Wireless Network Troubleshooting

Question 1

Reflection

Answer 1

• Wireless signals can bounce off some surfaces
  
  • Depends on the frequencies and the surfaces

• Too much reflection can weaken the signal
• A little multipath interference actually helps with
MIMO

• Position antennas to avoid excessive reflection
• May not be a problem for MIMO in 802.11n and
802.11ac

Question 2

Refraction

Answer 2

• Signal passes through an object and exits at a
different angle
• Similar to light through water

• Data rates are affected - Signal is less directional

• Outdoor long-distance wireless links
  
  • Changes in air temperature and water vapor

Question 3

Absorption

Answer 3

• Signal passes through an object and loses signal
strength
• Especially through walls and windows

• Different objects absorb differently as frequencies
change
• 2.4 GHz may have less absorption than 5 GHz

• Put the antennas on the ceiling
  
  • And avoid going through walls

Question 4

Latency and jitter

Answer 4

• Latency - Delays between transmission and reception
  
  • Jitter - Deviation from a predictable data stream
• Wireless interference and signal issues
  
  • Slower data rates
  • Increase in retransmissions
• Capacity issues
  
  • Many people using the same wireless frequencies

Question 5

Attenuation

Answer 5

• Wireless signals get weaker as you move farther from
the antenna
• The attenuation can be measured with a Wi-Fi
analyzer

• Control the power output on the access point
  
  • Not always an option
• Use a receive antenna with a higher gain
  
  • Capture more of the signal

• Move closer to the antenna - May not be possible

Question 6

Interference

Answer 6

• Interference
  
  • Something else is using our frequency

• Predictable
• Florescent lights, microwave ovens, cordless
telephones, high-power sources • Unpredictable -
Multi-tenant building

• Measurements
  
  • netstat –e
  • Performance Monitor

Question 7

Incorrect antenna type

Answer 7

• The antenna must fit the room
  
  • Or the distance between sender and receiver
• Omnidirectional
  
  • Useful on the ceiling
  • Not very useful between buildings
• Directional
  
  • Used often between two points
  • Or on a wall-mounted access point
• The access point may provide options
  
  • Connect different antennas

Question 8

Incorrect antenna placement

Answer 8

• Interference
  
  • Overlapping channels
• Slow throughput
  
  • Data fighting to be heard through the interference
• Check access point locations and channel settings
  
  • A challenge for 2.4 GHz
  • Much easier for 5 GHz

Question 9

Overcapacity

Answer 9

• Device saturation
  
  • Too many devices on one wireless network
  • There are only so many frequencies
  • The 5 GHz can really help with this
• Bandwidth saturation
  
  • Large data transfers
• Common in large meeting places
  
  • Conferences
  • Airports
  • Hotels

Question 10

Frequency mismatch

Answer 10

• Devices have to match the access point
  
  • 2.4 GHz, 5 GHz

• Verify the client is communicating over the correct
channel
• This is normally done automatically
• May not operate correctly if manually configured

• Older standards may slow down the newer network
  
  • 802.11b compatibility mode on 802.11n networks
• Every access point has an SSID
  
  • But did you connect to the right one?
• This can be more confusing than you might think
  
  • Public Wi-Fi Internet
  • Guest Internet
  • Internet
• Confirm the correct SSID settings
  
  • Should be listed in the current connection status

Question 11

Wrong passphrase

Answer 11

• Wireless authentication
  
  • Many different methods
• Required to connect to the wireless network
  
  • If not connected, check the authentication
• Shared passphrase
  
  • Common in a SOHO, not in the enterprise
• 802.1X
  
  • Used for the enterprise
  • Make sure the client is configured to use 802.1X

Question 12

Security type mismatch

Answer 12

• Encryption on wireless is important
  
  • Make sure the client matches the access point
• This is much easier these days
  
  • Almost everything is at the level of WPA2

• Some legacy equipment may not be able to keep up
• If you change the access point, you may not be able
to support it

• Migrate all of your WEP to WPA2
  
  • And any WPA

Question 13

Signal to noise ratio

Answer 13

• Signal
  
  • What you want
• Noise
  
  • What you don’t want
  • Interference from other networks and devices

• You want a very large ratio
• The same amount of signal to noise (1:1) would be
bad