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2012-09-27 05:52:15
Understanding Wireless basics

Chapter 8 Cram
Show Answers:

  1. What is the network name needed to connect to a wireless AP?
    SSID (Service Set Identifier).
  2. True or False: A wireless access point (AP) is both a transmitter and receiver (transceiver) device used for wireless LAN (WLAN) radio signals.
    True. A wireless access point (AP) is both a transmitter and receiver (transceiver) device used for wireless LAN (WLAN) radio signals.
  3. True or False: An AP can operate as a bridge, connecting a standard wired network to wireless devices, or as a router, passing data transmissions from one access point to another.
  4. What does an AP allow you to do? 
    The infrastructure wireless topology is commonly used to extend a wired LAN to include wireless devices. Wireless devices communicate with the wired LAN through a base station known as an access point (AP) or wireless access point
  5. What is a service set Identifier (SSID)?
    A network name needed to connect to a wireless AP. It is like a workgroup name used with Windows networking. 802.11 wireless networks use the SSID to identify all systems belonging to the same network. Client stations must be configured with the SSID to be authenticated to the AP. The AP might broadcast the SSID, allowing all wireless clients in the area to see the AP’s SSID. For security reasons, APs can be configured not to broadcast the SSID or to cloak it. This means that an administrator needs to give client systems the SSID instead of allowing it to be discovered automatically.
  6. What is a Basic Service Set (BSS)?
    —Refers to a wireless network that uses a singleAP and one or more wireless clients connecting to the AP. Manyhome offices are an example of a BSS design. The BSS is an example ofthe infrastructure wireless topology. Chapter 1 discusses wireless topologiesand other networks.
  7. What is an Extended Service Set (ESS)?
    —Refers to two or more connected BSSsthat use multiple APs. The ESS is used to create WLANs or largerwireless networks and is a collection of APs and clients. Connecting BSSsystems enables clients to roam between areas and maintain the wirelessconnection without having to reconfigure between BSSs.
  8. What is an Extended Service Set Identifier (ESSID)?
    —Although the terms ESSID and SSID are used interchangeably, there is a difference between the two. SSID is the name used with BSS networks. ESSID is the network name used with an ESS wireless network design. With an ESS, not all APs necessarily use the same name.
  9. What is a Basic Service Set Identifier (BSSID)?
    —The MAC address of the BasicService Set (BSS) AP. The BSSID is not to be confused with the SSID,which is the name of the wireless network.
  10. What is a Basic Service Area (BSA)?
    —When troubleshooting or designing wirelessnetworks, the BSA is an important consideration. The BSA refers tothe AP’s coverage area. The BSA for an AP depends on many factors,including the strength of the AP antenna, interference in the area, andwhether an omnidirectional or directional antenna is used.
  11. What are some steps to take when troubleshooting AP coverage?
    Increase transmission power: Some access points have a setting toadjust the transmission power output. By default, most of these settingsare set to the maximum output; however, this is worth verifying just incase. You can decrease the transmission power if you’re trying to reducethe dispersion of radio waves beyond the immediate network. Increasingthe power gives clients stronger data signals and greater transmission distances.

    Relocate the AP: When wireless client systems suffer from connectivity problems, the solution may be as simple as relocating the AP. You could relocate it across the room, a few feet away, or across the hall. Finding the right location can likely take a little trial and error.

    Adjust or replace antennas: If the access point distance is insufficientfor some network clients, it might be necessary to replace the default antenna used with both the AP and the client with higher-end antennas.Upgrading an antenna can make a big difference in terms of transmission range. Unfortunately, not all APs have replaceable antennas.

    Signal amplification: RF amplifiers add significant distance to wireless signals. An RF amplifier increases the strength and readability of thedata transmission. The amplifier improves both the received and transmitted signals, resulting in an increase in wireless network performance.

    Use a repeater: Before installing a new AP, you might want to thinkabout a wireless repeater. When set to the same channel as the AP, therepeater takes the transmission and repeats it. So, the AP transmission gets to the repeater, and then the repeater duplicates the signal and passesit on. This is an effective strategy to increase wireless transmission distances.
  12. What is the wireless antenna designed to help with?
    • . Work around obstacles
    • . Minimize the effects of interference
    • . Increase signal strength
    • . Focus the transmission, which can increase signal speed
  13. What is used to determine an antenna's strength?
    It's gain value.
  14. What is the gain value of an antenna that signals flow equally in all directions?
    0dBi gain value, this is called an isotropic antenna.  Used as a base point for measuring  actual antenna strength.

