introductiontocomputernetworks-国立政治大学资讯科学系.ppt

Introduction to Computer Networks – A Selective Overview 國立政治大學 資訊科學系 劉吉軒 副教授 Computer Communication Transfer a file of data Access information from a database Exchange of electronic mail Financial transaction Share the use of peripheral devices Access a remote supercomputer Industrial control/Business activity Basic Communication Functions Data Communication Networks Simple computer-to-computer Involved only two computers Two alternatives Point-to-point wire link Public carrier facilities Public switched telephone network (PSTN) Modem link Two Computers Only More Than Two Computers LAN – local area networks All computers are located in a single office or building or site Enable all computers to communicate with one another at different times Involve different techniques and equipments or devices LAN-based Systems Wider Area Computers are located in different sites Use public carrier facilities Wide Area Network (WAN) Enterprise-wide private network Lease dedicated transmission lines (circuits) from the public carriers Enterprise-wide Private Network More General Solutions Public switched data network (PSDN) most public carriers now provide this, in addition to providing PSTN such networks, like PSTN, are now interconnected internationally transmit data rather than voice Alternatively, convert existing PSTNs to enable data to be transmitted without modems ISDNs (Integrated Services Digital Networks) Public Carrier Data Networks Internet Embrace multiple networks, LAN-WAN-LAN Broadband Multiple-service Networks Traditional networks primarily support data-only services New applications Desktop video telephony Videoconferencing, etc. Require high transmission bit rates ATM (Asynchronous Transfer Mode) Broadband Multiple-service Networks Categories of Networks Local Area Networks (LANs) Metropolitan Area Networks (MANs) Wide Area Networks (WANs) Size, ownership, the distance it covers, physical architecture LAN Usually privately owned and links the