Re: Is nagle disabled?

[Rob van der Putten <rob@sput.nl>]

Hi there


On 10/09/16 13:37, Nicolas George wrote:

> Le quintidi 25 fructidor, an CCXXIV, Rob van der Putten a écrit :
> > So the question should have been 'Is delayed ack disabled'.
> > I have a hard finding decent information on the subject, so I did a bit of
> > experimentation;
> > I send tiny bits of data (two bytes at a time) to a little echo  server. As
> > it turns out, the use of delayed acks and therefore nagle, depends on the
> > time between sending the bits of data and the RTT.
>
> I do not think you can really test delayed ACK with an echo server: the
> principle of delayed ACK is to leave a little time to the application to
> send a reply, because then the ACK can be bundled with the reply, saving a
> packet.
>
> With an echo server, the reply comes immediately, never letting the delay
> for the ACK expire.

I use netcat6. From man nc;
nc6 --continuous --exec cat -l -p <port>
So the data goes from nc to cat and then back to nc.

Timestamps (epoch.microseconds) are dumped to a file on transmission and 
to an other file on reception of the 'echo'. Further check with tcpdump. 
Experiment on LAN and experiment over DSL;
When the time between the bits of data is larger then the RTT, data is 
send at two bytes per TCP packet.


Regards,
Rob