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[mehmet sulak <mehmet.sulak@xxxxxxxxx>]

Hi ,

Thank you for your response,

Here are my changes;

in file interval.h
//#define ROHC_WLSB_WIDTH_MAX to 64U (comment out)
#define ROHC_WLSB_WIDTH_MAX 256U  (new definition)

also added new enum value at "rohc_lsb_shift_t"

ROHC_LSB_SHIFT_UDP_SN = 128

to be used in UDP traffic.

also in files c_udp.c and d_udp.c

instead of using  "ROHC_LSB_SHIFT_SN" which is  -1

I used newly defined  "ROHC_LSB_SHIFT_UDP_SN" value


For the  trade-off between compression efficiency and robustness I observed
that for configurations

higher then lsb_w = 32 and p=16 makes UDP/IP header to 7 bytes. So I choose
the lsb_w=256 and p = 128 for greatest coverage.

Best Regards...


2018-02-08 17:17 GMT+03:00 Didier Barvaux <didier@xxxxxxxxxxx>:

> Hello,
>
> Sorry for not answering sooner. I could have saved you some time about
> the WLSB width :-/
>
> First of all, your changes seem correct. Please send me a patch, I'll
> check if I can integrate your changes in the next release.
>
> The increased size is indeed a consequence. You ask the library to be
> more robust, so it sends more information to achieve that goal.
>
> You have to choose a trade-off between a/ compression efficiency and b/
> robustness. Did you try to set smaller value for the WLSB width? Maybe
> 128 provides enough robustness? Maybe 192?
>
> Regards,
> Didier
>
>
> On Tue, 6 Feb 2018 17:31:18 +0300,
> mehmet sulak <mehmet.sulak@xxxxxxxxx> wrote:
>
> > After some trials I saw that;
> >
> > rohc_comp_set_wlsb_window_width()  method is working correctly, the
> > second parameter is just width of LSB window however I toughed that
> > it was the number of bits that are for  LSB  width.
> >
> > I set it as 256 to handle large number of problematic cases(by setting
> > ROHC_WLSB_WIDTH_MAX to 256U). Also I set  ROHC_LSB_SHIFT_SN  as 128 to
> > handle delayed packets.
> > (I defined new enumeration field whose value is 128 by updating
> > interval.h and setting new value in c_udp.c and d_udp.c files)
> >
> > The results are seems to perfect. Rohc decomress errors are seems to
> > minimized to very small values which stems from loss of initial
> > context packages.
> >
> > The drawback is that 28 byte UDP headers were compressed to 4 bytes
> > previously but with the solution that I tried they are now compressed
> > to 7 bytes.
> >
> > Is this normal behavior?
> >
> > Best Regards..
> >
> >
> >
> > 2018-01-30 17:26 GMT+03:00 mehmet sulak <mehmet.sulak@xxxxxxxxx>:
> >
> > > Thanks for your detailed response first;
> > >
> > > First I tried method  rohc_comp_set_wlsb_window_width(comp,8) by
> > > giving 8bits window width but I still observe the following in the
> > > log files;
> > >
> > > rohc_decomp_rfc3095.c:1463 parse_uo0() 4 SN bits = 0xe
> > >
> > > So I think it still uses 4 bit window length? If yes did I do
> > > something wrong?
> > >
> > > Secondly I think for UDP packets ROHC_LSB_SHIFT_SN(-1) is used for
> > > compressor and decompressor which makes parsing delayed packets
> > > impossible.
> > >
> > > So I need to use something half of (2 ^ lsb_width)  instead of -1 by
> > > adding a new enumeration value.
> > >
> > > Do have any idea about this parameter?
> > >
> > > Best Regards..
> > >
> > > 2018-01-29 22:11 GMT+03:00 Didier Barvaux <didier@xxxxxxxxxxx>:
> > >
> > >> Hello,
> > >>
> > >> > I am using Rohc comressor/decomressor pair on a lossy
> > >> > media(sometimes at receiver side some packets are lost) and the
> > >> > orderings of the  UDP packets are not guaranteed.(packets are
> > >> > not coming in right order all the time).
> > >> >
> > >> > I am using Unidirectional mode and observe some decomression
> > >> > failures about CRC check, malformed packets...
> > >> >
> > >> > Any recommendation to overcome these issues?
> > >>
> > >> The ROHC protocol provides several ways to handle packet loss or
> > >> reordering:
> > >>
> > >> a/ Increasing the width of the window used by the W-LSB algorithm
> > >>    improves the robustness of the ROHC protocol by sending more
> > >> bits for changing fields. Given a W-LSB width <wlsb_width>, up to
> > >>    (<wlsb_width> - 1) packets may be lost without causing
> > >> additional loss.
> > >>    The default width is set to 4 by the ROHC library ; please use
> > >> the rohc_comp_set_wlsb_window_width() function to change the
> > >> value ; see [1] for more details.
> > >>
> > >> b/ Increasing the number of transmissions N required for a changing
> > >>    static fields or a changing pattern for a dynamic field ensures
> > >> that the loss of N-1 packets during such a change will cause no
> > >>    additional loss.
> > >>    The default number of transmissions is set to 3 by the ROHC
> > >>    library ; there is no API to change the value at that time, but
> > >> you may change the value of the constant MAX_IR_COUNT in the
> > >> source file src/comp/rohc_comp_internals.h and re-build/re-install
> > >> the library.
> > >>
> > >> c/ Same as b/ but for lists of extensions headers (such as IPv6
> > >>    extension headers, GRE, AH...). Use the function
> > >>    rohc_comp_set_list_trans_nr() to change the value ; the default
> > >>    value is set to 5 ; see [2] for more details.
> > >>
> > >> d/ You may enable packet/context repair upon CRC failures, so that
> > >> the decompressor tries to fix the context or packet if it detects a
> > >>    decompression problem (due to packet loss/reordering for
> > >> example). The feature is disabled by default. Enable it with the
> > >> function rohc_decomp_set_features() and the feature
> > >>    ROHC_DECOMP_FEATURE_CRC_REPAIR ; see [3] for more details.
> > >>
> > >> Configuring options a-c is easier if you know the largest number of
> > >> consecutive losses that you may expect and/or you want to be
> > >> protected against.
> > >>
> > >> Let me know if my explanations are clear enough or if you need more
> > >> details. And, of course, let me know if one of the options solves
> > >> your problem.
> > >>
> > >> Regards,
> > >> Didier
> > >>
> > >>
> > >> [1] documentation of rohc_comp_set_wlsb_window_width():
> > >> https://rohc-lib.org/support/documentation/API/rohc-doc-2.1.
> > >> 0/group__rohc__comp.html#ga2b68070dddbc038cd55490952a7b3fa4
> > >>
> > >> [2] documentation of rohc_comp_set_list_trans_nr():
> > >> https://rohc-lib.org/support/documentation/API/rohc-doc-2.1.
> > >> 0/group__rohc__comp.html#ga32608bc06e1b0d1656e463eeb1ccbd7f
> > >>
> > >> [3] documentation of rohc_decomp_set_features():
> > >> https://rohc-lib.org/support/documentation/API/rohc-doc-2.1.
> > >> 0/group__rohc__decomp.html#ga2298148ca8dc277a1c1905f550f21f7b
> > >>
> > >>
> > >> _______________________________________________
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> > >
> > >
>
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