Wireless Network Troubleshooting | CompTIA Network+ N10-007 | 5.4

In this video you will learn about wireless network troubleshooting as it relates to RFI, signal strength, misconfiguration of wireless parameters, latency, multiple paths of propagation, incorrect AP placement, refraction, & absorption.

RFI (Radio Frequency Interference)

Wireless communication can be interrupted because of radio frequency interference.  Common RFI sources that impact wireless networks include 2.4GHz cordless phones, microwave ovens, baby monitors, & game consoles.

Signal Strength

The received signal strength indicator (RSSI) value measures the power of a wireless signal.  An RSSI value varies based on distance from a wireless antenna & physical objects interfering with line-of-sight communication with a wireless antenna (ex. drywall, metal file cabinets, & elevator shafts).  Some wireless networks automatically drop their wireless transmission rate when an RSSI value drops below a certain value.

Misconfiguration of Wireless Parameters

A variety of wireless parameters must match between a wireless client and a wireless access point for communication to occur.  For example, the client needs to be using a wireless standard supported by the wireless AP (such as 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, or you have a security type mismatch.  For example, a wireless client using WPA would not successfully communicate with a wireless AP using WPA2.  In addition, 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.  Finally, the most common issue is simply that the wrong passphrase is being used by the client to attempt to access the network.

Latency

Wireless 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 Propagation

An 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 Placement

Wireless 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 non-overlapping channels (ex. channels 1, 6, & 11 for wireless networks using the 2.4GHz frequencies).  A common design recommendation is that overlapping coverage areas (using non-overlapping channels) should have an overlap of approximately 10%-15%.  Also keep in mind the use of the 5GHz band, which offers many more non-overlapping channels.

Refraction

Refraction is the bending of a wave when it enters a medium where the speed is different.  It is important to track possible refraction when designing your wireless networks because if a signal changes direction in traveling from sender to receiver, it can cause lower data rates and high retries.  This can lead to an overall lessening of capacity.

Absorption

This occurs when a material is converting the signal’s energy into heat.  Varied materials have different absorption rates.  Wood and concrete can make a significant impact on signal strength because of how much they absorb the radio waves.

References

1. Sequeira, A. CompTIA Network+ Cert Guide.