Shulou(Shulou.com)06/01 Report--

The public Internet is a worldwide computer network, that is, it is a network that connects millions of computing devices all over the world. Most of these computing devices are traditional desktop PC, Linux-based workstations and so-called servers. However, more and more non-traditional Internet-side systems are being connected to the Internet. Indeed, at a time when many non-traditional devices are connected to the Internet, the term computer network is beginning to sound out of date. In Internet terms, all of these devices are called host or end system (end system).

The end system is connected to the packet switch (packet switch) through a communication link (communication link). There are many types of communication links, which are made up of different types of physical media, including coaxial cable, copper wire, optical fiber, and radio spectrum. Different links transmit data at different rates, and the transmission rate of the link is measured in bps. When one terminal system has data to send to another terminal system, the sender system segments the data and adds the first byte to each segment. In computer network terms, the resulting packet is called packet. These packets are sent over the network to the destination system, where they are assembled into initial data.

The packet switch receives an incoming packet from one of its inbound communication links and forwards the packet from one of its outbound communication links. From the sender system to the receiver system, a packet goes through a series of communication links and packet switches called the path through the network (route or path). The first packet-switched network came into being in the 1970s, and it is the "earliest ancestor" of today's Internet.

End systems, packet switches, and other Internet components all run a series of protocols (protocol) that control the reception and transmission of information on the Internet. TCP (Transmission Control Protocol, Transmission Control Protocol) and IP (Internet Protocol) are the two most important protocols in the Internet. The IP protocol defines the format of packets sent and received in routers and end systems. The main protocols of the Internet are collectively called TCP/IP. After pointing out the importance of Internet protocols, it is important that everyone can reach a consensus on the role of each agreement. This is where standards come into play. The Internet Standard (Internet standard) is developed by the Internet Engineering Task Force (Internet Engineering Task Force, IETF). The standard documentation for IETF is called request for comment (Request For Comment,RFC). RFC was originally used as a common request comment (hence the name) to solve the architectural problems faced by Internet pioneers. RFC documents tend to be highly technical and fairly detailed. They define protocols such as TCP, IP, HTTP (for web), and SMTP (an open standard for email).

The public Internet (that is, the global "network of networks") is a specific network, usually referred to as the Internet. There are also many private networks whose hosts cannot exchange information with hosts outside the private network. These private networks are often called intranet (Intraner) because they use the same types of hosts, routers, links, and protocols as the public Internet.

The previous discussion has identified many of the components that make up the Internet. We can also describe the Internet from a completely different perspective, that is, from the perspective of the infrastructure that provides services to applications. These applications include email, Web surfing, instant messaging, voice over IP, Internet broadcasting, streaming video, distributed games, peer-to-peer file sharing, television on the Internet, remote registration, etc. These applications are called distributed applications because they involve multiple end systems that exchange data. Importantly, Internet applications run on the end system, that is, whether they exchange data in the network core or not, but they do not care about the application that is the source or destination of the data.

The end system connected to the Internet provides an application programming interface (Application Programming Interface, API), and API specifies that software running on one end system requests Internet infrastructure to deliver data to specific destination software running on the other end system.

The Internet is an infrastructure on which new applications are constantly being invented and set up.

A protocol defines the format and order of messages exchanged between two or more communication entities, as well as actions taken in message transmission and / or reception or other events.

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