Subject: Architecture Enhancements for Multiplexed interfaces

From: "jim (j.) cobban" <[email-masked]>
Date: Mon, 4 Jul 1994 15:12:00 -0400

Although the architecture of reference is ambiguous on this point, it
is a fact that the vast majority, if not all, implementations of APPN
actually permit a connection between two nodes to be defined on only one
side.  Indeed it is extremely unlikely that the Connect-a-thon would have
gotten anywhere if every node to node connection had to be synchronized
across so many unlike platforms.  It is also clearly in the best interests of
our customers to do anything which will simplify their administrative load.
Permitting connections to be defined on only one end, and come up dynamically
on the other immediately cuts the administrative effort in half.

And yet, despite the fact that it works, and despite the fact that it is in
our customers' interest, the response from the APPN architects can be
paraphrased as falling somewhere between "It's not supposed to do that." and
"Why would you want to do that?"

The existing discussion of dynamic link stations couples them intimately with
connection networks.  A typical quote from the architecture is (p. 9-10)
"dynamic link stations (i.e., connection networks, discussed below)".  It may
be inadvertent, since people are so ignorant of Latin these days, but the
quote says "i.e." short for "id est" which is generally translated "that is".
It is used to introduce an alternate name for something.  In this case the
statement seems to be "dynamic link stations, otherwise known as connection
networks".

In any event the architecture monotonously introduces connection networks
whenever dynamic link stations are discussed.  More importantly the
architecture repeatedly warns "CP-CP sessions are not supported on ..
dynamic link stations".  Fortunately all of the implementations we have tried
have interpreted this as "Don't initiate a CP-CP session because this might
be a connection network link, but if the other guy wants to initiate a CP-CP
session, go right ahead."

It never seems to have occurred to the architects that somebody might just
set up a network node server and have it put up an "Open for Business" sign
without rigorously defining all of the adjacent nodes.  They seemed genuinely
mystified in the architecture SIG meeting that anyone would be unwilling to
have to maintain matched definitions on both ends of a link.

My concern is that someone might interpret the architecture literally and put
in code which will blow away CP-CP sessions arriving from a dynamic link
station.  I would like to see some language (and not Latin which the writers
clearly do not know how to use) which discusses single sided definitions and
the resulting dynamic link stations.