Network planning designer (1)

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This series of articles is written on the basis of the network planning designer tutorial book. The early stage is a summary and induction of the knowledge points of the network planning designer tutorial book. It is similar to the knowledge points in the tutorial, because the network planning designer exam design The knowledge points in the tutorial are not limited to the content of the tutorial, and some knowledge points are not detailed enough. Therefore, while summarizing the knowledge points in the tutorial, we will supplement the simpler knowledge points in the tutorial. During the summary process, such as If new knowledge points are discovered, they will be added in time on the basis of the original article. Later, new technologies that have emerged in recent years will be described later, because the author is also learning. If you find deficiencies, please give feedback in time. Thank you all. I have learned network-related knowledge, passed the network planning designer's exam, study together and make progress together, thank you.

1 Principles of Computer Networks

1.1 Introduction to Computer Networks

1.1.1 Computer network concept

1.1.1.1 Definition of computer network

A computer network is a system that connects a distributed computer system with independent functions through communication equipment and lines, and realizes resource sharing by software with perfect functions.

There are three main points of view for the understanding of computer networks:

1. Broad view: As long as a system that can realize remote information processing or a system that can further achieve resource sharing, it can become a computer network.
2. Resource sharing viewpoint: A computer network must be a system that is composed of computers with independent functions and can realize resource sharing.
3. User transparency point of view: A computer network is a supercomputer with rich resources and powerful functions. Its use is transparent to users. Users use the network as if they are using a single computer, without knowing the existence of the network, the location of resources, and other information.

Common computer application directions:

• Centralized and real-time processing of scattered information. For example: aviation booking system, industrial control system, military system, etc.
• Sharing resources, realizing the sharing of various resources, including information resources, hardware resources, and software resources.
• Electronic office and service. For example, modern office and business applications such as e-government, e-commerce, e-banking, e-customs, etc. realized with the help of computer networks.
• Communication. For example, the communication function of e-mail and instant messaging system.
• Distance Education. Using the Internet to provide a distance education platform, and with the help of a knowledge management system, students can learn more conveniently on their own and improve their learning efficiency.
• entertainment. Use the Internet to provide a variety of entertainment content.

1.1.1.2 The relationship between computer network, communication and network

Communication is the transfer of information, which refers to the transmission and exchange of information from one place to another, and its purpose is to transmit messages. The system that realizes the communication function is called the communication system. Among various communication methods, the communication method that uses "electricity" to transmit messages is called telecommunications, which is characterized by speed, accuracy, and reliability, and is hardly restricted by time, location, space, and distance. The communication systems are classified for different purposes, as follows:

• The communication system established for the main purpose of voice communication is called telephone network or telecommunications network;
• A communication system established for the purpose of transmitting TV signals is called a TV network;
• A network established for the purpose of data communication is called a data communication network.

Computer network is the product of the combination of computer technology and communication technology, which can realize the transmission, collection, distribution, processing, storage and consumption of data.

1.1.2 Computer network composition

1.1.2.1 Physical composition of computer network

The physical components of a computer network include: hardware, software, and protocols.

1.1.2.1.1 Hardware

• Two or more computers and terminal devices are collectively referred to as hosts, some of which act as servers and some of them act as clients.
• The front-end processor (FEP) or communication processor or communication control processor (CCP) is responsible for sending and receiving data. The simplest CCP is a network card.
• Connecting devices such as routers and switches, switches connect computers into networks, and routers interconnect networks to form a larger network.
• Communication lines, which specifically complete the transmission of signals from one place to another, include wired lines and wireless lines.

1.1.2.1.2 Software

There are mainly software that realizes resource sharing and various tool software that are convenient for users to use.

1.1.2.1.3 Agreement

The protocol is composed of grammar, semantics and time sequence, and the functions of each part are as follows:

• Syntax: specify the format of the transmitted data;
• Semantics: specify the function to be completed;
• Time sequence: stipulate the conditions and sequence relationships for performing various operations.

Protocol is the core of computer network. The functions that a complete protocol needs to complete are as follows:

• Line management
• Addressing
• Error control
• flow control;
• Routing
• Synchronization control
• Data segmentation and assembly;
• Sort
• Data conversion
• Safety management;
• Billing management.

1.1.2.2 Computer network function composition

In terms of function, a computer network consists of a resource subnet and a communication subnet. The relationship between the two is shown in the figure below, and its functions are as follows:

• Resource subnet: complete data processing and storage, equivalent to a computer system;
• Communication subnet: complete data transmission, it is the additional communication equipment and communication line for connecting to the network.
  
  In terms of working methods, a computer network consists of an edge part and a core part. The relationship between the two is shown in the figure below, and its functions are as follows:
• Edge part: the host directly used by the user;
• Core part: Consists of a large number of networks and routers, providing connectivity and switching services for the edge.
  

