An essential element within 802.11u is the use of the Access Network Query Protocol (ANQP). ANQP is a query and response protocol used between the network and a mobile device to discover a range of information such as the network authentication types supported, venue name, roaming agreements in place, throughput of the backhaul link, well known port numbers that are open, and other metadata useful in the network selection process.
The mobile device uses GAS to post an ANQP query to an 802.11u-capable AP. In turn, the AP provides the hotspot operator's domain name and network access identifier (NAI) realm list. GAS and ANQP effectively allow a mobile device to query the network before being authenticated to determine if the hotspot is operated by one of its roaming partners as well as the EAP method and credential type to use.
Armed with this information, the mobile device examines its own credentials to get the realm with which it knows it can connect. It then compares its own realm list to the list of the roaming partner realms received from the AP to determine to which network it should be able to successfully authenticate to.
If there's more than one match the device uses operator policy to determine which wi-fi network to join. This policy or operator profile is provided by the operator and stored within the phone itself. It typically provides an ordered list of preference levels and domain name pairs for each roaming partner. The mobile device then compares the hotspot operator's domain names with this list and selects the network having the highest preference level. After all this the mobile device authenticates automatically to the best network using its credentials without requiring any direct user action.
The use and value of 802.11u goes beyond just making life easier for the end-user. Mobile operators around the world are now keenly interested in how to leverage unlicensed wireless technologies, like wi-fi, to offload their mobile data networks from the explosion of media-rich data traffic running over them. Hotspot 2.0 and 802.11u are immensely useful in helping operators and their subscribers make better use wi-fi in a seamless manner for this purpose.
Beyond mobile operators, cable operators that don’t own or operate networks using licensed wireless spectrum are also looking at potentially significant new sources of revenues from the use of 802.11u. With millions of cable modem subscribers, a cable operator can use 802.11u to help offload traffic within homes or venues where it provides cable service – working with mobile operators to wholesale its cable plant in order to offload mobile data traffic without users even being aware of what’s happening. The cable operators can then realise revenue from the wireless operator’s data traffic that is flowing over their cable network. The net effect is that the mobile operator eases congestion and increases its wireless footprint without any capital investment, and end-users realise a much better wireless experience.
Ultimately, 802.11u and Hotspot 2.0 promise to make connecting to wi-fi services as easy, seamless and secure as today’s 3G cellular experience. And just in time.
Louis Au is Vice President of Asia Pacific Ruckus Wireless Inc.
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