Limitation of nonStandardData

Pete Cordell pete.cordell at BT-SYS.BT.CO.UK
Mon Dec 1 14:02:32 EST 1997

Dear All,

I have noticed that there is a limitation in H.225 (and H.245) on how
nonStandardData is included in messages.  Basically only one
non-standard element can be included in each PDU.  This is because of
the syntax:

        nonStandardData NonStandardParameter,

What is really required for a truly extensible protocol is:

        nonStandardData SEQUENCE OF NonStandardParameter,

This is especially important if a gatekeeper wants to insert
nonStandardData into a message that already has nonStandardData added in
to it by an endpoint.

This may be too late to fix for H.225, but we can fix this for the
H.450.x protocols.

Pete Cordell
BT Labs
E-Mail: pete.cordell at
Tel: +44 1473 646436
Fax: +44 1473 645499

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