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From: ravi@hubcap.UUCP
Newsgroups: comp.hypercube
Subject: Re: Question on hypercube routing
Message-ID: <293@hubcap.UUCP>
Date: Tue, 14-Jul-87 15:50:48 EDT
Article-I.D.: hubcap.293
Posted: Tue Jul 14 15:50:48 1987
Date-Received: Fri, 17-Jul-87 01:34:01 EDT
Sender: fpst@hubcap.UUCP
Lines: 36
Approved: hypercube@hubcap.clemson.edu

In article <291@hubcap.UUCP> wen-king@VLSI.CALTECH.EDU (Wen-King Su) writes:
>
>In article <285@hubcap.UUCP> ravi@CS.UCLA.EDU writes:
><>The obvious solution to this problem is to randomly choose the direction
>  >bits that differ instead of scanning from right to left or left to right. 
>  >each message at a randomly chosen bit for that message. 
>
>If you do this, you may have problems with deadlock due to lack of queue
>space along the path of the message.  One reason for using the routing
>algorithm described by pase in his article is that the algorithm is proven
>to be deadlock free provided that the destination node will eventually
>consumes all messages it receives.  This particular routing algorithm is
>call the e-cube routing algorithm.

I can see the possibility that a message will never reach its
destination when it is routed in an arbitrary direction (no longer
shortest path routing) instead of a direction towards the destination. 
A case can be made for doing this in a congested situation when buffers 
in the chosen direction are full. 

However when one chooses a direction toward the destination I 
see no reason why it should deadlock. I would appreciate if you
can give us the argument as to why it deadlocks or any references pointing
to the deadlock proof. 

ravi

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
T. M. Ravi 
UCLA Computer Science Department, 3680 Boelter Hall, UCLA
Los Angeles, CA 90024	          Phone: (213) 825-2266
ARPA : ravi@CS.UCLA.EDU
UUCP : {...sdcrdcf, ihnp4, trwspp, ucbvax}!ucla-cs!ravi
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