Re: Descepancy in 7-to-8 bit decoding

[Ajay Garg <ajaygargnsit () gmail com>]

Hi Pascal.

Thanks for the reply.
Information provided by you solve our issue !!!



Thanks and Regards,
Ajay


On Sun, Jan 12, 2014 at 4:31 PM, Pascal Quantin <pascal.quantin () gmail com>wrote:

> Hi Ajay,
>
> the corresponding character in the bitstream is code point 64 that
> corresponds to a '@' character in ASCII but that translates to character '
> *¡*' in the GSM 7bit alphabet (see 3GPP 23.038 chapter 6.2.1). The '@'
> character in GSM 7bit alphabet is code point 0.
> So my understanding is that your decoder is wrong as it seems to use the
> ASCII table instead of the GSM 7 bits one and that Wiresahrk output is
> correct.
>
> Best regards,
> Pascal.
>
>
> 2014/1/12 Ajay Garg <ajaygargnsit () gmail com>
>
> > Hi all.
> >
> > (This might actually serve as a follow-up to
> > http://www.wireshark.org/lists/wireshark-users/201311/msg00014.html, but
> > since the issue this time is a bit different, I preferred starting a new
> > thread, so as not to clutter up things).
> >
> >
> > We captured some USSD network traces, and found that the following *7-bit
> > encoded* message was being transferred over the wire :
> >
> > *c2301b249dbb663617ce056abee56510391d668354b1584c151bb914532a111883c15fcdb43b0422be41d2612d070abbc9a0b25bfdce83a65422681866b3e720fa1b1474e741ce32fdfe96af41c0180cfe6abb40d6201324c391c3f9b90b44350d4141389c9d7701*
> >
> >
> >
> > Wireshark shows the decoded-message to be
> >
> >
> > *Bal Rs.36.8. More dial *111*1#.STD¡10p/Min! Do RC59 and enjoy STD Calls
> > to Any Network ¡10p/m. VAL 28days. T&C Apply.*
> >
> > while our 7-to-8 bit decoder shows this to be
> >
> >
> > *Bal Rs.36.8. More dial *111*1#.STD@10p/Min! Do RC59 and enjoy STD Calls
> > to Any Network @10p/m. VAL 28days. T&C Apply.*
> >
> > (Note the difference of "¡" and "@").
> >
> >
> > The wireshark rpm being used is wireshark-1.6.16-2.fc17.i686
> >
> >
> > Is this another case of using a special charcater ("*¡*" in the present
> > case), when some particular byte-stream is received?
> > Or am I being plain stupid?
> >
> >
> >
> > We will be grateful for some pointers, that could help clear our doubts !!
> >
> > Looking forward to a reply
> >
> >
> >
> >
> > Thanks and Regards,
> > Ajay
> >
> >
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-- 
Regards,
Ajay

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