IMO you could do like packet-eth.c does, it registers two dissectors
("eth_withfcs", "eth_withoutfcs") anyway and has a common dissector
that will determine one or the other (based on a preference maybe).You could register one to handle ENCAP_WITH_FCS and ENCAP_WITHOUT_FCS or use heuristics instead. However you decide to go, I believe that having two registered dissectors instead of an alternative one is a good idea anyway. Luis On 2/5/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > > Hi luis, > > > Right, it seems the problem with the FCS is not only a problem of Datalink. > Up to now, if you read a K12 file, and if the record/file for the stack is > pointing to mtp2, the MTP2 dissector is called. > With the current MTP2 dissector, there is no problem with .rf5 record, > because the FCS are ignored. > But, if you are reading a MTP2 frame from an other capture device, the FCS > are present(at least for the board I am using). > And in the ITU Q703 norma, the FCS are mentionned too, so they should be > present. > > So, the problem is how to find a solution to have a MTP2 dissector > compatible with both format (without FCS, and with FCS). > My first patch was with an option to have a checksum validation. > But, if the option is enabled, the rf5 record are detected as malformed, > because of these 2 bytes missing, (and because the SCCP dissector has not > be modified to accept such frame). > > Now, if I change the datalink to indicate the presence of Checksum, do I > will have to call a specific MTP2_FCS dissector ? Or is it possible to read > the datalink on the pinfo structure in the current MTP2 dissector, to call > a specific code for the FCS validation ? > In this case, it could work with K12 files too, as the datalink is set to > WTAP_ENCAP_K12. > Am I rigth, or do I missed something ? > > Best regards > Florent > > > > > > "Luis Ontanon" > <[EMAIL PROTECTED]> To: "Developer support > list for Wireshark" > Sent by: > <[email protected]> > [EMAIL PROTECTED] cc: > reshark.org Subject: Re: > [Wireshark-dev] Add checksum validation option for MTP2 > > > 05/02/2007 15:41 > Please respond to > Developer support list > for Wireshark > > > > > > On 2/5/07, [EMAIL PROTECTED] > <[EMAIL PROTECTED]> wrote: > > Hello Jeff, > > Thank you for your comments, I will follow your advices and request a new > > DLT for MTP2 with FCS. > > But before, I will, first, ask for the agreement of the board > manufacturer. > > I hope they will not disagree.. > > > > In the same time, if someone has samples of use for the MTP2 DLT, it > could > > be very helpfull. > > Maybe, the right way will be to have : > > - DLT_MTP2_noFCS for K12 files, > > k12 files use a single WTAP_ENCAP_K12 and the actual protocol is > choosen by name by the user associating it with the ".stk" file > declared for a given port. As far as the dissecctor handle called by > the name "mtp2" does not change its behaviour there's no problem. > > > - DLT_MTP2_FCS, for this board. > > - and to keep the current DLT_MTP2 for compatibility. > _______________________________________________ > Wireshark-dev mailing list > [email protected] > http://www.wireshark.org/mailman/listinfo/wireshark-dev > > > > > _______________________________________________ > Wireshark-dev mailing list > [email protected] > http://www.wireshark.org/mailman/listinfo/wireshark-dev > -- This information is top security. When you have read it, destroy yourself. -- Marshall McLuhan _______________________________________________ Wireshark-dev mailing list [email protected] http://www.wireshark.org/mailman/listinfo/wireshark-dev
