When should I Lease Computer Equipment?
Computer network refers to the connection of multiple computers with independent functions and their external devices with different geographical locations through communication lines. Under the management and coordination of network operating systems, network management software and network communication protocols, resource sharing and information are achieved. Computer system passing by. [1]
- Chinese name
- computer network
- Field of use
- the Internet
- Features
- Information transmission and sharing
- Category
- Network operating system
- Computer network refers to the connection of multiple computers with independent functions and their external devices with different geographical locations through communication lines. Under the management and coordination of network operating systems, network management software and network communication protocols, resource sharing and information are achieved. Computer system passing by. [1]
Computer Network Definition Classification
Computer network
- Computer networks are also called computer communication networks. The simplest definition of a computer network is: some interconnected, for the purpose of sharing resources,
- In addition, from a logical function point of view, a computer network is a collection of computer systems that connect multiple computers with communication lines based on the purpose of transmitting information. A computer network consists of a transmission medium and communication equipment. [2]
- From the user's perspective, a computer network is defined as follows: there is a network operating system that can be automatically managed for the user. It is called to complete the resources called by the user, and the entire network is transparent to the user like a large computer system. [2]
- A more general definition is: a system that uses geographically dispersed computer systems and communication equipment with independent functions to connect in different forms using communication lines, and implements a system of resource sharing and information transfer with well-functioning network software and protocols. [2]
- On the whole, a computer network is to interconnect computers distributed in different geographical areas with specialized external equipment using communication lines to form a large-scale and powerful system, so that many computers can easily transfer information to each other and share hardware and software. , Data and other resources. In simple terms, a computer network is an assembly of many autonomously working computers that are interconnected by communication lines. [2]
- The simplest computer network has only two computers and one link connecting them, that is, two nodes and one link. [2]
Computer network press connect
- A computer network is a collection of autonomous computers interconnected by lines. To be precise, computers, terminals, and their auxiliary devices with independent working capabilities distributed in different geographical locations are connected and configured with communication equipment and communication lines. Network software to achieve computer resource sharing system. [2]
Computer network on demand
- A computer network is a group of independent, but interconnected, computers that perform computer tasks together. These systems are called computer networks. [3]
Computer Network Development
- Since the advent of computer networks, its speed of development and its wide range of applications have been amazing. Throughout the development of computer networks, it has roughly gone through the following four stages: [2]
Computer network
- The first generation of computer networks before the mid-1960s was a single computer-centric remote online system. The typical application is an aircraft booking system consisting of a computer and more than 2,000 terminals across the United States. The terminal is a computer. Peripherals, including monitors and keyboards, without CPU and memory. With the increase of remote terminals, a front-end machine (FEP) was added in front of the host. At that time, people defined computer networks as "systems connected for the purpose of transmitting information, realizing remote information processing, or further achieving resource sharing." Such communication systems already had the embryonic form of a network. [2]
Computer network formation stage
- The second-generation computer network from the mid 1960s to the 1970s was interconnected by multiple hosts through communication lines to provide users with services. It emerged in the late 1960s, and is typically represented by the ARPANET developed by the US Department of Defense's Advanced Research Projects Agency . The hosts are not directly connected by lines, but are interconnected by the interface message processor (IMP) after being transferred. The IMP and the interconnected communication lines are responsible for the communication tasks between the hosts, forming a communication subnet. Hosts interconnected by the communication subnet are responsible for running programs and providing resource sharing to form resource subnets. At this time, the network concept was "a collection of computers with independent functions interconnected for the purpose of sharing resources with each other", forming the basic concept of computer networks. [2]
Computer Network Interconnection Phase
- The third generation computer network from the late 1970s to the 1990s was an open and standardized network with a unified network architecture and compliance with international standards. After the rise of ARPANET, computer networks have developed rapidly. Major computer companies have successively introduced their own network architectures and software and hardware products that implement these structures. Because there is no uniform standard, it is difficult to interconnect products from different manufacturers. People urgently need an open, standardized and practical network environment. As a result, two kinds of internationally most important architectures have emerged, namely the TCP / IP system Structure and OSI architecture of the International Organization for Standardization. [2]
Computer network high-speed network technology stage
