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Transcript
Chaos, Communication and Consciousness Module PH19510 Lecture 12 Data Networks Across the World Overview of Lecture Early data communications Circuit switching The modem – Data over phone lines Packet switched networks ARPAnet, SERCnet Internet protocols World Wide Web Early Data Communications 1793 Chappe tower network 1850s onward – Telegraph network 1889 Automatic switching of telephones 1940 George Stibitz used teletype to send instructions & receive back data. Circuit Switching Dedicated connection between nodes Established for duration of communications Guaranteed capacity Inefficient use of resources The Modem Modulate & Demodulate Convert 1s and 0s into sounds for transmission over telephone line Originally acoustic coupling Must be in audio (400Hz-4Khz) range Encode 1 & 0 as tones Nowadays up to 56kbps over conventional phone system Computer Networking in the 1960s & 70s Remote users connected to central facilities Several terminals multiplexed over dedicated phone line Multiplexer shares connection between users Minicomputer/ mainframe Terminals Direct Connection Multiplexer Packet Switching - 1965 3 key ideas Decentralised network, multiple routes between nodes Information split into message blocks (packets) Delivery of packets by store & forward Efficient use of resources Reliable What’s in a packet ? Source Address (IP) Destination Address (IP) Length of packet in bytes Total number of packets in message Sequence Number Checksum Data ARPANET (USA) Advanced Projects Research Agency (USA) First Packet switched Network, Q4, 1969 4 Nodes University of California, Los Angeles Stanford Research Institute University of California, Santa Barbara University of Utah Interface Message Processors (IMPs) deal with packet switching. IMPs connected to mainframe/minis at each node. ARPAnet in 1977 X.25 networks Simlar principles to ARPAnet 1974 SERCnet linked UK universities & research institutes became JANET IPSS – International Packet Switched System 1st international PSS US, Canada, Europe, Australia Request For Comment (RFC) Building networks is a collaborative enterprise. RFC mechanism came out of ARPA Serve as mechanism for dissemination for information Some become adopted as standards Inter-networking By early 80s, several different networks ARPAnet, SERCnet, UUCP, Tymenet, AOL… Gateways linked some networks Difficult to transfer data/information across Solution – TCP/IP protocol sits ‘on-top’ of different networks allows seamless integration Layers of Protocol Break networking into series of ‘layers’ Application – Web browser, email etc Transport – Get messages from host to host (TCP) Network – Get packets across single network (IP) Data Link – Protocol over single link in network (UDP) Physical – Cables, connectors Seamless networking – from NOAA Growth of the net Map of the Internet - 2005 The World Wide Web Service running on the internet 1990 First implementation Tim Berners-Lee, CERN Browser – World Wide Web Server – info.cern.ch Pages – CERN Telephone book Review of Lecture Early data communications Circuit switching The modem – Data over phone lines Packet switched networks ARPAnet, SERCnet Internet protocols World wide Web