Pete,

H.225.0 says that it is optional for an EP to receive and act on these messages. The message type is encoded in the _Q.931 header_ which has a corresponding CHOICE in the ASN.1 h323-message-body type. I think you are confusing the Q.931 message-type field with the ASN.1 CHOICE component. When an EP encounters an optional Q.931 message which it does not support, it will discard this message based on the Q.931 message type and not parse all of the subsequent IEs including the User-User IE, which contains all of the tunneling stuff we are talking about. IOW, the EP will not even see all of the supposedly common fields to which you are referring.

Paul Long ipDialog

---------- Original Message ---------------------------------- From: Pete Cordell pete@TECH-KNOW-WARE.COM Reply-To: Mailing list for parties associated with ITU-T Study Group 16 Date: Tue, 7 Nov 2000 17:50:05 -0000

I mentioned this on the other list, but this is a different thread.

As it happens it is not necessary for an EP to understand all Q.931 messages that might contain tunnelled H.245, early or otherwise. The tunnelled H.245 is always in the same place for all messages. All you have to do is find the UUIE, extract the ASN.1, and chuck it to the ASN.1 decoder. As the H.245 (and H.450) are not in the message specific part of the ASN.1 structure it will be interpretable (sp!) in all cases*, even if SETUP ACKNOWLEDGE and NOTIFY are sent.

Therefore there is no need to make interpretation of CALL PROCEEDING and PROGRESS in there entirety mandatory.

Earlier I suggested the following text (slightly revised) should be added to the start of the tunnelling section to cover this:

"If an entity implements H.245 tunnelling, then it shall extract and act on H.245 information contained in all received Q.931 messages (including those that it does not otherwise understand) irrespective of how it decides to handle the other elements of the Q.931 message."

Pete.

• The ASN.1 does actually require to have knowledge of all messages types up

to the ellipsis in h323-message-body, and up to the corresponding ellipsis in the sub-types. However, once decoded it doesn't actually have to do anything with these parts, which is the true burden of making them mandatory.

============================================= Pete Cordell Tech-Know-Ware pete@tech-know-ware.com

+44 1473 635863

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