- The fourth-generation computer network from the 1990s to the present, due to the mature development of local area network technology, the emergence of fiber optic and high-speed network technology, the entire network is like a large computer system transparent to users, and has developed into the Internet represented by the Internet . [2]
Computer network composition
- The classification of computer networks is the same as the general classification of things. It can be classified according to the different characteristics of things (that is, the attributes of things). A computer network is generally composed of multiple computers (or other computer network equipment) connected together physically (or logically) through a transmission medium and software. In general, the composition of a computer network basically includes four parts: a computer, a network operating system, a transmission medium (which can be tangible or intangible, such as a wireless network's transmission medium is space), and corresponding application software. [3]
Computer network function
Computer network data communication
- Data communication is one of the most important functions of computer networks. Data communication is a communication method and communication service that uses data transmission technology to transfer data information between two terminals according to a certain communication protocol. It can realize the transfer of data information between computers and computers, computers and terminals, and terminals and terminals. It is the third largest communication service after the telegraph and telephone services. The information transmitted in data communication is expressed in the form of binary data. Another feature of data communication is that it is always associated with telematics. It is a generalized information processing including scientific computing, process control, information retrieval and other content. [2]
Computer network resource sharing
- Resource sharing is one of the main purposes for people to build computer networks. Computer resources include hardware resources, software resources, and data resources. The sharing of hardware resources can improve the utilization of equipment and avoid repeated investment in equipment, such as using a computer network to establish a network printer; the sharing of software resources and data resources can make full use of existing information resources, reduce labor during software development, and avoid Repeated construction of large databases. [2]
Centralized computer network management
- The development and application of computer network technology have changed modern office methods, business management, and so on. At present, there are many management information systems and office automation systems. Through these systems, centralized management of daily work can be achieved, improving work efficiency and increasing economic benefits. [2]
Computer network for distributed processing
- The development of network technology makes distributed computing possible. For large-scale topics, they can be divided into many small topics, which are completed by different computers, and then concentrated together to solve the problem. [2]
Computer network load balancing
- Load balancing refers to the work being evenly distributed to each computer system on the network. The network control center is responsible for distribution and detection. When a computer is overloaded, the system will automatically transfer the load to a lighter computer system to handle it. [2]
- It can be seen that the computer network can greatly expand the functions of the computer system, expand its application range, improve reliability, provide convenience for users, at the same time reduce costs, and improve performance-price ratio. [2]
Computer network classification
- Although there are various standards for dividing network types, geographical division is a universal network division standard that everyone agrees on. According to this standard, various network types can be divided into four types: local area network, metropolitan area network, wide area network, and Internet. Generally speaking, a local area network can only be in a small area. A metropolitan area network is a network interconnection of different regions. However, it should be noted that the network division here does not distinguish geographically in a strict sense. the concept of. The following briefly introduces these types of computer networks. [4]
Computer network local area network
- local area network
- The characteristics of this network are: narrow connection range, few users, easy configuration, and high connection speed. At present, the fastest speed of the local area network is the current 10G Ethernet. The IEEE 802 Standards Committee defines a number of major LAN networks: Ethernet, Token Ring, Fiber Distributed Interface Network (FDDI), Asynchronous Transfer Mode Network (ATM), and the latest wireless LAN (WLAN). These will be described in detail later. [4]
Computer network metropolitan area network
- Metropolitan Area Network Diagram
- Many MANs use ATM technology to make the backbone network. ATM is a high-speed network transmission method for data, voice, video, and multimedia applications. ATM includes an interface and a protocol, which can switch between constant and changing traffic on a regular transmission channel. ATM also includes hardware, software, and media consistent with the ATM protocol standard. ATM provides a scalable backbone infrastructure to accommodate networks of different sizes, speeds, and addressing technologies. The biggest disadvantage of ATM is that the cost is too high, so it is generally used in government metropolitan area networks, such as postal services, banks, and hospitals. [4]
Computer network wide area network
- Wide area schematic
- The above mentioned several classifications of the network. In fact, the real thing we meet most often is the local area network, because it can be large or small. It is relatively easy to implement in the unit or the family. It is also the most widely used one. Kind of network, so in the following we need to make a further understanding of the local area network and the access equipment in the local area network. [4]
Computer network wireless network
- With notebook computers and personal digital assistants
- Wi-Fi
