III. Wireless LAN

AP-assisted Client Mobility

Products:
VigorAP 710
VigorAP 800
VigorAP 802
VigorAP 810
Show all

Keywords:
Client Mobility
Minimum RSSI
Mobility
RSSI
Show all

When using multiple Access Points, wireless clients moving between access points have control of which wireless access point they remain connected to. This can result in a wireless client choosing to stay connected to a distant access point, even when moving to a now nearer wireless access point could result in a better connection.

By not moving to the nearer wireless acess point, the client wouldn't benefit from the stronger signal and possibly better connectivity. The wireless access point will also need to send wireless transmissions further, spending more time transmitting to the more distant client than local ones, due to the difference in achievable wireless transmission rates.

VigorAP wireless access points improve this situation by using DrayTek's AP-assisted Client Mobility feature. DrayTek's AP-assisted Client Mobility tracks a wireless client's Signal Strength (RSSI) between the associated / connected access point. When a device moves out of optimal range for connection to a VigorAP access point, the VigorAP will check that device's achievable signal strength with other VigorAP access points.

If another VigorAP indicates that it can achieve better signal strength for that wireless client, the original VigorAP will disconnect that client, allowing the wireless client to re-associate with the nearer VigorAP, resulting in better signal strength, with potentially better wireless throughput and lower latency.


Applicable Products

  • VigorAP 710
  • VigorAP 810
  • VigorAP 900
  • VigorAP 902
  • VigorAP 903
  • VigorAP 910C
  • VigorAP 912C
  • VigorAP 918R
  • VigorAP 918RPD
  • VigorAP 920R
  • VigorAP 920RPD
  • VigorAP 960C
  • VigorAP 1000C
  • VigorAP 1060C

How It Works

How It Works

In the [Wireless LAN] > [Roaming] menu, there are multiple options to control how clients move between access points:

ModeDescription
Minimum Basic Rate Disassociates wireless clients when their throughput rate decreases to the specified level. The Rate can decrease when signal strength decreases or where interference causes the achievable Rate to decrease. This does not check signal quality with other VigorAP access points.
Disable RSSI Requirement Clients are allowed to remain connected to a VigorAP until the client loses signal or chooses to associate with another closer VigorAP. The VigorAP does not control the association of wireless clients to the VigorAP.
Strictly Minimum RSSI Disassociates wireless clients when their signal strength goes below the specified value. This does not check signal quality with other VigorAP access points.
Minimum RSSI
(Recommended)
When clients go below the specified signal strength value, the VigorAP checks potential signal strength with other VigorAPs and will disassociate a wireless client if that client can achieve a better signal with a nearer VigorAP.

Minimum RSSI Mode

DrayTek VigorAP wireless access points that support AP-assisted Client Roaming, when configured to help wireless clients move between access points with Minimum RSSI mode, will keep track of the Signal Strength (RSSI) of each wireless client connected to the VigorAP, along with the RSSI value of all nearby wireless clients, whether they are associated with that particular VigorAP or not.

Example

  1. When a wireless client moves out of range of a VigorAP access point, determined by an RSSI Threshold value that can be configured on each VigorAP, the VigorAP will send a request over the wired network connecting the VigorAP access points.
    This request will check whether any other VigorAP access points can achieve better Signal Strength to that wireless client.



  2. The VigorAP access points on that network will then reply with its own detected Signal Strength (RSSI) values for that wireless client.
    The VigorAP that sent the request will then determine whether to move that client off using the configured thresold values. By default, a VigorAP will not move a wireless client off to another VigorAP unless that Signal Strength value is 5 dBm higher (typically 15-20% difference).


  3. The original VigorAP that the now distant client is associated with, can then determine that there is a nearer VigorAP that the client can connect to. The original VigorAP disassociates the wireless client and temporarily blocks that client from reassociating.

    The original VigorAP passes this information to the nearer VigorAP and the wireless client can then reassociate with the closer VigorAP.
    The wireless client will reconnect within a few seconds, the shorter distance lowers the risk of interference and increases potential Transmission Rates, providing a better connection experience, with typically higher throughput and less latency / packet loss over the wireless link.

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