Re: [Discuss-gnuradio] UDP Re-transmission

[Marcus Müller]

Hi Dustin!

Good thing you removed the Packet Encoder and Packet Decoder – these
blocks are buggy, we don't know how to repair them, and thus, they will
soon be gone from GNU Radio. That's why they are in the "deprecated"
category.

The fact that it works with a file source but not with a UDP source
does coincide with the observation that the failure rate of these
blocks is strongly dependent on the fine temporal aspects of how they
get input.

But without them, you don't have a packetizer – and thus, none of this
works because your receiver simply can't know what the start of a
transmission is, or what symbols belong to a byte and so on.

I must admit I don't have an easy solution for this. Are you fixed on
using GFSK?

Best regards,
Marcus
On Mon, 2018-06-18 at 10:05 -0500, D J wrote:
> Hello all,
> 
> I need some advice.  I'm trying to take UDP datagrams from one port,
> transport them over an RF link to a receiver, and then send them back
> over another UDP port.  Sounds simple, but I'm having a difficult
> time with it.
> 
> Originally I was doing this to transmit text and image files:
> 
> [file source]-->[Packet Encoder]-->[GFSK Mod]-->[UHD USRP Sink
> (B200)]
> 
> [Osmocom SDR Source (BladeRF)]-->[GFSK Demod]-->[Packet Decoder]
> -->[file sink]
> 
> It worked great using files, but once I replaced the File source and
> sink blocks with UDP source (port 9003) and sink (port 9004), It
> wouldn't work.  I also had to remove the packet encoder and decoder
> blocks.  
> 
> [UDP source 9003]-->[gfsk mod]-->[UHD USRP Sink (B200]
> [Osmocom SDR Source (BladeRF]-->[gfsk demod]-->[UDP sink 9004]
> 
> Troubleshooting: Using Wireshark to sniff the source and sink ports,
> I could see that the data going to the UDP sink port (9004) was
> completely different from what was sent on the UDP source port.  When
> I connect the UDP source/sinks together directly, UDP traffic is
> passed and the datagrams match. I removed the radios and connected
> the GFSK mod/demod blocks directly and the problem persists.  Also,
> unless I decimated the received samples by 8, the datagrams on the
> UDP sink port were different sizes from those on the UDP source
> port.  The UDP, IP, and Ethernet headers are intact, but the payload
> on the receive side is just random hex 01 and hex 00.  
> 
> Has anyone implemented something like this before? What am I doing
> wrong?
> 
> Thank you,
> Dustin  
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