Wireshark-bugs: [Wireshark-bugs] [Bug 7615] Enhancemnt to GSM RLCMAC dissection adding dissectio
Date: Thu, 6 Sep 2012 23:07:20 -0700 (PDT)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=7615

Mike Morrin <wireshark@xxxxxxxxxxxxxxx> changed:

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--- Comment #24 from Mike Morrin <wireshark@xxxxxxxxxxxxxxx> 2012-09-06 23:07:18 PDT ---
Created attachment 9095
  --> https://bugs.wireshark.org/bugzilla/attachment.cgi?id=9095
revised patch with interface based on header type rather than MCS

OK... That was more work than I expected...

I have created a new patch that passes in the header type for EGPRS packets. 
This makes sense because in a real protocol stack, the header type is encoded
in the burst stealing bits, allowing the header can be decoded, giving the CPS
IE, which then allows the data blocks to be decoded, so wireshark now follows
the same practice.

I found that there was a (previously overlooked) alignment error in decoding
the last octet of some headers due to the last "octet" having less than 8 bits,
and both the protocol stacks I have here assume that the left-hand bits are
missing (as per the figures in 44.060).  I corrected this by making a small
extension to the NULL encoding in packet-csn.[ch] to allow a NULL field to
consume more than 0 bits.

With the accomanying updated GSMTAP patch, this can be tested using the same
test traces as before.

Note that in bug 7686 there is some severe tidy up of this dissector, so I did
not want to change too much here.

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