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When providing Wireless network connectivity either for guest Internet access or a working environment, ensuring that it is fast and reliable is essential. The speed and reliability of wireless can often be limited by interference caused by nearby wireless networks or when there are many clients connecting to the same Access Point.

To improve the user experience of the wireless network, DrayTek Vigor Access Points incorporate features designed to optimise the utilisation of the wireless network and improve its effectiveness, by more intelligently handling connections to single and multiple access points at both the wireless radio level and network level.

These features can help your wireless network achieve the best possible speeds with legacy 802.11b/g/n clients connecting to the 2.4GHz frequency band and faster 5GHz capable 802.11n (up to 300mbps) and 802.11ac (up to 1300mbps) clients using the 5GHz band.

Airtime Fairness - Aims to maximise the total wireless throughput by improving how time is shared between wireless clients to prevent slower clients from negatively affecting other users and to enable faster clients to obtain higher speeds that they're capable of.

Band Steering (Dual Band VigorAPs only) - Increases capacity for Vigor Access Points by directing wireless clients, that are capable of connecting to 5GHz wireless networks, to the less congested and faster 5GHz (802.11n and 802.11ac) band. The aim is to more evenly distribute wireless clients between the AP's wireless radios.

AP Assisted Mobility - Allows VigorAP access points on the network to improve how clients handle moving between VigorAPs. It intelligently allows VigorAPs to disassociate clients from a VigorAP, when the client could get a better connection with a nearer VigorAP access point.

Mobile Device Management - Control which type of devices connect to your VigorAP access points, for instance, to stop desktop and laptop computers connecting to a network intended for guest's mobile phones and tablets.

Applicable Products:

  • VigorAP 710
  • VigorAP 810
  • VigorAP 900
  • VigorAP 902
  • VigorAP 910C

What is Airtime Fairness?

Wireless networks transmit and receive on a single channel; if multiple wireless clients are downloading files or watching videos at the same time, the access point must share the airtime (the duration that the channel is used for) between these clients by transmitting data packets to one client, then another and repeats this for all clients connected to the wireless network.

Ideally, all of the wireless clients operate at the same speed and are at the same distance from the access point and have optimally performing drivers, however, in any wireless network, there will usually be a mix of faster and slower clients. This can cause issues once there are enough clients on the network in that the amount of airtime / throughput available to each device can become significantly limited, which would result in downloads stalling and videos buffering constantly.

One significant cause of this is that slower devices, either through interference, distance or older wireless standards, require more time to receive the same amount of data as a faster client, which results in less airtime available to the other, faster clients.

Airtime Fairness is designed to give all wireless clients equal access to the airtime of the access point so that faster clients and slower clients each have equal access to the overall air-time of the access point.


How Airtime Fairness works

Without Airtime Fairness, the access point will serve each client equally, as defined by the mechanism in the 802.11 standard of providing equal probability to each client that it can access the wireless channel. When all clients operate at the same speed, they would have the same airtime because they're transmitting at a similar rate.

When there are mixed clients, such as an 802.11g 54mbps client and an 802.11n 300mbps client (or two 802.11n clients that are using different datalink rates due to their relative position from the access point or interference), there is a significant difference in the speed of transmission for each packet, which results in the slower clients taking a longer time period to complete the transmission of it's packet. The end result would be that a significantly higher proportion of the access point's time is used when sending packets to these slower clients.

This results in disproportionately slow throughput for faster clients when slower clients are receiving data because the airtime available becomes limited by the transmission time for the slowest clients.


Without Airtime Fairness

In this example, Station A is an 802.11g client capable of 54mbps throughput at most and Station B is an 802.11n client capable of up to 300mbps throughput. Sending a single packet to Station A takes longer than Station B, but the access point shares packet transmissions equally between the two.
Station B is only able to achieve a low throughput when the access point is sending packets to Station A:

With Airtime Fairness

Airtime Fairness improves this by controlling the rate at which packets are sent to slower clients, which allows the access point to send more packets to the faster clients in between the points where it sends data to the slower clients.

In this example, Station A is still receiving packets but the access point puts a longer delay between when those packets are sent, allowing it to send many more packets to Station B, which results in higher throughput for Station B. If Station B is downloading a file or loading a webpage, that could complete much more quickly, leaving the channel free for Station A to use, resulting in a better throughput and usage experience for each station:

With Airtime Fairness, instead of speeds being limited solely by the speed of the slowest clients, speeds are more representative of the speeds possible with each wireless client, resulting in higher throughput to faster clients and less interruptions to downloads by each client, giving a better overall throughput and experience to clients of a DrayTek Vigor access point with Airtime Fairness enabled.

