Shaping TCP ACK packets

Shaping TCP ACK packets

[John A. Sullivan III]

Hello, all.  I've seen several sites recommend prioritizing TCP ACK packets using tc.  Is that a good idea? I have two reservations:

1) If my line is congested, isn't delaying ACKs a good way to slow down the conversation? Accelerating ACKs under congestion sounds a bit like stuffing more food in my mouth when I'm already choking.

2) By messing with normal coordination of TCP, do I risk making a mess.  Specifically, can I create problems with out of order packet delivery - send an ACK before the packet which should have preceded it? I suppose in a well behaved protocol that wouldn't happen but I'm not sure.  Thanks - John

Re: Shaping TCP ACK packets

[Eric Dumazet]

Le lundi 05 décembre 2011 à 23:18 -0500, John A. Sullivan III a écrit :
> Hello, all.  I've seen several sites recommend prioritizing TCP ACK
> packets using tc.  Is that a good idea? I have two reservations:
> 
> 1) If my line is congested, isn't delaying ACKs a good way to slow
> down the conversation? Accelerating ACKs under congestion sounds a bit
> like stuffing more food in my mouth when I'm already choking.
> 
It depends which way is congested. Sites recommends prioritizing ACKS on
the up way, because most of the time ADSL links are assymetric. an
uplink is congested.


> 2) By messing with normal coordination of TCP, do I risk making a
> mess.  Specifically, can I create problems with out of order packet
> delivery - send an ACK before the packet which should have preceded
> it? I suppose in a well behaved protocol that wouldn't happen but I'm
> not sure.  Thanks - John
> --

Well, if you prioritize true acks (packets with no payload), there is no
reorder problem per se.