Chaos, Communication and Consciousness Module PH19510

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Chaos, Communication and ConsciousnessModule
PH19510

• Lecture 12
• Data Networks Across the World

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Overview of Lecture

• Early data communications
• Circuit switching
• The modem Data over phone lines
• Packet switched networks
• ARPAnet, SERCnet
• Internet protocols
• World Wide Web

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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.

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Circuit Switching

• Dedicated connection between nodes
• Established for duration of communications
• Guaranteed capacity
• Inefficient use of resources

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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

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Computer Networking in the 1960s 70s
Minicomputer/mainframe

• Remote users connected to central facilities
• Several terminals multiplexed over dedicated
  phone line
• Multiplexer shares connection between users

Terminals
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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

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Whats in a packet ?

• Source Address (IP)
• Destination Address (IP)
• Length of packet in bytes
• Total number of packets in message
• Sequence Number
• Checksum
• Data

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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.

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ARPAnet in 1977
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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

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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

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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

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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

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Seamless networking from NOAA
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Growth of the net
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Map of the Internet - 2005
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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

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Application Layer

• Application specific data
• Application layer protocols
• HTTP world wide web
• FTP File Transfer Protocol
• SMTP email
• Send message to ltaddressgtltportgt

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Transport Layer (TCP)

• Take message from application layer
• Break message into packets
• Put sequence numbers on packets
• Pass to Networking layer
• Re-transmit faulty packets
• Put received packets in correct order
• Discard duplicate packets

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Network Layer (IP)

• Takes data from Transport Layer
• Provide unique global addressing
• Deal with routing
• Unreliable
• Best efforts at getting data through
• Rely on upper layer to ensure relability
• Connectionless protocol
• Send packets on without establishing prior
  connection

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Data Link Layer

• Takes data from Network layer
• Prepares for transmission on physical layer
• Depends on medium
• Modem Speed etc.
• Ethernet Ethernet addresses, collision avoidance

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Physical Layer

• Cables, Plugs Sockets
• Voltages, Frequencies etc

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Review of Lecture

• Early data communications
• Circuit switching
• The modem Data over phone lines
• Packet switched networks
• ARPAnet, SERCnet
• Internet protocols
• World wide Web