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Flow Control

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• What is Flow Control ?
  • In data communication, we are attaching communication devices of differing capabilities (some more powerful (i.e., faster) than others, has more memory, etc. etc.)

  • When unrestrainted, faster and more capable machines can overrun the buffer utilization in slower and less capable machines and the communication will become very unreliable due to buffer overflow.

  • Flow control mechanisms allow communicating devices to set limits on how much resources (buffer space) a device will need to realize a communication.

• Where are Buffers Used ?
  • In sender: to hold frames for retransmission
  • In receiver: to hold frames that arrived out of sequence

• Sliding Window Revisited
  • The sender window size is the amount of buffer space that the sender used (cliamed) to hold frames for retransmission.
  • The receiver window size is the amount of buffer space that the receiver will use to buffer out-of-order frames.