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Re: [Discuss-gnuradio] Packet drop from Ethernet (A BIG PROBLEM)

From: Nikos Balkanas
Subject: Re: [Discuss-gnuradio] Packet drop from Ethernet (A BIG PROBLEM)
Date: Wed, 9 Mar 2016 23:23:26 +0200

Hi Mostafa,

You seem to be confused about sample resolution. There is sample resolution taking place at the FPGA, and sample resolution that can take place at uhd driver in the host. Important to know is that usrp ADCs will sample at 16 bits I/Q (32 bits) /sample. That's a hardware limit you cannot improve upon. If you reduce that at the FPGA to 8bits you save bandwidth from your ethernet. If you change it at the driver, you only make it compatible with your userspace app. Both are controlled at the same place, the streamer. FPGA resolution is configured at stream_args.otw_format, while uhd output resolution is configured at stream_args.cpu_format. For more info check the uhd_usrp_get_rx_streamer at http://files.ettus.com/manual/globals_func_u.html

You also are using a PCI NIC for transfer. These are cheap but notoriously bad. I've tried both a DG-Link and a TP-Link and couldn't get over 300 Mbps, using Realtek's r8169 driver, without even having anything else in my PCI bus. 


On Wed, Mar 9, 2016 at 11:33 AM, Mostafa Alizadeh <address@hidden> wrote:

Hi Nikos,

This is exaclty the issue related to the GNURadio application rather than USRP because the problem is from the host. That is not possible to transfer 30 Msps, however, what about 20 Msps? I expect to be able to transfer 20 Msps at least.

Another point that you mentioned is "changing the resolution of the samples". In contrast, as far as I know, if you change the sample resolution it does not reduce the bit rate of the Ethernet interface, however, it changes the interpretation of the samples! It is easy to run a program for different sample resolution and observe that there is no change in the bit rate of the Eth. Interface.

How to change the ethernet parameters or anything else ( if any idea ) to reduce packet dropping??

Thanks in advance,

On Mar 9, 2016 11:25 AM, "Nikos Balkanas" <address@hidden> wrote:

This issue is better addressed to address@hidden. Briefly I can tell you that you can never reach 30M samples/sec over a 1 GbE interface.
30 x 32/bits/sample = 960. Need a bit for metadata, packet overheads, etc. you will drop packages. Especially if your NIC is PCI based :(
Try reducing your sample resolution to 8 bits. You may have better luck.


On Wed, Mar 9, 2016 at 9:42 AM, Mostafa Alizadeh <address@hidden> wrote:

Hello all,
I stuck on an incridible challenge in sending/receiving a large bandwidth. I have an USRP N210 and an WBX daughterboard, while I must be able to capture/transfer up to 30Msample/sec(1Gig ethernet limit ), with the sample rate of 25Msps or even 20Msps I have some dropped packets. Based on my knowledge, this is due to CPU which does not have enough time to capture from Ethernet, however, I have the powerful one, 12 core CPU. When I have a large GNURadio program to run, there are some dropped packets. I searched everywhere but I did not find a complete description of the solution. What is (are ) the solution(s )? Please help me with any information! :(

Best regards

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