Benchmark_rx n_right always 0

I am using benchmark_tx/benchmark_rx to transmit data on 2.41GHz:
./benchmark_rx.py -f 2.41G
./benchmark_tx.py -f 2.41G

While I can receive packages at the rx end, the n_right field of every
package is always 0. I know it means the package failed the CRC check.
What
might be the cause? I am using two USRP N210s and daughter boards are
XCVR2450. The following are the displayed message at rx end:
*belltestbed@belltestbed-OptiPlex-790:~/Desktop/gnuradio/gr-digital/exales/narrowband$
./benchmark_rx.py -f 2.41G *
linux; GNU C++ version 4.6.3; Boost_104601;
UHD_003.004.002-128-g12f7a5c9

*
*
>>> gr_fir_ccf: using SSE
– Opening a USRP2/N-Series device…
– Current recv frame size: 1472 bytes
– Current send frame size: 1472 bytes
*
*
UHD Warning:

  • Unable to set the thread priority. Performance may be negatively
    affected.*
  • Please see the general application notes in the manual for
    instructions.*
  • EnvironmentError: OSError: error in pthread_setschedparam*

No gain specified.
Setting gain to 49.500000 (from [0.000000, 99.000000])
*
*
UHD Warning:

  • The hardware does not support the requested RX sample rate:*
  • Target sample rate: 0.050000 MSps*
  • Actual sample rate: 0.195312 MSps*

Symbol Rate: 25000.000000
Requested sps: 2.000000
Given sample rate: 195312.500000
Actual sps for rate: 7.812500
*
*
Requested sample rate: 50000.000000
Actual sample rate: 195312.500000
Warning: Failed to enable realtime scheduling.
Using Volk machine: avx_32
ok = False pktno = 65 n_rcvd = 1 n_right = 0
ok = False pktno = 67 n_rcvd = 2 n_right = 0
ok = False pktno = 68 n_rcvd = 3 n_right = 0
*ok = False pktno = 69 n_rcvd = 4 *n_right = 0
*ok = False pktno = 70 n_rcvd = 5 *n_right = 0
*ok = False pktno = 71 n_rcvd = 6 *n_right = 0
*ok = False pktno = 72 n_rcvd = 7 *n_right = 0
*ok = False pktno = 73 n_rcvd = 8 *n_right = 0
*ok = False pktno = 74 n_rcvd = 9 *n_right = 0
*ok = False pktno = 75 n_rcvd = 10 *n_right = 0
*ok = False pktno = 76 n_rcvd = 11 *n_right = 0
*ok = False pktno = 189 n_rcvd = 12 *n_right = 0

On Tue, Jun 5, 2012 at 11:47 AM, Weixian Z. [email protected] wrote:

linux; GNU C++ version 4.6.3; Boost_104601; UHD_003.004.002-128-g12f7a5c9
Hi Weixian,

Remember that these benchmark examples have no error correcting codes
in them, so a single bit error will cause the packet CRC check to
fail. Likely reasons for this include low SNR, nonlinearities in the
receiver/transmitter chain, and multipath channels. You might also
have a frequency offset between the two USRPs that’s just a bit
outside of the channel filter’s bandwidth such that you are distorting
it enough to cause errors but not so much that many of the bits are
still getting through.

Tom