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From: ljm@FTP.COM (leo j mclaughlin iii)
Newsgroups: comp.protocols.tcp-ip
Subject: telnet and Nagle's algorithm
Message-ID: <9105172007.AA28847@ftp.com>
Date: 17 May 91 20:07:26 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: ljm@ftp.com
Organization: The Internet
Lines: 44

>
>...Based on the responses I received, I would suggest the following
>additions to RFC1122/1123:
>  
>    1. Where a terminal emulator is running on a workstation directly
>       on the Internet, the system SHOULD ensure that escape sequences are
>       transmitted in a single TCP packet....
>

The basic problem (and the reason folk warned you away from the algorithm
you are now using) is that there is no such thing as a TCP packet.  A TCP
connection just transfers streams of bytes with no record boundries.  Every
so often this list gets a question along the lines of 'I do a write of N bytes
but sometimes my read doesn't get all N bytes'.  The answer is that any
assumptions made about how TCP traffic is handled are eventually doomed
to failure.

>
>The writers of RFC 1122 (Requirements for Internet Hosts) were
>apparently aware of this kind of problems, because they gave SHOULD
>status to the Nagle Algorithm, and MUST status to letting an application
>turn it off....
>
>...I would remind implementors that RFC1122 says they MUST allow an
>application to turn off Nagle.  Does anyone know how this is done in
>practice?  I don't think a site configuration option really meets this
>requirement, but perhaps I misinterpret the spec.
>

Yet more bad news.  The primary reason for allowing Nagle's algorithm to be
turned off was X-Windows.  Nagle's algorithm is very bad for any application
(such as X-windows) with short bursts of high priority traffic.  For these
sorts of applications, most (all?) vendors who do Nagle allow 'no Nagle' as
an option when opening a connection.

Thus, it is the *application* which can turn off Nagle, not the user.  Even
worse from your point of view, the one application you would have a very
tough time convincing people should be un-Nagled, the one application which
generates the overwhelming majority of 'wasteful' small packets in the
Internet, the one application for which Nagle was designed, is telnet.

enjoy (or more accurately, sorry),
leo j mclaughlin iii
ljm@ftp.com