In many cases the total combined throughput (sum of the all the wireless client's throughput) achieved across on the wireless network is increased with airtime fairness enabled because the faster clients are given more opportunity to fulfill their potential.

Applicable Products:

  • VigorAP 900
  • VigorAP 902
  • VigorAP 910C

What is Band Steering

DrayTek Vigor Access Points that support Dual Band operation each have a 2.4GHz and 5GHz wireless radio. If there are many more clients connecting to one of these radios than the other, the Access Point cannot make effective use of both its radios, wasting possible capacity and bandwidth.

If the decision of which band to connect to is made by the client(s) instead of the Access Point, this can lead to more clients connecting to the 2.4GHz band, which suffers more significantly from congestion, caused by other wireless networks and other wireless systems such as Bluetooth that use the 2.4GHz band.


How it works

Band Steering is designed to 'steer' wireless clients that support both 2.4GHz and 5GHz bands to the faster and less congested 5GHz bands, where possible. This is used for wireless networks that present the same SSID and wireless security configuration on both bands.

This is achieved by detecting when a client attempts to connect on both 2.4GHz and 5GHz; The client is deliberately stopped from connecting to the 2.4GHz SSID temporarily so that it will connect to the 5GHz network. Band Steering does not delay the client from connecting and no action is required from the end-user; the Vigor Access Point will negotiate the connection automatically.

The result of encouraging 5Ghz capable clients to connect to the 5GHz band is a less congested 2.4Ghz wireless network. This improves the experience for clients using the 2.4GHz wireless network due to the lower number of other clients connected.

The total capacity (number of clients that can connect) is increased by sharing clients more evening between each Access Point's band. With clients more evenly distributed between both the APs 2.4Ghz and 5Ghz bands, the overall utilisation of the throughput with each Vigor Access Point is increased.


Applicable Products:

  • VigorAP 710
  • VigorAP 810
  • VigorAP 900
  • VigorAP 902
  • VigorAP 910C

What is AP Assisted Mobility

When using multiple VigorAP Access Points, wireless clients moving between access points have control of which VigorAP they stay connected to and might choose to stay connected to a distant access point, even if reconnecting to a now nearer VigorAP would result in a better connection.

If this occurs, it can result in lower wireless speeds and a less reliable wireless connection, even when there are enough VigorAPs to effectively cover an area.

 

 

The purpose of DrayTek's AP Assisted Mobility is to monitor the Signal Strength (RSSI) of clients connected to each VigorAP and intelligently disassociate clients with low signal strength.

For instance a client moving between two VigorAP access points is automatically disassociated from a now distant VigorAP so that they can re-associate with a closer VigorAP.

 


How it works

When AP Assisted Mobility is enabled on multiple VigorAPs that support the feature, the Minimum RSSI setting allows the APs to communicate details of client signal strength over the wired network.

When a wireless client moves beyond the optimal range of a VigorAP, it checks with other VigorAPs on the network to determine whether or not other VigorAPs have a better signal strength to that client. If another VigorAP does have higher signal strength, the client is disassociated so that they can reconnect to the nearer access point.

This check allows clients that do not have a nearer VigorAP, such as a tablet on the edge of the overall wireless network's range, to stay connected and use the network instead of simply being disconnected when the RSSI goes below the specified level, eliminating the risk of this feature causing wireless network dead spots.

Applicable Products:

  • VigorAP 710
  • VigorAP 810
  • VigorAP 900
  • VigorAP 902
  • VigorAP 910C

What is Mobile Device Management

Mobile Device Management (MDM for short) is a feature that allows a VigorAP to determine what type of device is connecting, with details of the device manufacturer and operating system that the device is running.

Using this information, the VigorAP can apply policies to either block or allow clients of specified types for specific SSIDs, building on the VigorAP's MAC based Access Control List with an automated system that can automatically block devices of a specific type.

Example

A network with both an "Office" SSID for office computers / infrastructure only and a "Guest" SSID for all devices.

It is possible to control what can connect to the "Office" network segment, so that only desktop PCs, laptops and wireless printers can connect. If someone attempts to connect a mobile phone or iPad to the "Office" network, the AP can block them: