Wireshark-bugs: [Wireshark-bugs] [Bug 4433] Wrong decoding of LTE S1AP UEContextReleaseCommand
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Fri, 29 Jan 2010 12:24:44 -0800 (PST)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=4433

--- Comment #6 from reeagbo <alex.garcia.b@xxxxxxxxx> 2010-01-29 12:24:41 PST ---
Hi,

I guess this is a tricky one. I enclose a full trace, i guess it makes things
easier.

Actually, the length of MME-UE-S1AP-ID is 4 bytes. This byte 30 that is C0 in
other messages is used for ASN.1 coding for the UE-S1AP-ID-pair, which
according to 36.413 is Sequence, so the meaning of that byte would be:
30      ASN.1 format: Universal/Constructed/Sequence

In other messages, where MME-UE-S1AP-ID and ENB-UE-S1AP-ID come separate, not
in this UE-S1AP-ID-pair field, the equivalent byte has a different content:
C0    ASN.1 format: Private/Primitive/...

That´s why they are different. I was wrong to think that 30 is part of the
MME-UE-S1AP-ID. Here is the corrected decoding:

00      Critically - Reject
07      Open Type Length
30      ASN.1 type Universal/Constructed/Sequence    <----problem happens here
21      MME-UE-S1AP-ID Byte 1
40      MME-UE-S1AP-ID Byte 2
00      MME-UE-S1AP-ID Byte 3
0F      MME-UE-S1AP-ID Byte 4
00      eNB-UE-S1AP-ID Byte 1
02      eNB-UE-S1AP-ID Byte 2
00 02   Cause
40      Critically - Ignored
02      Open Type Length
05      Radio Network
40      Unknown

Alex.

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