Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucsd!orion.oac.uci.edu!ucivax!gateway
From: eskovgaa@uvcw.uvic.ca (Erik Skovgaard)
Newsgroups: comp.protocols.iso.x400
Subject: UA under '84 X.400
Message-ID: <242*eskovgaa@uvcw.UVic.ca>
Date: 11 Dec 90 00:20:35 GMT
References: <1990Dec9.211434.2896@mlb.semi.harris.com>
Lines: 39
Approved: usenet@ICS.UCI.EDU
In-Reply-To: <<554167*JPALME@QZ>
Autoforwarded: true

The main problem with P3 is that you have no control over what you
want to take delivery of.  If you are using a UA with (only) P3 on
a PC you must take everything the MTA is spewing at you.

This may not be a problem in most cases, but consider the following
scenario:

Mr X has a large PC at work.  This PC has 100MB storage and can render
ISO 6937 text, voice (bilatteral agreement) and G3Fax.

At home he has a small PC with only a single 720K floppy drive and
this PC can only render and generate standard IA5 text.

If Mr. X is at work and connects up to his local friendly MTA he
will get all the messages queued up for delivery to him.  That is
all fine, because he has registered his UAs capabilities with his
MTA and his MTA will not deliver (e.g.) G4Fax which Mr. X's UA
cannot handle.

Now, however, Mr. X decides to work at home one day.  He establishes
a connection to his friendly MTA and the MTA dumps all the messages
queued up for Mr. X.  Unfortunately, he runs out of disk space
before he can take delivery of all messages.  His UA then aborts
the connection.  This leaves some messages queued up at the MTA.
Sofar, no problem.  He can always re-establish the connection
when he has a clean disk.

Alas, he has been delivered a G3Fax message which he cannot display
on his screen.  He has no way of transferring this message to his
PC at work, since they use different file formats.  The message is
effectively lost.

There are some other problems in the 1984 P3, but the main point is
that it restricts you.  That is why they defined P7 (and incidently,
also fixed P3 up).  With P7 you can selectively retrieve messages of
any type you want and you can also specify size limits and priority
limits.

                                           ....Erik.