Subject: Telcordia SG 16: Lack of Propper Tagging in H.248

From: Selvam Rengasami <[email-masked]>
Date: Thu, 27 Jan 2000 08:17:41 -0500

The ASN.1 specification of the protocol contained within Annex A lacks proper
tagging for the defined parameters.  In order to clearly distinguish messages,
parameters, and values included, unique tagging is an essential requirement of
the protocol. Thus, with the existing specification, a receiving entity would
have a difficult time trying to determine whether a received transaction
contained an AddRequest, a ModifyRequest, MoveRequest, etc.

Note that the ABNF as described in Annex B contains tags (or tokens) for the
different parameters.

Section 3.1 of a Telcordia Technologies contribution to SG 16 (which can be
found at
ftp://standard.pictel.com/avc-site/Incoming/telcordia-h248_asn1-tagging.DOC )
provides a modified ASN.1 including tags.

-Selvam Rengasami
Telcordia Technologies
Tel:  +1 732 758 5260
E-mail:  [email-masked]

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From: Pekka Pessi <[email-masked]>
Date: Mon, 31 Jan 2000 14:41:21 +0200

>contained an AddRequest, a ModifyRequest, MoveRequest, etc.

        The ASN.1 syntax defined in MEGACO draft 13 has AUTOMATIC TAGS. It
        means that ASN.1 compiler automatically adds tags to SEQUENCE or
        CHOICE components. Therefore, adding implicit tags only confuses
        here. Please see X.680 (12/97) sections 12.3, 24.2, 24.7 - 9, 26.3
        and 28.2.

        Best regards,
                                        Pekka Pessi