extraneous data and malformed packet in Hopping Channel

[moemu...@gmail.com]

Hi every one ..

First of All i send 5 msg to mobile .

i have hoping channel , i capture the spectrum using USRP N210 with 10M sampleRate and then channelize it to 4 channel with 1M sampleRate.

then i use grgsm_hopping_example.grc to put it in one binary File "h.binary"

https://drive.google.com/file/d/127okn3mIWMqcr73LVJz77YIcgeZiQFnx/view

then decode it using Kc Like this

grgsm_decode -b h.binary -f 1835e6 -s 1e6 -m SDCCH8 -t 2 -k 'F76A9298F93E6F31'

and then i got this in wireshark " also attach wireshark capture"

and this

and in last msg i have the number but also without tp-user-data with malformed packet

can Someone tell me what happen , and how can i fix this !

[Vasil Velichkov]

Hi moemusa0090,

On Wednesday, July 25, 2018 at 10:25:00 AM UTC+3, moemu...@gmail.com wrote:

then decode it using Kc Like this

grgsm_decode -b h.binary -f 1835e6 -s 1e6 -m SDCCH8 -t 2 -k 'F76A9298F93E6F31'

Which gr-gsm and wireshark versions do you use?

When I run the above command using the latest development branch (commit ac140210c93deb8918f7ab964c2ba8791aea711e) I get only 38 gsmtap packets and there is no any SMS-DELIVER in it.

[moemu...@gmail.com]

Wireshark version 2.6.1

and grgsm from master brunch

https://github.com/ptrkrysik/gr-gsm/tree/master

[Vasil Velichkov]

Hi,

On Wednesday, July 25, 2018 at 2:03:40 PM UTC+3, moemu...@gmail.com wrote:

and grgsm from master brunch

https://github.com/ptrkrysik/gr-gsm/tree/master

In the master branch there are few bugs that are fixed in the development branch.

One of them is https://github.com/ptrkrysik/gr-gsm/pull/362 and the fix is https://github.com/ptrkrysik/gr-gsm/commit/bc2a23e0e7454fcba9770644055ac4d048db61e5

In short the return code of gsm0503_xcch_decode was not check and as a result a lot of malformed messages (with CRC errors or not successfully decrypted) were sent to Wireshark and Wireshark displays them as malformed because they are actually malformed.

You could validate this by applying this commit on top of current master (git cherry-pick bc2a23e0e7454fcba9770644055ac4d048db61e5), reinstall (make install) and then after running grgsm_decode you will get only 38 valid packets in the Wireshark.

My other advice is to use the development branch as it contains other bug fixes as well.

[moemu...@gmail.com]

I install development branch , and as you say i have only 38 packet

So Now what is the problem , is it in my SDR , OR Bad Resiver Quality  ?

[Piotr Krysik]

W dniu 25.07.2018 o 09:25, moemu...@gmail.com pisze:

> Hi every one ..
>
> First of All i send 5 msg to mobile .
>
> i have hoping channel , i capture the spectrum using USRP N210 with 10M
> sampleRate and then channelize it to 4 channel with 1M sampleRate.
>
> then i use grgsm_hopping_example.grc to put it in one binary File
> "h.binary"
>
> https://drive.google.com/file/d/127okn3mIWMqcr73LVJz77YIcgeZiQFnx/view
>

Try also to connect C0 output of the "GSM Receiver" block to "CX channel
hopper". Can you also show configuration of the "GSM Receiver"?

--
Best Regards,
Piotr Krysik

[moemu...@gmail.com]

thank you for replay ,,

i will Connect C0 to Cx channel hopper , but still same output

and this Configuration of GSM Receiver

"osr = 4"