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Re: [lwip-devel] Question regarding calling tcp_output() from tcp_input(


From: Joel Cunningham
Subject: Re: [lwip-devel] Question regarding calling tcp_output() from tcp_input() each time
Date: Tue, 08 Aug 2017 13:32:03 -0500


On Aug 8, 2017, at 1:18 PM, address@hidden wrote:

this tcp_output() from tcp_input() is causing enormous amount of empty ack towards the other end point.

Of course that's not too good, but noone has provided a decent, working solution for this, yet. Feel free to provide one :-)
One accepted improvement are "delayed ACKs" where we only send an empty ACK for every 2nd segment.

We are already delaying ACKs.  See tcp_ack() macro.

RFC 1122 says a receiver is only allowed to stretch 2 MSS, so every 2 * MSS there must be an ACK.  I believe our stack is ACKing every 2 segments regardless of the size, but I’ve seen this behavior in other stacks (either FreeBSD or NetBSD).

https://tools.ietf.org/html/rfc1122#page-96

enormous amount of empty ack towards the other end point.

More than every 2 segments, i.e. for every segment?  If not, then things are working as intended

Joel


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