    Where dB stands for decibels.
  15. What is the rule of thumb for doubling the antenna's effective power?
    Every 3dB doubles strength
  16. The dB in dBi stands for decibels and the i stands for the hypothetical isotropicantenna.
  17. What kind of wireless antenna's are their?
    Omnidirectional and directional
  18. What is an omnidirectional antenna?
    An omnidirectional antenna is designed to provide a 360-degree dispersed wave pattern. This type of antenna is used when coverage in all directions from the antenna is required. Omnidirectional antennas are advantageous when a broad-based signal is required. For example, if you provide an evensignal in all directions, clients can access the antenna and its associated accesspoint from various locations. Because of the dispersed nature of omnidirectionalantennas, the signal is weaker overall and therefore accommodatesshorter signal distances. Omnidirectional antennas are great in an environment that has a clear line of sight between the senders and receivers. The power is evenly spread to all points, making omnidirectional antennas well suited for home and small office applications.
  19. What are directional antennas?
    Directional antennas are designed to focus the signal in a particular direction.This focused signal enables greater distances and a stronger signal betweentwo points. The greater distances enabled by directional antennas give you aviable alternative for connecting locations, such as two offices, in a point-topoint configuration.

    Directional antennas are also used when you need to tunnel or thread a signal through a series of obstacles. This concentrates the signal power in a specific direction and enables you to use less power for a greater distance than an omnidirectional antenna. Table 7.1 compares omnidirectional and directional wireless antennas.
  20. Which two construction materials significantly weaken wireless signals?
    Concrete and steel
  21. Tips to troubleshoot wireless signal quality?
    . Antenna: Perhaps the first and most obvious thing to do is to make surethat the antenna on the AP is positioned for best reception. It oftentakes a little trial and error to get the placement right. Today’s wirelessaccess cards commonly ship with diagnostic software that displays signalstrength and makes it easy to find the correct position.

    . Device placement: One factor that can degrade wireless signals is RFinterference. Because of this, you need to try to keep wireless devicesaway from appliances that output RF noise. This includes microwaves,electrical devices, and certain cordless devices using the same frequency,such as phones.

    . Network location: Although there may be limited choice, as much aspossible try to reduce the number of obstructions that the signal mustpass through. Every obstacle strips a little more power from the signal.The type of material a signal must pass through also can have a significantimpact on signal integrity.

    . Boost the signal: If all else fails, you can purchase devices, such as wirelessrepeaters, that can amplify the wireless signal. The device takes thesignal and amplifies it to make it stronger. This also increases the distancethat the client system can be placed from the AP.
  22. What is a wireles radio channel?
    A channel is the band of RF used for the wireless communication. EachIEEE wireless standard specifies the channels that can be used. The 802.11astandard specifies radio frequency ranges between 5.15 and 5.875GHz. Incontrast, 802.11b and 802.11g standards operate in the 2.4 to 2.497GHzrange. IEEE wireless standards are discussed later in this chapter.
  23. What is a hertz?
    Hertz (Hz) is the standard of measurement for radio frequency. Hertz is used tomeasure the frequency of vibrations and waves, such as sound waves and electromagneticwaves. One hertz is equal to one cycle per second. Radio frequency ismeasured in kilohertz (KHz), 1,000 cycles per second; megahertz (MHz), one millioncycles per second; or gigahertz (GHz), one billion cycles per second.
  24. Which channel has a wider frequency band?
    802.11a.  As far as channels are concerned, 802.11a has a wider frequency band, enabling more channels and therefore more data throughput. As a result ofthe wider band, 802.11a supports up to eight nonoverlapping channels.802.11b/g standards use the smaller band and support only up to three nonoverlapping channels.
  25. Should you use overlapping channels?
    NO.  It is recommended that nonoverlapping channels be used for communication.In the United States, 802.11b/g use 11 channels for data communication, as mentioned; three of these—channels 1, 6, and 11—are nonoverlapping. Most manufacturers set their default channel to one of the nonoverlapping channelsto avoid transmission conflicts. With wireless devices you can select which channel your WLAN operates on to avoid interference from other wireless devices that operate in the 2.4GHz frequency range.
  26. When troubleshooting a wireless network be aware of what?
    Overlapping channels
  27. What does iwconfig command do?
    Linux users can use the iwconfig command to view the state of your wireless network. Using iwconfig, you can view such important information as the link quality, AP MAC address, data rate, and encryption keys, which can be helpful in ensuring that the parameters in the network are consistent.
  28. IEEE 802.11b/g wireless systems communicate with each other using radio frequencysignals in the band between 2.4GHz and 2.5GHz. Neighboring channels are5MHz apart. Applying two channels that allow the maximum channel separationdecreases the amount of channel crosstalk and provides a noticeable performanceincrease over networks with minimal channel separation.
  29. What is the wireless standard today?
  30. What does data rate refer to?
    Data rate refers to the theoretical maximum of a wireless standard, such as 100Mbps.
  31. What does throughput refer to?
    Throughput refers to the actual speeds achieved after all implementation and interference factors.