- Wireless networks, especially wireless local area networks, have many advantages, such as ease of installation and use. However, wireless local area network also has many shortcomings: for example, its data transmission rate is generally low, much lower than that of wired local area network; in addition, the wireless LAN's bit error rate is also relatively high, and the mutual interference between sites is relatively strong. There are different ways to implement the user's wireless network. Some universities abroad have installed many antennas on their campuses, allowing students to sit under the trees and view library materials. This is achieved by digitally communicating between two computers directly via a wireless local area network. Another possible way is to use a traditional analog modem to communicate through a cellular telephone system. Many cities in foreign countries have been able to provide Cellular Digital Packet Data (CDPD) services, so wireless local area networks can be established directly through the CDPD system. Wireless network is a research hotspot at home and abroad, and research on wireless network is driven by huge market demand. The characteristic of the wireless network is that users can access the computer network at any time and any place, and this feature makes it have a strong application prospect. Many wireless network-based products have appeared, such as Personal Communication System (PCS) phones, wireless data terminals, portable video phones, personal digital assistants (PDAs), and so on. The development of wireless networks depends on the support of wireless communication technology. Wireless communication systems mainly include: low-power cordless telephone systems, analog cellular systems, digital cellular systems, mobile satellite systems, wireless LANs, and wireless WANs. [4]
Computer network performance
- Computer network performance generally refers to its several important performance indicators. But in addition to these important performance indicators, there are some non-performance characteristics that also have a great impact on the performance of computer networks. [5]
- 1. Computer network performance indicators
- Performance indicators measure the performance of computer networks from different aspects. [5]
- (1) Speed
- The signals sent by the computer are all in digital form. Bit is a unit of the amount of data in a computer, and it is also a unit of the amount of information used in information theory. The English word bit is derived from binary digit, meaning a "binary digit", so a bit is a 1 or 0 in a binary digit. The rate in network technology refers to the rate at which a host connected to a computer network transmits data over a digital channel. It is also known as the data rate or bit rate. Speed is one of the most important performance indicators in computer networks. The unit of rate is bit / s (bit per second). [5]
- (2) Bandwidth
- "Bandwidth" has two different meanings. [5]
- Bandwidth originally refers to the bandwidth of a signal. The bandwidth of a signal refers to the frequency range occupied by various frequency components contained in the signal. For example, the standard bandwidth of a telephone signal transmitted on a traditional communication line is 3.1 kHz (from 300 Hz to 3.4 kHz, which is the frequency range of the main component of speech). The unit of bandwidth in this meaning is hertz (or kilohertz, megahertz, gigahertz, etc.). [5]
- In computer networks, bandwidth is used to indicate the ability of the network's communication lines to transmit data, so network bandwidth represents the "highest data rate" that can be passed from one point in the network to another in a unit time. "Bandwidth" generally refers to this meaning. The unit of bandwidth in this meaning is "bits per second", which is recorded as bit / s. [5]
- (3) Throughput
- Throughput represents the amount of data that passes through a network (or channel, interface) in a unit of time. Throughput is more often used as a measure of real-world networks in order to know exactly how much data can actually pass through the network. Obviously, throughput is limited by the bandwidth of the network or the rated speed of the network. For example, for a 100Mbit / s Ethernet whose rated rate is 100Mbit / s, then this value is also the absolute upper limit of the throughput of the Ethernet. Therefore, for a 100Mbit / s Ethernet, its typical throughput may only be 70Mbit / s. Sometimes throughput can also be expressed in bytes or frames transferred per second. [5]
- (4) Delay
- Delay refers to the time required for data (a message or packet, or even bits) to be transmitted from one end of the network (or link) to the other. Delay is an important performance indicator, and it is sometimes called delay or delay. The delay in the network is composed of the following different parts. [5]
- Delay in sending.
- The transmission delay is the time required by the host or router to send the data frame, that is, the time from the first bit of the transmitted data frame to the completion of the transmission of the last bit of the frame. [5]
- Therefore, the transmission delay is also called transmission delay. The formula for calculating the transmission delay is: [5]
- Transmission delay = data frame length (bit / s) / channel bandwidth (bit / s) [5]
- It can be seen that, for a certain network, the transmission delay is not constant, but is directly proportional to the frame length (bits) sent, and inversely proportional to the channel bandwidth. [5]
- Transmission delay.
- The propagation delay is the time it takes for an electromagnetic wave to travel a certain distance in the channel. The formula for calculating the propagation delay is: [5]
- Propagation delay = channel length (m) / propagation rate of electromagnetic waves on the channel (m / s) [5]
- The propagation rate of electromagnetic waves in free space is the speed of light, which is 300,000 km / s. The propagation rate of electromagnetic waves in network transmission media is slightly lower than in free space. [5]
- Processing delay.
- When a host or router receives a packet, it takes a certain amount of time to process it. For example, it analyzes the header of the packet, extracts the data part from the packet, performs error checking, or finds an appropriate route. This results in processing delay. [5]
- Delay in line.
