WHACK (was: Re: [Standards-JIG] Reliable message delivery (the tcp problem))

Jacek Konieczny jajcus at jajcus.net
Wed Apr 26 06:55:18 UTC 2006

On Tue, Apr 25, 2006 at 10:38:41PM +0100, Dave Cridland wrote:
> I think you're duplicating TCP level ACKs there needlessly

The problem is, that TCP level acks are very hard to utilize at
application level. Operating system knows which data was not received by
the remote party, but there is no easy way for application to get that
information and bind it to corresponding stanzas sent.

> In general, hop-by-hop reliability is only a problem in as much as it 
> can be difficult to know whether the connection is still alive. 

... and when it become dead, so the application is able to tell the user
which messages could be lost. We could save some bandwith by not trying
too keep exact account of stanzas delivered to link peer, but
application should be able to detect which stanzas were delivered for
sure and which could be lost. And the number of "probably lost" stanzas
should never be too big, so there is no need to buffer too much (stanzas
sent) on application side.


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