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From: pv@Eng.Sun.COM (Peter Vanderbilt)
Newsgroups: comp.protocols.iso.x400
Subject: Re: DATA Compression and X400 standards
Message-ID: <9011151813.AA14225@polya.Eng.Sun.COM>
Date: 15 Nov 90 18:17:04 GMT
Lines: 28
Approved: usenet@ICS.UCI.EDU

Assuming that compression of P2 body parts is a good thing, is there a
standard mechanism to use for identifying compression?

The simpliest mechanism is to just use an external body part with a
different object id (OID) for each different compression.

Alternatively, one could use the parameters part with a field to
indicate what kind of compression is used, where each compression
algorithm is assigned an OID.

The first mechanism has the problem that it requires "M*N" OIDs -- an
OID has to be allocated (and configured) for each pair of data type and
compression algorithm.  The second mechanism only requires "M+N" OIDs
-- one for each data type and one for each compression algorithm.  But
the second mechanism has the problem that it requires wide-spread
implementation to achieve the desired independence -- which seems like
a major hurdle.

Does anybody have info on whether the standards people considered body
part compression and, if so, how they expected it to be implemented?
Is anyone implementing it currently and, if so, how?

(Along the lines of the second mechanism, in practice it appears to be
useful to carry an identifying string with a body part -- is there any
hope that implementors would agree to a standard way to carry labels in
the parameters part?)

Pete