Re: [lwip-users] Enabling ACK_DELAY

[Kieran Mansley]

On Fri, 2007-08-10 at 13:42 -0400, Steve Waligurski wrote:
> Hi,
>  
> I'm in the process of porting an existing application to a new
> platform that uses lwIP.  This application operates in real time using
> a series of commands from a server.  The application layer of this
> client always responds to the server application with an ACK, NAK  or
> some form of data. To reduce overhead, the stack in the original
> product used the application response to return the network ACK. In
> lwIP though, I see a network ACK followed immediately by an
> application response.   Is there any way to remove the network ACK?
> I've noticed there is a constant TF_ACK_DELAY but it does not seem to
> have any impact on these ACKs.  I have turned off Nagle so not to
> conflict with TF_ACK_DELAY.  Thanks

It's probably possible, but it would be a non-general modification to
the stack that you'd need to do yourself, rather than just a
configuration option.  Network ACKs can be sent for many reasons, and
some may be delayed (to try and piggyback them on data packets as you
want) and others may not.  There are two functions: tcp_ack() and
tcp_ack_now(); the former may delay an ACK (or send it now if there was
already one delayed), the latter will try and send one straight away.
Have a look through the source for how these are used and you may be
able to get the behaviour you need.

Hope that helps

Kieran