89 core concepts of computer networks

Hey guys, this is cxuan. Welcome to read my latest article. As you all know, I have been serializing computer networks for a certain period of time. When I learn about a new technology or new framework, I want to name it first. To understand what the concept is, it can be seen that the concept is very helpful to us. The concepts in computer networks are also very complicated and difficult to understand. So here, I have summarized 89 common concepts in computer networks, and I hope it will be helpful to you.

1. host: Any device on a computer network that can connect to the network is called a host or end system, such as mobile phones, tablets, TVs, game consoles, cars, etc. With the advent of 5G, there will be more More and more terminal devices are connected to the network.
2. Communication link: A communication link is a physical path that is connected by physical links (coaxial cable, twisted pair, fiber optic lights).
3. Transmission rate: The unit is bit/s or bps, used to measure the data transmission rate of different links from one end system to another.
4. grouping: When one end system sends data to another end system, it usually divides the data into pieces, and then adds the first byte to each segment, thus forming the professional term for computer networks: grouping. These packets are sent to the end system through the network, and then the data is processed.
5. router: It is the link layer switch , which is a kind of switch, mainly used for the purpose of forwarding data.

6. path: a series of communication links and packet switches that a packet has gone through is called the path through this network.
7. Internet service provider: also called ISP, not lsp. This is easy to understand, that is, network operators, China Mobile, China Telecom, and China Unicom.
8. network protocol: The network protocol is a rule, standard or agreement established for data exchange in a computer network.
9. IP : Internet Protocol, which specifies the packet format sent and received between the router and the end system.
10. TCP/IP protocol cluster: not only TCP protocol and IP protocol, but a series of protocols based on TCP and IP protocol, such as ICMP protocol, ARP protocol, UDP protocol, DNS laundry, SMTP protocol, etc.
11. Distributed application: An end system that exchanges data between multiple end systems is called a distributed application.
12. socket interface: refers to the socket interface, this interface specifies the way of data exchange between end systems via the Internet.
13. protocol: The protocol defines the standards followed by the format and sequence of messages exchanged between two or more communicating entities.
14. 160da9ad4981d9 Client role of the requester in the client-server architecture, usually end systems such as PCs and smartphones.
15. server: plays the role of the server in the client-server architecture, usually a large server cluster plays the role of the server.
16. forwarding table: a record of the mapping relationship of the message path inside the route.
17. Delay: Delay refers to the time required for a message or packet to be transmitted from one end of the network to the other end. Delays are classified into transmission delay, propagation delay, processing delay, queuing delay, and total delay. = Transmission delay + propagation delay + processing delay + queuing delay.
18. Packet loss: refers to the phenomenon of packet loss in computer networks.
19. Throughput: Throughput refers to the number of successfully transmitted data per unit time in a computer network.
20. message: usually refers to the application layer grouping.
21. message segment: The grouping of the transport layer is usually called a message segment.
22. Datagram: Usually the network layer grouping is called a datagram.
23. frame: Generally, the grouping of the link layer is called a frame.
24. customer-service system: it is a network application-oriented architecture. The different end systems in the system are divided into two types: client and server. The client sends a service request to the server, and the server completes the requested service, and sends the processing result back to the client. In the client-server architecture, there is a host that is always open called server (Server), which provides services from client (client). Our most common server is the Web server, which serves requests browser.

25. CIDR : Use any length to separate the network ID and host ID of the IP address
26. P2P system: Peer-to-peer architecture, which is equivalent to no server. Everyone is a client. Each client can send and respond to requests.

27. IP address: IP address is the Internet Protocol address, an address that uniquely identifies a host on the Internet. Every device connected to the network will have an IP address, which is divided into internal network IP and public network IP.
28. port number: In the same host, the port number is used to identify different application processes.
29. URI : Its full name is (Uniform Resource Identifier), and the Chinese name is the Uniform Resource Identifier. Using it, you can uniquely mark resources on the Internet.
30. URL : Its full name is (Uniform Resource Locator), the Chinese name is Uniform Resource Locator, which is actually a subset of URI.

