Wireless Networks Review Question

Q1 Name the mandatory requirements of an 802.11 wireless site survey. (Choose all that apply.) A. Application analysis B. Coverage analysis C. Throughput analysis D. Spectrum analysis E. Security analysis

Answer: B, D. Although often overlooked, checking for potential sources of RF interference is considered a mandatory requirement when conducting a site survey. Both spectrum analysis and visual inspection should be used to search for potential sources of interference. Coverage analysis involves certifying RF cell boundaries and is the main reason for a site survey. Application and throughput analysis are considered an optional requirement. The site survey interview will determine security expectations; however, security is not usually part of the site survey itself.

Q2 What type of solution must be deployed to provide continuous connectivity when a client station roams across layer 3 boundaries? (Choose all that apply.) A. Nomadic roaming solution B. Proprietary layer 3 roaming solution C. Seamless roaming solution D. Mobile IP solution E. Fast secure roaming solution

Answer: B, D. The only way to maintain upper-layer communications when crossing layer 3 subnets is to provide either a Mobile IP solution or a proprietary layer 3 roaming solution.

Q3 Mr. Harkin, the WLAN administrator at the ACME Company, discovers that water has damaged some coaxial cables to one of the company’s outdoor wireless bridges. He replaces the cabling but soon discovers that the equivalent isotropically radiated power (EIRP) leaving the bridge antenna now exceeds the power output limit of his nation’s regulatory body. What might have happened? (Choose all that apply.) A. Water also damaged the wireless bridge B. He installed a shorter cable C. He installed higher-grade cabling D. He installed lower-grade cabling E. The old cable was 50 ohms and the new cable is 75 ohms

Answer: B, C. The shorter cable will result in less power loss and could exceed power output regulations. Cabling is rated for dB loss per 100 feet. If he installed a higher-grade cable that is rated for less loss per 100 feet, this could also exceed power output regulations.

Q4 What can be done to fix the hidden node problem? (Choose all that apply.) A. Increase the power on the access point. B. Move the hidden node station C. Increase power on all client stations D. Remove the obstacle

Answer: B, C, D. The hidden node problem arises when client stations cannot hear the RF transmissions of another client station. Increasing the transmission power of client stations will increase the transmission range of each station, resulting in increased likelihood of all the stations hearing each other. Moving the hidden node station within transmission range of the other stations also results in stations hearing each other. Removing an obstacle that prevents stations from hearing each other also fixes the problem.

Q5 How many channels are considered non-overlapping in the 5 GHz UNII bands? A. 3 B. 12 C. 11 D. 23 E. 6

Answer: B. The 802.11a amendment requires 20 MHz of separation between the center frequencies of ERP-OFDM channels in the 5 GHz UNII bands to be considered non-overlapping. There are 4 channels each of the three UNII bands, each with 20 MHz of separation for a total of 12 non-overlapping channels. In the future, 11 more channels may be used by 802.11a radios.

Q6 What type of interference is caused by overlapping frequencies within overlapping coverage cells? A. Inter-symbol interference B. Physical interference C. All-band interference D. Narrowband interference E. Co-channel interference

Answer: E. Overlapping coverage cells with overlapping frequencies causes co-channel interference (CCI), which causes a severe degradation in performance and throughput. If overlapping coverage cells also have frequency overlap, frames will become corrupt, retransmissions will increase, and throughput will suffer significantly.

Q7 What variables might affect range in an 802.11 WLAN? (Choose all that apply.) A. Wavelength B. Free space path loss C. Brick walls D. Trees E. All of the above

Answer: E. Higher-frequency signals have a smaller wavelength property and will attenuate faster than a lower-frequency signal with a larger wavelength. Higher-frequency signals therefore will have shorter range. In any RF environment, free space path loss (FSL) attenuates the signal as a function of distance. Loss in signal strength affects range. Brick walls exist in an indoor physical environment, while trees exist in an outdoor physical environment. Both will attenuate an RF signal, thereby affecting range.