Re: Tails and Dogs


PADLIPSKY@USC-ISI.ARPA
14 Feb 1986 12:41:47 EST


In response to your message sent 13 Feb 1986 05:14-EST

Vint--
   Always good to hear from you, especially on the present topic,
and even more especially since it lets me avoid being churlish
(which would have been the case had I had to answer the other
response independently; now I can merely observe that I'm sure
you agree that in the context of the TCP-IP "bulletin board"
Gateways must be IP Gateways unless otherwise specified and
connections must be TCP connections U.O.S. and hence Gateways
can't drop connections, without being explicitly rude to "Rudy.Nedved"
[if I remember aright], and I might even go so far as to imagine
you'd agree that it's at best peculiar to enter a discussion
with a declaration that you don't believe the terms being
discussed can be defined). [Well, I never said it would let me
avoid being a little snide, but good grief, this isn't SF-Lovers!
I mean, I'll apologize if he was being facetious about undefinability
--though the business about Gateways dropping connections
certainly suggests that he's not using our definitions--but it
really is annoying, and rather insulting, to get a message that
in essence says Since I don't know what you're talking about,
you can't know what you're talking about. (That's probably more
than the incident's worth--but you should have seen my longhand
draft of a day or two ago.)]
   At any rate, subject to a little interpretation of the last
paragraph I find myself in complete agreement with your comments--
particularly the second paragraph, which I take to be an elegant
statement of what I was trying to say in the first place.
The real question, in my mind, anyway, is what's meant by "looking
at" the layers severally. Consider the (I think treacherous) analogy
to staggered work hours and traffic congestion: what if somebody said
Gee, that works so well that not only will we make it mandatory, we'll
also send traffic cops into the buildings and have them turn off
the elevators and lock the stairwells so those damn commuters can't
flood our scarce street resources? Not only bad safety engineering
practice, but really dubious on Constitutional grounds, yes? Well,
isn't it even more dubious on Layering grounds to HAVE TO use fewer
TCP connections or HAVE TO send out fewer datagrams (in the full
awareness some will have to be retransmitted)? That is, it's
perfectly licit to expect the Hosts to use the net intelligently,
but when push comes to shove the net's there for the Hosts' benefit,
not conversely, so the net has no business "demanding" the Hosts'
lay off--except, of course, by giving the Gateways-part-of-the-net
an analogue to the IMPs' ability to keep the ready line down (or
whatever the equivalent is in HDLC/LAP B/whatever). And strong
though my feelings are against arguing with the inventors of things
about what the things are for, if you of all people support the
use of TCP windows for something other than Host-Host flow control,
well, let's step into the nearest time machine and go back around
a dozen years and talk about what's wrong will NCP ALL again.
   Another way of attempting to express my concern is that while
I have considerable sympathy (and even empathy) for people who are
trying to split logs with toy hatchets because nobody will give them
real ones, and will even buy whatever wood they can generate for me,
I don't think they've got any business telling me I shouldn't look
for somebody with a chain saw if I need more wood to keep the house
warm enough to live in. I'm not asking for "infinite resources,"
just appropriate technology.
   But that's probably what your last paragraph meant anyway...
and I daresay Dave wouldn't really let the cops lock the stairwells,
even if I'm not so sure what he'd do with the elevators....
   cheers, map
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