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From: JOHNSON@NUHUB.ACS.NORTHEASTERN.EDU.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Vertically Moving Congestion  (VMC)
Message-ID: <8702200048.AA02250@ucbvax.Berkeley.EDU>
Date: Wed, 18-Feb-87 18:09:00 EST
Article-I.D.: ucbvax.8702200048.AA02250
Posted: Wed Feb 18 18:09:00 1987
Date-Received: Fri, 20-Feb-87 22:20:14 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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Approved: tcp-ip@sri-nic.arpa


     Hi people.

     From time to time there has been discussion on the list about what 
happens when you try to solve a congestion problem at a particular 
layer.  Vary often you end up solving the problem at the layer you 
wanted only to find that a new layer has become congested.  This can 
be called Vertically Moving Congestion or VMC.

     We've probably all seen VMC happen in many different networks.  I
went to a DECUS not long ago and talked to some DECNET wizards.  They of
course knew of the problem but hadn't addressed it.  I don't think the 
x.25 gang have and I'm not sure about ISO.  I haven't heard a lot about 
this from the TCP/IP bunch either.

     Some time ago I tried to arouse a little interest in VMC on the
list and that's exactly what I got, a little interest. 

     Time has passed and to the best of my knowledge the problem still 
exists (unless somebody snuck the solution by when I was asleep).  I was 
wondering whether or not anyone had given any more thought to the 
following question:  What kind of traffic monitoring/resource use
information needs to be passed vertically to help alleviate the problem?

     Another interesting question:  Is the problem solvable? 

     I've been thinking about this for some years now, ever since I 
first ran into it.  I'm not even sure I've gotten to the rule of thumb 
stage for an answer yet.

     Am I showing my ignorance of the literature here?  Has someone 
solved this behind my back?  Does anybody really care?

     Any takers?  


Chris Johnson
Northeastern University

csnet:      johnson@nuhub.acs.northeastern.edu
arpa:       johnson%nuhub.acs.northeastern.edu@relay.cs.net
at&t:       (617) 437-2335