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Date:      Wed, 12 Aug 1998 15:58:31 PDT
From:      Bill Fenner <fenner@parc.xerox.com>
To:        Didier Derny <didier@omnix.net>
Cc:        support@yard.de, hackers@FreeBSD.ORG
Subject:   Re: network problem with FreeBSD/Yard (yardnetd) 
Message-ID:  <98Aug12.155840pdt.177515@crevenia.parc.xerox.com>
In-Reply-To: Your message of "Wed, 12 Aug 98 02:07:23 PDT." <Pine.BSF.3.96.980812110547.2406G-100000@omnix.net> 

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In message <Pine.BSF.3.96.980812110547.2406G-100000@omnix.net> you write:
>1/ I suppose that a setsockopt(socket... TCP_NODELAY..)
>   would have the same result for the yard application if it was 
>   inserted in the yard code ?

It depends on exactly what the problem is.  There's a common problem
which is caused by sending several small packets in a row; the Nagle
algorithm (and sender silly window syndrome avoidance) say that you
may not send one small packet when another small packet is outstanding.
If the other end delays its ack, then your small packets stay outstanding
for a long time.  Turning off Nagle and sender SWS avoidance (by setting
TCP_NODELAY) prevents this from happening.

>2/ what are the implication of setting ...ack_delayed=0 for the system ?

Traffic on interactive TCP sessions (e.g. telnet, rlogin, ssh) will
approximately double, since the client will send a keystroke that you
typed and the server will ACK it, and then the server will send another
packet with the echoed keystroke.  With delayed acks, the ACK piggybacks
on the echoed keystroke.

>3/ What should I say to Yard to have this problem solved ?

Ask them to set TCP_NODELAY?

  Bill

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