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Hi all,
Thanks for your help.
I think what Atte said is more close to what I meet. In my case,I
saw that TCP
receiving worked well at first. But it got slow down after receivied
several
packets. It seems to be that we can't directly send ack via tcp_recved but
only
can send it via another packet arrived or tcp_fasttmr. So it gets slow
down after
sender has sent TCP_WND size of data.
Regards,
Bo-Er
K.J. Mansley
wrote:
> I thought that the stack should, if asked to send an ACK when
one has
> already been delayed, send a dedicated packet out at that
point. i.e.
> There should only be one outstanding delayed
acknowledgement at once.
> This would mean that if as in your case the
stack is only receiving
> data, it would send ACKs for every other
packet, rather than wait 250ms
> as you report.
>
> The
implementation of tcp_ack() backs this up:
>
> #define
tcp_ack(pcb) if((pcb)->flags & TF_ACK_DELAY) {
\
>
(pcb)->flags &= ~TF_ACK_DELAY;
\
>
(pcb)->flags |= TF_ACK_NOW;
\
>
tcp_output(pcb);
\
>
} else {
\
>
(pcb)->flags |= TF_ACK_DELAY;
\
>
}
>
> If the TF_ACK_DELAY flag is already set, it is cleared, and
TF_ACK_NOW
> set instead. The call to tcp_output() should then
dispatch the
> acknowledgement straight away.
>
> However,
as this doesn't match what you are seeing, there might be
> something
wrong. I'm not sure what though.
This is because tcp_recved()
only does an ack if there are no acks
pending (delayed or
otherwise):
if (!(pcb->flags & TF_ACK_DELAY)
&&
!(pcb->flags & TF_ACK_NOW))
{
/* ... comment deleted ...
*/
tcp_ack(pcb);
}
This effectively
nullifies the tests in tcp_ack() in this case. I
resolved this problem
(probably not very cleanly) by adding an extra
else to above test that
sends out an ack if there is already a
TF_ACK_DELAY pending on the pcb and
the receive window is big enough.
I had the same problem when doing an
application that only receives a
huge amount of data without sending out
anything.
- Atte
--
GARLIC GUM IS NOT FUNNY
GARLIC GUM IS
NOT FUNNY
GARLIC GUM IS NOT FUNNY
GARLIC GUM IS NOT FUNNY
Bart
Simpson on chalkboard in episode
7G13
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