🚀 go-pugleaf

The different ports in the Directory actually has a historical
background.  They originally envisioned that DUAs would come
in different flavours, some capable of Read operations only, some
(more sophisticated) could do Search operations and others could
do Modify operations.

The ports were envisioned to be implemented as different Application
Contexts, but they subsequently decided that an X.500 product must
implement all three ports, thus, we only have one flavour of DAP.

I am not sure, why X.400 is divided the same way, but it helps
the understanding of the object-oriented description technique.

You may also note another difference between the service
descriptions of X.400 and X.500.  In X.400, the service of the UA
to the User is describer (in very abstract terms), in X.500 the
DUA service to the end-user is not described.

                                          ....Erik.

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Erik Skovgaard
PSC (Pacific) Inc.