How to set up liquid wireless roaming?

Tags: trouble-free switching

There are several different ways to implement wireless roaming with more than one access point (or multiple routers set as access points) in such a way that wireless clients can connect to any access point without being noticed and without having to connect to another WiFi network.

 Many access points

The simplest configuration consists in configuring multiple access points (or routers set as access points) of any brand, connecting them to the same WiFi network using the same DHCP server, the same SSID, the same type of security (ie WPA2-AES, etc. ), Same password, but on different channels.

This type of configuration allows customers to navigate the coverage area and toggle between access points without seeing breaks in most cases. It is suitable for most home installations, but has several limitations: clients switch to a different access point, when the signal drops enough that it can not be used, they will not use a stronger signal when they are within two access points. In addition, the VoIP / Skype connection can be interrupted in a fraction of a second when switching between access points.

 Uniform roaming

 The best way to ensure that your clients (laptops) pick up the strongest access point (AP) is to perform a site survey, and configure the TX power and choose a channel that provides the correct coverage. You need to keep in mind that it is the client that chooses to roam, and that on some client utilities, you can have some adjustment. There is no adjustment on the AP that ensures that a client uses the AP with the strongest signal.

Again it is the client that decides when to roam and which AP to connect to based on what it perceives the signal to be. The Wireless domain services (WDS) and Fast secure roaming utilize cached credential to aid with fast roams, but do not tell a client when to roam or which AP to connect to. These adjustments can sometimes be performed on the client utility.

One should understand that the re-association occurs only when the signal from the first access point becomes null (signal=0). If there is not an active data transfer, then yes the signal strenght must be pretty weak. If there is an active link (high data rate), then the roaming will be occur based on the RF level retries and AP signal strength.

What happens in the background that the client will move to another AP based on information the client receives from the AP beacons. The AP embeds in its beacon some Cisco proprietary information concerning signal strength, number of users, % of time spent transmitting and bit error rates. The client analyzes the information from all AP beacons it receives and then associates with the one that is the "best".

The following information is included in the beacon:

Backbone Connection ( Is the AP on the backbone ? )
RSSI  ( Signal Strength )
% of transmitter loading ( Percentage of time the transmitter is actually in use )
Number of users associated to the AP, using this data, the client will roam.

If you need customers to use a stronger signal when they are within two access points, you need a function called "smooth transfer" (trouble-free switching, trouble-free roaming, zero forwarding). It must be supported by access points because it is not part of the WiFi specification. Seamless roaming allows communication between access points, allowing customers to use a stronger / better signal, or less-charged AP when they are within the reach of multiple access points, and customers will not notice any connection interruptions when switching between access points, even in VoIP case. This type of installation does not work with most routers set as access points, usually requires enterprise-level APs that support this feature.

Wi-Fi network

Wireless Mesh systems consist of many devices of the same type connected wirelessly and communicating with each other, serving customers similarly to access points, extending the wireless coverage of a single access point without the limitations and inconveniences of the speed of amplifiers / extension cords.

Client devices

Client devices should have drivers to set roaming aggressiveness.

Then, depending on the needs, the client devices will switch faster or slower when moving between zones.

IN SUM:

If you want to have a professional wifi roam in your company (without waiting, switching with long delays, breaking connections) you must have access points working with the controller that support this function correctly.