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network technique

Comprehensive sharing and organic collaboration of resources

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Network technology is a new technology developed from the mid-1990s, which integrates scattered resources on the Internet into Organic entirety To realize the comprehensive sharing and organic collaboration of resources, so that people can transparently use the overall capacity of resources and obtain information on demand. Resources include High performance computer , storage resources Data resources 、 information resources 、 Knowledge resources , expert resources Large database , network, sensor, etc. The current Internet is limited to information sharing, and the network is considered to be the third stage of the development of the Internet. The network can be constructed Regional Network, enterprise internal network, LAN network, and even Home Network And personal networks. The fundamental characteristic of the network is not necessarily its size.

Chinese name: network technique
Foreign name: network technique

Rise time: Mid 1990s
Features: Comprehensive sharing and organic collaboration of resources

catalog

development history

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Internet Scope of application From the earliest military and national defense, it has expanded to domestic academic institutions in the United States, and then quickly covered all fields around the world. The nature of operations has also changed from scientific research Education oriented gradually turned to commercialization.

In scientific research, we often encounter the problem of "sowing seeds and reaping beans". The emergence of the Internet is just like this: its prototype is 1969 U.S. Department of Defense The network established by the Advanced Research Projects Agency for military experiments is called ARPA NET， At the beginning, there were only four hosts design goal When part of the network Causes of war When damaged, the rest can still operate normally; In the early 1980s, ARPA and the Communications Agency of the US Department of Defense successfully developed Heterogeneous network Of TCP/IP Agreement and put into use; In 1986 US Congress Supported by the National Science Foundation Communication line Connect some supercomputers distributed in different places and replace ARPANET with NFSNET; After more than ten years of development, the Internet came into being.

In the early 1990s, China joined the Internet as the 71st national network, and China has opened the Internet to the public through China interconnection network ( CHINANET ）Or China Education and Research Network (CERNET) can be connected to the Internet. As long as there is a microcomputer Modem And a domestic direct dial telephone can easily enjoy Internet resources; This is one of the reasons why the Internet gradually "climbs" into ordinary people's homes; Second, friendly user interface, rich information resources The humanized feeling close to life enables non professional family users to not only apply freely, but also feast their eyes on it, and even use it to enhance their work, study and life, and truly achieve "staying at home, you can accomplish things in the world, and be smart and contemporary".

In 2017, for the first time, China will“ Digital economy ”Write Government Work Report 。

Issued by the State Council in January 2022《 The 14th Five Year Plan for Digital Economy Development 》, from infrastructure 、 Data elements 、 Digital industrialization 、 Industrial digitalization And other aspects proposed 11 key points Construction project And proposed that by 2025, China Proportion of added value of core industries of digital economy in GDP Up to 10%, Data element market The system is initially established and the digital economy governance system is more perfect.^[1]

Professional courses

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Phase I

Course content

1. Computer operation

2. Office Automation

3. Computer English

four Computer assembly And Maintenance

Stage training objectives

Master basic computer operation and daily life Office software , printer Scanner Etc. daily office equipment Use, computer assembly and common Troubleshooting And basic knowledge of design.

Phase II

Course content

one Enterprise network data communication Basics

2. Construction and maintenance of small and medium-sized enterprise network

3.window server Primary application of operating system

4. Advanced application of window server（ Active Directory Management, domain control management)

five AutoCAD engineering drawing draw

Stage training objectives

1. Skillfully master the establishment and maintenance of enterprise network, and master the network Generic cabling Basic method.

2. Install and maintain the architecture and management of windows server.

Employment direction

be engaged in Small and medium-sized enterprises Network management and Windows server construction, network construction, network operation, network application, etc.

Phase III

Project practice 1： Typical network structure conceptual design And optimization

1. Linux system management

2.linux network service

three Network attack and defense Basics

four network equipment Advanced applications

Project Practice II: Enterprise server And high-end applications of network equipment

1. Computer programming and Website construction

2. Database Application Foundation (SQL Server)

3. Enterprise network security and management

4. Enterprise network security Comprehensive Practice

5. Enterprise Mail system Organization and maintenance (optional)

6. Enterprise Server Advanced Application (Elective)

Project Practice III: Intelligence application system Expansion, deepening and comprehensive practice

Stage training objectives

1. Install and manage various Linux environments application service ; Completed independently Enterprise network Daily operation and maintenance of. 2. Be able to skillfully use and debug network equipment to set up the campus network and quickly eliminate network operation failures

1. Master database backup and recovery

2. Master the enterprise network security management

3. Establishment and maintenance of enterprises Mail system

Employment direction

Engaged in network Structural design , network system management Database management 、 Network security management And other positions

Authoritative certification: Professional qualification certificate Xinhua- Microsoft IT Assistant Engineer CIW Information network security CEAC Network Engineer

Practical training project

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Home Network project

Office network project

Hospital network project

Supermarket network project

Campus network construction project

Application Collection

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The Internet is so wonderful that beginners can't help wondering: What can it do? In general, the Internet is a set of applications that complete useful communication tasks through the network. The following section will start with applications and show some of the most popular functions of the Internet, including: E-mail , WWW, file transfer Remote login 、 Newsgroups , information inquiry, etc.

