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Chapter 13. Troubleshooting Network Issues > Wireless Troubleshooting

Wireless Troubleshooting

Troubleshooting wireless networks can require a variety of skill sets. For example, some troubleshooting scenarios might require an understanding of antenna theory and the radio frequency spectrum. However, the Network+ exam focuses on more common wireless issues, as presented in Table 13-5.

Table 13-5. Common Wireless Troubleshooting Issues
IssueDescription
RFIWireless communication can be interrupted because of radio frequency interference (RFI). Common RFI sources that impact wireless networks include 2.4-GHz cordless phones, microwave ovens, baby monitors, and game consoles.
Signal strengthThe Received Signal Strength Indicator (RSSI) value measures the power of a wireless signal. An RSSI value varies based on distance from a wireless antenna and physical objects interfering with line-of-sight communication with a wireless antenna (for example, drywall, metal file cabinets, and elevator shafts). Some wireless networks automatically drop their wireless transmission rate when an RSSI value drops below a certain value.
Misconfiguration of wireless parametersA variety of wireless parameters must match between a wireless client and a wireless access point (AP) in order for communication to occur. For example, the client needs to be using a wireless standard supported by the wireless AP (for example, IEEE 802.11a/b/g/n). Wireless channels must also match. However, wireless clients usually automatically set their channel based on the wireless AP’s channel. Encryption standards must match. For example, a wireless client using WPA would not successfully communicate with a wireless AP using WPA2. Additionally, the service set identifier (SSID) of a wireless AP must be selected by the wireless client. In many cases, a wireless AP broadcasts its SSID, and a wireless client can select that SSID from a listing of visible SSIDs. In other cases, a wireless AP does not broadcast its SSID, thus requiring a wireless client to have a matching SSID manually configured.
LatencyWireless networks can experience more delay than their wired counterparts. One reason for the increased delay is the use of carrier sense multiple access collision avoidance (CSMA/CA) in WLANs, which introduces a random delay before transmitting data, in an attempt to avoid collisions. Another, yet similar, reason for the increased delay is the fact that all wireless devices associated with a single wireless AP are in the same collision domain, introducing the possibility of collisions (retransmissions), which can increase delay.
Multiple paths of propagationAn electromagnetic waveform cannot pass through a perfect conductor. Admittedly, perfect conductors do not exist in most office environments. However, very good conductors, such as metal file cabinets, are commonplace in offices. As a result, if the waveform of a wireless transmission encounters one of these conductive objects, most of the signal bounces off the object creating multiple paths (modes) of propagation. These multiple modes of propagation can cause data (specifically, bits) to arrive at uneven intervals, possibly corrupting data. This problem is similar to multimode delay distortion, which is seen in multimode fiber-optic cabling.
Incorrect AP placementWireless APs should be strategically located in a building to provide sufficient coverage to all desired coverage areas. However, the coverage areas of wireless APs using overlapping channels should not overlap. To maintain coverage between coverage areas, you should have overlapping coverage areas among wireless APs using nonoverlapping channels (for example, channels 1, 6, and 11 for wireless networks using the 2.4-GHz band of frequencies). A common design recommendation is that overlapping coverage areas (using nonoverlapping channels) should have an overlap of approximately 10–15 percent.



  

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