WiFi Roaming Basics and How it Works

This page describes WiFi roaming basics and mentions how wifi roaming works. It mentions WiFi roaming test solution.

WLAN network typically consists of STA (i.e.Station or client), AP (i.e. Access Point or router or hotspot) and AAS (Authentication Server). The WLAN network is also referred as wifi network.

WiFi network serve local STAs within the home or office premises or it serve STAs across the different rooms or between two buildings. Based on this fact, wifi roamings are of two types viz. internal and external.

Internal roaming happens when STA-1 moves from area coverage by AP-1 to area coverage of AP-2. External roaming happens when STA-1 moves from AP-1/AP-2 to the area coverage of AP-3 which is located in different building or far from its home WLAN network. Let us understand how wifi roaming works.

How WiFi roaming works

wifi roaming

The figure-1 depicts WiFi roaming types. STA-1 continuously monitors wifi signals from nearby APs. When it finds that signal from AP with which it is connected becoming lower that the nearby AP, it initiates process called handover or association.

WLAN APs are RADIUS clients for 802.1x. As we know 802.1x is the standard for access authorization between STA and AP. The RADIUS is the standard used for communication between AP and AS (Authentication Server). It (Access Point) initiates authentication as soon as Station (STA) attempts to associate with AP. Once the authentication is successful, AP allows STA to join and start the data communication as usual. Here AAS plays role of providing all the

Following are the roles of STA, AP and AS.
STA -> Act as Supplicant, it is the roaming client.
AP -> Authenticator, it forwards the roaming request to AS.
AS -> Authenticating Server.

Following procedure is followed in Wifi roaming scenario:
• AP request identity from STA using EAPOL.
• STA sends identity of itself to AP. AP forwards received STA identity to AS via EAP.
• Both AS and STA have EAP authentication dialog.
• Once the dialog is successful, STA and AS share a common session key.
• AS transmits session key to AP in RADIUS attribute as part of "RADIUS accept message".
• AP enables controlled port for MAC address of STA. It can also enable WEP key.

WiFi roaming test solution

Veriwave has developed wifi roaming test solution. It offers complete automatic tests to analyze WLAN network of infrastructure type and mobile WLAN STAs roaming between APs.
The Wifi roaming tests provide following measurements:
• Roaming Delay
• Network capacity
• call quality while roaming
• Test results in different file formats e.g. HTML/CSV etc.


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