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Flow control methods (Delays (Some basics (Giga (BW : 10^9, Data: 2^30),…

- - - - L is lenghth of data, b is bandwidth
  - - - BW : 10^9
      - Data: 2^30
    - - BW: 10^6
      - Data: 2^20
    - - BW: 1000
      - Data: 1024
  - - - distance/velocity
- - - - Time Out (TO) timer: time for which sender waits after which it re-sends the data
        
        S&W + TO is aka ARQ or Automatic repeat reQuest
    - - So we have sequence num with each data packet; no duplication
    - - Due to delayed receivin of ack. some data pack. may get lost
        
        To solve this we associate a number with each ack.
- - - - min sequence num needed for packets in window = 1+2a
        
        bits for sequence num = ceiling[log(1+2a)]
    - - GBN or Go back N
        
        Important points:
        
        1 Sender Window size is N; N>1 as N=1 will be same as S&W
        
        2 Receiver Window size is always 1
        
        Cummulative ack used
        
        How is it implemented here?
        
        we use ack timer: ack is sent for packets received within this time
        
        what is the ack num sent back?
        
        1 plus the highest packet num
        
        Why called Go Back?
        
        As we go back from last transmitted packet when Time out occurs; re propagating them
        
        Condition to avoid duplication problem: avail seq num = N + 1
        
        BW usage high
        
        CPU usage and implementation : moderate
      - SR or Selective Repeat
        
        Important points
        
        Ws > 1
        
        Wr = Ws
        
        Ack are independent
        
        Here receiver can even send a -ve ack indicating corrupt packet. this isnt possble in Go Back N (discarded silently)
        
        Here selectively only that packet sent whose ack isnt received; hence num of re transmissions are less
        
        has efficiency same as Go back N
        
        Complex to implemnt as searchin and sortin needed in this
        
        CPU usage high
        
        BW usage moderate
      - Some basic
        
        Two types of ack.
        
        Cummulative: one ack for many packets
        
        Independent : ack for each packet
    - - To solve this the required condition is : avail seq num >= Ws + Wr