89 Core Concepts of Computer Networks

主机: Any device on a computer network that can connect to the network is called a host 端系统, such as mobile phones, tablets, TVs, game consoles, cars, etc. With the arrival of 5G, there will be more and more terminal devices Access the network.
Communication link: A communication link is a physical path composed of physical links (coaxial cables, twisted pairs, optical fibers, etc.) connected together .
Transmission rate: The unit is bit/s or bps, used to measure the rate at which different links transmit data from one end system to another.
Packeting: When one end system sends data to another end system , the data is usually fragmented and header bytes are added to each segment , forming the technical term for computer networks: packetization . These packets are sent over the network to the end system where the data is processed.
Router: Like a link layer switch , it is a type of switch and is mainly used for forwarding data.
Path: A series of communication links and packet switches that a packet travels through is called a path through the network.
Internet Service Provider : Also called ISP, not lsp. It is easy to understand that it is network operators , such as China Mobile, China Telecom and China Unicom.
Network protocol: Network protocol is the rules, standards or conventions established for data exchange in computer networks .
ip: Internet Protocol, which specifies the format of packets sent and received between routers and end systems.
TCP/IP protocol cluster : not only TCP protocol and IP protocol, but a series of protocols based on TCP and IP protocols, such as ICMP protocol, ARP protocol, UDP protocol, DNS protocol, SMTP protocol, etc.
Distributed Application: An end system in which multiple end systems exchange data with each other is called a distributed application.
Socket interface : refers to the socket interface. This interface specifies the way for data exchange between end systems through the Internet .
Protocol: The protocol defines the standards followed by the format and sequence of messages exchanged between two or more communication entities.
Client: Plays the role of the requester in the client-server architecture, usually a PC, smartphone and other terminal systems.
Server: plays the role of the server in the client-server architecture, usually a large server cluster plays the role of the server.
Forwarding table: A record that records the mapping relationship of message paths internally in routing.
Delay: Delay refers to the time it takes for a message or packet to be transmitted from one end of the network to the other. Delay classification includes sending delay, propagation delay, processing delay, and queuing delay. Total delay = Sending delay + propagation delay + processing delay + queuing delay.
Packet loss: In computer networks, it refers to the phenomenon of packet loss.
Throughput: Throughput in computer networks refers to the amount of data successfully transmitted per unit time .
Packet: Usually refers to a packet at the application layer. It is the basic unit of communication in a computer network. It is a block of data sent in a network transmission to pass information between different computers or devices. A message usually consists of a message header and a body.
Message segment: The packets at the transport layer are usually called message segments. Segment is a unit of data used for transport layer communication in a computer network. It is a data structure located above the network layer (IP layer) and below the transport layer (such as TCP or UDP). A message segment consists of a message segment header and a data part.
Datagram: Network layer packets are usually called datagrams.
Frame: Generally, the grouping of the link layer is called a frame.
Client-service system : It is a network application -oriented architecture. Different end systems in the system are divided into two categories: 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 a client-server architecture, there is an always-on host called , which provides services 服务器(Server)from . 客户(client)Our most common server is that of Web 服务器a web server serving 浏览器 requests from .
CIDR: Split the network identifier and host identifier of an IP address using any length.
P2P system: Peer-to-peer architecture, which is equivalent to no server. Everyone is a client. Each client can both send requests and respond to requests.
IP address: It is an Internet Protocol address, an address that uniquely identifies a host on the Internet. Every device connected to the network will have an IP address, and this IP is divided into internal IP and public IP.
Port number: Within the same host, port numbers are used to identify different application processes.
URI: Its full name is (Uniform Resource Identifier), and its Chinese name is Uniform Resource Identifier . It can be used to uniquely mark resources on the Internet.
URL: Its full name is (Uniform Resource Locator), and its Chinese name is Uniform Resource Locator. It is actually a subset of URI.
HTML: HTML is called Hypertext Markup Language and is a markup language. It includes a series of tags. Through these tags, the document format on the network can be unified and scattered Internet resources can be connected into a logical whole. HTML text is descriptive text composed of HTML commands. HTML commands can describe text, graphics, animations, sounds, tables, links, etc.
