6 comments to Screencast 5

  1. Bryan Chu says:

    Hi, if anyone can answer this it would be great.

    I don’t understand why the blue and red packets can coexist at the same time in the buffer diagrams.

    If there are packets to be sent (red), and there is space available (blue), shouldn’t it be filled up?


    • Ooi Wei Tsang says:

      Red packets are the ones that have been sent.

      • Bryan Chu says:

        sorry, to be more precise i’m referring to slide 56, red is marked “cannot send” while blue is unused sender buffer.

        or is red “cannot send” because of rwnd conditions?

        • Ooi Wei Tsang says:

          I see. You are referring to Lecture 4, not Lecture 5.

          The sender cannot send those red sequence numbers because the sequence numbers are outside of the sending window. The sender has to send in increasing sequence number (fill the sequence number from left to right).

          There is no rwnd technically when we talk about SR and GBN. But the sending window is used for flow control.

  2. yangshun says:

    I believe TCP stands for Transmission Control Protocol and not Transport Control Protocol, as shown in slide 13 of the lecture notes.

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