The most basic function of a computer network is resource sharing. Computer networks have two basic functions: data communication and resource sharing, of which the latter is the most essential function. 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 computer networks to establish network printers; the sharing of software resources and data resources can make full use of existing information resources, reduce labor in the software development process, and avoid Repeated construction of large databases.
#The operating environment of this article: Windows 7 system, Dell G3 computer.
Computer network refers to the connection of multiple computers and their external devices with independent functions in different geographical locations through communication lines. Under the management and coordination of network operating systems, network management software and network communication protocols , a computer system that realizes resource sharing and information transfer.
Computer networks have two basic functions: data communication and resource sharing, of which the latter is the most essential function.
Resource sharing means that multiple users share hardware and software resources in a computer system. In the network system, the main resources that end users can share include processor time, shared space, various soft equipment and data resources, etc. Resource sharing is one of the main goals achieved by 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 computer networks to establish network printers; the sharing of software resources and data resources can make full use of existing information resources, reduce labor in the software development process, and avoid Repeated construction of large databases.
Two basic principles of resource sharing:
The law of large numbers:
The law of large numbers says: If The number of users is very large, and their resource usage requirements are sudden and random. When all users are considered as a whole, the user's overall resource usage requirements become quite smooth and stable, and they are also Predictable.
Economies of scale:
Economies of scale say: when the resources and the number of users in a system increase in proportion at the same time, within a certain range, the system The larger the scale, the more economical the system is.
Sharing Category
1. Sharing of data and applications.
1.1 Print Sharing Establish a print server in the LAN to provide printing services to all users on the LAN.
1.2 Mail function The mail server can provide user name-based mail forwarding, distribution, carbon copy and other services for all employees within the enterprise, and can complete convenient management, backup, and Delete, recover, restore and other tasks.
1.3 The most common applications for online chat are Whiteboard, Netmeeting, WebEx and other applications, which can realize real-time and fast voice and video communication between users located in different physical locations.
1.4 Real-time messaging applications such as Yahoo IM and MSN can realize message forwarding within the local area network and the Internet.
1.5 Database The database server is an important part of the enterprise LAN, which can realize functions such as data sharing, redundancy reduction, centralized storage and management, maintainability and security.
2. Common network storage is file sharing services, which use FTP and TFTP services to enable users to conveniently and securely access resources on shared servers on workgroup computers, and Most ftp resources are free.
3. Resource Backup With the development of network attacks and viruses, resource backup has become an indispensable part of resource sharing. Most modern enterprises adopt real-time and efficient resource backup methods to ensure that when the network crashes It can protect company information to the greatest extent and play the greatest role in disaster recovery.
4. Personal connections: including customer resources, capability resources and other things that can be applied to each other.
5. Equipment.
Expand knowledge:
Computer network is also called computer communication network. The simplest definition of a computer network is: a collection of interconnected, autonomous computers that share resources. If this definition is used, the early terminal-oriented networks cannot be regarded as computer networks, but can only be called online systems (because many terminals at that time cannot be regarded as autonomous computers). But as hardware prices fall, many terminals have a certain degree of intelligence, so the strict boundaries between "terminals" and "autonomous computers" are gradually lost. If a microcomputer is used as a terminal, according to the above definition, the early terminal-oriented network can also be called a computer network.
From a logical function point of view, a computer network is a collection of computer systems that use communication lines to connect multiple computers for the basic purpose of transmitting information. A computer network consists of transmission media and communication equipment.
From the user's perspective, a computer network is defined as follows: there is a network operating system that can be automatically managed by the user. It calls the resources called by the user, and the entire network is transparent to the user like a large computer system.
Division of computer networks
(1) According to the coverage and scale of the network: local area network, metropolitan area network, and wide area network.
(2) According to transmission medium: wired network, optical fiber network, wireless network.
(3) According to data switching mode: circuit switching network, message switching network, packet switching network.
(4) According to communication mode: broadcast transmission network, point-to-point transmission network.
(5) According to service mode: client, server network, peer-to-peer network.
Performance indicators of computer networks
Performance indicators measure the performance of computer networks from different aspects.
(1) Rate
The signals sent by the computer are all in digital form. A bit is a unit of data in a computer and a unit of information used in information theory. The English word bit comes from binary digit, which means a "binary number", so a bit is a 1 or 0 in a binary number. The rate in network technology refers to the rate at which a host connected to a computer network transmits data on a digital channel. It is also called data rate or bit rate. Speed is the most important performance indicator in computer networks. The unit of rate is bit/s (bits per second).
(2) Bandwidth
"Bandwidth" has the following two different meanings.
① Bandwidth originally refers to the frequency 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 telephone signals transmitted over traditional communication lines is 3.1 kHz (from 300 Hz to 3.4 kHz, the frequency range of the main components of speech). The unit of bandwidth in this sense is Hertz (or kilohertz, megahertz, gigahertz, etc.).
② In computer networks, bandwidth is used to represent the ability of the network's communication lines to transmit data. Therefore, network bandwidth represents the "highest bandwidth that can be passed from one point in the network to another point in a unit time." data rate". This is what the "bandwidth" generally mentioned here means. The unit of bandwidth in this sense is "bits per second", recorded as bit/s.
(3) Throughput
Throughput represents the amount of data passing through a certain network (or channel, interface) within a unit time. Throughput is more often used as a measurement of real-world networks to know how much data is actually able to pass through the network. Obviously, throughput is limited by the bandwidth of the network or the rated rate of the network. For example, for a 100Mbit/s Ethernet, its 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 by the number of bytes or frames transmitted per second. [5]
(4) Latency
Latency 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. time. Latency is a very important performance indicator. It is sometimes called delay or latency.
(5) Delay-bandwidth product
Multiply the two measures of network performance discussed above - propagation delay and bandwidth, and you will get another very useful metric: propagation delay Bandwidth product, that is, delay bandwidth product = propagation delay × bandwidth.
(6) Round trip time (RTT)
In computer networks, round trip time is also an important performance indicator. It means from the time the sender sends data to the time the sender receives the data from the receiver. The total time elapsed for the receiving party's confirmation (the receiving party sends a confirmation immediately after receiving the data).
When using satellite communications, the round trip time (RTT) is relatively long.
(7) Utilization rate
There are two types of utilization rate: channel utilization rate and network utilization rate. Channel utilization refers to what percentage of the time a channel is used (data passes through). The utilization of a completely idle channel is zero. The network utilization is the weighted average of the channel utilization of the entire network.
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