Tuesday, November 23, 2010

Networking - Circuit & Packet Switching, Frame Relay & ATM


  • Point to point communication not usually practical 
    • Devices are too far apart 
    • Large set of devices would need impractical number of connections 
  • Solution is a communications network


Simplified Network Model


Wide Area Networks
  • Large geographical area 
  • Crossing public rights of way 
  • Rely in part on common carrier circuits 
  • Alternative technologies 
    • Circuit switching 
    • Packet switching 
    • Frame relay 
    • Asynchronous Transfer Mode (ATM)

Circuit Switching
  • Dedicated communications path established for the duration of the conversation 
  • e.g. telephone network

Packet Switching
  • Data sent out of sequence 
  • Small chunks (packets) of data at a time 
  • Packets passed from node to node between source and destination 
  • Used for terminal to computer and computer to computer communications

Frame Relay
  • Packet switching systems have large overheads to compensate for errors 
  • Modern systems are more reliable 
  • Errors can be caught in end system 
  • Most overhead for error control is stripped out

Asynchronous Transfer Mode
  • ATM 
  • Evolution of frame relay 
  • Little overhead for error control 
  • Fixed packet (called cell) length 
  • Anything from 10Mbps to Gbps 
  • Constant data rate using packet switching technique

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