A wireless distribution system (WDS) is a method of interconnecting access points (AP) in a wireless local area network (LAN) without requiring that they connect through a wired backbone. The IEEE 802.11 standard defines a distribution system as the infrastructure used to connect access points.
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Wireless distribution systems are a method of distributing infrastructure in a way that enables the expansion of a wireless network. They are used by several industries to increase the range of a network when physical wiring is not possible.
The most common use of a wireless distribution system is to bridge a WLAN spanning two buildings. The simplest WDS consists of two access points configured to forward messages to each other, working in conjunction with an antenna that enables line-of-sight communication.
A WDS requires two or more Wi-Fi base stations, or access points, which act as one system. The access points forward network packets from user sessions to other WDS access points while also accepting new user connections. Access points typically connect through an Ethernetswitch.
The concept of a mesh network is similar to a WDS; however, mesh networks are newer and have features like automatic discovery and configuration of mesh routers. Mesh networks are also more dynamic and fault-tolerant than WDS. If a link in the mesh router fails, the mesh network can find alternative paths. By comparison, there is no alternative failover mechanism if a WDS link fails.
These help topics apply to Wi-Fi 5 access points (AP120, AP125, AP225W, AP320, AP322, AP325, AP327X, AP420) managed by Wi-Fi Cloud. For new Wi-Fi 6 access points managed by WatchGuard Cloud (AP130, AP230W, AP330, AP430CR, AP432), see About Wi-Fi in WatchGuard Cloud .
With the information in the capacity planning section of this guide, you can determine how many APs are required for specific deployment use cases. In this section, you determine where to put the APs and the wireless channels to use.
To make sure that all users in your environment receive a strong wireless signal, consider these guidelines when you install your WatchGuard APs.
The signal strength is the wireless signal power level received by the wireless client.
The noise level indicates the amount of background noise in your environment.
The signal-to-noise ratio (SNR) is the ratio between the signal strength and the noise level.
For example:
Interference caused by Wi-Fi or non-Wi-Fi devices can greatly reduce performance of wireless networks. To optimize the performance of your wireless network you must be able to identify, locate and avoid sources of interference. To help you to identify sources of interference, you can perform a spectrum analysis during the pre-installation and post-deployment phases .
Game controllers for the Microsoft Xbox use non-Wi-Fi 2.4 GHz wireless technology. Game controllers use their own frequencies and use frequency-hopping. Though the channel utilization of these devices is quite low, these controllers can adversely affect Wi-Fi performance in the 2.4 GHz band.
Xbox game controller frequency spectrum chart. Source: Metageek
Microwave ovens operate in the upper channels of the 2.4 GHz band. Microwave ovens have been known to have severe impacts on performance for nearby APs and clients operating on channels 6 to13. Do not put APs near microwave ovens, but when it is unavoidable, we recommend you use channel 1 for the 2.4 GHz radio.
Microwave oven frequency spectrum chart. Source: Metageek
Bluetooth devices are frequency hoppers that can affect all channels in the 2.4 GHz band. Fortunately, Bluetooth devices do not stay on a single frequency for very long and they operate with relatively low power, so their impact is limited.
Bluetooth frequency spectrum chart. Source: Metageek
The Smart Spectrum feature in WatchGuard Wi-Fi Cloud detects and identifies interference sources, both Wi-Fi and non-Wi-Fi. The interference data is collected by the DCS (Dynamic Channel Selection) algorithm for more informed AP channel changes that result in improved overall network performance and user experience.
When you enable ACD/DCS (auto channel) selection, APs select channels to avoid both Wi-Fi and non-Wi-Fi interference. It is preferable that wireless networks not routinely change their channel plan because channel plan changes can be disruptive to the wireless network.
Unwanted sources of interference from devices such as rogue APs, cordless phones, and non-Wi-Fi cameras can reduce wireless network performance. To mitigate this issue, provide a spectrum policy that informs all users about the types of devices that are not permitted at your deployment site.
Additional sources of interference are even more of a problem for static channel plans, (where auto channel selection is disabled), because manual intervention is required to locate and remove the source of the interference or to change the channel plan to avoid the interference. We recommend you have a spectrum policy to help minimize wireless network disruptions caused by sources of interference introduced into your network.
In WatchGuard Discover, you can perform Spectrum Analysis that helps you detect various types of interference, non Wi-Fi interference, or interference that can also be transient in nature that decreases the performance of your wireless network. Spectrum analysis enables you to visualize the radio frequencies operating in your area and determine the strength of the detected signals.
