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Ärende: FidoNews 29:40 [02/06]: General Articles
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                        GENERAL ARTICLES
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                Notes on a topless echomail distribution system.
                By Michiel van der Vlist, 2:280/5555


Fidonet echomail distribution is traditionally based on top down
structures. While Fidonet itself was designed as a peer to peer
network, echomail terminology is full of terms like uplink, downlink,
hubs and backbones. For a specific echomail area, a node has one
uplink and zero or mode downlinks. Peering links are only found at the
top of the so called backbone if it consists of a backbone ring. AKA a
fully connected polygon.

Such a rigid structure is needed to avoid so called dupes. Messages
arriving more than once. Dupes can happen when there is more then one
path between nodes. One way to prevent dupes is to ensure that there
is only one path between the downlinks and the uplinks.


                            Backbone
                             /   \
                            /     \
                           /       \
                         Hub       Hub
                        /  \      /   \
                       /    \    /     \
                     node  node node  node

Another one is dupe prevention by seen-by.

                        A----------B
                        | *      * |
                        |   *  *   |
                        |   *  *   |
                        | *      * |
                        C----------D


These four nodes form a so called fully connected polygon. They are
all connected to each other. The seen-bys prevent that a message from
A arriving at B will be sent on to C and D, because they are already
in the seen-by.

There is no theoretical limit on the size of a fully connected polygon
but there are practical limits. Five is about the practical maximum.

A standard echomail topology is a backbone of one to five nodes
forming a fully connected polygon. Each backbone member feeds a number
of hubs who in turn feed a number of downlinks.

Such a configuration works fine for preventing dupes.

But is has drawbacks.
It is a top down configuration and one of the drawbacks of that is
that it has a top from which things can be controlled. The most recent
example was in the summer of 2011 when the North American Backbone
tried to grab control of Fodonews, causing a schism in te process, but
there have been many other examples in the history of Fidonet. The R28
CSO wars come to mind.

The cost sharing wars ended when the main distrubition went from POTS
to Fido over IP, reducing the cost to almost zero, so there no longer
was any cost to fight over. We thought that freed Fidonet from the
power of the distributors to control the distribution of echomal, but
unfortunately it didn't as the 2011 Fidonews coup has demonstrated.

So in the summer of 2011 the NAB set all of Fidonet outside of Z1 to
read only for the Fidonews echo. And than something unexpected
happened. To circumvent the censoring, sysops all over the world
starting laying new links. Without any coordinations whatsover. Just
find a link that is not censored. They knew this was going to cause
dupes, but the idea was to first restore the links and worry about the
dupes later. What evolved was what I have named the NADS, the New
Anarchy Distribution Network. Some have called it GONADS which is
quite appropriate as it takes balls to knowingly and willingly
breaking a 25 year old taboo: that of causing dupes. Up until then
that had been an almost mortal sin.


Yes, there were some dupes. But not as many as was feared. Not by FAR
as many. So then the idea arose to lay some more links. And some more.
Against inituition this did not cause an increase of dupes. In
retrospect this is not so strange. When everyone links up with
everyone we are back to a fully connected polygon. So when approaching
such a configuration one can expect the dupes to go down  again.

And there we have it. The NADS. Others have called it the Fidoweb.
Maybe a better term as that is what it looks like.

The result is a topless distribution system. No "top" to control it
from and as a side benefit, it is far less sensitive to SPOF. If there
is a path that dupes can follow, there is an alternate path in case a
node drops out. The price is a manageable increase in traffic. In the
POTS age, that would have increased the cost. In the Fido over IP age:
who cares?


¸ Michiel van der Vlist, all rights reserved.
Permission to publish in the FIDONEWS file echo, the FIDONEWS
discussion echo and the FNEWS_PUBLISH echo as originating from 2:2/2



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