PER ASN.1 encoding of Sequence Of Elements - Boundary Conditions

Paul E. Jones paulej at PACKETIZER.COM
Sat May 12 13:00:44 EDT 2001


Manoj,

It is legal, but one should not do this unless the protocol prescribes it.
For example, in H.323 version 4, an empty list of alternate gatekeepers is
used to signal to the endpoint that it should delete any list it may have
previously received.  Usage like this, which has a well-prescribed meaning,
is useful.  However, empty lists in places that make no sense will probably
do nothing but create confusion.  In any case, entities must be prepared to
decode them.

Paul

----- Original Message -----
From: "Paul, Manoj" <mpaul at TRILLIUM.COM>
To: <ITU-SG16 at mailbag.cps.INTEL.COM>
Sent: Friday, May 11, 2001 8:30 PM
Subject: PER ASN.1 encoding of Sequence Of Elements - Boundary Conditions


> Hi All,
>
>   Is it a valid situation if a "Sequence Of" element is encoded with
number
> of components as 0? PER rules dictate that the lower bound on the number
of
> components is set to 0, if lower bound is not explicitly defined. Since
the
> minimum is 0, one can encode the "Sequence Of" element with 0 components.
>
> What would it mean to encode a Sequence Of with no components encoded? In
> this
> case, though, there may be a few bits added to the field list for the
length
> determinant of Sequence Of with value 0.
>
> Thanks
> Manoj.
>
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