This table shows the approximate signal strengths required to support MCS rates for various channel widths. 256-QAM requires higher signal strengths than 64-QAM because of the greater constellation density required to support 256-QAM. However, wider channels also require higher levels of signal strength compared to narrow channels to support a given modulation scheme.
For example, 64-QAM/MCS-7 requires -62 dBm for 40 MHz channels, but the requirement jumps to -58 dBm for 80 MHz channels. To design a network to support 256-QAM/MCS-9 with 80 MHz channels pervasively, requires a signal strength of -52 dBm or higher throughout the deployment. This means that APs should be located every 30 to 50 feet, depending on the environment, clients, and AP capabilities. While there may be high density and high /throughput use cases (such as an auditorium) where designing for 256-QAM is recommended, most high density deployments are designed to support 64-QAM pervasively.
Signal Strengths Required to Support MCS Rates for Various Channel Widths
Modulation Scheme
20 MHz
40 MHz
80 MHz
80+80 MHz
160 MHz
11ac 64-QAM/MCS-7
-64 dBm
-62 dBm
-58 dBm
-55 dBm
-55 dBm
11ac 256-QAM/MCS-8
-59 dBm
-56 dBm
-53 dBm
-50 dBm
-50 dBm
11ac 256-QAM/MCS-9
-58 dBm
-54 dBm
-52 dBm
-49 dBm
-49 dBm
Higher density modulation requires higher levels of signal strength, and wider channels require higher signal strength compared to narrower channels. As a result, the cell size for an AP that supports 256-QAM is much smaller than that of an AP that supports 64-QAM, as shown in this diagram.
Use a predictive site survey software application to develop an AP placement plan estimate coverage and capacity. You can use a predictive site survey planning application to generate a recommended AP placement and channel plan, including coverage, SNR, and interference information to help with your deployment.
You must provide input on these factors for correct capacity planning:
WatchGuard provides to partners a Wi-Fi Customer Requirements Questionnaire to assist in creating predictive site surveys. For more information, log in to your partner account on the WatchGuard web site and go to Product > Selling Secure Wi-Fi.
To make sure you have an accurate predictive site survey, measure the actual attenuation values for obstructions within the deployment site. You can use these attenuation values in your site survey. To measure attenuation values, you must use an AP and a smart with an application such as WiFi Analyzer.
To perform the measurement, check the signal level detected by the client when the client and AP are 5 meters apart with a clear line of sight (LoS). Then, check the signal level again at the same distance with the obstruction between the AP and the smart .
The difference between the LoS (line of sight) reading and the second reading is the measure of attenuation level for the obstruction. The attenuation values you obtain can improve the accuracy of your predictive site survey.
Example:
This table shows the estimated values of attenuation for common materials found in typical deployments. Note the variability in attenuation for a specific type of material (for example, concrete and brick wall +/- 10 dB). Precise attenuation values produce a more accurate predictive site survey.
Attenuation Estimations
RF Attenuators
Estimated Attenuation in 2.4 GHz
Estimated Attenuation in 5 GHz
Steel door
16 dB (+/- 3 dB)
28 dB (+/- 3 dB)
Concrete or brick wall
12 dB (+/- 6 dB)
20 dB (+/- 10 dB)
Coated or double-pane
12 dB (+/- 1 dB)
20 dB (+/- 1 dB)
Cubicle wall
4 dB (+/- 1 dB)
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6 dB (+/- 2 dB)
Wood door
4 dB (+/- 1 dB)
6 dB (+/- 1 dB)
Glass or window (not tinted)
3 dB (+/- 1 dB)
7 dB (+/- 1 dB)
Drywall (interior)
3 dB (+/- 1 dB)
4 dB (+/- 1 dB)
Ceiling tiles, curtains, blinds
1 dB (+/- .5 dB)
2 dB (+/- 1 dB)
You can increase or decrease power due to several factors such as antenna gain and attenuation loss due to distance between APs and clients
Before you choose a one-for-one AP replacement approach, make sure these conditions are true:
Even if DFS channels are not used, 5 GHz channels outnumber 2.4 GHz channels by a wide margin. This means that if both 5 Ghz and 2.4 GHz radios are active on all APs in a network designed for capacity, there is a high probability that the APs could create harmful co-channel interference (CCI) in the 2.4 GHz band. Another factor is that 2.4 GHz frequencies provide greater coverage range than 5 GHz frequencies. To minimize the amount of self-induced CCI in the 2.4 GHz band, we recommend you disable 2.4 GHz radios on some of the deployed APs .
