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					Computer Networks                                Prof. Hema A Murthy




                                        Issues
         • What if file is very large?
                – Heavy retransmissions
                – Very inefficient
         • Requires splitting the file.
                – Split file into what units?
                      • packets?




Indian Institute of Technology Madras
Computer Networks                                              Prof. Hema A Murthy




                 Packetised File Transmission
         • At A:                            • At B:
                – Packetise file              – Receive packet by
                – Transmit each packet          packet
                  separately with its own     – Check for errors
                  error control               – Acknowledge
                – If erroneous retransmit       reception of packet
                                              – Assemble packets and
                                                save to a file




Indian Institute of Technology Madras
Computer Networks                                         Prof. Hema A Murthy




          Packet based transmission: Issues
         • A Protocol is required:
                –   Start / end of a packet
                –   Start / end of a file
                –   Start / end of a byte
                –   Error control mechanism used
                –   Sequence number for each packet
                      • Out of order arrival of packets



Indian Institute of Technology Madras
Computer Networks                                          Prof. Hema A Murthy




                    A Layered Approach to Error
                              Control
         •    files: checksum
         •     messages: ?
         •     packets: CRC
         •     bytes: parity
         •     bits: voltage levels
         •     bare wire
         •    Different error control mechanisms at different
              layers

Indian Institute of Technology Madras

				
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posted:8/9/2012
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Description: networks