- When packets are transmitted through the network, they must pass through many routers. However, after entering the router, the packets must be queued in the input queue for processing. After the router determines the forwarding interface, it will also wait in the output queue for forwarding. This creates queuing delays. [5]
- In this way, the total delay experienced by the data in the network is the sum of the above four delays: [5]
- Total delay = sending delay + propagation delay + processing delay + queuing delay [5]
- (5) Delay Bandwidth Product
- Multiplying the two measures of network performance discussed above, propagation delay and bandwidth, yields another useful metric: the propagation delay bandwidth product, and the instantaneous bandwidth product = propagation delay × bandwidth. [5]
- (6) Round trip time (RTT)
- In computer networks, the round-trip time is also an important performance indicator, which indicates the total time that has elapsed since the sender sent the data and the sender receives the acknowledgement from the receiver (the receiver sends the acknowledgement immediately after receiving the data). [5]
- When using satellite communications, the round-trip time (RTT) is relatively long. [5]
- (7) Utilization
- There are two types of utilization: channel utilization and network utilization. Channel utilization refers to the percentage of time a channel is being used (with data passing), and the utilization rate of a completely idle channel is zero. Network utilization is a weighted average of channel utilization across the network. [5]
- 2. Non-performance characteristics of computer networks
- These non-performance characteristics have a great relationship with the performance indicators introduced earlier. [5]
- (1) Expenses
- The price of the network (including the cost of design and implementation). The performance of a network is closely related to its price. Generally speaking, the higher the speed of the network, the higher its price. [5]
- (2) Quality
- The quality of a network depends on the quality of all the components in the network and how those components make up the network. The quality of the network affects many aspects, such as the reliability of the network, the simplicity of network management, and some performance of the network. However, the performance of the network is not the same as the quality of the network. For example, some networks that have acceptable performance fail after running for a period of time and become unable to continue to work, indicating that the quality is not good. High-quality networks are often more expensive. [5]
- (3) Standardization
- The hardware and software of the network can be designed in accordance with common international standards or specific private network standards. It is best to adopt the design of international standards, so that it can get better interoperability, easier to upgrade and repair, and easier to get technical support. [5]
- (4) Reliability
- Reliability is closely related to the quality and performance of the network. Higher-speed networks are not necessarily less reliable. However, it is often more difficult for higher-speed networks to run reliably, and the cost is also higher. [5]
- (5) Scalability and upgradeability
- When the network is constructed, it should be considered that it may need to be expanded (that is, scaled up) and upgraded (that is, improved performance and version) in the future. The higher the performance of the network, the higher its expansion cost and the more difficult it is. [5]
- (6) Easy to manage and maintain
- Without good management and maintenance of the network, it is difficult to achieve and maintain the designed performance. [5]
Computer network related applications
- In the 21st century, mankind will fully enter the information age. The important characteristics of the information age are digitalization, networking and informationization. To achieve informatization, we must rely on a perfect network, because the network can transfer information very quickly. Therefore, the Internet has now become the lifeblood of the information society and an important foundation for developing the knowledge economy. The Internet has had an inestimable impact on many aspects of social life and on social and economic development. [3]
- The network mentioned here refers to the "three networks", that is, telecommunications networks, cable television networks, and computer networks. These three networks provide different services to users. Users of telecommunications networks can get services such as telephone, telegram and fax; users of cable television networks can watch various TV programs; computer networks can allow users to quickly transfer data files, and find and obtain various useful information from the network, Includes image and video files. These three kinds of networks all play a very important role in the process of informationization, but among them, the computer network is the fastest growing and plays a core role. With the development of technology, telecommunication networks and cable television networks are gradually integrated into the technology of modern computer networks (also known as computer communication networks), which has led to the concept of "network convergence". [3]
- Since the 1990s, the computer network represented by the Internet has developed rapidly. It has gradually developed from the original education and research network to a commercial network, and has become the second largest in the world after the global telephone network. The internet. The Internet is changing every aspect of our work and life. It has brought huge benefits to many countries and accelerated the process of the global information revolution. The Internet is the biggest change in communications since the invention of printing. People now live, work, study and interact with the Internet. [3]
- Computer networks provide users with two of the most important functions, connectivity and sharing. [3]
- The reason why so many computer networks are established is mainly because the use of computer networks is favored by individuals and companies. [3]
- 1. Commercial use.
- 1. It mainly implements resource sharing and finally breaks the tyranny of geography. It mainly uses the client-server model. [3]
- 2. Provide a powerful communication medium. For example: E-mail, video conference. [3]
- 3. E-commerce activities. For example, various vendors buy subsystems and then assemble these parts. [3]
- 4. Do various transactions with customers through the Internet. Such as: bookstores, audiovisual purchase goods or services at home. [3]
- Second, family use
- 1. Access remote information. For example: browse Web pages for information on art, business, cooking, government, health, history, hobbies, entertainment, science, sports, travel, and more. [3]
- 2. Communication between individuals. For example: instant messaging uses <QQ, MSN, YY>, chat rooms, peer-to-communication <shared through a central database, major network disks, but easy to cause copyright violations> [3]
- 3. Interactive entertainment. Such as: video-on-demand, instant comment and participation in activities <television live network interaction>, online games. [3]
- 4. E-commerce in a broad sense. Such as: paying bills electronically, managing bank accounts, and processing investments. [3]
- Third, mobile users
- Based on wireless network. [3]
- 1. Movable computer: notebook computer, PDA, 3G mobile phone. [3]
- 2. Military: A war cannot rely on LAN devices to communicate. [3]
- 3, applications such as truck fleets, taxis, courier cars. [3]
- Social issues
- The widespread use of the Internet has led to new social, ethical and political issues. [3]