The diagram below is an example of a 40 MHz channel plan that does not use DFS channels. In the US, as well as in several other regions, there are only four non-overlapping 40 MHz channels available if DFS channels are not used. The example plan minimizes CCI because adjacent APs do not use the same frequencies.
This is an example of an 80 MHz channel plan that uses DFS channels. In the US, as well as in several other regions, there are six non-overlapping 80 MHz channels available if DFS channels are used. As with the 40 MHz plan, the example plan minimizes CCI because adjacent APs do not use the same frequencies.
WatchGuard APs for indoor use are usually mounted on walls or ceilings. Outdoor APs are usually mounted on walls and poles.
More information about mounting options are provided in the WatchGuard AP Hardware Guides.
Information about WatchGuard AP antenna radiation patterns (internal and external) can be found in corresponding device data sheets located on the WatchGuard website.
While not as common as ceiling mounts, wall-mounted APs are also appropriate for most rooms. Wall-mounted APs can also be found in large rooms, such as auditoriums, where ceiling mounts are not practical because of ceiling height or accessibility. If you mount APs with a wall mount, consider the antenna radiation patterns, including back lobe patterns, of the AP model you deploy.
Most wireless network deployments use ceiling mounts. When you mount APs to a ceiling, it is preferable to mount APs below the ceiling. Do not hide APs above a dropped ceiling for aesthetic or physical security purposes. The ceiling space can include metallic structures such as pipes or AC ducts that can attenuate RF transmissions.
These factors can affect the reliability and performance of the wireless network:
For full wireless coverage and to make sure that all clients on your environment receive a strong wireless signal, consider these guidelines for the location and placement of your WatchGuard APs:
There are many post-deployment site survey tools available. The Ekahau Site Survey (ESS) is one of the most popular tools for this purpose. Like most site survey tools, ESS supports both passive and active site surveys. An active survey measures sent packets and received packets. This mode is used to determine metrics such as packet loss and packet delay. A passive survey listens to probes and beacons passively and is useful for creation of coverage and SNR (Signal to Noise Ratio) maps. ESS also supports a hybrid survey mode that simultaneously performs a passive and active survey. We recommend you use the hybrid mode.
These are guidelines for a post-deployment validation survey:
This table provides a summary of the recommendations for an AP placement and channel plan.
Recommendations
Notes
Use a predictive site survey application.
The predictive site survey can automate the AP placement and channel capacity planning process.
Consider 1-for-1 AP replacement.
Only implement 1-for-1 replacement if conditions are true as outlined in the One-for-One AP Replacement section of this guide.
SNR should be 25 dB or greater throughout the coverage area.
Minimum RSSI should be -62 dBm throughout the coverage area.
If designing for 256 QAM rates everywhere the minimum RSSI should be -52 dBm (w/ 80MHz channels).
Clients should see two to three APs (on different channels) at RSSI of -70 dBm or greater.
Consider deploying one full-time WIPS sensor for every three to five APs.
Depends on security requirements.
Distance between two APs should be approximately 30 to 70 feet.
Reduce AP transmit power.
Classroom:
5 GHz: 8 to 16 dBm
2.4 GHz: 4 to 10 dBm
Auditorium or Lecture Hall:
5 GHz: 5 to 12 dBm
2.4 GHz: 3 to 10 dBm
APs may be ceiling or wall-mounted.
Consider back lobe radiation of antenna when you use a wall mount.
Disable 2.4 GHz radios on a percentage of APs.
Percentage of APs with disabled 2.4 GHz radios depends on how many unique 5 GHz channels are in use. The more 5 GHz channels in use the greater the % of APs that should have there 2.4Ghz radios disabled.
AP placement and channel plan should use channels to minimize CCI and ACI.
Stagger APs across floors.
Consider directional antennas for very high client density deployments.
For high ceilings (higher than 30 feet / 9.14 meters), high gain (6-9 dB) patch antennas are recommended.
Adjust AP output power in relation to antenna gain.
Know the antenna radiation patterns and focus gain towards clients.
Do not place APs near lighting fixtures or conductive material.
Do not place APs above ceiling tiles.
Perform a thorough post -deployment site survey.
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