# Re: file source with gr-ieee802.11 tx **URL:** \ **Category:** GNU Radio\ **Created:** [July 31, 2015, 2:11pm UTC](https://www.ruby-forum.com/t/re-file-source-with-gr-ieee802-11-tx/242828 "2015-07-31T14:11:03Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [July 31, 2015, 2:11pm UTC](https://www.ruby-forum.com/t/re-file-source-with-gr-ieee802-11-tx/242828/1 "2015-07-31T14:11:03Z")
> 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. ---
**Author:** ![Jason\_Matusiak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/edb3f5/32.png) [@Jason\_Matusiak](https://www.ruby-forum.com/u/Jason_Matusiak)\ **Post date:** [July 31, 2015, 3:12pm UTC](https://www.ruby-forum.com/t/re-file-source-with-gr-ieee802-11-tx/242828/2 "2015-07-31T15:12:58Z")
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