E-mail

With the global access to the Internet, the first thing people think of is that they can use it to provide personal communication, and this communication should be able to combine the speed of telephone and the reliability of postal services. This idea takes root, sprouts and grows, and the final fruit is Email 。 Through it, everyone can have their own private mailbox to store the letters that have been received but have not yet been read. The email address includes user name add host name , and separated by the @ symbol in the middle, such as the communication between two people at the beginning E-mail software More complex and diverse services can be realized, including: One to many 's sending, forwarding and replying, including voice, image, etc Multimedia information Etc; It can even be done as long as your mail arrives and hangs on you beeper Give prompt on beeping; People can also order the information they need online just like they order newspapers and magazines, and send it to them regularly via email.

WWW

World Wide Web (usually called WWW) is often translated into Chinese“ web ”In addition to the similar pronunciation, it also reflects its varied connotation. With the help of a browser software, users can Address bar Enter the page address (or domain name) you want to view, and then you can connect to the WWW server pointed to by the address to find the required image and text information. WWW access feels like shopping malls. You can wander aimlessly or move forward with a goal; However, when users finally get the content they want, they may have crossed thousands of mountains and rivers, so it is sometimes called "Web surfing". The page content stored by WWW server is HTML Written in Hyper Text Mark up Language HTTP The Hyper Text Transferring Protocol is transferred to the user.

file transfer

Although e-mail can also deliver documents, it is generally used for short information transfer 。 The Internet provides FTP (File Transfer Protocol), which enables users to send or receive very large data file : When the user issues an FTP command, connect to the FTP server After that, you can enter the command to display the stored File directory , or copy files from a directory and transfer them to your computer through the network. FTP server provides an authentication User permissions Method (user name and password are used) to limit non Authorized user Access to. However, many system administrator In order to expand the impact, the anonymous ftp service setting is opened - anonymous ftp allows users without registered names or passwords to access specified files on the machine, and the special user name it uses is "anonymous".

Remote login

Remote login Users are allowed to connect from one machine to another remote machine and establish an interactive login connection. After logging in, each keystroke of the user is transmitted to the remote host, which processes the characters and sends them back to the local machine, as if the user is directly operating on the remote host. Remote login usually requires a valid login account to accept the authentication of the other host. Common login programs include TELNET, RLOGIN, etc.

Usenet newsgroup

Usenet News is a discussion group on the Internet. Usenet organizes discussions under a set of titles called "newsgroups". Users can read the news sent by others or publish their own articles. Newsgroups There are dozens of categories and thousands of groups of "news", and on average, hundreds of "news" are published in each group every day. The way of news group intervention is also very casual. You can talk loudly, ask questions, or just watch others talk. The above list is only the main content of the Internet Cultural Corridor, but not all. The Internet is always developing and bringing forth new ideas. This will be the next content of the Internet Development trend 。 Network research Originated in the past decade U.S. government High performance computing research project supported by. The goal of this study is to integrate multiple High performance computer 、 Large database Large scientific research equipment Communication equipment , visualization equipment and various sensors into a huge super computer system To support scientific computing and scientific research 。

Microsoft The company develops Concentration On the data network, focus on the use of Network sharing Information, not network Computing power , which reflects differences in academic and research fields. In fact, many network technologies used in academic fields can become commercial applications.

Globus is Argonne National Laboratory Network technology of R&D projects 12 universities and research institutions across the United States participated in the project. Globus Yes resource management , safety information service And data management network computing And develop network computing tools that can run on various platforms to help plan and build large networks Test platform , develop large-scale applications suitable for large-scale network system operation. Globus technology has American Space It has been applied in 8 projects, including the Bureau Network, the European Data Network and the National Technology Network of the United States. In August 2005, IBM（ IBM ）Announcing billions of dollars in research and development of network computing, and Globus Cooperative development Open network computing standards, and claimed that the value of the network is not only limited to scientific computing, but also has good prospects for commercial applications. network computing And Globus have received unprecedented attention from behind the scenes to the front stage.

China attaches great importance to the development of network technology 863 Program China's national network project supported by the major special project of "high-performance computers and their core software" has made innovative achievements in high-performance computers, network software, network environment and applications. It has 18 trillion times of aggregate computing capacity, supports network research and network application Of Network test Bed, China's national network, was officially put into operation on December 21, 2005. This means that through network technology, China has been able to effectively integrate across the country Mainframe To form a powerful Computing platform , help scientific research institutions and scientific and technical worker To share computing resources data sharing And collaboration.

key technology

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Networked key technology yes Network node Broadband network system resource management and task scheduling Tools, application layer visualization tools. The network node is network computing Resource providers, including high-end servers Cluster system Large MPP system storage device , database, etc. broadband Network system It is a necessary means to provide high-performance communication in the network computing environment. Resource management and task scheduling tools are used to solve key problems such as resource description, organization and management. The task scheduling tool performs tasks in the system according to the current system load dynamic scheduling , improve the system's operating efficiency 。 Network computing is mainly Scientific computing , which is often accompanied by mass data 。 If the calculation results are converted into intuitive Graphic information Can help researchers get rid of difficulties in understanding data. This needs to develop the ability to transmit and read in network computing, and provide friendly user interface Visual tools for.

research status

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Network computing usually focuses on large-scale application projects. According to Globus technology, large-scale application projects should be completed by many organizations, which form a“ virtual organization ”The computing resources owned by each organization are shared in the virtual organization to complete the project collaboratively. For sharing, what is valuable is not the device itself but the interface or interface of the entity.

