Liaison Statement from MPEG to ITU-T SG 16 (SC 29 N 2312)

Sakae Okubo okubo at GCTECH.CO.JP
Fri Dec 5 17:01:16 EST 1997

Paul Long wrote:
> > 4. As I understand it, for some strange reason, because the order of the
> > members of a SET OF is intended to be un-important the compiler takes it
> > upon itself to sort the values entered into some form of order!!!  This
> > seems a waste of time and is a step best avoided by using SEQUENCE OF.
> I've never heard of this before. I'll check with Bancroft. Sounds like a
> bug in the OSS compiler, which by the way we don't use for reasons like
> this.

[Bancroft's response follows. Apparently there is no reason _not_ to use
SET OF, because H.245, and H.225.0, and presumably H.450 use BASIC PER,
not CANONICAL PER, so there is no sorting.]

This is true in the case of DER, which mandates this behavior.  DER
encoders does not take it upon themselves to do this; it is required in
order to produce a valid DER encoding.  This is also true in the case of
CER and the canonical variants of PER.  It is not true for the
non-canonical variants of PER or for BER.

As far as the OSS ASN.1 Tools go, DER is supported, so here SET OF's are
sorted as required.  The OSS ASN.1 Tools at this time does not support
the canonical variants of PER, so no such sorting occurs for PER. Since
all the sorting algorithms are in place for DER, it is easy to provide
canonical PER support if it is required.

Paul Long___________________________
Smith Micro Software, Inc.__________

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