to provide services to the next layer. To implement this layer protocol, you also need to use the services provided by the lower layer

< 3 > connection

  • A combination of two peer entities for a business line data communication

< 4 > services

  • Is a set of primitives or operations that each layer provides to its immediate upper layer through a layer interface, i.e. the service is “vertical”
  • Service users in this layer see only the service and not the underlying protocol. The following protocol is for the service user abovetransparent
    • Connection-oriented Services
      • The connection-oriented service has three phases: connection establishment, data transfer and connection release
    • Connectionless service (connectionless)
      • Communication between two entities does not require a connection to be established
      • It’s an unreliable service. The service is often described as “best effort delivery” or “best effort.”

The relationship between two layers

Characteristics of connection-oriented services

  • The data transmission process of connection oriented service must go through three stages: connection establishment, connection maintenance and connection release
  • The connection-oriented service transport connection is similar to a communication pipeline, in which the sender puts data in one end and the receiver takes it out from the other end, and the packet does not carry the address of the destination node during the data transmission
  • The connection-oriented data transmission has the same data order and good transmission reliability, but the protocol is complex and the communication efficiency is not high
  • It is suitable for sending many packets to the same destination within a certain period

Characteristics of connectionless services

  • The data transmission process in connectionless service does not need to go through connection establishment, connection maintenance and connection release
  • Each packet of a connectionless service carries the complete destination address, which is transmitted independently in the system
  • In the process of packet transmission, the packets received by the destination node may be out of order, repeated and lost
  • The connectionless service has poor reliability, but the protocol is relatively simple and the communication efficiency is high

Connection-oriented services are not the same as “reliable services”

The protocol is complicated

<5> Examples of famous protocols

Occupying two hilltopsThe blues’And the men stationed in the valleyWhite armyThe fight. The balance of power is: one blue army on a mountaintop can’t beat the White army, but two blue army on a mountaintop working together can beat the White army. The Blues on a hilltop planned to attack the Whites at noon the next day. They sent messages to friendly forces on top of another hill. But the communication lines were bad, and the possibility of error in the message was great. Therefore, friendly forces receiving the message must send a confirmation message. But the confirmation message can also be wrong. Can a protocol be devised that allows the Blues to work together and therefore win 100% of the time?

Such an agreement clearly cannot be achieved!

The TCP/IP architecture

  • TCP/IP protocol architecture

  • Indicates the TCP/IP protocol

  • The TCP/IP architecture used today on the Internet

  • TCP/IP protocol family

Everything Over IP IP over Everything IP serves a wide variety of applications

Client-server approach to Internet application layer

  • Client – server mode used by TCP/IP application layer protocols

  • A computer process, “process,” is a running computer program. Processes that communicate with each other to solve specific application problems are called “application processes”

  • The specific content of the application layer is to specify the protocol that application processes follow during communication

  • Client and server are two application processes involved in communication

  • The client-server approach describes the relationship between processes that serve and are served

  • The client is the service requester and the server is the service provider

  • The client and server processes communicate using the TCP/IP protocol

  • More powerful computers can run multiple server processes simultaneously

After the order

<1> What is the difference between a lowercase and an uppercase English name Internet and Internet?

  • Internet: The Internet is a general term that refers to the interconnection of multiple computer networks
  • Internet: The Internet is a term used to describe the world’s largest, open, specialized computer network consisting of numerous interconnected networks. It refers to the Internet that uses THE TCP/IP protocol
  • The Internet is actually a two-way application of the Internet

<2> Main differences between circuit switching, message switching and packet switching

  • Circuit switching is the establishment of a temporary dedicated channel, after the use of disconnecting, suitable for real-time communication of data volume
  • Message switching does not establish a path on the communication node, but combines the information into a message and adopts the virtual stored-forward mechanism, which has a high utilization rate of the line but a large delay
  • Packet switching is the packet exchange of fixed length, the buffer of switching node can be reduced, and the transmission delay is also smaller. Generally divided into packet, virtual circuit, cell switching

<3> Differences between network protocols and network services

  • Differences in definition
    • Network protocol A set of rules, standards, or conventions established for the exchange of data in a computer network. Protocol is rule, convention, and service is function, ability
  • Hierarchical differences
    • Network protocol is due to the complexity of the connection between network nodes. In the formulation of the protocol, the complex components are usually decomposed into some simple components, and then they are compounded. Protocol is the relationship between the peer layer of the communication parties, which is in the horizontal direction
    • A service is a vertical relationship between the upper and lower levels of communication and is provided from the bottom up
  • The difference between horizontal and vertical
    • The protocol is “horizontal”, that is, the protocol is the rule that controls the communication between two peer entities
    • The service is “vertical”, that is, the service is provided from the lower layer to the upper layer through the layer indirect port. The upper layer using the provided services must exchange commands with the lower layer, which are called service primitives in OSI

They combine. A protocol is a horizontal relationship between the peers of the communication parties, while a service is a vertical relationship between the upper and lower levels of communication at one end, and is provided from the bottom up

  • The difference between horizontal and vertical
    • The protocol is “horizontal”, that is, the protocol is the rule that controls the communication between two peer entities
    • The service is “vertical”, that is, the service is provided from the lower layer to the upper layer through the layer indirect port. The upper layer using the provided services must exchange commands with the lower layer, which are called service primitives in OSI