Repeated Acknowledgements in TCP

king99

king99

@king99-bh2V1z • Oct 22, 2024

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Hi ,
In order to guess packet loss :-TCP uses repeated ack , But can any one explain what is repeated ack and how it is different than ack ?

Thanks !!

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  • durga ch

    durga ch

    @durga-TpX3gO • Apr 26, 2011

    Hi
    I am not too sure of repeated ACK, but there are instances when duplciate ACKs are sent

    The whole process of error detection and recovery is :-
    when a TCP session is made, the sender sends 1 packet , the reciever ACKs with ACK1 and the sender does a SYC-ACK1 which indicates that 1 packet has been succesfulyl transmitted.
    Now doing this for every packet means - heavy wastage of time and BW.
    Thus TCP windowing was introduced, where ACKs are done for a SET of packets

    SO now,
    Sender sends 1 packet ; reciever does ACK2 ; sender does SYC-ACK2
    sender now increases the packet size to 2 as it knows the reciever and the link are able to process 1 packet finely
    it does -- 1,2 packets ; reciever does ACK3 ; sender does SYC-ACK3

    likewise the sender keeps in incrementing the window size till it feels sometime is going wrong. like below

    Sender -- 1,2,3,4,5,6,7,8 ; reciever does ACK7 ; sender realises that7, 8 th packet has been missed and resends the packet 7,8 and reciver does a ACK 9 , prompting the sender to do a SYC- ACK9
    remeber that the ACKs from the reciver indicates what next seq id it expecting.

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