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Wireshark-bugs: [Wireshark-bugs] [Bug 8903] New dissector for Air/Ground Datalink ICAO doc 9705

Date: Sun, 07 Jul 2013 22:14:57 +0000

Comment # 2 on bug 8903 from
Hi Anders,

my question in return would be:

if I use two encodings (PER or BER) in a common dissector for OSI and ATN how
do I decide which encoding is currently used - try and error ? 

What if two different data sets turn out to produce the same bit sequence while
one is encoded with PER and the other with BER ?  

Both session and presentation dissectors are only one octet long for ATN and
only used two times at connection establishment (in conjunction with ACSE
AARQ/AARE).

I feel that the code is more maintainable if ATN session and presentation code
is packaged with ACSE in the "atn-ulcs" dissector. 

>From my point of view there are some differences between "acse" and "atn-ulcs": 
1.)
I use AARQ and AARE messages for implementing my own mechanism to detect ATN
"conversations". This argument would be void if the functions in
"conversation.h" would work for the "cotp" dissector, but unfortunately they
don't.
2.)
"atn-ulcs" contains air/ground specific functions to determine the 24-bit
address of an aircraft or whether the message is uplink or downlink.
This information is essential for decoding the ATN application level messages.
3.)
"atn-ulcs" calls the appropiate subdissecor ("atn-cm" or "atn-cpdlc") if the
AeQualifier is contained within an AARQ PDU. This function is ATN-specific.

regards

Mathias


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