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

[Nikos Balkanas]

Hi Mostafa,

This is a usrp issue, and depends exactly on the hardware. Before you look into the host for optimizing its networking parameters, you should make sure that your hardware can handle it.

For example reducing the sample resolution in your N200. ADCs in USRPs use quad sampling, which means they generate I/Q (imaginary/real) data for each sample. At full resolution, this is 16 bits each or 32 bits/Sample. At reduced sample resolution, which takes place in the FPGA, you get 8 + 8 = 16 bits/sample, therefore half the bandwidth of full resolution going through the wire.

Now, you should be able to handle 20 MS/s at full resolution, 20x32 = 640 Mbps. But a lot of NICS have problems, especially the PCI ones. What is your NIC? What is your OS?

BR,

Nikos

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,
Mostafa

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

Hi,

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.

HTH,

Nikos

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
Mostafa

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