Lab Manual for CWNA Guide to Wireless LANs, Second Edition
Lab Manual Solutions 3-1
Chapter 3 Solutions
NOTE: Lab 3.4 sets up the Linksys wireless router and must be completed in order
for all other Linksys-related labs to work later in the lab manual.
Activity Questions, Lab 3-1
3.
Use the correct formula to calculate what 15 watts is in dBm.
Answer: 10log15000= 41.8 dBm
4.
Use the correct formula to calculate what 31 dBm is in watts.
Answer: log-1(31/10) = 1259 mW = 1.26 watts
5.
Calculate the change in power in dBm.
Answer: 10log(75/50) = 1.76 dBm
7.
What is the EIRP in dBm using a radio with a transmit power of 17 dBm, losses of 2 dBm in cables
and connectors, and using a 9-dBi antenna?
Answer: 17 – 2 + 9 = 24 dBm
8.
Using the rule of 10’s and 3’s, what is 16 mW + 6 dBm in dBm?
Answer: 24 = 16 so it doubles 4 times; 4x3=12; 12 dBm + 6 dBm = 18 dBm
9.
Using the rule of 10’s and 3’s, what is 16 mW + 6 dBm in mW?
Answer: 16 x 2 x 2 = 64 mW
10. Convert 64 mW to dBm and compare your answer to the answer given in Step 8. How accurate was
your estimation using the rule of 10’s and 3’s?
Answer: 10log64 = 18.1 dBm; 18 versus 18.1 – very accurate
Review Questions, Lab 3-1
1.
Why must wireless administrators learn about power calculations?
Answer: Because power is regulated by the FCC
2.
As milliwatts increase by a factor of 10, how does dBm increase?
Answer: Add 10
3.
As milliwatts increase by a factor of 2, how does dBm increase?
Answer: Add 3
4.
The relationship between milliwatts and dBm is linear. True or False?
Answer: False
5.
If power units are all given in dBm, you can simply add or subtract to get the total power output. True
or False?
Answer: True
Activity Questions, Lab 3-2
2.
Use the Windows standard calculator to calculate the radius of the Fresnel zone.
Answer: r = 43.3xsqrt[0.25/(4x5.725)] = 4.52 feet
3.
Do you consider this level of blockage a problem? Why or why not? If you consider this blockage a
problem, what is the most obvious way to solve the problem?
Answer: Yes; It is greater than 40%; Trim the trees down until they are not a problem
4.
What is another possible way to reduce the blockage in the Fresnel zone?
Answer: Raise the antennas
Lab Manual for CWNA Guide to Wireless LANs, Second Edition
5.
Lab Manual Solutions 3-2
What effect will raising the antennas have on the radius of the Fresnel zone?
Answer: None, because antenna height is not part of the equation
Review Questions, Lab 3-2
1.
As distance between the antennas increases, what happens to the radius of the Fresnel zone?
Answer: Increases
2.
As link frequency increases, what happens to the radius of the Fresnel zone?
Answer: Decreases
3.
What are two common solutions to a Fresnel zone blockage problem?
Answer: Remove obstruction; raise antennas
4.
What is the maximum percentage of Fresnel zone blockage that can usually be tolerated?
Answer: 40%
5.
Why aren’t Fresnel zone calculations done on indoor links?
Answer: The distance is not great enough to have an effect; also, there are more important factors with
indoor wireless, such as concrete or metal walls
Activity Questions, Lab 3-3
7.
What is the gain in dBi for the antenna you are using with your access point?
Can the antenna you are using work outdoors as well as indoors?
What is the horizontal beamwidth for your antenna?
What is the vertical beamwidth for your antenna?
What is the indoor range in feet for your antenna at 6 Mbps?
What is the indoor range in feet for your antenna at 54 Mbps?
Answer: 2.2 dBi; No; 360 degrees; 65 degrees; 300 feet; 90 feet
8.
How does the gain on this ceiling mount antenna compare to the gain on your antenna?
How does the range of the ceiling mount antenna compare to the range of your antenna?
How does the vertical beamwidth of the ceiling mount antenna compare to the vertical beamwidth of
your antenna?
Answer: 5.2 dBi versus 2.2 dBi; It has greater range than the regular dipole; It has less vertical
beamwidth than the regular dipole
Review Questions, Lab 3-3
1.
Why is it important to know the horizontal and vertical beamwidth of a particular antenna?
Answer: To make sure you have adequate cell coverage for your WLAN
2.
What is the relationship between range and frequency?
Answer: In general, the higher the frequency, the shorter the range
3.
What is the relationship between gain and range?
Answer: In general, the higher the gain, the longer the range
4.
Why do you think the horizontal beamwidth on the wall mount antennas is less than on the
omnidirectional antennas?
Answer: Because being mounted against the wall prohibits 360 degrees of transmission
5.
What is the relationship between bandwidth and range?
Answer: In general, the higher the bandwidth, the shorter the range
Lab Manual for CWNA Guide to Wireless LANs, Second Edition
Lab Manual Solutions 3-3
Activity Questions, Lab 3-4
3.
What is the IP address of your Ethernet connection?
Answer: Varies
7.
What is the default SSID on this router? What is the default channel configured on this router?
Answer: linksys; Channel 6
8.
Is security mandatory on the Linksys router? What is the default security setting?
Answer: No; Disabled
11. What is the IP address of the wired NIC now? Is it the same as the one you recorded in Step 3? If it is
different than previously recorded, why do you think this is so?
Answer: 11. Varies, but on 192.168.1.0 network; No; The Linksys router does network address
translation (NAT)
12. Are you connected wirelessly to the Linksys router?
Answer: Varies
16. What is the default router name?
Answer: WRT54G (may be different, but it should be the model of the router)
19. What is your profile name? What is your wireless mode frequency and connection speed? How is
your signal strength described?
Answer: Infrastructure Mode; Varies; Varies, but could be Excellent or Good, for example
20. What is happening to the signal strength as you get farther away from the wireless router? What is the
description of your signal strength now?
Answer: Gets weaker as you travel farther from access point; Varies, but could be Fair or Poor, for
example
Review Questions, Lab 3-4
1.
What is the default wireless mode setting, SSID, and channel assignment for the Linksys wireless
router?
Answer: Mixed mode; linksys; channel 6
2.
What does “mixed mode” indicate?
Answer: It will accept 802.11b or 802.11g clients.
3.
The Linksys wireless router can do network address translation as well as DHCP. True or False?
Answer: True
4.
What is the default gateway for the Linksys wireless router?
Answer: 192.168.1.1
5.
What is the relationship between distance from the access point and wireless signal strength?
Answer: The greater the distance, the weaker the signal