What is a computer network,? ?,The computer network is the computer system in different geographical location and function of independent by communication lines are interconnected, the system realizes the sharing and communication of cyber source in the network management software,sketch map,Mainfunction:to achieve the data communication and resource sharing1,Basic function: data communication Main features: resource sharing Classification: wide area network （WAN）：Tens to thousands of kilometers local area network （ALN） A few meters to a few kilometers metropolitan area network（MAN）（Between WAN and LAN）,1.2The basis of computer communication,2、The main technology - the maximum transmission rate index of data communication,1、Data communication - in the form of an electrical signal to the data transmitted from one end to the other end.,3、Modulation, demodulation (Modem): converting the data signals and analog signals.,Baseband transmission (BAB): the original form of the signal into the line. Broadband transmission (BRB): converting the data signal in the computer for analog signal transmission,Parallel communication Serial communication,4、Baseband and broadband transmission,5、mode of data transmission,1.2.2Computer network system and network protocol,1, Network protocol: must follow the stipulated in the communication process. 2、Network system is generally divided into seven layers:,The physical layer Data link layer The network layer Transport layer The session 会话layer The presentation layer Application layer,123Computer network operating system,Single operation Network management,Dual function of the software,124 network devices,Server, workstation, network card, modem, communication lines, communication equipment.,modem,network card,INTERNET与,Network,modem,1.3 Computer LAN,Small range The transmission rate is generally megabits per second (Mbps) (ten to 100 million) Transmission medium using twisted pair, coaxial cable, optical cable Extensive use of bus type, star type structure, supports both point-to-point communication and multipoint communication. Easy installation, maintenance, high reliability. Easy to learn,1.3.1Characteristics,INTERNET与,network,LAN,1.3 Computer local area network,一、Composition：,hardware system,software system,The server (using high-grade machine, rich shared resources) The workstation (personal computer) NIC (network adapter) Lines of communication communication device,1、 hardware system,sketch map of LAN,server,Novell network （operating system (OS)：Netware） Windows NT （operating system (OS)：Windows NT Server),2、 software system,1.4INTENRET Multiple LANs interconnected became a global internet. The Internet is mainly to solve the problem of different network protocols, in order to make the computer network of different types can be connected.,Internet,The main machine,Internet hardware：,Repeater (amplifying signal function, used to connect the long line) Bridge (connecting two similar network, expanding the number of users in the network) Router (bridge, the network and the network connection data - the source host - multiple routers - the destination host) gateway (online different types of different network protocols),Internet is a global, the most influential, the most abundant information resources in the internet,1 What is Internet,143 Internet languageTCP/IP,TCP/IP is a set of protocols. It is the communication between Internet computer must be a common communication rules,3、File Transfer Protocol（FTP） FTP is one of the traditional service. FTP allows users to transfer files between two computers on the internet,