From a technical perspective, sharing is the interoperability of resources or entities. Globus technology settings, network environment The interoperability under means that a set of general protocols need to be developed to describe the message format and message exchange rules. A series of services need to be developed based on the TCP/IP protocol/ Internet Protocol ）On web services The principle is the same. Define the application first in the service Programming interface , based on these interfaces Software development tools 。

Globus network computing protocol is established in Internet Protocol Based on the communication, routing, name resolution and other functions in the Internet protocol. Globus protocol is divided into construction layer adjoining course , resource layer, collection layer and application layer. Each layer has its own services, application programming interfaces and software development tools, and services where the upper layer protocol calls the lower layer protocol. Global applications in the network need to call the operating system through the services provided by the protocol.

The function of the construction layer is to provide shared resources in the network, which is a physical or logical entity. frequently-used shared resource Including processing capacity storage system , Contents network resource 、 distributed file system , distributed computer pool Computer cluster Etc. The connection layer is the network in the network transaction processing Communication and Authorization control The core agreement of. Between resources submitted by the construction layer Data exchange All are implemented under the control of this layer. Authorization verification and security control between resources are also implemented here. The role of the resource layer is to control a single resource, perform security handshake with available resources, initialize resources, monitor resource operation, and count resource usage data related to payment. The function of the collection layer is to collect the controlled resources submitted by the resource layer for the virtual organization application program Share, call. In order to manage and control the sharing from applications, the aggregation layer provides directory services 、 resource allocation , schedule, resource agent Resource monitoring Diagnosis, network startup load control , account management and other functions. The application layer is the application program of users on the network. It first calls the corresponding service through the application programming interface of each layer, and then calls the resources on the network through the service to complete the task. Application development involves a lot of Library function 。 In order to facilitate the development of network applications, it is necessary to build support network computing Library functions for.

Globus Architecture It has been adopted by some large networks. Researchers have been weather forecast , high energy physical experiment , aircraft research and other fields have developed some applications based on Globus network computing. Although these applications are still experimental, they prove that network computing can accomplish a lot Supercomputer Incompetent large application tasks. It can be predicted that network technology will soon set off the next wave of Internet waves. Facing the coming Third generation Internet Applications, many developed country They have invested a lot of research funds, hoping to seize the opportunity and grasp the future destiny.

China has also increased its investment in networking. The Computing Institute of the Chinese Academy of Sciences named its own network“ Vega Vega Grid, which aims to have large-scale data processing High performance computing 、 resource sharing And improve resources Utilization Ability. And other domestic and foreign Network research Compared with projects, the biggest feature of Vega Network is "service network". Many industries in China, such as energy, transportation, meteorology, water conservancy, agriculture and forestry, education, environmental protection, etc., are critical to high performance Computing network I.e information network The demand for. It is expected to see more networks in two or three years Technology application example.

application area

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Network technology application area It is very wide, mainly in the following aspects.

Distributed Supercomputing Distributed supercomputing will be distributed in different places Supercomputer With high speed network connections Get up and use the network middleware software "Glue" together to form a much more powerful Computing platform 。

Distributed instrument System Distributed Instrument System Usage Network management Valuable instrument systems distributed around the country provide a means of remote access to instruments and equipment to improve the utilization rate of instruments and facilitate the use of users.

Data intensive computing Parallel computing The technology is often driven by some computing intensive applications, especially some applications with huge challenges, which greatly promotes the high performance Parallel Architecture 、 Programming environment , large-scale visualization and other fields. The applications of data intensive computing are much more than those of computing intensive computing, and its corresponding data network focuses more on data storage, transmission and processing, Computing network It focuses more on the improvement of computing power. The leading project in this field is the DataGrid project carried out by the European Nuclear Center, which aims to deal with the Large Hadron Collider PB/s magnitude continuously generated experimental data 。

Remote immersion is a special networked virtual reality environment. It is a realistic reflection of reality or history, and visualizes high-performance computing results or databases. "Immersion" means that people can fully integrate into it: participants from different places gather in the same place through the network virtual space You can roam freely, communicate with each other, and virtual environment Interact to make it change. Dozens of remote immersion applications have been developed, including virtual history museum , Collaboration learning environment Etc. Remote immersion can be widely used for interaction Scientific visualization , education, training, art, entertainment industrial design , information visualization and many other fields.

information integration The network was originally integrated Heterogeneous computing The identity of the platform appears, and then enters the field of distributed massive data processing. Information network through unified information switching Architecture and a large number of middleware And provide users with "information is readily available" services. Network information integration will be more applied to business. Applications and information distributed around the world can be seamlessly integrated and communicated through the network, thus forming new business opportunities.

