Wireshark · Wireshark-dev: Re: [Wireshark-dev] ASN.1 enumeration extension coding question

["Nichols, Roger" <Roger.Nichols@xxxxxxxxxxxx>]

I found the same book, and found the passage being referred to here.  It
is in section 20.6.4.

Tomas, are you planning to issuing a patch? Has .7 progressed too far
along the release cycle to have this change applied there?

thanks,
--roger

-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx
[mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Sergio Mayoral
Sent: Tuesday, December 18, 2007 4:32 AM
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] ASN.1 enumeration extension coding question

Hi,

I am also having this problem. I found a book called
"ASN.1 Communication between Heterogeneous Systems"
written by Olivier Dubuisson, who looks to be an expert on ASN.1, where
it is explicitly said:

- If the ENUMERATED type is extensible (or if the module includes the
EXTENSIBILITY IMPLIED clause in its header), a preamble of one bit is
appended to the bit-field (without being octet-aligned).

"Normally small non-negative whole number encoding"

- if 0 <= n <= 63, a 0-bit is appended to the bit-field (without being
octet-aligned), followed by the binary encoding of n on 6 bits.

Regards

--- "Nichols, Roger" <Roger.Nichols@xxxxxxxxxxxx>
wrote:

> 
> Hi,
> 
> Is this the proper forum to ask a question about 'why' something is 
> coded the way it is?
> 
> We are developing a V.34 enabled T.38 end point, and are confused by 
> the Wireshark decoding.  It seems the Wireshark decoder is aligning 
> fields which are extension values.  For example, the 2002
> T.38 ASN.1 notation
> for V.34 Data Field values.  We are not aligning these enumeration 
> values, but Wireshark does.  See line 1211 of packet-per.c, a comment 
> which says to align without giving a reference, and
> 1214 which does the
> alignment.  Reading ITU X.691 section 13, I would not expect this 
> beahvior.  As Wireshark community is the only place I know of an 
> existing product which handles the V.34 additions to T.38, it seems a 
> good place to ask.  Why are these values aligned?
> We could not find an
> ITU reference giving us reason to do so.
> 
> Thanks,
> 
> Roger Nichols
> Firmware Engineer
> 
> Cantata Technology, Inc. (a Dialogic company)
> 15 Crawford Street
> Needham, MA 02494
> USA
> 
> Tel:    781 292 9399 
> Fax:    781 453 3521
> Email:  roger.nichols@xxxxxxxxxxxx
> Web:    www.dialogic.com
> 
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