Troubleshooting Checklist for Wireless Client Stability of SonicWall built-in Wireless Devices

Sometimes after deployment of a SonicWall firewall with a built-in wireless radio, wireless devices will start to become unstable, dropping connection to the radio and reconnecting at random intervals. Despite this, the signal strength may show nearly full or completely full signal strength.

These symptoms are most often indications of issues in the wireless environment. There are a number of environmental considerations that can contribute to this, and can usually be narrowed down to those listed below:

Step 1: Make certain the Firewall is 2-3 feet away from EMI sources (Sources of Electro-Magnetic Interference) .
 

Electricity and Magnetism go hand in hand:  Any electronic device puts out an electro-magnetic field.  Often times smaller firewalls, used in a home or small business environment, are dropped into an existing network with little consideration for EMI sources.  Any device that consumes power generates an EMI field.  The more power the device draws, the larger the field.  Some common things to avoid are:

• Desktop or Server Computer Towers
• Subwoofer speakers
• Servers
• Appliances (Refrigerators, Washer/Dryers, etc)
• Air conditioning units
• Battery-Backup Surge Protectors

Step 2: Avoid setting the wireless-enabled firewall on flat metal surfaces.
 

Placing a wireless-enabled firewall on or adjacent to a flat metal surface, such as on top of a metal filing cabinet or next to a steel beam, can cause the wireless signal to bounce into itself as it leaves the firewall, causing interference before it can even leave the area of the firewall.
 
Imagine dropping a pebble on the surface of a still pool, and watching the ripples flow away.  Consider for a moment that the pattern that those ripples form are a signal, similar to wireless radio waves coursing through the air when seen from a top or side view.  Now imagine that when you dropped the pebble, you did so right next to the edge of the pool.  The waves will bounce back off the wall at the edge, and those 'bouncing' waves will go back to interfere with new waves that are being created, and depending on variables, can break up the original signal.  This is very much what occurs when a wireless device is placed on a flat metal surface:  It is that much harder for all devices to get wireless signal.
 

Step 4:  Keep the Firewall at least 10-15 feet from other wireless transmitting devices
 

• Cordless Telephones / Wifi-VOIP systems
• Car Alarms
• Baby Monitors
• Bluetooth devices
• Car Alarms
• Digital 2 way Radios 

• Microwave Ovens
• Medical Equipment
• Ham Radios
• Large Appliances (Washers/Dryers, Refrigerators) 
• Intercoms
• Walkie-Talkie
  

Step 5:  Make certain wireless clients are 10-15 feet away from the SonicWall if transmitting at full power.
 

SonicWall wireless Radios are powerful.  When a client device, such as a laptop, is directly on top of a wireless firewall, it might pick up the wireless signal, but when backed up even a foot away, it is unlikely that a stable signal will be maintained until removed at least 10-15 feet from the unit, if the Wireless Radio is transmitting at full power.  This is due to the fact that the first wireless wave must be able to transmit out at a certain distance from the device.  However, if the environment is ideal and free from other access points and physical obstructions, it is theoretically possible to get wireless within 150-300 feet.  Most environments are not this ideal, so 100 feet is usually more likely, giving around a 90 foot radius of wireless.  This is what is often referred to as the "wireless donut effect". 

If most wireless devices are going to be within 20-40 feet of the radio and are expected to be closer than the 10-15 foot radius, it will be necessary to drop the wireless transmit power down to 1/4th, or even 1/8th of the full transmit power.  This is done under Wireless > Advanced in the 5.8 firmware.
 

  Step 6: Make certain the wireless channel is not being overrun by a competing access point.
 

Even if you have successfully kept the SonicWall at 10-15 feet from other wireless transmitting devices, it is possible that another wireless access point with a strong signal can be interfering with your wireless signal. A look under Wireless > IDS will show you other access points in range of your SonicWall firewall.  Closer or more powerful devices show up with a high percentage of dBm (Decibel-milliwatts).

The percentage is merely a reflection of the signal seen in Decibel-milliwats. Signal between 35%-50% may or may not start to interfere with your network signal if on the same channel. Anything seen at 51%-64% is likely to interfere with the wireless in that area, and anything higher than 65% will almost certainly overwhelm your network if you are transmitting on any channel within 5 channels.

Decibel-milliwats are a logarithmic value measured in "-[n] dBm". Signal between 35-50 percent represents roughly a range between -69dBm and -60dBm, 51%-64% percent corresponds to a range between -59 and -50dBm, 65%-80% is between -49dBm to -40dBm.  A signal at 70% is 100 times more powerful than a signal at 50%. 

It is worth noting that this IDS scan will only see signal from the point of view of the firewall itself, NOT from the Point of view of the client devices, (such as where users will actually be sitting with their laptops and wireless enabled smartphones, etc). If there is signal from another wireless device nearby that is interfering with users in the back of the room where signal is actually desired, the SonicWall itself might not be able to determine this. It is always recommended to perform a wireless site survey before configuration of a wireless network or wireless access points.

How to Test:

Once these steps have been performed, check the stability of the wireless client signal.  If it does not improve, a full wireless site survey is recommended.

Troubleshooting:

Always make certain wireless stability issues are not isolated to a single client, or to a small number of clients. Performing tests from multiple kinds of wireless devices is ideal, such as those that have MIMO vs SISO capability, or clients that are dual band, or even wireless G only. Even testing from multiple devices that use similar radios can reveal issues with specific devices.