Wireshark-bugs: [Wireshark-bugs] [Bug 5055] wrogn decoding of GTP Prime (GTP') Packets

Date: Wed, 28 Jul 2010 02:07:52 -0700 (PDT)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=5055

--- Comment #4 from ernst.vogel@xxxxxxxxxxxx 2010-07-28 02:07:51 PDT ---
(In reply to comment #3)
> As it's not possible to distinguish a GTPv2 header from a GTPv2' header the
> code
> has to be rearanged to have different entry points for the assigned ports one
> for GTP and one for GTP'.
> TS 32.295 version 9.0.0 Release 9:
> 5.1.3 Port usage
> Transporting the CDRs from the CDFs to the CGF over the Ga reference point may
> facilitate charging.
> The Path Protocol may be UDP (compliant with STD 0006[404]) or TCP (compliant
> with STD 0007[405]) over IP.
> • UDP as the Path Protocol
> Ports for signalling the request messages:
> - The UDP Destination Port may be the server port number 3386 which has been
> reserved for GTP'.
> Alternatively another port can be used, which has been configured by O&M,
> except Port Number 2123
> which is used by GTPv2-C.
> - The UDP Source Port is a locally allocated port number at the sending network
> element.
> NOTE: UDP Source Port number should be different than UDP Source Port number
> allocated to GTPv2 (see TS
> 29.274 [201]).
> Ports for signalling the response messages:
> - The UDP Destination Port value shall be the value of the Source Port of the
> corresponding request
> message.
> - The UDP Source Port shall be the value from the Destination Port of the
> corresponding request message.
> • TCP as Path Protocol
> The TCP Destination Port may be the server port number 3386, which has been
> reserved for G-PDUs. Alternatively,
> another port may be used as configured by O&M. Extra implementation-specific
> destination ports are possible but
> all CGFs shall support the server port number.
> The TCP Source Port is a random port, locally assigned at the sending network
> element.

Because there is no Protocol Type Flag in the GTPv2 header, the decoding has to
be done in two steps:

It's a GTP Prime (GTP') Packet when:
1. the (UDP)-Port is 3386 (Port 3386 is reserved for GTP' but CAN also be used
for GTPv0)
AND
2. the Protocol-type Flag is set to 0 (for GTPv0 and GTPv1 the protocol type
flag is set to "1", "0" defines a GTP Prime (GTP') packet, the 

Is it possible to adapt the decoding this way?

Best Regards
Ernst

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