Packets

• MB file transferred across network with 56Kbps capacity will require 12 minutes:

5x106 bytes * 8 bits/byte 60 secs/minute * 56x103 bits/second

= 11.9 minutes

• All other computers will be forced to wait 12 minutes before initiating other transfers

• If file is broken into packets, other computers must only wait until packet (not entire file) has been sent
• From previous example, suppose file is broken into 1000 byte packets
• Each packet takes less than .2 seconds to transmit:

1000 bytes * 8 bits/byte 56x103 bits/second

= .143 seconds

• Other computer must only wait .143 seconds before beginning to transmit.

• Dividing data into small packets allows time-division multiplexing
• Each packet leaves the source and is switched onto the shared communication channel through a multiplexor
• At the destination, the packet is switched through a demultiplexor to the destination