Issues with H.235
Euchner Martin
Martin.Euchner at MCHP.SIEMENS.DE
Wed Sep 15 11:26:31 EDT 1999
Pete, Bancroft, Pekka and others,
now as I'm back from my long vacation I want to throw in my bits to this discussion. (By the way, I will try to answer or comment all the other pending emails which have been sent to me).
1.) RandomVal/INTEGER:
It is true that H.235 has defined this as an arbitrary long integer for some reason which I can't remember. I've heard also that there are implementations that can only process 32-bit integers.
H.323 Annex J uses RandomVal only as an increasing sequence number/counter. Thus, Annex J does not really require RandomVal as an arbitrary long integer; a 32-bit integer would be sufficient for that purpose while still guaranteeing sufficient security.
H.235 Version 2 could restrict the scope of the RandomVal Integer to 32 bits; if this is considered useful and we can all agree to this. Please let me hear your opinions on this.
2.) nonStandardParameter: I can only guess why H.235 has chosen a simpler definition than H.225.0: Apparently, H.235 does not need the H.221 non-standard support; this was considered not necessary. Thus h221NonStandard was left out in the structure leaving the Object identifier. I hope that this simplification does not cause real implementation difficulties.
3.) I do not quite understand why you consider object identifiers limited? In my opinion, the concept of object identifiers is quite flexible and targeted for interoperability. H.323 Annex J section 8 shows a proposal for the various object identifiers used.
Regards,
Martin.
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-----Original Message-----
From: Pete Cordell [SMTP:pete at TECH-KNOW-WARE.COM]
Sent: Wednesday, September 08, 1999 9:26 AM
To: ITU-SG16 at mailbag.cps.intel.com
Subject: Issues with H.235
Dear All,
I'm implementing some of the H.235 stuff and have a few concerns.
RandomVal is defined as INTEGER only. This is not a particularly helpful
definition as in theory this could be a million bit + integer if needed.
Not many computers support such types! In fact, a well known ASN.1 compiler
maps this to an int which is a signed 32-bit value on our platform. Is this
sufficient? Without further discussion about the range of this value I feel
there is a potential for interoperability problems.
Perhaps we can say that RandomVal will never be more than 32 bits long, and
then add a type like RandomSeq as an OCTET STRING for cases when we need a
longer random value.
There are also a few other issues, for example:
nonStandardParameter in H.235 is defined differently to that in H.225. Why
is that?
Similarly tokenID only takes an OID. Again, why such a limited format?
Regards,
Pete
=============================================
Pete Cordell
pete at tech-know-ware.com
=============================================
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