Wireshark · Wireshark-users: Re: [Wireshark-users] Descepancy in 7-to-8 bit decoding

[Pascal Quantin <pascal.quantin@xxxxxxxxx>]

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@xxxxxxxxx>

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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