Information integration, such as information network, service network Knowledge network And so on, which is the popular application direction of the network in recent years. In 2002, the Globus Alliance and IBM Online forum Posted on Openness network service The architecture and its detailed specifications combine the Globus standard with the support of commercial web Service standards Combine. In 2004, the Globus Alliance, IBM and HP (HP) and others jointly released a new network standard draft, transforming the detailed specification I of the open network service architecture into six specifications for expanding the World Wide Web services. Network services have been completely integrated with the World Wide Web services, marking the advent of the era of network commercialization.

Standards are the key to the development of network technology. Just like the TCP/IP protocol is Internet As the core of, building network computing also needs to define the core - standard protocols and services. Some standardization groups are taking active action. So far, although there is no formal standard for network computing core technology The relevant institutions and enterprises have reached an agreement that the United States Argonne National Laboratory And University of Southern California information science The Globus computing tool software jointly developed by the college has become the actual standard of network computing, and 12 famous computer and software manufacturers have announced that they will use Globus computing tool software. As an open architecture and Open standards Infrastructure, Globus computing tool software provides many basic services needed to build network applications, such as security Resource discovery , resource management, data access, etc. All major network projects are based on the protocols and services provided by Globus computing tool software.

In addition to standards, the lack of security, manageability and talent is also an urgent problem for network computing, otherwise it will not become the business architecture of enterprises. Many problems still need to be solved before commercial applications can be realized. Even so, the prospect of building a global network is still irresistible.

In addition, the application of network technology also gave birth to Cyberlinguistics 。 This door Emerging disciplines It is a well-known scholar in China Zhou Haizhong It was first proposed by professor in 2000. In his article "A New Language Discipline -- Cyberlinguistics", he studied the object of cyber linguistics research method , research tasks, subject attributes and positioning issues, etc; Since then, cyber linguistics has attracted the attention of the international academic community.

major function

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In general, computer network The following main functions can be provided:

resource sharing

The emergence of the network makes resource sharing very simple. Both sides of the communication can cross the barriers of time and space and transmit information anytime and anywhere.

information transmission And centralized processing

Data is transmitted to the server through the network, and then sent back to the terminal after centralized processing by the server.

load balancing And Distributed processing

Load balancing is also a specialty of the network. A typical example: a large ICP （Internet Content Provider ）In order to support more users to visit his website, WWW servers with the same content have been placed in many places around the world; Through certain techniques, users in different regions can see the same page placed on the server nearest to them, so as to achieve load balance of each server, and users can save many wasted roads.

integrated information service

A major trend of network development is multidimensional, that is, to provide integrated information services on a set of systems, including resources from political, economic, and other aspects, and even at the same time provide Multimedia information , such as image, voice, animation, etc. In the trend of multidimensional development, many new forms of network applications are emerging, such as:

① E-mail -- this should be one of the most convenient ways for people to communicate online. The recipient does not have to be online when sending an email, but he can see his own letters whenever he opens his mailbox in the future.

② Online transaction It is to do business through the Internet. Some of them are to be settled directly through the network, which requires a higher security of the network.

③ video on demand This is a new entertainment or learning project Intelligent community , hotels or schools. Its form is similar to TV station selection, but the content of the program is transmitted through the network.

④ Online conference - also known as video conference, as the name implies, is to hold meetings through the network. It is related to video on demand The difference is that all participants need to actively send images to the outside world. In order to achieve real-time simultaneous transmission of data, images, and sounds, it has processing speed Put forward the highest requirements.

The above functions of the network are just a few examples. We will use more detailed cases in the future to enrich your understanding of the network.

Classification composition

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On what basis and how is the network composed?

There are many types of computer networks, and there are different classifications. Network Press Switching technology It can be divided into: line switching network Packet switched network ； Press Transmission technology It can be divided into: broadcast network, non broadcast multiple access network, point-to-point network;

According to topological structure, it can be divided into general line, star, ring, tree, full mesh and partial Mesh network ； Press Transmission medium It can also be divided into Coaxial cable , twisted pair, optical fiber or satellite. Here we mainly talk about the network divided according to the network distribution scale: LAN, MAN WAN And inter network.

LAN

- LAN ( Local Area Network )

A network formed by interconnecting various communication devices in a small area, Coverage Generally confined to rooms, buildings or parks. LAN is characterized by short distance, small delay Data rate High and reliable transmission.

Common LAN types include: Ethernet （Ethernet）、 Token Ring Network （TokenRing）、 Fiber distributed data interface （FDDI）、 Asynchronous transmission Mode (ATM), etc transmission speed 、 data format There are many differences in many aspects. Among them, Ethernet is the most widely used one Bus structure LAN is the fastest growing and most economical LAN at present.

Common devices of LAN include:

*The network interface card (NIC) is plugged into the computer a main board Slot, which is responsible for transferring data conversion For the format recognized by other devices on the network Network media Transmission. Its main technical parameters are bandwidth, bus mode, electrical Interface mode Etc.

* Hub (Hub) is a single bus shared device, providing many network interface , is responsible for connecting multiple computers in the network. The so-called sharing means that all ports of the hub share one port data bus Therefore, the average amount and rate of data transmitted by each user (port) are limited by the total number of active users (ports). Its main performance parameters include Total bandwidth 、 Number of ports , intelligence (whether network management is supported), scalability (Yes No cascade And stacking), etc.