Web page: Also called Web Page, it is composed of objects. 对象(object) Simply put, it is a file. This file can be an HTML file, a picture, a Java application, etc. They can all be found through URI. A Web page contains many objects, and a Web page can be said to be a collection of objects.
Web server: The official name of the Web server is that Web Serverthe Web server can provide documents to Web clients such as browsers, and can also place website files for the world to browse; it can place data files for the world to download. Currently, the three most mainstream web servers are Apache, Nginx, and IIS.
CDN: The full name of CDN is Content Delivery Network, that is 内容分发网络, it applies caching and proxy technology in the HTTP protocol to respond to client requests on behalf of the origin site. CDN is a network built on the basis of the existing network. It relies on edge servers deployed in various places and uses the load balancing, content distribution, scheduling and other functional modules of the central platform to enable users to obtain the content they need, reduce network congestion, and improve user experience 就近. Access responsiveness and hit rate.
WAF: WAF is an application protection system安全策略 . It is a product that specifically provides protection for Web applications by executing a series of HTTP/HTTPS attacks . It is at the application level 防火墙and specializes in detecting HTTP traffic. It is a product that protects Web applications. Applied security technology.
WebService: It is a kind of Web application program, and WebService is a remote calling technology across programming languages and operating system platforms .
HTTP: A type of TCP/IP protocol suite. It is a convention and specification for transmitting hypertext data such as text, pictures, audio, and video between two points in the computer world.
Session: Session is actually the cache of client sessions , which is mainly designed to make up 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 a block for this request 内存空间. This object is the Session object, and the storage structure is ConcurrentHashMap.
cookie: A cookie in the HTTP protocol includes Web Cookie and 浏览器 Cookie, which is 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 with the next request. Typically, it is used to determine whether two requests come from the same browser, for example if the user remains logged in.
SMTP protocol: The protocol that provides email services is called SMTP protocol. SMTP also uses the TCP protocol at the transport layer. The SMTP protocol is primarily used to transfer email messages between systems and provide notifications about incoming messages.
DNS protocol: Since the IP address is an address that the computer can recognize, 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 map the network address that is easy for us to remember as an IP that the host can recognize. address.
TELNET protocol: Remote login 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.
SSH protocol: SSH is a secure encryption protocol built on the application layer . Because TELNET has a very obvious shortcoming, that is, during the process of sending data packets between the host and the remote host, the data packets are transmitted in plain text without any security encryption. The consequence of this is that it is easy for criminals on the Internet to sniff the data packets. Some bad things, for data security, we generally use SSH remote login .
FTP protocol: File Transfer Protocol, one of the application layer protocols. The FTP protocol consists of two components, namely FTP server and FTP client. The FTP server is used to store files, and users can use the FTP client to access resources located on the FTP server through the FTP protocol. The FTP protocol has high transmission efficiency and is generally used to transfer large files .
MIME type : It represents the resource type of the Internet. The 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.
Demultiplexing: At the receiving end, the transport layer will check fields such as the source port number and destination port number, and then identify the receiving socket, thereby delivering the data of the transport layer segment to the correct socket. The process is called For demultiplexing.
Multiplexing: On the sender side, the process of collecting data blocks from different sockets, encapsulating header information for the data blocks to generate message segments, and then passing the message segments to the network layer is called multiplexing. Reuse.
Well-known port numbers: In the host application, port numbers from 0 to 1023 are restricted and are called well-known port numbers. These port numbers generally cannot be occupied.
One-way data transmission: The flow of data can only be one-way, that is, from the sending end -> the receiving end.
Bidirectional data transmission: The flow of data is bidirectional, also called full-duplex communication. The sender and receiver can send data to each other.
Connection-oriented: Connection-oriented means that an application process needs to do so握手 before sending data to another application process, that is, they must first send preliminary message segments to each other to establish parameters to ensure data transmission.
Three-way handshake: The establishment of a TCP connection requires the sending of three message segments. The establishment process of this connection is called a three-way handshake.
Maximum segment length : MSS , which refers to the maximum value taken out from the cache and placed in the segment.
Maximum transmission unit: MTU, which refers to the size of the payload that both communicating parties can receive. MSS is usually set based on MTU.
Dissolved in ACK: It is to confirm the ACK of a certain message segment again. The loss of the message segment will lead to the occurrence of redundant ACK.