1.1.2.3 Composition of computer network elements

In terms of its components, computer networks include computers, routers, switches, network cards, communication lines, modems, etc. The functions of each element are as follows:

• Computer: including client and server;
• Network card: Attached to the computer, there is also an external network card such as a USB interface, which is responsible for connecting with the communication line to complete the sending and receiving work;
• Switch: used to connect a small range of computers into a network;
• Router: used to interconnect multiple networks to form a larger network;
• Modem: Connect an isolated computer to the network, such as audio modem, ADSL modem, satellite modem, etc.

1.1.3 Computer network classification

1.1.3.1 Classification by distribution range

According to the distribution range, the computer network can be divided into wide area network, metropolitan area network, local area network and personal area network. The description is as follows:

• Wide Area Network (WAN): Generally distributed in areas above tens of kilometers.
• Metropolitan Area Network (MAN): Generally distributed in an urban area, the technology of wide area network is generally used, and one can be regarded as a smaller wide area network.
• Local area network (LAN): Generally distributed in the range of tens of meters to several kilometers. Traditionally, wide area networks use switching technology, and local area networks use broadcast technology.
• Personal area network (PAN): generally refers to the network carried by the family or even individuals, generally distributed within a few meters, used to connect household appliances, consumer electronic equipment, and a small number of computer equipment into a small network to adopt wireless communication Mainly way.

1.1.3.2 Classified by topology

According to the topological structure, the computer network can be divided into basic forms such as bus network, star network, ring network, tree network, grid network, etc. The network topology structure diagram is shown in the figure below, and the specific instructions are as follows:

1. Bus-type network: Connect computers with a single bus.
   Its advantages are: easy to build a network, convenient to add or remove nodes, and save lines.
   The disadvantage is that the communication efficiency is not high under heavy load.
2. Star network: Each terminal or computer is connected to the central device by a separate line, and the central device is generally a switch or router.
   Its advantages are: simple structure, easy network construction, low delay, and easy management.
   The disadvantages are: high cost, and the central node is sensitive to failures.
3. Ring network: All computer ring interface devices are connected into a ring, which can be a single ring or a double ring. The signal in the ring is transmitted in one direction. The transmission direction of the signals on the two rings in the double ring network is opposite, and it has the function of self-healing. .
4. Tree network: The nodes are organized into a tree structure, which is hierarchical.
5. Mesh network: In general, each node has at least two paths connected to other nodes.
   Grid type networks are divided into regular and irregular types.
   Its advantage is: high reliability.
   Its disadvantages are: complicated control and high line cost.

1.1.3.3 Classification by exchange technology

According to the switching technology, the network can be divided into line switching network, message switching network, and packet switching network.

1. Circuit switching network: A dedicated path is established between the source node and the destination node for data transmission, including three stages: connection establishment, data transmission, and disconnection. A typical circuit switching network is a telephone network.
   Its advantage is: the data is transmitted directly, the delay is small.
   The disadvantages are: low line utilization, inability to make full use of line capacity, and inconvenient error control.
2. Message switching network: encapsulate user data with source address, destination address, length, check code and other auxiliary information into a message, and send it to the next node. After the next node receives the message, it temporarily stores the message, and then forwards it to the next node when the output line is free, and repeats this process until it reaches the destination node. This type of network is also called a store-and-forward network.
   Its advantages are:
   ① It can make full use of line capacity (multiplexing technology can be used, and idle time can be used);
   ② It can realize the conversion of different data rates between different links;
   ③ It can realize one-to-many and many-to-one access ;
   ④ error control may be implemented;
   ⑤ format conversion can be realized.
   The disadvantages are:
   ① Increased resource overhead, such as auxiliary information leading to time and storage resource overhead;
   ② Increased buffer delay;
   ③ The sequence of multiple messages may be wrong, and additional sequence control mechanisms are required;
   ④ Buffers are difficult to manage because of the The size of the message is uncertain, and the receiver cannot predict the size of the message before receiving the message.
3. Packet switching network: also known as packet switching network, its principle is to divide data into shorter fixed-length data blocks, add destination address, source address and other auxiliary information to each data block to form packets, and transmit them in a store-and-forward manner .
   Its advantages:
   ① It can make full use of line capacity (multiplexing technology can be used, and idle time can be used);
   ② It can realize the conversion of different data rates between different links;
   ③ It can realize one-to-many and many-to-one access;
   ④ Error control can be realized;
   ⑤ Format conversion can be realized;
   ⑥ The buffer is easy to manage;
   ⑦ The average delay of packets is smaller, and the average buffer occupied in the network is less;
   ⑧ Easier to standardize;
   ⑨ More suitable for application.

1.1.3.4 Classification by agreement

According to the key protocols of the network layer, it can be divided into: IP network, IPX network, etc.; wireless network can be divided into Wi-Fi network, Bluetooth network.

1.1.3.5 Classification by transmission media used

According to the transmission medium, it is divided into two categories: wired network and wireless network.
Wired networks are classified as follows:

1. Twisted pair network;
2. Coaxial cable network;
3. optic fiber network;
4. Hybrid fiber coaxial network.

The wireless networks are classified as follows:

1. radio;
2. microwave;
3. Infrared.