*Switch switching hub 。 It also has many interfaces, providing multiple network node Interconnection. However, its performance is greatly improved than that of a shared hub: it is equivalent to having multiple buses, so that each port device can independently transmit data without being affected by other devices. In front of users, each port has independent and fixed bandwidth. In addition, the switch also has functions that the hub lacks, such as data filtering Network Segmentation , broadcast control, etc.

*The distance expansion of cable LAN needs to be realized through cables. Different LANs have different connecting cables, such as optical fiber Twisted pair , coaxial cable, etc.

Metropolitan area network

MAN(Metropolitan Area Network)

The coverage of MAN is limited to one city, and there are few targeted technologies for the metropolitan area network, which are generally based on the actual situation through the LAN or WAN To achieve.

WAN

- WAN (Wide Area Network)

WAN connection The geographical scope is large, often a country or a continent. The purpose is to make the remote distribution of LAN interconnection , so its structure is divided into end systems (user sets at both ends) and communication system (intermediate link). The communication system is WAN It mainly includes the following:

*Public telephone network PSTN (Public Switched Telephone Network), with a speed of 9600bps~28.8kbps, and a maximum of 115.2kbps after compression. The transmission medium is an ordinary telephone line. It is characterized by low cost, easy establishment and wide distribution.

* Integrated Services Digital Network I.e ISDN (Integrated Service Digital Network) is also a dial-up connection mode. The low-speed interface is 128kbps (high-speed up to 2M). It uses ISDN lines or installs ISDN services on ordinary telephone lines through telecommunications bureaus. ISDN is a number transmission mode It has the characteristics of fast connection and reliable transmission, and supports the number identification of the other party. ISDN charges slightly more than ordinary phones, but its dual channels enable it to support two independent applications at the same time, which is more suitable for individuals or small offices Network access Mode.

*The leased line, called DDN in China, is a point-to-point connection mode with a speed of 64kbps~2.048Mbps. The advantage of the special line is that the data transmission is better guaranteed and the bandwidth is constant; But the price is expensive, and the point-to-point structure is not flexible enough.

* X.25 Web is an early and still widely used WAN Mode, the speed is 9600bps~64kbps; It has redundant error correction function and high reliability, but the side effects are slow speed and large delay;

* Frame relay Frame Relay is a relatively new technology developed on the basis of X.25. The speed is generally 64kbps~2.048Mbps. Frame relay is characterized by flexibility: it can realize one to many connection, and Large time It can transmit data beyond the agreed rate, and is a good connection option for commercial users.

*Asynchronous Transfer Mode (ATM) is a Cell exchange The network is characterized by high speed, low delay and guaranteed transmission quality. ATM mostly uses optical fiber as Connecting media The speed can be as high as gigabit (109bps), but the cost is also high.

WAN The difference from LAN is that the line usually needs to be paid. Most enterprises cannot build their own lines, but need to rent existing links, so most of the cost of WAN is spent here. People often consider how to optimize the bandwidth and use "good knives on the blade".

Common WAN devices include:

*Router（ Router ）The WAN communication process looks for the path to the destination according to the address. This process is called "Routing" in the WAN. Routers are responsible for establishing routes between each WAN and LAN according to the address, and sending data to the final destination.

* Modem （ Modem ）As a signal conversion equipment between terminal system and communication system, it is one of the essential equipment in WAN. There are two types: synchronous and asynchronous. They are respectively used to connect with the synchronous and asynchronous serial ports of the router. Synchronous can be used for special lines Frame relay , X.25, etc., asynchronous connection is used for PSTN.

Inter network

The Internet is a series of local area networks and WAN Therefore, the technology included is also the existing LAN and WAN Technologies Synthesis of. The Internet is currently the largest and most typical inter network.

Problems

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In the first part, we talked about the brief history of Internet development and its applications in all aspects. Because of the Internet Rich and colorful Will attract more and more people to join in: For users, the Internet is gradually penetrating into all aspects of our work and life, greatly changing the Traditional thinking And lifestyle; As for the Internet, the active participation of users has led to the rapid expansion of this global network? Tolerance Faced with bandwidth shortage IP address Resources shortage and other severe challenges.

Bandwidth shortage

According to mid 1995 estimates, there were more than 150 countries and regions More than 60000 networks are connected to the Internet, about 4.5 million computers are connected to the network, and 40 million users directly use the Internet. Today, the Internet has been opened to most countries and regions in the world. A new network is connected almost every 30 minutes, and the number of hosts quadruples every year, Number of users It is estimated that by the end of this century and the beginning of the next century, the Internet will connect nearly 100 million computers, reaching one billion users. It is difficult for people to accurately estimate the future. In any case, these figures are enough to explain the crisis of the Internet: just like a steel wire rope with many heavy objects suspended, the rope is in danger of breaking as the weight increases; In fact, users travel on the Internet through many such "wire ropes". The more users there are, the heavier the load of the rope is. If any of them is not solid, it will become a bottleneck, leading to network access failure. Therefore, the reinforcement of "steel wire rope" - the increase of bandwidth capacity is imperative, from Internet backbone to branch to end user Many mature or developing link technologies have emerged to meet this demand. We will focus on the types of links that users care about most Access technology 。

Lack of IP address

We introduced IP address The format and classification of IPv4 - It is a 32-bit Binary number Therefore, the total address capacity is 232, that is, hundreds of millions of addresses. And according to TCP/IP protocol (Like many other protocols), each node in the interconnected network must have its own unique address as an identifier. Obviously, compared with the growing number of users mentioned above, the existing IP address resources have been overwhelmed and will soon be used up - some predictions indicate that the Internet Development speed Calculation, all IPv4 address The distribution will be completed between 2005 and 2010.

