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CCNP Wireless FAQ: Solving Noise and Interference Problems

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CCNP Wireless FAQ: Solving Noise and Interference Problems

Q1. For reliable network operation, signal strength is more important than SNR. True or false?

Answer: False.SNRis more important than signal strength.

Q2. A reliable wireless link needs a line-of-sight path and an unobstructed Fresnel zone. True or false?

Answer: True.

Q3. Will the noise level always be low in a rural area?

Answer: Not necessarily. Noise in a rural area might be low or it might be high.

Q4. How many nonoverlapping 2.4 GHz channels are available for use in the United States?

Answer: There are three nonoverlapping channels.

Q5. The consequence of a low SNR is reduced network throughput. True or false?

Answer: True.

Q6. Reusing a DSSS frequency at the same AP location requires how many decibels of antenna isolation?

Figure: Frequency Plan

ccnp-wireless-faq-solving-noise-interference-problems
Answer: Reusing the same frequency in the same location requires approximately 121 dB of antenna isolation.

Q7. To avoid interference, collocated FHSS sectors should use different hopping sequences and different hopping sets. True or false?

Answer: False. CollocatedFHSSsectors should use different hopping sequences within the same hopping set.

Q8. When is the SNR highest at an AP?

Answer: TheSNRis the highest just after theAPhas been installed. As time passes, the noise level increases and theSNRgoes down.

Q9. When the percentage of retransmitted packets reaches 20 percent, you should start looking for the cause of the network slowdown. True or false?

Answer: False. The network performance starts to slow down when the retransmit percentage goes above 10 percent. Start looking for the cause when the retransmit percentage goes above 10 percent.

Q10. Explain why it is necessary to write down the results of your noise-reduction efforts.

Answer: It is necessary to write down the results of your noise-reduction efforts so that you don’t waste time repeating the same tests the next time a noise problem occurs.