Re: [lwip-users] seq number & ACK issue

[PHAM ANH THIEN]

hi Kieran,

thanks for your fast reply!

I just read "Prentice Hall - Internetworking with TCP-IP, Volume I - Principles, Protocols and Architecture, 4rd Ed [Comer, Scan, OCR] - 2000 - (By Laxxuss)" book at item 13.5 "The Idea Behind Sliding Windows" they talk about sliding window term, it allows sender send more packets before receive ACK, let say we set sliding window with 3 packets in the window so sender will send 3 packets then receive ACK.

My question is in lwip stack got any setting like this? I saw TCP_WND, default setting is 1500 but when i change it to 4*1500 the result still same.

thanks and best regards,
Thien

On Tue, Mar 2, 2010 at 4:28 PM, Kieran Mansley <address@hidden> wrote:

On Tue, 2010-03-02 at 15:54 +0700, PHAM ANH THIEN wrote:
>
> 1. Why i always receive ACK packets after 2 packets data sending? is
> there
> any setting to change it (for example: after 5, 6... packets sending i
> will
> receive ACK)?

That's the way TCP works, and there isn't an option to change it.  It
tries to avoid sending an ACK for every packet, but sends one for at
least every two packets to ensure things continue to work.

> 2. How unacked->seqno is created? and why sometime this value less
> than 0 as
> above log?

That looks wrong, it should always be positive as seqno is unsigned.

Kieran



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