One way to solve the problem of IP address shortage is to find a way to delay resource exhaustion. At present, the most widely used technology is NAT (Network Address Translation, network address It enables enterprise users to use self defined addresses in internal network applications and translate them into legal Internet addresses only when Internet access is required; Its biggest advantage is that users do not need to change the internal address structure when they join the Internet, but only need to implement it at the internal and external boundaries address translation , and multiple users can reuse the same legal address, thereby greatly saving address resources; However, NAT conversion also increases the complexity of the network, and it can not prevent the trend of decreasing available addresses.

As a pair IPv4 To solve the problem, a new definition of IP address came into being, which is described below IPv6 。

Develop technology

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How to solve the problem of Internet Development bottleneck ？ What is the new application trend of Internet?

The development of the Internet is first to get out of the predicament and expand the capacity, and then it is possible to continue to launch new applications and use them freely. We will start with the development of network lines and talk about the communication hotspots Broadband access technology , and the new application trend of Internet.

Access technology

Access technology is also called“ Last kilometer ”Technology, which refers to a connection from the end user to the local telecommunication service provider. What you are familiar with are PSTN Dial up, ISDN, leased line and other technologies, and access in recent years technological development Fast and mature:

ADSL

A DSL also called asymmetric digital subscriber line , DSL family technology (HDSL, VDSL IDSL And so on). Its biggest advantage is to use the existing telephone Twisted pair As Transmission medium , so the cost is low; The access bandwidth is relatively Telephone line The PSTN transmitted (currently the highest is 115.2Kbps) is much faster Office terminal To user's Downlink rate Theoretically, it can reach 7-8M, and the actual downlink rate is generally 1.5-2Mbps Uplink rate It is hundreds of Kbps, which is also much higher than PSTN; ADSL Asymmetry And end user The network access characteristics of are consistent -- most applications of individual users obtain data from the Internet in the form of customers, such as WWW and FTP, and only send a large amount of data to the network in a few times, such as sending attached Multimedia information As a result, the amount of downlink data is large and the amount of uplink data is small, which is also asymmetric.

Cable modem

Cable Modem It is a very suitable access technology for home users. It's in Cable television On the basis of Distribution network The backbone of Service node Completed at photoelectric conversion , and then Coaxial cable take Transmission signal Delivered to users' homes, it can effectively realize Internet access, TV on demand, data phone and other services, and has broad market prospects. Cable transmission is also asymmetric. The downlink rate of each service node can reach 10-30Mbps and the uplink rate can reach about 2M. However, unlike ADSL, it is a shared network. The actual available bandwidth per user is inversely proportional to the number of Internet users connected to the node. Even so, the bandwidth that users can enjoy is considerable.

The biggest obstacle to the application and development of cable modems is the two-way transformation of cable lines -- traditional Cable TV Mostly One way transmission ； The data access is bidirectional, so the line transformation must be implemented to adapt to this Item new Application of. There is also a temporary solution before the transformation is completed: downward Data transfer TV cable is used, and telephone cable is used for uplink data Echo 。

Wireless access technology

As a supplement to wired access, in areas where wired access is not convenient Wireless communication equipment The access of users to the local exchange network is collectively referred to as Wireless access system 。 Wireless local loop System technology It comes from the following three aspects:

(1) From Cellular mobile communication system ；

(2) From Regional system communication system , digital cordless telephone system Digital microwave and satellite communication system 。

The regional system mainly refers to Trunking communication system 。

(3) It is derived from the dedicated wireless local loop system, which adopts high power, large coverage and low cost. With its unique advantages, it was quickly accepted by the market and developed rapidly. Almost all the major communication companies in the world have typical products.

CDMA（ Code Division Multiple Access ）Compared with its derivative wireless local loop technology, it has incomparable advantages with other wireless access technologies and represents the development direction of wireless access technology.

The development of access technology fully reflects“ Triple play ”Application trend of ADSL: ADSL uses the original voice carrier telephone line to transmit data, cable Modem Use the original Image carrier Cable TV transmits data, which everyone is familiar with IP phone Voice is transmitted through various data carriers. Therefore, the future Data network The TV network and the telephone network will no longer be isolated from each other, and they will jointly undertake data, voice, and image integration services, easing the pressure on Internet bandwidth.

