Interpretations of 802.11 counters report on WCS

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Sep 30th, 2009
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Dear Sir,

My customer recently deployed WLCs and WCS in their environment. However, recently they experienced slow performance. To futher finding out the root cause, I generated the 802.11 counters report from the WCS and noticed the following parameters is shown.

Tx/Rx Fragment Count/Sec and FCS Error Count/Sec

1. Can I make the assumptions that the overall transfer of packet rate in that interval is the Total of Tx/Rx Fragment Count/Sec and FCS Error Count/Sec?

2. If the output rate of Tx/Rx Fragment Count/Sec and FCS Error Count/Sec are the same, does it mean that 50% of the packet are corrupted and this high FCA Error Count/Sec will cause performance degradation to the wireless througphput?

3. What is the baseline of the FCS Error Count/Sec that is acceptable? As for the case with wired, 1% error rate is acceptable. Will wireless have the same baseline?



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ivillegas Tue, 10/06/2009 - 11:59
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FCS error count is the number of frames that were transmitted/received with a bad checksum (CRC value) in the ethernet frame. These frames are dropped and not propagated onto other ports. Usually we check FCS errors at the asic level so they never even hit the backplane. Few of these errors are OK, but could also be an indication of bad cables, NICs,etc.

Catalyst keeps track of Tranmit FCS and Receive FCS. The Receive FCS is normal since its coming from the cable, Transmit FCS errors, however, should not occur and are an indication of bad hardware in the Catalyst. The FCS counter is a sum of Tx and Rx FCS errors.

jandonegui Mon, 10/17/2011 - 09:20
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Could you please explain the concept of Transmit FCS Error ?

The FCS is added to a frame, so that the receiver can check if there have been any transmission errors. So, how can there be a Transmit FCS Error ?


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