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gr_ieee-80211 receiver

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gr_ieee-80211 receiver

LiLi
Hi, everyone

I am using gr-ieee-80211 to recieve wifi packets on 2.4G.
The operating system is Ubuntu.The version of GNU RADIO is 3.7.5, and we use USRP N210 with SBX daughterboard.
Our purpose:
Capture packets of 802.11 protocol on 2.4G or the other band SBX daughterboard
Our problems:
When the Wireshark Connector was connected to 'WIFI Decode MAC', it can't receive any frame but an empty file. I want to figure out the cause, but it may consume a long time for a beginner. I think the main cause may exist in the 'WIFI Decode MAC' or the Wireshark Connector in the view that the latter can receive frames before the former.
Another tricky problem which I want to make clear is that whether the surroundings contains pure 802.11g frame. Could you show me the possible reasons? As I target to captured frames on 2.4GHz , how should the parameters of the Wireshark be recomposed?

Best,
Li Li
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Re: gr_ieee-80211 receiver

Bastian Bloessl-3

Hi,

LiLi <[hidden email]> writes:

> Hi, everyone
>
> I am using gr-ieee-80211 to recieve wifi packets on 2.4G.
> The operating system is Ubuntu.The version of GNU RADIO is 3.7.5, and we use
> USRP N210 with SBX daughterboard.
> Our purpose:
> Capture packets of 802.11 protocol on 2.4G or the other band SBX
> daughterboard
> Our problems:
> When the Wireshark Connector was connected to 'WIFI Decode MAC', it can't
> receive any frame but an empty file. I want to figure out the cause, but it
> may consume a long time for a beginner. I think the main cause may exist in
> the 'WIFI Decode MAC' or the Wireshark Connector in the view that the latter
> can receive frames before the former.

I don't believe it's a problem with the Wireshark or 'Decode MAC'
block. It's more likely that something goes wrong earlier. This can have
a lot of reasons (gain setting, wrong sample rate, wrong channel,
overruns, ...). You might find something useful here:

https://www.wime-project.net/installation/

If you still have problems, it would be helpful if you could provide
some more details on what happens and what you did to debug. Something
like are frames detected? Are only frames detected or is frame detection
triggered all the time? Did you try the setup with other transceivers?
Does the constellation diagram look good, etc.

> Another tricky problem which I want to make clear is that whether the
> surroundings contains pure 802.11g frame. Could you show me the possible
> reasons? As I target to captured frames on 2.4GHz , how should the
> parameters of the Wireshark be recomposed?

There is nothing you can do in the receiver. You have to make sure that
the device that you want to monitor sends 11a/g/p frames. Others are at
the moment not supported.

How to configure the mode depends on your device. (If you open a network
with a MacBook it works for me. Maybe that could be a simple test.)

Best,
Bastian

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Re: gr_ieee-80211 receiver

James Shimer
From my experience with QAM PHY, there are some basic debug tools to verify you are locked on the received signal.  Personally, I like the constellation plot, it's an easy visual to see if your QAM symbols are "hitting" the right spot.  Typically you have Modulation Error Ratio, SNR etc.  I dunno if gnuradio gives a MER, but putting in the constellation plot should be trivial.  You want those types of tools for verifying the PHY....  We used to buy test equipment for that but SDR allows younto build those tools in.....

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Re: gr_ieee-80211 receiver

LiLi
Hi,
We couldn't capture anything when we put wireshark connector after 'decode MAC'. When debug was enable   of 'decode Mac', we found the packets were all dropped. We tried to read codes of decode MAC block. We got a question below:
code lines :
if(result.checksum() != 558161692) {
                dout << "checksum wrong -- dropping" << std::endl;
                return;
        }

why result.checksum() should be a constant value(i.e.558161692) ?  

Thanks!

Best,
Li Li
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Re: gr_ieee-80211 receiver

Bastian Bloessl-3
Hi,

On 04/13/2017 12:20 PM, LiLi wrote:
> Hi,
> We couldn't capture anything when we put wireshark connector after 'decode
> MAC'. When debug was enable   of 'decode Mac', we found the packets were all
> dropped. We tried to read codes of decode MAC block. We got a question
>

My previous comment still applies. Really, these very last blocks in the
decoding chain aren't your problem. Please see the other email.

Best,
Bastian

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Re: gr_ieee-80211 receiver

LiLi
In reply to this post by LiLi
If we want to capture frames from a route, we should change the codes.
The codes on github can capture frames  which generate by the wifi_tx codes bacause the value of FCS is constant. After we change the value OF FCS to be an adaptive one, the frames from a route can be captured.
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Re: gr_ieee-80211 receiver

Bastian Bloessl-3

> On 9. May 2017, at 08:26, LiLi <[hidden email]> wrote:
>
> If we want to capture frames from a route, we should change the codes.
> The codes on github can capture frames  which generate by the wifi_tx codes
> bacause the value of FCS is constant. After we change the value OF FCS to be
> an adaptive one, the frames from a route can be captured.
>

FCS stands for frame check sequence. If the FCS doesn’t match the constant in the code, the frame is corrupt. It’s true that if you disable the FCS check that you “receive” more frames.  You will also see the corrupt ones.

(If you wonder why the FCS compares against a constant, you should have a look at the standard.)

Best,
Bastian
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Re: gr_ieee-80211 receiver

Cristian Rodríguez
Hi.

Did you check the name of the wireshark file is the same in the flowgraph and in the temp file (if you are using the .sh file into the app folder)?

Best regards,

Cristian

2017-05-09 4:26 GMT-05:00 Bastian Bloessl <[hidden email]>:

> On 9. May 2017, at 08:26, LiLi <[hidden email]> wrote:
>
> If we want to capture frames from a route, we should change the codes.
> The codes on github can capture frames  which generate by the wifi_tx codes
> bacause the value of FCS is constant. After we change the value OF FCS to be
> an adaptive one, the frames from a route can be captured.
>

FCS stands for frame check sequence. If the FCS doesn’t match the constant in the code, the frame is corrupt. It’s true that if you disable the FCS check that you “receive” more frames.  You will also see the corrupt ones.

(If you wonder why the FCS compares against a constant, you should have a look at the standard.)

Best,
Bastian
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