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I have been reading the book "High Performance Browser Networking" by Ilya Grigorik about the slow-start algorithm, which is used for congestion avoidance. While I do understand its concepts, there were these phrases that confused me

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How does the phrase network segment have anything to do with the window size? I can't get the fact that the book mentioned "upgrade from sending 1 segment to 4 segments"

Thank you in advance

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  • I would suggest understanding what window-based protocols do. You can read about Go-Back-N and/or selective repeat for example in this book or any other networking book of your choice. On a very high level, window size is the number of segments that can be sent out,, without receiving an ACK. More detailed explanation requires a lot of pictures, so I refer to the reference.
    – Effie
    Commented Jan 23, 2023 at 11:02
  • @Effie Thank you for your resource. I will check that book out.
    – John Pham
    Commented Jan 23, 2023 at 15:50

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"1 network segment" refers to the same amount of data as maximum segment size MSS - the maximum size you can send in an unfragmented IP packet (with a payload size of the maximum transmission unit MTU).

Accordingly, the initial window size was 1*MSS, then 4*MSS and now 10*MSS.

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  • Thank you for your explanation. Make more sense to me now
    – John Pham
    Commented Jan 23, 2023 at 15:50
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TCP PDUs (Protocol Data Units) are called segments because TCP is a stream protocol where the application sends data to TCP, and TCP segments the data into chunks called segments to send over the network.

TCP is a transport protocol that sends segment to the network protocol that encapsulates the segments into packets to send to the data-link protocol that encapsulates the packets into frames. The reverse happens on the receiving end, where the data-link protocol strips off the frame, sending the frame payload (packet) to the network protocol that strips off the packet and sends the payload (segment) to TCP. TCP only knows about segments, and knows or cares nothing about packets and frames. TCP will strip off the segment from the data to pass the data to the application.

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  • Thank you for your help. I think I should read about the TCP protocol itself first.
    – John Pham
    Commented Jan 23, 2023 at 15:51

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