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https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3009





--- Comment #12 from David Castleford <david.castleford@xxxxxxxxxxxxxxxxxx>  2009-03-09 03:52:54 PDT ---
(In reply to comment #9)
> (My apologies for taking a while to get back to this).
> 
> While testing the latest version of the dissector using the attached capture
> file, I noticed the following (on my Windows system):
> 
> 1. Immediately after opening/loading the capture file, I expand the 
>     "ISMACryp Protocol" line. I then see:
> 
>    "AU Headers length: 56 (bits) Error - expected total AU headers size \
>   (56 bits) does not match calculated size (32 bits) - Check parameters"
> 
> 
> 2. I then select frame #2 and and then select frame #1 again.
>    The expansion of the "ISMACryp Protocol" line no longer shows the 
>    Error text !!
> 
>    Do you get this behavior in your environment ?
> 
>    (Note: I made no changes to the default parameters [other than setting 97 as
>     the dynamic payload type).
> 
> 3. I then saved just the first 3 frames ("save as") of the capture file to a 
>    new file.
> 
>    When I open this new file and expand the "ISMACryp protocol" line I get the 
>    Error text. For this file: no amount of selecting other frames clears the
>    Error text. ??
> 
> I'm not sure what's going on, but maybe a good place to start would be to
> determine the issue with the 3 frame file (assuming you see the same
> behavior I'm seeing).
> 
>
I could not reproduce the behaviour. Updated code now fixes the problems I had
observed so now should be ok. 
> --------
> 
> On a different note, a significant number of the preferences are used to affect
> the actual dissection of messages in that the preferences specify whether
> certain fields are present (or the actual field lengths) in PDUs of this
> protocol.
> 
> I'm curious. How does this work in the real world ??
> That is: how does a receiver of frames of this protocol determine whether
> certain fields are present and so on ?? 
> Is there some kind of separate configuration channel ?
>
yes, as per RTP streams, setup information in SDP (type in SDP to see the info
relating to RTP and ISMACryp).
I couldn't figure out how to link these automatically to ISMACryp so the values
have to be set manually via preferences. As you will see from SDP:
For RTP payload type 96, ISMACryp v11, IVLength=4, KILenth=1, avc-video
For RTP payload type 97, ditto,        ditto,     ditto,    aac-hbr

> (I have no familiarity at all with this protocol).
> 


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