Aharpo.248
net.news.map
utcsrgv!utzoo!decvax!ucbvax!mhtsa!harpo!jerry
Mon Jan 18 11:43:39 1982
Re: Usenet Logical Map
I have been studying the Shannon's map (thanks again for
producing it).   There are a lot of machines and the network
is getting bigger every day, but it still has a simple structure.
The heart of the network is the following machines.


                                   duke===============================+
                                     |                                |
                                     |                                |
                                   decvax                             |
                                     |                                |
                                     |                                |
                                   ucbvax                             |
                                     |                                |
                                     |                                |
          +=======+======+=========ihnss=====+======+=======+         |
          |       |      |                   |      |       |         |
          |       |      |                   |      |       |         |
        houxi   cbosg  vax135               rdb---eagle---mhtsa       |
          |       |      |                   |              |         |
          |       |      |                   |              |         |
          +=======+======+=========harpo=====+==============+         |
                             |       |                                |
                             |       |                                |
                           zeppo---chico==============================+


Note that except for the machines between harpo and ihnss this is a
simple ring.  Most of these machines are the root of a
tree of other machines.  Rather than list the individual machines in
these trees I give the number of machines at each depth.  (The root
is listed as depth 0.)

   DEPTH       0       1       2       3       4       5
---------------------------------------------------------
duke*           1       7       1
decvax          1       10      6
ucbvax          1       2       8       8       10      5
ihnss           1       20
houxi*          1       25      5
cbosg           1       1
vax135          1       1
rdb             1
eagle           1       1       6
mhtsa           1       2       2       1
harpo           1       2       2
chico           1       1

*(The networks that hang off duke and houxi are not trees. These numbers
 are the shortest path from each machine to the root. The network that
 hangs off houxi fails to be a tree because one machine at level 2 talks
 to two machines at level 1)

The machines that are farthest appart are some of the depth 5
machines in the ucbvax tree which take 10 hops to communicate.

Is this a good structure?  Well, this depends on the goodness
criteria, and a lot depends on the nature of the links
(I.e. polled vs. immediate, and if polled with what
frequency).

Problem: The arpa net connections are at some depth in the ucbvax tree.
Problem: The failure of almost any machine breaks the net into two.
        The only failures that don't isolate at least one other machine
        are the leaves of the trees, houxe, houxg, mcnc, tucc, rdb, and zeppo.
Problem: Some of the major "ring" hops are polled rather than immediate.

Advantage: Only the ring machines and three machines off duke and houxi
          ever receive an item more than once.  Only harpo and ihnss ever
          receive an item more than twice.

                                               Jerry Schwarz
                                               harpo!jerry

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