IPv6 technology

Just when people are worried about the problems faced by IPv4, IPv6 appears, which brings people a near perfect solution:

● As phone number Just like the upgrade, IPv6 provides 128 bit IP addresses, which greatly increases the number of addresses, thus solving the IP address resource crisis;

● IPv6 adopts the structure of "aggregatable global unified computing address", which makes the IP address structure the same as that of the network topological structure (connection form), thus reducing the size of Routing table , enabling routers to efficiently determine routes;

● IPv6 has the function of automatically assigning IP addresses to users, which greatly reduces the network Administrative expenses 。

Although IPv6 has obvious advantages over IPv4, there are many practical difficulties in upgrading addresses worldwide. To this end, the Internet Research Organization IETF A set of transition scheme from IPv4 to IPv6 has been formulated, including three mechanisms: IPv4 compatible IPv6 address , dual IP protocol stack and IPv6 based on IPv4 tunnel.

Electronic Commerce

In the first chapter of the history of Internet development, we introduced various Internet based applications, but they are just the means people use to achieve certain goals, just like primitive people learned to use tools. E-Commerce is a comprehensive transformation of various technologies based on network applications in all walks of life, showing a new and bright world for people. Electronic commerce may not be completed through the Internet, but the rapid development of the Internet has provided fertile ground for it to take root. Famous Amazon The company should say that it dares to be the first to build its own books Supporting services Our huge empire has become a model of e-commerce operation. Compared with the applications mentioned before, e-commerce is more like a concept, and its implementation has no fixed format. Use various technologies on the Internet or your own network to build Intranet 、 Extranet Among them, the formulation of strategies is the key to development. Regardless of the progress, e-commerce is bound to be a major development trend of Internet applications.

Looking at the development history of the Internet for more than ten years, it is hard to tell what it will be like in the future, but the Internet will continue to change our lives and promote human civilization No one can deny the development of.

Definition meaning

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How to define Network Protocol What does it mean?

A protocol is a combination of a series of regulations on the way in which devices in the network exchange information. It determines the rate of information exchange, transmission code, code structure Transmission control Step, error control and many other parameters are defined.

The network is interconnected Large groups Therefore, if you want to join this group, you can't do whatever you want. Just as a country or a race has its own language, everyone must be familiar with it and use it to talk, each node in the interconnected network also needs to have a common "language" according to its Defined rules To control the transmission of data, this language is often heard of as "protocol". The protocol defines a number of parameters such as a br/>code, code structure, transmission control steps, and error control for how the devices in the network exchange information.

For network beginners, complicated protocols often make people headache No -- what role do these agreements play? What is the connection between them? Why does Agreement A need to supplement Agreement B? These problems are unclear and often become obstacles to further learning. In fact, this problem should be understood as follows: there were nationalities with different languages first, and then with the development of society, there was a need for communication between different nationalities. The same is true of the network. At first, people only need to make some simple agreements to ensure that users within a limited range comply with the network; Later network size More and more big, so we can consider making more strict Rules and regulations I.e. agreement; In order to realize the interconnection of multiple different networks, many new protocols will be added as supplements or grow into new unified standards.

Data transmission from source to destination in the network requires a series of processing. To facilitate understanding, let's use a metaphor here. If we compare the data to chocolate, we can use the equipment for processing chocolate as the source and the consumers' hands as the purpose to see what will happen Transmission process 。 Chocolate factories usually add a layer of packaging to each chocolate, and then put several chocolate boxes into one chocolate box, and then put several chocolate boxes into one Outer packaging ， Transportation company Many boxes of chocolates will also be put into a container. After arriving in the city where the consumers live, the carriers, wholesalers, retailers and consumers will open different packaging layers. Different levels of packaging and unpacking require different specifications and equipment, and computer networks also have different packaging and transmission levels International Organization for Standardization ISO was proposed in 1978“ Open Systems Interconnection Reference Model ”, that is, the famous OSI (OpenSystem Interconnection ) Seven layer model , which will be introduced in the following pages, and will not be discussed here. The protocol of the network is used for these different network layer Of Code of conduct Of. The network has formed many different protocol family Each protocol family has corresponding protocols at each layer of the network, among which the ICP/IP protocol family is the Internet specification, which is also what we are going to talk about today.

Definition, hierarchy and function of TCP/IP protocol

What is TCP/IP protocol, divided into several layers, and what are their functions?

TCP/IP protocol family It contains many sub protocols with different functions. For this reason, we also use the layering method described above to analyze its structure. TCP/IP hierarchical model It is divided into four layers: application layer Transport layer , network layer, data link layer 。 There are also five layers of TCP/IP protocol: physical layer 、 data link layer 、 Internet layer (network layer), transport layer and application layer.

TCP/IP five layer model

The specific corresponding relationship with the 7-tier model is shown in the figure:

TCP/IP network protocol

TCP/IP (Transmission Control Protocol/Internet Protocol) is the most widely used protocol in the world at present. Its popularity is closely related to the rapid development of the Internet, TCP/IP has proved to do this, making Network interconnection Become easy to get up

Come, and let more and more networks join in, become the Internet's Factual criterion 。

*Application layer -- The application layer is the general name of the applications that all users are facing. TCP/IP protocol family has many protocols at this level to support different applications. Many familiar Internet based applications can not be realized without these protocols. If we conduct web (WWW) Access uses HTTP protocol and file transfer FTP protocol , for sending e-mail SMTP DNS protocol for domain name resolution and remote login Telnet Protocols and so on belong to the TCP/IP application layer; As far as users are concerned, they see that most of the operating interfaces built by software are graphical, while the actual background running is the above protocol.