31. HTML : HTML is called hypertext markup language, which is a kind of marking language. It includes a series of tags. Through these tags, the document format on the network can be unified, and the scattered Internet resources can be connected as a logical whole. HTML text is descriptive text composed of HTML commands. HTML commands can describe text, graphics, animations, sounds, tables, links, etc.
32. Web page: Web page is also called Web Page , it is composed of objects, a object (object) is simply a file, this file can be an HTML file, a picture, a Java application, etc., they can all pass URI Come find. A Web page contains many objects, and a Web page can be said to be a collection of objects.
33. Web server: The official name of the Web server is Web Server . The Web server can provide documents to web clients such as browsers, and can also place website files for the world to browse; data files can be placed for the world to download. The three most mainstream web servers are Apache, Nginx, and IIS.
34. CDN : The full name of CDN is Content Delivery Network , that is, content distribution network. It uses the cache and proxy technology in the HTTP protocol to replace the origin site to respond to the client's request. CDN is a network built on the basis of the existing network. It relies on edge servers deployed in various places, through the load balancing, content distribution, scheduling and other functional modules of the central platform, so that users obtain the required content nearby and reduce network congestion. Improve user access response speed and hit rate.
35. WAF : WAF is a application protection system , which is a product that provides protection for web applications by implementing a series of security policies firewall that specializes in Detecting HTTP traffic is a security technology to protect Web applications.
36. WebService : WebService is a Web application, WebService is a cross-programming language and cross-operating system platform remote call technology .
37. HTTP : A type of TCP/IP protocol suite, which is a convention and specification for transmitting text, pictures, audio, video and other hypertext data between two points in the computer world.
38. Session : Session is actually a cache of client sessions, which is designed to compensate for the stateless nature of HTTP. The server can use Session to store some operation records of the client during the same session. When the client requests the server, the server will open up a memory space for this request. This object is the Session object, and the storage structure is ConcurrentHashMap .
39. Cookie : Cookies in the HTTP protocol include Web Cookie and browser cookies, which are a small piece of data sent by the server to the web browser. The cookie sent by the server to the browser will be stored by the browser and sent to the server together with the next request. Usually, it is used to determine whether two requests are from the same browser, for example, the user remains logged in.
40. SMTP protocol: The protocol that provides e-mail services is called the SMTP protocol, and SMTP also uses the TCP protocol in the transport layer. The SMTP protocol is mainly used to transfer mail information between systems and provide notifications about incoming letters.
41. DNS protocol: Since the IP address is an address that can be recognized by the computer, and it is inconvenient for us humans to remember this kind of address, in order to facilitate human memory, the DNS protocol is used to call our easy-to-remember network address mapping as the host can recognize IP address.

42. TELNET protocol: Telnet protocol, which allows the user (Telnet client) to communicate with a remote device through a negotiation process. It provides the user with the ability to complete remote host work on the local computer.

43. SSH protocol: SSH is a secure encryption protocol built on the application layer. Because TELNET has a very obvious disadvantage, that is, when the host and remote host send data packets, it is transmitted in plain text without any security encryption. The consequence is that it is easy to sniff the data packets by criminals on the Internet. Some bad things, for data security, we generally use SSH for remote login.
44. FTP protocol: file transfer protocol, one of the application layer protocols. The FTP protocol includes two components, which are divided into FTP server and FTP client. The FTP server is used to store files, and users can use the FTP client to access the resources located on the FTP server through the FTP protocol. The FTP protocol is very efficient and is generally used to transfer large files.

45. MIME type, it represents the type of Internet resources, general types include hypertext markup language text.html text/html, xml document.xml text/xml, ordinary text.txt text/plain, PNG image.png image/png , GIF graphics.gif image/gif, JPEG graphics.jpeg,.jpg image/jpeg, AVI files.avi video/x-msvideo, etc.
46. : At the receiving end, the transport layer will check the source port number and destination port number and other fields, and then identify the receiving socket, so as to deliver the data of the transport layer segment to the correct socket. It is called demultiplexing.
47. Multiplexing: At the sender, data blocks are collected from different sockets, and then header information is encapsulated for the data blocks to generate message segments, and then the process of passing the message segments to the network layer is called multiple Multiplexing.
48. known port number: In the host application, the port number from 0 to 1023 is restricted and is called a well-known port number. Generally, these port numbers cannot be occupied.
49. One-way data transmission: The flow of data can only be one-way, that is, from the sending end -> the receiving end.
50. Two-way data transmission: The flow of data is two-way, also called full-duplex communication, and the sender and receiver can send data to each other.
51. connection-oriented handshake before an application process sends data to another application process, that is, they must first send a preparatory segment to each other to establish parameters to ensure data transmission.
52. Three-way handshake: The establishment of a TCP connection requires three message segments to be sent. The process of establishing this connection is called a three-way handshake.

