[Standards-JIG] Re: The Ack Hack.

Michal vorner Vaner michal.vaner at kdemail.net
Sat May 13 12:15:14 UTC 2006


On Sat, May 13, 2006 at 09:25:46AM +0200, Pavel Šimerda wrote:
> On 2006-05-13 03:26, Trejkaz wrote:
> > On Friday 12 May 2006 01:28, Pavel Šimerda wrote:
> > > I don't know what whitespace pings really do aside from sending
> > > whitespace, which is not enough.
> >
> > All it does is gives faster disconnection, that's right.  And even then,
> > you really need both sides to be doing it, to get any kind of reliability.
> 
> How does it do faster disconnection... is it in some way a ping-response 
> mechanism? I can't find any docs for this...

No, it just forces TCP to be sending something and discover it is dead.
Connection that does not send anything will look like alive even if long
time dead.

> If it is only both clients sending whitespace, it's not really a ping. If it 
> is request-response, it should be documented.
> 
> My connection sometimes goes one way and doesn't go the other (many 
> retransmits occur). I saw after reconnection, that in groupchats my messages 
> arrived. (seems to be a NAT problem)
> 
> Some people told me that there are difficulties working with tcp under 
> different OSes. That you sometimes can't get the info about what was sent and 
> what was not sent.
>
No, this is the same on all OSes. You put data to the socket and expect
it to get there. And TCP is designed to either deliver it or die. So, if
it ends OK, you are sure everything got there. If it dies in unclean
way, you shuold consider the whole stream as invalid. TCP was not
designed to keep long-term connection, but to transfer data and
terminate.

> I don't know if psi and ejabberd use whitespace pings... but if they do, it's 
> no good for me. People can send me messages for 15 more minutes (glad it's no 
> more, at least) and they get lost immediately.

They use, or if noone ever sent you something, you could look online
indefinitely. And you would disconnect the 15 minutes someone send you
something.

-- 

Work with computer has 2 phases. First, computer waits for the user to tell it what 
to do, then the user waits for the computer to do it. Therefore, computer work 
consists mostly of waiting.

Michal "vorner" Vaner
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