1.1.3.6 Classification according to the degree of relevance between users and the network

The computer network can be divided into backbone network, access network and resident network according to the degree of user and network association.

1.1.4 Network Architecture

1.1.4.1 Layering and Architecture

The network architecture refers to the precise definition of the functions that constitute the various components of the computer network and the computer network itself. The network is very complex. In order to facilitate research and discovery, it needs to be modeled in the way of architecture. The architecture usually has the characteristics of layering. The basic principles of layering are as follows:

• The interface between the layers is clear and natural, easy to understand, and communicate with each other as little as possible;
• The definition of each layer function is independent of the specific realization method;
• Maintain the independence of the lower layer from the upper layer, and use the services provided by the lower layer in one direction.

1.1.4.2 Interface, protocol and service

• Interface refers to the rules of communication between two adjacent levels within the same system.
• Protocol refers to the rules of communication between corresponding layers that implement the same function between the two parties. The protocol consists of syntax, semantics and timing.
  ① Syntax: specify the format of the transmitted data;
  ② Semantics: specify the functions to be completed;
  ③ Timing: specify the conditions and sequence relationships for performing various operations.
  
• Service refers to the function call provided for the immediately adjacent upper layer. Each layer can only call the service provided by the immediately adjacent lower layer, and the service is provided through the service access point (SAP). The services provided by computer networks are divided into three categories, as follows:
  
  ① Connection-oriented service and connectionless service;
  connection-oriented service: refers to the establishment of a connection between the two parties before the communication, and then the data can be transmitted. After the transmission is completed, the connection needs to be released, such as : Make a call;
  connectionless service: it means that the two parties do not establish a connection before communicating, and when data needs to be sent, they are sent directly, for example: writing letters are delivered by the post office.
  ② Response service and non-response service;
  response service: refers to that the receiver gives the corresponding response to the sender after receiving the data, and the response is automatically realized by the transmission system, not by the user, such as: file transfer service ;
  No response service: the receiver does not automatically give a response after receiving the data. If a response is needed, it is implemented by the higher layer, such as: WWW service.
  ③ Reliable service and unreliable service.
  Reliable service: means that the network has error detection, error correction, and response mechanisms to ensure that data is correctly and reliably transmitted to the destination;
  unreliable service: means that the network cannot guarantee that the data is correctly and reliably transmitted to the destination, and the network is only as correct as possible. Reliability is a best-effort service.

1.1.4.3 Data transfer unit

• Service data unit SDU: The data that should be transmitted in order to complete the function required by the user. The service data unit of the Nth layer is recorded as N-SDU;
• Protocol control information PCI: information that controls the operation of the protocol, and the protocol control information of the Nth layer is recorded as N-PCI;
• Protocol data unit PDU: The data unit of protocol exchange. The protocol data unit of the Nth layer is denoted as N-PDU.

The relationship between the three: N-SDU+N-PCI=N-PDU=(N-1)SDU.

1.1.4.4 OSI/ISO and TCP/IP architecture model

The relationship between the OSI structure model and the TCP/IP architecture model is shown in the following figure:

1.1.4.4.1 OSI model

The International Standardization Organization (ISO) proposed a network architecture model in 1978, called the Open System Interconnection Reference Model (OSI). OSI has 7 layers, from low to high: physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer. The OSI model hierarchy is as shown in the figure below, and the functions of each layer are as follows:

• Physical layer: Transmit bits transparently on the link. The work that needs to be completed includes: line configuration, determining the data transmission mode, determining the signal form, encoding the signal, and connecting the transmission medium.
• Data link layer: Turn unreliable channels into reliable channels, group bits into frames, provide point-to-point frame transmission on the link, and perform error control and flow control.
• Network layer: Route selection, congestion control, sequence control, and packet transmission between the source node and the destination node to ensure the correctness of the message. The network layer controls the operation of the communication subnet, so it is also called the communication subnet layer.
• Transport layer: Provide reliable and transparent data transmission between end-to-end to ensure the correctness of message sequence and data integrity.
• Session layer: Establish the connection between the logical name and physical name of the communication process, provide methods for establishing, managing, and terminating sessions between processes, and handle synchronization and recovery issues.
• Presentation layer: Realize data conversion, provide standard application interfaces, public communication services, and public data presentation methods.
• Application layer: Various services that are opaque to users, such as E-mail.

1.1.4.4.2 TCP/IP model

The US Department of Defense Advanced Research Projects Agency (DOD-ARPA) proposed the TCP/IP model in 1969 when studying ARPANET, from low to high: network interface layer, Internet layer, transport layer, application layer, the TCP/IP structure model is shown in the figure below As shown, the main protocols of each layer are as follows:

• Application layer: DNS, HTTP, SMTP, POP3, FTP, TELNET, SNMP;
• Transport layer: TCP, UDP;
• Internet layer: IP, ICMP, ARP, RARP.