Telecommunicationsandthe Internet培训课件.ppt

Types of Networks Computer networks are commonly classified by size, distance covered, and structure. The most commonly used classifications are: PBX (Private Branch Exchange) LAN ( Local Area Network) WAN ( Wide Area Network) MAN ( Metropolitan Area Network) PAN ( Personal Area Network) Private Branch Exchanges A private branch exchange (PBX) supports local phone and data communications, as well as links to outside phone and data networks. PBX is a special-purpose computer designed for handling and switching office telephone calls at company site. PBX can store, transfer, hold, and redial telephone calls. Since they use ordinary telephone lines, PBX systems have limited bandwidth. The advantage of digital PBX over local networking is that PBX does not need special wiring. Local Area Network Printer Computer3 Computer2 Network Gateway Computer1 Other Network Network Operating System Server Local Area Network LAN is used to connect PCs or resources (e.g. printers) in one building or several buildings in close proximity. LAN has higher transmission capacity than PBX (Private Branch Exchange). LAN can transmit video and graphics. LAN is more expensive to install than PBX and less flexible. It requires new wiring each time a LAN is moved. The server acts as a librarian. It stores programs and data files for network users. The server determines who will get access to what and in what sequence. Sever can be powerful PCs with large hard-disk capacity, workstations, minicomputers, or mainframes. The network gateway connects the LAN to public networks, such as the telephone network, or to other corporate networks. Local Area Network A gateway is a communications processor that can connect dissimilar networks by translating from one set of protocols to another. LAN can use twisted wire, coaxial , or fiber-optic cable. LAN also can use wireless technology. The network operating system (NOS) can reside on every computer in the network, or it can reside on a single server.