大学计算机基础英语教学 (2)

Network Concept

Computer networking may be considered a branch of electrical engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of the related disciplines.
Network Protocol


A network protocol defines rules and conventions for communication between network devices. Protocols for computer networking all generally use packet switching techniques to send and receive messages in the form of packets. OSI protocols are a family of standards for information exchange. These were developed and designed by the International Organization of Standardization (ISO). In 1977 the ISO model was introduced, which consisted of seven different layers. This model has been criticized because of its technicality and limited features.
physical topologies and logical topologies


The cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits. The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token Ring is a logical ring topology, but is wired as a physical star from the Media Access Unit.
Network Classification

Computer network can be classified on the different criteria, such as scale, Connection Method, Functional Relationship (Network Architectures), or Network Topology.
Wired
technologies Wireless technologies
By Scale

computer networks may be classified according to the scale, in Local Area Network (LAN), Metropolitan Area Network (MAN), and Wide Area Network (WAN).


Wide Area Network is a network system connecting cities, countries or continents, a network that uses routers and public communications links. The largest and most well­known example of a WAN is the Internet.
7 Layers
Data transmission
local area network

A LAN is a group of computers and associated devices that share a common communications line or wireless link to a server. Typically, a LAN encompasses computers and peripherals connected to a server within a distinct geographic area such as an office or a commercial establishment. Computers and other mobile devices use a LAN connection to share resources such as a printer or network storage.
CHAPTER 6 ONLINE CONNECTION
introduction

A network is the collection of devices that have the ability to communicate with each other.A basic understanding of networking is important for anyone managing a server. Not only is it essential for getting the services online and running smoothly, it also gives the insight to diagnose problems.
characteristics of a Computer Network

People can play a CD music from one computer while sitting on another computer. They may have a computer that does not have a DVD or BluRay (BD) player. In this case, people can place a movie disc (DVD or BD) on the computer that has the player, and then view the movie on a computer that lacks the player. People may have a computer with a CD/DVD/BD writer or a backup system but the other computer(s) does not (don't) have it. In this case, people can burn discs or make backups on a computer that has one of these but using data from a computer that does not have a disc writer or a backup system. People can connect a printer (or a scanner, or a fax machine) to one computer and let other computers of the network print (or scan, or fax) to that printer (or scanner, or fax machine). People can place a disc with pictures on one computer and let other computers access those pictures.
A Local Area Network is a computer network covering a small Networks geographical area, like a home, office, or groups of buildings. Metropolitan Area Network (MAN) are large computer network usually spanning a city. They typically use wireless infrastructure or Optical fiber connections to link their sites.


In 1984, Apple Macintosh is launched and the first domain is registered in 1985. By 1995, the bulk of US internet traffic is routed through interconnected network service providers and Microsoft Windows 95 is launched.

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History of Network

Around 1960s-1970s, ARPANET commonly thought of as the predecessor to the Internet and created by the US Department of Defenses Advanced Research Projects Agency (ARPA). The first known fully operational packet-switching network, the ARPANET was designed to facilitate communication between ARPA computer terminals during the early 1960s, at a time when computers where far too expensive for widespread usage.
Structure of LAN

The structure of LAN is following the structure of network, also been called topology of network. Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network. Essentially, it is the topological structure of a network and may be depicted physically or logically. Physical topology is the placement of the various components of a network, including device location and cable installation, while logical topology illustrates how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be