*Transport layer - This layer is mainly used to provide communication between applications, TCP /The IP protocol family includes TCP and UDP 。

*Network layer - TCP/ IP A key layer in the protocol family, which mainly defines the IP address format, so that data of different application types can be transmitted smoothly on the Internet. IP protocol is a Network layer protocol 。

* Network interface layer -- This is the lowest layer of TCP/IP software, responsible for receiving IP addresses data packet And send it through the network, or receive physical frames from the network and extract IP datagram , to IP layer 。

1． TCP / UDP agreement

TCP (Transmission Control Protocol ）And UDP (User Datagram Protocol) are transport layer protocols. TCP provides data in the IP environment Reliable transmission , its services include data stream Transmission, reliability and effectiveness Flow control 、 full duplex Operation and Multiplexing 。 adopt Connection oriented 、 end to end And reliable packet transmission. Generally speaking, it is to create a well connected channel for the data sent in advance, and then Data transmission ； UDP does not provide reliability, flow control or error recovery functions for IP. Generally speaking, TCP corresponds to applications with high reliability requirements, while UDP corresponds to applications with low reliability requirements and economical transmission. TCP supported application protocol Mainly: Telnet 、 FTP , SMTP, etc; The application layer protocols supported by UDP mainly include: NFS（ Network File System ）、SNMP（ Simple Network Management Protocol ）, DNS (Primary Domain Name System), TFTP (Universal File Transfer Protocol), etc.

Definition of IP protocol, classification and characteristics of IP address

What is an IP protocol? How are IP addresses represented? How are they classified? What are their characteristics?

In order to facilitate addressing and hierarchical network construction, IP addresses are divided into five categories: A, B, C, D, and E. In commercial applications, only A, B, and C are used.

IP Protocol Internet Protocol , which supports interconnection between networks Datagram Protocol, which is linked to TCP TCP/IP protocol (Transmission Control Protocol) constitutes the core of TCP/IP protocol family. It provides complete functions of inter network connection, including IP datagram provisions interconnection network IP address format in the range.

On the Internet, in order to realize the communication between nodes connected to the Internet, each node (the computer connected to the network) must be assigned an address, and it should be ensured that this address is unique throughout the network, which is the IP address.

The IP address (IPv4: IP version 4) is represented by 32 binary bits, one for every 8 binary bits

Integer, intermediate by decimal point Interval, such as 159.226.41.98, there are four groups of 8-bit binary numbers in the entire IP address space, which are composed of the address of the network where the host is located (similar to the number of troops) and the host's identification in the network (similar to the number of soldiers in the troops).

In order to facilitate addressing and hierarchical network construction, IP addresses are divided into five categories: A, B, C, D, and E. In commercial applications, only A, B, and C are used.

* Class A address : The network ID of class A address is represented by the first group of 8-bit binary numbers, and the host ID in the network

It accounts for three groups of 8-bit binary numbers. Class A addresses are characterized by that the value of the first binary number of the network ID must be "0". It is not difficult to calculate that 126 Class A addresses are allowed Network segment (The range ranges from 0 to 127. 0 is reserved and represents all IP addresses, while 127 is reserved and is used to test loop reuse, so subtracting two is 126). Each network allows about 16.7 million hosts, which are usually allocated to networks with a large number of hosts (such as Backbone network ）。

* Class B address : The network ID of the class B address is represented by the first two groups of 8-bit binary numbers. The host ID in the network accounts for two groups of 8-bit binary numbers. The feature of the class B address is that the first two binary numbers of the network ID must be "10".

16384 Class B addresses are allowed Network segment Each network allows 65533 hosts, which is suitable for networks with more nodes (such as regional networks).

* Class C address : The network ID of the class C address is represented by the first three groups of 8-bit binary numbers. The host ID in the network accounts for one group of 8-bit binary numbers. The feature of the class C address is that the first three binary numbers of the network ID must be "110". The network with class C address allows 254 hosts, which is applicable to the network with few nodes (such as Campus network ）。

In order to facilitate memory, we usually use 4 Decimal number To represent an IP address, decimal numbers are used Period ".". This representation of IP address is also called dotted decimal Law. If expressed in this way, the IP address range of Class A network is 1.0.0.1 － 127.255.255.254; IP address range of Class B network: 128.1.0.1 － 191.255.255.254; The IP address range of Class C network is 192.0.1.1 － 223.255.255.254.

Class D address : range from 224-239, Class D IP address The first byte starts with "1110", which is a specially reserved address. It does not point to a specific network. This type of address is used in multicast. Multipoint Broadcast address It is used to address a group of computers at a time. It identifies a group of computers that share the same protocol.

Class E address : The range is 240-254, starting with "11110", reserved for future use. All zero ("0.0.0.0") addresses correspond to the current host. All "1" IP addresses ("255.255.255.255") are current Subnet The broadcast address of.

because network address Nervousness Host address Relative surplus, adopt Subnet mask To specify the network segment number.

TCP/IP protocol and low-level data link layer and physical layer This is also an important feature of TCP/IP. Because of this, it can widely support Physical network Structure. TCP/IP has been used to connect to intercontinental networks, national networks and trans regional networks.

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