There's been a lot of talk about the mobile operators using Wi-Fi offload to economically plug coverage gaps in their wireless WANs. So how do the network-to-network transitions actually happen?
T-Mobile has successfully offloaded voice calls to users' home Wi-Fi networks for some time using Unlicensed Mobile Access (UMA), based on a 3GPP standard called Generic Access Network, which extends mobile IP access into their core networks.
More recently, the IEEE has approved another extension to 802.11 standards, 802.11u, which specifies how Wi-Fi access networks interface with carrier mobile WANs. The amendment was approved for publication in February, so it's possible that infrastructure and device-makers alike will begin incorporating it into their products going forward.
Dave Stephenson, senior technical lead at Cisco, explains that 802.11u enables the Wi-Fi network to detect you, let your device know it's available and advertise its services to you. Both the client device and Wi-Fi APs must support 802.11u for this to happen.
Today, your device finds a Wi-Fi network, but doesn't get enough information to decide if it can automatically authenticate without your intervention, says Stephenson. With 802.11u running on both client and AP, though, your device will send a query to the AP asking for something called a network access identifier (NAI) realm list -- a list of all the mobile operators' names that are allowed to automatically move a subscriber device's connectivity onto the Wi-Fi hotspot. If your operator's name is on the list, your device will automatically authenticate and offload.
Mobile operators already have roaming agreements with other cellular operators. Wi-Fi offload requires similar roaming agreements, but cellular operators would strike them with hotspot network operators instead of other cellular providers.
That means there are quite a number of relationships to be formed and the availability of 802.11u-enabled devices and infrastructure equipment to start making it happen. Cisco has said it is working with France Telecom's mobile subsidiary, Orange, for offload using 802.11u. Cisco also announced a relationship with Samsung at the recent Mobile World Congress event in Barcelona to help get 11u onto smartphones.
Chris Kozup, director of borderless networks at Cisco, points out that basic offload is the place to start, but that once connectivity among networks is achieved, it "paves the way for new service delivery." He pointed to retailers, for example, who fear that their physical stores are turning into demo centers where shoppers come to test and play with products, then go home and order off the Internet based on best price.
With service advertisement, though, retailers could reward customers for buying in the store with, say, an electronic coupon that is good for the day or the hour or some such.
This becomes possible with a component of 802.11u, the Mobility Services Advertisement Protocol (MSAP), which enables 802.11u-enabled mobile devices to query for local services prior to authenticating to the Wi-Fi network.