Internet concept and TCP/IP layered model

The internet is the largest, most user and most influential computer internetwork in the world. This module introduces the concept of the Internet and the TCP/IP layered model.

First, the concept of the Internet

The concept of the Internet, which can also be thought of as the structure of the Internet, can be understood in the following ways:

From the point of view of network communication, the Internet is a large data communication network connected by TCP/IP to the internal network of various countries, institutions and departments.

From the point of view of information resources, Internet is an information resource network which integrates various information resources in various fields and departments, and aims at sharing.

From a technical point of view, the Internet is a "different network interconnection Network (Internet)", which is formed by many networks (including LAN, metropolitan area Network and wide area Network) interconnection.

Discuss:

The country is interconnected by backbone networks, and each country consists of a backbone network, a metropolitan area network and a user Resident campus network (LAN), which allows users to share resources from any country in the world.

Internet for Network interconnection

Hardware support-such as routers and various lines-connects the geographically dispersed networks physically.

The software supports the--TCP/IP protocol. The internet is a network based on TCP/IP protocol.

Second, TCP/IP layered model

The TCP/IP layered model (TCP/IP model) and the corresponding relationship with the OSI Reference model are shown in 1.

Fig. 1 The TCP/IP model and the corresponding relationship with the OSI reference Model

As can be seen from Figure 1, the TCP/IP model consists of 4 layers:

Network interface Layer--the physical layer and data link layer corresponding to the OSI reference model;

Network Layer--the network layer corresponding to the OSI reference model;

Transport Layer-the transport layer corresponding to the OSI reference model;

Application Layer-corresponds to the 5, 6, and 7 layers of the OSI reference Model.

Discuss:

The TCP/IP model does not include the physical layer, and the network interface layer below is the physical network.

Principle Architecture

The OSI Reference Model has 7 layers, the TCP/IP model consists of 4 layers, because the OSI reference model of the session layer, presentation layer, application layer and the TCP/IP model of the application layer corresponds to the OSI reference Model of the physical layer, the data link layer and the TCP/IP model of the network interface layer, in order to introduce the principle of convenience, A compromise approach is often adopted, using a five-layer protocol principle architecture, shown in 2.

Figure 25 Principle architecture of Layer protocol

The main features of the TCP/IP protocol are as follows.

High reliability

TCP/IP uses a re-confirmed method to ensure reliable data transmission, and the use of "window" flow control mechanism to further guarantee the reliability.

Security

To establish a TCP connection, each end of the connection must agree with the security control of the connection. IP has several fields in its control packet header that allow selective protection of the transmitted information.

Flexibility

TCP/IP requires the lower layer to support the Protocol, and no special requirements for upper-level application protocols. Therefore, the use of TCP/IP is not limited by the transmission media and the network application software.

Summarize

From the point of view of network communication, the Internet is a large data communication network connected by TCP/IP to the internal network of various countries, institutions and departments, and from the point of view of information resources, the Internet is a kind of information resource network which integrates various information resources in various fields and departments, and aims to share them. From a technical point of view, the Internet is a "network of different network interconnection (Internet)", which is formed by interconnection of many networks (including LAN, metropolitan area Network and wide area network).

The layered TCP/IP model and its correspondence to the OSI Reference Model are:

Network interface Layer--the physical layer and data link layer corresponding to the OSI reference model;

Network Layer--the network layer corresponding to the OSI reference model;

Transport Layer-the transport layer corresponding to the OSI reference model;

Application Layer-corresponds to the 5, 6, and 7 layers of the OSI reference Model.

The main features of the TCP/IP protocol are: High reliability, security and flexibility.

Internet concept and TCP/IP layered model