Wireless Network Troubleshooting Flashcards
Reflection
- 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
Refraction
• 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
Absorption
• 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
Latency and jitter
- 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
Attenuation
• 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
Interference
- 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
Incorrect antenna type
- 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
Incorrect antenna placement
- 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
Overcapacity
- 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
Frequency mismatch
- 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
Wrong passphrase
- 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
Security type mismatch
- 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
Signal to noise ratio
- 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
