Re: Request for a new DLT for MTP2 with FCS (repost)

[Florent.Drouin () alcatel-lucent fr]

      Hello,


As requested few days before, I would like to use a new DLT to distinguish
between MTP2 without FCS (the current DLT_MTP2) and MTP2 with FCS.
This new DLT would be used to validate the FCS, and so to identify "noise",
or damaged frames, due to bad transmission.
 As I did not find an other way to identify mtp2 frames with FCS, specially
in case of malformed frame, I think this could be a valuable argument to
introduce a new DLT.
Once selected on the capture device, this DLT will be used for all the
frames captured. So we should not have the problem encountered with the
Ethernet datalink, where the FCS are sometimes present, sometimes not.

This patch do not change the behaviour of ERF_FCS_BITS, so it preserves the
backward compatibility.
But now, if the variable ERF_FCS_BITS is not defined, and only in this
case, the length of the FCS will be determined according to the linktype.

This has the advantage to be easier for the user, and for the wireshark
mtp2 dissector.
You just have to choose the datalink, and libpcap will produce the
corresponding format, that can be fully decoded by wireshark ( I will
provide the modification needed for the MTP2 dissector to decode the FCS).

The patch is a zipper tar file, based of libpcap-2007.02.12

(See attached file: mtp2_fcs_diff.zip)

Best regards
Florent

Attachment: mtp2_fcs_diff.zip
Description:

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