Fast retransmission: retransmits the lost segment before the segment timer expires.
Selective acknowledgment: In the case of message segment loss, TCP can choose to acknowledge out-of-order message segments. This mechanism is usually used together with retransmission.
Congestion control: Congestion control refers to a method used to suppress the sending end from sending data when there are too many packets in the network during a certain period of time, so that the receiving end has no time to process it, causing a performance degradation of part or even the entire network. A method to continue sending segments after time or network conditions improve.
Four waves: TCP needs to send four message segments to disconnect the link. This disconnection process is four waves.
Routing algorithm: An algorithm in the network layer that determines the path for sending packets.
Forwarding : It refers to the action of moving packets from an input link to the appropriate output link.
Packet scheduling: Packet scheduling discusses how packets are transmitted through the output link. There are three main scheduling methods: first-in-first-out, priority queuing and "round robin and weighted fair queuing".
IPV4: The fourth version of the Internet Protocol and the most widely used version. IPv4 is a connectionless protocol, and connectionlessness does not guarantee reliable delivery of data. Use 32-bit addresses.
IPV6: The sixth version of the Internet Protocol. The address length of IPv6 is 128 bits. The biggest problem of IPv4 is the insufficient network address resources, which seriously 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 obstacles for multiple access devices to connect to the Internet.
Interface: the boundary between the host and the physical link
ARP protocol : ARP is a protocol that solves address problems. Through 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 use ARP to find the address of the next hop route. However, ARP only applies to IPv4, not IPv6.
RARP: RARP is a protocol that reverses the ARP protocol and locates IP addresses through MAC addresses.
Proxy ARP: Used to solve the problem of ARP packets being isolated by routers. Proxy ARP can be used to forward ARP requests to nearby network segments.
ICMP protocol: Internet Message Control Protocol. If an IP packet fails to reach the target host for some reason during IP communication, an ICMP message will be sent. ICMP is actually a part of IP.
DHCP 协议: DHCP is a dynamic host configuration protocol. Using DHCP, you can automatically set the IP address, centrally manage IP address allocation, and achieve plug-and-play.
NAT 协议: Network Address Translation Protocol, which means that when all hosts with local addresses are connected to the network, they must be converted into global IP addresses on the NAT router before they can communicate with other hosts.
IP 隧道: IP tunneling technology refers to the process in which a router encapsulates a network layer protocol into another protocol and then transmits it across the network to another router.
单播: The biggest feature of unicast is one-to-one. Early landline phones are an example of unicast.
Broadcasting: We usually broadcast gymnastics when we were children. This is an example of broadcasting. The host is connected to all end systems connected to it, and the host sends signals to all end systems.
多播: 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.
任播: Anycast is a communication method that selects a receiving end among specific multiple hosts. Although very similar to multicast, the 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. The selected specific host will then return a unicast signal before communicating with the target host.
IGP: Internal gateway protocol, generally used for routing autonomous systems built by enterprises themselves.
EGP: Exterior Gateway Protocol, EGP is commonly used to exchange routing information between network hosts.
RIP : A distance vector routing protocol widely used in LAN networks.
OSPF: It is a link state protocol proposed based on OSI's IS-IS protocol. This protocol can also effectively solve network loop problems.
MPLS: It is a label switching technology. Label switching sets a label for each IP data packet and then forwards it based on this label.
节点: Generally refers to the equipment in the link layer protocol.
链路: Generally, the communication channel connecting adjacent nodes along the communication path is called a link.
MAC 协议: Media Access Control Protocol, which specifies the rules for frame transmission on the link.
奇偶校验位: An error detection method, mostly used in error detection of computer hardware. Parity check is usually used in data communication to ensure the validity of data.
向前纠错: The receiver's ability to detect and correct errors is called forward error correction.
以太网: Ethernet is one of the most common LAN technologies today. It specifies the content of physical layer connections, electronic signals and MAC protocols.
VLAN: Virtual LAN (VLAN) is a group of logical devices and users. These devices and users are not restricted by physical location. They can be organized according to factors such as functions, departments, and applications, and communicate with each other as if they were They are the same in the same network segment, so it is called a virtual LAN.
基站: The infrastructure of the wireless network.

89 Core Concepts of Computer Networks

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