No concensus for ASN.1 extension support (was: Re: APC-1265)

Joerg Ott jo at TZI.ORG
Sat Sep 6 11:50:20 EDT 1997


I am wondering whether you are missing the point here.  Jim and Mark
have stated clearly how things are supposed to work:

- H.225.0 signaling carries a protocol identifier in the mandatory part
  of all relevant PDUs (RAS as well as call signaling channel)

- H.323/H.225.0 describe in each revesion explicitly which version of
  H.245 to use and which features of this to implement.
  (And, for clarity, this is *NOT* done in the ASN.1, but in the
  references section of the document!)

Hence you can deduce the H.245 version from the H.225.0 version number
which is determined IN-BAND in the first PDU exchange between any two
H.323 systems.  And, of course, you cannot add anything to H.245 without
this being appropriate reflected in the H.323/H.225.0 specification.

Also: you are talking about no H.323 version signaling?  H.225.0 and H.323
go together at all times!  H.225.0 defines the protocol syntax and H.323
the procedures; so there is no difference between an H.225.0 and an H.323
version number!

But you are right that we should pay attention problems that might arise
from version conflicts and to clearly specify how systems are to behave
if they encounter that their peer runs a lower version number.


Joerg Ott
jo at
Universitaet Bremen, Germany                              fax + 49 421
TELES AG                                                voice + 49 421

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