Re: file source with gr-ieee802.11 tx

The wifi_tx example GRC comes with a Socket PDU source.

Just send UDP packets to the port specified containing a IEEE 802.11 packet’s
amount of data per UDP packet;
netcat/nc/ncat is sadly no good for this, because it doesn’t allow specification
of packet sizes.

You can also use a file source, stream to tagged stream, tagged stream to PDU
flow graph.

To be honest, GNU Radio is kind of lacking a simple “take n items from the input
stream and generate a PMT pair
(n, items), send that over your message port” block, which would take roughly 10
lines of python to write (and
not much more C++) – so you might as well do that.

This is something I have struggled with as well. A lot of examples I’ve
seen are for streaming data (which is admittedly probably want most
people are wanting).

I have been more interested in sending a packet (or a series of packets)
over the air (the end goal being letting someone connect to my UDP
source block and handing me their data they want to send). I have
played with the WiFi block a bit recently and unfortunately was always
using netcat…

1 - Are you saying that the data’s packet being handed to the socket PDU
has to be exactly as long as the pdu_length? That is something I think
I must have glossed over.

2 - I don’t believe there is a way to dump just the payload of the
802.11 packet, right? Basically, if I sent “Hello World” to the Socket
PDU (which means my pdu_length would need to be set to 11, right?), is
there a way to have those 11 characters be passed out a UDP sink on the
receiver end? Right now the only thing I can see to do is to utilize
the Wireshark Connector and dump the pcap output to file, then take info
and extract the payload from there in post-processing. Is that right?

Thanks.

Hi,

(n, items), send that over your message port" block, which would take roughly
10 lines of python to write (and
using netcat…

1 - Are you saying that the data’s packet being handed to the socket PDU
has to be exactly as long as the pdu_length? That is something I think
I must have glossed over.

You can pass data of any size of up to 1500 bytes (minus a bit for
headers).

2 - I don’t believe there is a way to dump just the payload of the
802.11 packet, right? Basically, if I sent “Hello World” to the Socket
PDU (which means my pdu_length would need to be set to 11, right?), is
there a way to have those 11 characters be passed out a UDP sink on the
receiver end? Right now the only thing I can see to do is to utilize
the Wireshark Connector and dump the pcap output to file, then take info
and extract the payload from there in post-processing. Is that right?

The transceiver wraps your payload in some headers that add stuff like
MAC address, frame type, and CRC. These are the minimum fields that are
required so that a WiFi card actually accepts the frame.

There is currently no option to dump raw bytes, but its a trivial
modification of the Wireshark block (dump without a PCAP header).
If you want to printed bytes as hex-values on the console that should
work with the parse block.
Or you could use a Debug Message block and print the PDUs coming out of
the PHY / MAC, depending on what you want to see.

Best,
Bastian

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