[e2e] seeking help recalling a network term

Chris Edmondson-Yurkanan chris at cs.utexas.edu
Tue Jun 13 19:54:18 PDT 2006


I know how much you like history, so here's some fun:

That was Donald Davies concept (who independently invented packet 
switching in the UK in 1965); he used the term isarithmic, the Greek 
term for "equal").

John McQuillan's 1974 dissertation on routing describes it as follows:

"One major thrust of the research at NPL has been a study of so-called 
"isarithmic" networks in which the number of packets and packet 
"containers" is held constant.  This is essentially a flow control 
mechanism designed to prevent congestion.... but such a technique does 
have an impact on the appropriate routing doctrine..."

This concept was first published in 1971:
ACM second symposium on Problems in the optimizations of data 
communications systems.
(at SIGCOMM's 2nd sponsored conference ;-)

Davies wrote in the paper:
The Control of Congestion in Packet Switching Networks
(which has  a 72 version in IEEE Trans. on Communications)

"Since data-carrying packets must be created and destroyed, the balance 
is kept by using empty packets.  Thus when a normal, data-carrying 
packet arrives at its destination it is replaced by an 'empty' which, 
is put back into the system.  When data is ready to enter the network, 
an empty packet must be found and replaced by a data-carrying 

Eventually, they switched to permits to avoid the unnecessary traffic 
of empties.  And as routing algorithms improved, isarithmic congestion 
control no longer helped.

Donald Davies Oral History 1986:

"As a means of controlling the number of packets, it occurred to me to 
give them a permit before they could get into the network.  The idea 
was, I think a good one, and in simulation it seemed to work, but it 
had the danger that permits could get lost and so the thing had a nasty 
collapsing process if some part of the network was doing the wrong 
thing... I don't think the idea was ever more than a theoretical one... 
quite interesting to statisticians who liked the idea of this...

that's it,

On Jun 13, 2006, at 7:27 PM, Joe Touch wrote:

> PS - found it via some indirect means; it's isarithmic ;-)
> Joe
> Joe Touch wrote:
>> Hi, all,
>> I apologize if this is a simple question:
>> I'm trying to recall the name for a network where the number of
>> packets/tokens/empty-frames inside the net is a constant, i.e., where
>> real data can be put into these units when empty, and emptied at the
>> destination, but that the whole net is otherwise just shuffling around
>> these 'holes'.
>> I'm recalling a term akin to "idempotent" or "isomorphic" - though I
>> know both are wrong ;-) Does anyone recall the term for these nets?
>> (I recall their being vogue in the late 1980's, but not much after 
>> that).
>> Thanks,
>> Joe
Chris Edmondson-Yurkanan
(chris at cs.utexas.edu)
Contact info:  www.cs.utexas.edu/~chris/

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