Re: [lwip-users] why ACK is happen every package

[yueyue papa]

Hi Kieran,

Thank you for answer.

I make following changed

#define TCP_WND                 (TCP_MSS*4)
==>
#define TCP_WND                 (TCP_MSS*8)

So as to received more data without frequent update windows.

The result is what I expected, the ACK is send every two TCP segment.

But the performance is not increase because of duplicated ACK.

xx.120 is lwIP working
xx.184 is host.

Which parameters cause lwIP send so much duplicate ACK for the host?

On Thu, Mar 11, 2010 at 5:29 PM, Kieran Mansley <address@hidden> wrote:

On Wed, 2010-03-10 at 13:02 +0800, yueyue papa wrote:
> Hi All,
>
> The lwIP 1.3.2 is used.  I found the my lwIP ack the data every TCP
> segment.  Why i meet this result?
>
> The ACK should not happen every TCP segment. The lwipopts.h is
> attached.

I think the ACKs are being sent because there has been a significant
change in the available receive window.  Before each ACK there is zero
window available, and so once a certain amount becomes available it
makes sense to tell the sender about it straight away.  There is a
configuration option for this: TCP_WND_UPDATE_THRESHOLD.  The default
value for this is TCP_WND/4  (despite the comment in tcp.c saying it is
TCP_WND/2!).  If you want to send window updates less frequently, you
can make that value bigger by adding it to your lwipopts.h, at the risk
of reduced performance.

Kieran



_______________________________________________
lwip-users mailing list
address@hidden
http://lists.nongnu.org/mailman/listinfo/lwip-users

download_2.pcap
Description: Binary data