Plans Under Way for Roaming between Cellular and Wi-Fi Networks
by Sixto Ortiz Jr.
Cellular and Wi-Fi provide important services to many users. Industry observers say users' ability to move smoothly between the two systems would make mobile technology more useful. However, such roaming is currently difficult.
Now, providers of mobile-phone and Wi-Fi-based hot-spot services are working to bring the technologies together by enabling seamless, standardized roaming between the two types of networks, including those offered by different providers.
The Global System for Mobile Communications Association (GSMA), the Wireless Broadband Alliance (WBA), and the Wi-Fi Alliance (WFA) are spearheading this effort.
These capabilities would be advantageous for cellular companies, especially those that also provide hotspot services.
The demand for wireless data is rising exponentially and straining cellular networks. Carriers thus want to offload some of that traffic to Wi-Fi networks.
The new roaming technology would also benefit users who currently must manually manage the often-baffling process of accessing Wi-Fi networks from mobile devices. Moreover, Wi-Fi would provide them with faster data rates.
"The goal is seamless hands-off and transparent authentication," said Craig J. Mathias, principal with the Farpoint Group, a wireless-industry analysis firm. "The required technologies already exist, so the key lies with integrating those into a cohesive whole."
The Drive for Roaming
Exploding smartphone use has driven the increased utilization of cellular networks for sending data.
Roaming between cellular and Wi-Fi networks will be critical if carriers hope to carry all the traffic this yields and meet their data-capacity expectations and those of their customers, noted Mathias.
Roaming capabilities would be particularly well-suited for implementation in high-density, high-demand areas such as major cities and big college campuses.
Wi-Fi offers a low deployment cost, enormous capacity, and efficient frequency usage, Mathias explained.
Many mobile carriers run their own Wi-Fi networks. Some enable access to other providers' hotspots. However, this typically requires users to check a list of nearby networks, enter a username and password for the selected service, and then sometimes pay for access.
And service providers must perform multiple steps to authenticate and bill users.
Cellular and Wi-Fi networks use different approaches for tasks such as network selection, user authentication, and billing, which also makes roaming difficult.
The primary issue has been convincing the pertinent companies and organizations to work together to use existing technologies to develop a framework for overcoming the barriers to roaming.
Enabling Roaming
Several specifications promise to help enable roaming between cellular and Wi-Fi networks.
Hotspot 2.0
A key part of the effort to deliver seamless cellular-to-Wi-Fi roaming is Hotspot 2.0, a specification that the WFA — a consortium of equipment manufacturers, hotspot providers, and cellular carriers — has developed.
This specification enables interoperability between different manufacturers' equipment, such as access points, smartphones, and routers, said Tiago Rodrigues, program director with the WBA, a Wi-Fi service-provider consortium.
Hotspot 2.0 uses the IEEE 802.11u standard to allow automatic network discovery and selection for mobile devices.
For example, 802.11u lets a device on a cellular network discover an appropriate Wi-Fi network to connect with. The standard does this by enabling networks to announce information about themselves, such as whether they are private or public and whether users must pay to utilize them.
Hotspot 2.0 also uses IEEE 802.1x, which works with the Extensible Authentication Protocol to enable authentication-based security for accessing Wi-Fi networks.
Adoption of these standardized approaches by both cellular and Wi-Fi networks would let users roam between them more easily, said WFA senior marketing manager Kevin Robinson.
The WFA plans to launch its Passport Certification Program this year to verify that products meet Hotspot 2.0 specifications.
Next-Generation Hotspot
The WBA's Next-Generation Hotspot technology, scheduled for completion later this year, enables roaming at the network level.
According to Rodrigues, the WBA and the GSMA are working together on NGH.
When finished later this year, NGH will extend the capabilities of the WBA's Wireless Roaming Intermediary Exchange (WRIX) framework for roaming between Wi-Fi networks to also enable roaming between Wi-Fi and cellular networks.
GRX
The GSMA will extend its GPRS (General Packet Radio Service) Roaming Exchange (GRX) for cellular networks to also allow roaming between GSM cellular and Wi-Fi networks.
GRX acts like a hub that aggregates GPRS connections between roaming users, making it more efficient to interconnect networks.
Billing
A critical issue is enabling cellular and Wi-Fi systems to exchange information about roaming customers so that users can be billed and all participating providers can be paid for the services they provide, said Maribel Lopez, principal and founder of Lopez Research, a market-analysis firm.
Cellular and Wi-Fi networks use different billing technologies.
For example, GSM-based cellular systems use the Transferred Account Procedure and CDMA networks use the Cellular Intercarrier Billing Exchange Record.
TAP and CIBER capture data about network usage by people who roam from other networks. They then transfer the information to the user's home network so that the operator of that network can bill the subscriber for the roaming charges.
Wi-Fi networks work with AAA (authentication, authorization and accounting), which uses the Remote Authentication Dial-in User Service (RADIUS) protocol to provide the same functions.
Roaming proponents aim to develop an interworking procedure that would map functions between the billing approaches so that they could interoperate.
Roaming into the Future
Enabling roaming between cellular and Wi-Fi networks will be essential to the cellular industry's future, said Farpoint's Mathias.
The WFA, WBA and GSMA are thus working to ensure that their approaches function well together, said Kevin Robinson at the WiFi Alliance.
However, noted Rodrigues, some of the pieces are already in use.
For example, he explained, several service providers—such as Swisscom, TeliaSonera, Portugal Telecom, BT, and PCCW — already operate Wi-Fi networks that work with 802.1x and EAP authentication.
However, warned Mathias, mapping existing authentication mechanisms between Wi-Fi and cellular systems will be challenging because cellular carriers will have write a lot of code to accomplish this complex task.
In addition, Rodrigues noted, there are concerns in areas such as quality of service. Some cellular and Wi-Fi networks could offer different QoS levels.
Rodrigues also said frameworks should enforce policies uniformly across the different types of networks.
Mathias said he expects broad deployment of the technologies that enable roaming in, for example, cellular base stations, Wi-Fi equipment for carriers, and network management systems.
However, he said, this process will require considerable evolution.
He predicted that high volume deployments are at least four to five years away, and deep market penetration will require seven to 10 years.
