Recovery after zero-window (without persist timer) - TCP-IP

This is a discussion on Recovery after zero-window (without persist timer) - TCP-IP ; Assume TCP session between Host A and Host B. When Host-A advertises window of 0 to Host-B, Host-B uses persist timer to send probe packet every so many sec (in 5 to 60 sec range). This is fine but introduces ...

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Thread: Recovery after zero-window (without persist timer)

  1. Recovery after zero-window (without persist timer)

    Assume TCP session between Host A and Host B.

    When Host-A advertises window of 0 to Host-B, Host-B uses persist timer

    to send probe packet every so many sec (in 5 to 60 sec range). This is
    fine but introduces atleast 5 sec delay in B resuming the
    transmissions.


    Is it possible for a Host-A to send a pure window update without Host-B

    probing it (as soon as A detects that its recv_win has opened). Also
    assume Host-A has no data to send..can it send a pure window update
    pkt?


    Basically, is there a provision to overcome recovery from win=0 state
    without using persist timer.


    Thanks,
    Vishal.


  2. Re: Recovery after zero-window (without persist timer)

    vishal.study@gmail.com wrote:
    > Assume TCP session between Host A and Host B.


    > When Host-A advertises window of 0 to Host-B, Host-B uses persist
    > timer to send probe packet every so many sec (in 5 to 60 sec
    > range). This is fine but introduces atleast 5 sec delay in B
    > resuming the transmissions.



    > Is it possible for a Host-A to send a pure window update without
    > Host-B probing it (as soon as A detects that its recv_win has
    > opened). Also assume Host-A has no data to send..can it send a pure
    > window update pkt?


    Absolutely. There is nothing in the TCP specs to preclude Host-A from
    sending a "spontaneous" window update once a sufficient quantity of
    window becomes available.

    Of course, IIRC there is nothing in the TCP specs that says it must

    > Basically, is there a provision to overcome recovery from win=0
    > state without using persist timer.


    Robustness would seem to dictate that one needs a persist timer on the
    sender.

    rick jones
    --
    a wide gulf separates "what if" from "if only"
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

  3. Re: Recovery after zero-window (without persist timer)

    Rick Jones wrote:

    > Robustness would seem to dictate that one needs a persist timer on the
    > sender.


    I left-out the biggest reason - the window update, as it is likley
    piggy-backed on a "bare" ACK segment, is not going to be retransmitted
    when that ACK is lost. Hence the requirement for a persist timer.

    rick jones
    --
    portable adj, code that compiles under more than one compiler
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

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