Submission: APC-1772: On H.323 Robustness Architecture Using DDP and SCTP

[Qiaobing Xie]

H.323 experts,

The ASN.1 code for H.450.2 contains the following structure:
"argumentExtension      CHOICE
                        {extensionSeq   ExtensionSeq,
                        nonStandardData NonStandardParameter }    OPTIONAL,"
duplicated inside many larger structures such as CTInitiateArg, CTSetupArg, CTIdentifyRes, CTUpdateArg, SubaddressTransferArg, etc.

Feeding the code as is into the ASN.1 compiler will result in multiple _choice structures (_choice1, _choice2, _choice3, etc.) for the same exact structure:
"CHOICE {extensionSeq   ExtensionSeq,
                        nonStandardData NonStandardParameter }    OPTIONAL"

We can do some optimization and save some code (desperately needed for embedded platforms) by modifying the ASN.1 code and defining a new structure as follows:
ExtensionASN    ::=CHOICE
                {
                extensionSeq                    ExtensionSeq,
                nonStandardData         NonStandardParameter
                }

And use ExtensionASN structure in all the CTXArgument structures  that use the above structure, for example:
CTInitiateArg ::=       SEQUENCE
                        {
                        callIdentity            CallIdentity,
                        reroutingNumber         EndpointAddress,
                                argumentExtension     ExtensionASN    OPTIONAL,
                            ...
                        }
Since implementers should not touch the ASN.1 code on their own and the H.450.2 document will have to go through the ITU process of producing a new revision to have a fix like this, my questions are:
Does anyone see any problem with this optimization? Will a modification like this have any effect on bits going on the wire (it shouldn't)? Can this proposal break backward compatibility?
Is there a compelling reason for writing the structures the way they are in the H.450.2 document?

Thanks for all your responses
Hani ElGebaly

Intel Corporation

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