IEEE 802.11u and Hotspot 2.0 Explained

This page describes the IEEE 802.11u version of the WLAN standard, which is crucial for Hotspot 2.0 functionality. Mobile data offloading, which involves using alternative network technologies to deliver data originally intended for cellular users, is achieved through two primary methods: femtocells and Wi-Fi.

Mobile data offloading provides an alternative to cellular wireless data communication, often delivering improved performance. A femtocell is a small base station that connects to a service provider’s network via broadband connectivity. (For more details, refer to a femtocell tutorial). Wi-Fi, on the other hand, uses unlicensed spectrum for mobile data offloading.

The 802.11u standard enhances the capabilities for better interworking with external networks like 3G and 4G.

Before the advent of 802.11u, 3G subscribers utilized Wi-Fi networks to fulfill their internet service needs. However, the enhanced features introduced in IEEE 802.11u have led to increased Wi-Fi network usage. This is primarily due to the inclusion of interworking information in the beacon frame. This allows the mobile device to make informed decisions about the network before even initiating an association request.

As a result, roaming between Wi-Fi service providers and cellular service providers has become a seamless experience. Roaming can be established easily, with the necessary information transmitted or advertised directly within the beacon frame. This 3G-WLAN interworking is specifically defined within the 802.11u standard.

How Hotspot 2.0 Works According to IEEE 802.11u

A network compliant with IEEE 802.11u, featuring an 11u compliant radio signal, is known as Hotspot 2.0. The devices used within a Hotspot 2.0 network are referred to as HS2.0 capable devices (i.e., clients) and HS2.0 capable Access Points (APs).

This standard builds upon the IEEE 802.11-2007 standard, defining the PHY and MAC layer specifications. 802.11u introduces amendments for inter-working with external networks, such as cellular networks. The figure above illustrates a Hotspot 2.0 network as defined in the IEEE 802.11u standard.

Here’s a breakdown of how Hotspot 2.0 works:

1. AP Beacons with HS2.0 Capabilities: The Access Point broadcasts its Hotspot 2.0 capabilities.
2. Device Probes with HS2.0 Support: A device (STATION) that supports HS2.0 searches for compatible APs.
3. Device Selects AP and Performs ANQP Request: The device selects an AP, initiates an ANQP (Access Network Query Protocol) request, and determines the AP’s capabilities and the available service providers.
4. AP Responds to ANQP Query: The AP responds to the ANQP query, providing the requested information to the device.
5. Device Compares Information and Associates: The device compares the received information (provisioned profile) with the available options and associates with the best BSSID (Basic Service Set Identifier).