53. Maximum segment length: MSS, which refers to the maximum value taken from the cache and put into the segment.
54. Maximum Transmission Unit: MTU, which refers to the size of the payload that both parties can receive. MSS is usually set according to MTU.
55. Redundant ACK: It is to reconfirm the ACK of a certain segment. The loss of the segment will cause the appearance of redundant ACK.
56. fast retransmission: Retransmit the lost segment before the segment timer expires.
57. Selection confirmation: In the case of packet loss, TCP can choose to confirm the out-of-sequence packet. This mechanism is usually used together with retransmission.
58. Congestion control: Congestion control refers to a way to restrain the sender from sending data when there are too many packets in the network for a certain period of time, making the receiving end too late to process, causing part or even the entire network to degrade. A method to continue sending segments after a period of time or after the network condition improves.
59. waved four times: TCP disconnection requires four message segments to be sent. This disconnection process is waved four times.

60. routing algorithm: an algorithm that determines the packet transmission path in the network layer.
61. forwarding: It refers to the action of transferring packets from an input link to a suitable output link.
62. Packet Scheduling: Packet scheduling discusses how packets are transmitted via the output link. There are three main scheduling methods: first-in first-out, priority queuing, and "round-robin and weighted fair queuing".
63. IPv4 : The fourth version of the Internet Protocol, which is also a widely used version. IPv4 is a connectionless protocol, and connectionless does not guarantee the reliable delivery of data. Use 32-bit addresses.
64. IPv6 : The sixth version of the Internet Protocol. The IPv6 address length is 128 bits. The biggest problem with IPv4 is the lack of network address resources, which severely restricts the application and development of the Internet. The use of IPv6 not only solves the problem of the number of network address resources, but also solves the barriers for multiple access devices to connect to the Internet.
65. interface: the boundary between the host and the physical link.
66. ARP protocol: ARP is a protocol to solve the address problem. Through the IP bit clues, the MAC address of the next network device used to receive data can be located. If the target host and the host are not on the same link, you can find the address of the next hop route through ARP. However, ARP only applies to IPv4, not IPv6.
67. RARP : RARP is a protocol that reverses the ARP protocol and locates the IP address through the MAC address.

68. Proxy ARP: Used to solve the situation that ARP packets are isolated by routers. Through proxy ARP, ARP requests can be forwarded to adjacent network segments.
69. ICMP protocol: Internet Message Control Protocol. If an IP packet fails to reach the target host for some reason during IP communication, then an ICMP message will be sent. ICMP is actually a part of IP.

70. DHCP protocol: DHCP is a dynamic host configuration protocol. Use DHCP to automatically set IP addresses, manage IP address allocation uniformly, and achieve plug and play.
71. NAT protocol: Network address translation protocol, it means that when all hosts with local addresses access the network, they will be translated into global IP addresses on the NAT router before they can communicate with other hosts.
72. IP tunnel: IP tunnel technology refers to the process in which the router encapsulates the network layer protocol into another protocol so as to cross the network and transmit to another router.
73. Unicast: The biggest feature of unicast is one-to-one. Early fixed telephones are an example of unicast.

74. Broadcasting: We usually broadcast gymnastics when we were young. This is an example of broadcast. The host is connected to all end systems connected to him, and the host sends signals to all end systems.

75. Multicast: Multicast is very similar to broadcast. It also sends messages to multiple receiving hosts. The difference is that multicast needs to be limited to a certain group of hosts as the receiving end.

76. Anycast: Anycast is a communication method in which a receiver is selected from a specific multiple hosts. Although it is similar to multicast, its behavior is different from multicast. Anycast selects a host that best meets the network conditions from many target clusters as the target host to send messages. Then the selected specific host will return a unicast signal, and then communicate with the target host.

77. IGP : Internal gateway protocol, generally used for routing autonomous systems built by enterprises.
78. EGP : External Gateway Protocol, EGP is usually used to exchange routing information between network hosts.
79. RIP : A distance vector routing protocol, widely used in LAN networks.
80. OSPF : is a link state protocol based on OSI’s IS-IS protocol. This kind of agreement can also effectively solve the network loop problem.
81. MPLS : It is a label switching technology. The label switching sets a label for each IP data packet, and then forwards it according to this label.
82. node: generally refers to the equipment in the link layer protocol.
83. link: The communication channel that connects adjacent nodes along the communication path is generally called a link.
84. MAC protocol: media access control protocol, which specifies the rules for frame transmission on the link.
85. parity bit: an error detection method, mostly used in computer hardware error detection, parity is usually used in data communication to ensure the validity of data.
86. Forward Error Correction: The receiver's ability to detect and correct errors is called forward error correction.
87. Ethernet: Ethernet is the most common local area network technology today. It specifies the physical layer connections, electronic signals, and the content of the MAC protocol.
88. VLAN : A virtual local area network (VLAN) is a group of logical devices and users. These devices and users are not restricted by their physical location. They can be organized according to factors such as functions, departments, and applications. The communication between each other is like They are the same in the same network segment, so they are called virtual local area networks.
89. base station: wireless network infrastructure.

postscript

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