Re: [Wireshark-commits] rev 36659: / /trunk/epan/dissectors/: Makefile.common packet-rohc.c

[Martin Mathieson <martin.r.mathieson () googlemail com>]

On Sat, Apr 16, 2011 at 2:44 PM, Anders Broman <a.broman () bredband net>wrote:

>  Martin Mathieson skrev 2011-04-16 15:18:
>
>
>
> On Sat, Apr 16, 2011 at 1:38 PM, Anders Broman <a.broman () bredband net>wrote:
>
> >  Martin Mathieson skrev 2011-04-16 14:03:
> >
> > Hi Anders,
> > There is already most of the ROHC profile in packet-pdcp-lte.c.  I'd been
> > meaning to separate it out so that it could be used from other places (e.g.
> > when I create UMTS PDCP...)
> >
> > Martin
> >
> >  I missed that, how to proceed? I think the ROHC code should live in a
> > separate file I have a trace
> > with Ethertype ROHC for instance.
> > Regards
> > Anders
> ROHC should definitely be in a separate file, which I hadn't got around to
> doing.  My code was mostly written around 3 years ago, but to be honest
> hasn't been used much.
>
> My implementation needs a few hints to decode the ROHC frame. Here are the
> ROHC fields in packet-pdcp-lte.h - they are what my company's decoder needs
> to have supplied to it.
>
>
>
>   /* RoHC settings */  83 gboolean rohc_compression;  84 unsigned short
> rohc_ip_version;  85 gboolean cid_inclusion_info;  86 gboolean
> large_cid_present;  87 enum rohc_mode mode;  88 gboolean rnd;  89 gboolean
> udp_checkum_present;  90 unsigned short profile;
> From a very quick look, I see that your implementation is hard-wired to
> RTP/IPv4, and comments about maybe using preferences or conversation info to
> work out other fields.  My preference would be to attach info similar to the
> above, and let each user fill it in as they can (leaving the possibility to
> override with preferences).
>
> How about in dissect_rohc() look for private data and in the private data
> supply a ROHC struct
> similar to
>
> #define ASN1_CTX_SIGNATURE 0x41435458  /* "ACTX" */
>
> typedef struct _asn1_ctx_t {
>   guint32 signature;
> :
>
> with the needed decoder input in that way it can be called from other
> places supplying the needed information
> or if no struct is received use the preferences set. Some of the data can
> be inferred it the IR/IR-DYN packets are seen
>  but that requires context tracking.
>
> Could you supply the struct defenition, so it'll fit your data?
>
> Regards
> Anders
I haven't really looked into how easy it'd be to track the context and work
out some of the ROHC fields.

Yes, the above is what is currently done with PDCP-LTE.

The pdcp_lte_info struct has information for both the PDCP frame and the
ROHC frame, and the ROHC part was what I pasted into my earlier message in
this thread.  What I'd need to do is split them - fill in the PDCP half, and
if there was ROHC present, fill that in and attach it to the PDCP frame.
One MAC frame may contain many PDCP/ROHC frames, but rather than attach an
array of structs (as I think UMTS RLC does), I just attach one struct and
keep overwriting the contents just before the decoder is called.

LTE MAC and RLC also already do the same thing with structs for the context
they need in order to decode. They either get the info from the log file
format (in my case) or parsed from special headers that precede the PDU (see
the UDP heuristic formats, but special ethertypes have also been used for
MAC).

The first step is probably to work out if all of these context fields are
really needed, and work out how you can start off by hard-coding them when
your ethertype is seen, or maybe from some signalling that sets up the ROHC
conversation.

Martin


> My very next task happens to be to configure LTE PDCP, RLC and MAC with
> info found in RRC, and some of these fields can be given then, whereas
> others are the internal state of the contexts, which is hard to know
> (without doing a full ROHC simulation!)...
>
> It'd be good to merge them into one standalone dissector that I could then
> call from PDCP (LTE and UMTS sometime).  I noticed for example that you
> don't decode all of the feedback options, so maybe my implementation could
> help speed up the adding of some of these.
>
> There is a screenshot of my decoder in http://wiki.wireshark.org/PDCP-LTE,
> but I expect I could send you a trace file later on.
>
> Best regards,
> Martin
>
>
>
>
> >   On Sat, Apr 16, 2011 at 12:44 PM, <etxrab () wireshark org> wrote:
> >
> > > http://anonsvn.wireshark.org/viewvc/viewvc.cgi?view=rev&revision=36659
> > >
> > > User: etxrab
> > > Date: 2011/04/16 04:44 AM
> > >
> > > Log:
> > >  Add a basic ROCH dissector.
> > >  Limitations:
> > >  - Small CID
> > >  - RTP profile
> > >  - IPv4
> > >
> > > Directory: /trunk/epan/dissectors/
> > >  Changes    Path               Action
> > >  +4 -3      Makefile.common    Modified
> > >  +984 -0    packet-rohc.c      Added
> > >
> > >
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