Wi-Fi-cellular roaming pros and cons, powered by ANDSF, highlighted by 4G Americas

After years of fits and starts, demand for cellular/Wi-Fi roaming appears to be reaching a fever pitch, which is in turn driving companies and standards groups to respond with solutions they say will allow smartphone users to blissfully travel across Wi-Fi networks with all of the same services (like voice, texting and so on) they are used to receiving while on cellular networks.

The latest noise on the topic comes from 4G Americas, which released a white paper on how operators can offer Intelligent Network Selection (INS) by using the 3GPP's Access Network Discovery and Selection Function (ANDSF) framework. Importantly, Ericsson (NASDAQ:ERIC) and AT&T (NYSE:T) executives worked on the paper and added their names to its conclusions.

"Wi-Fi is an important unlicensed spectrum technology for most operators and the intelligent integration of Wi-Fi and Cellular will provide a benefit to both operators and their customers," stated Farooq Bari of AT&T and co-project leader of the 4G Americas technical group that authored the white paper.

4G Americas WiFi Cellular boundary

Figure 1: Four key challenges at the Wi-Fi / Cellular boundary (Source: 4G Americas)

As 4G Americas outlines in its white paper, there are a wide range of standards, frameworks and acronyms aimed at smoothing connections between Wi-Fi networks and 3G and 4G cellular networks. 4G Americas wrote that the recent Hotspot 2.0 effort, which is being defined by the Wi-Fi Alliance (WFA), Next Generation Hotspot (NGH) and Wireless Broadband Alliance (WBA), is "aimed at facilitating and automating a secure and trusted Wi-Fi connection with the ability to use a variety of user- or device-based credentials." Hotspot 2.0 also hopes to improve Wi-Fi network discovery and selection.

But, as 4G Americas notes, the cellular industry, through the 3GPP, has also been working on the Wi-Fi/cellular roaming via EAP-AKA/SIM based authentication and S2a-based Mobility over GTP (SaMOG) Trusted Access. Specifically, 4G Americas said the 3GPP has spent several years standardizing the ANDSF, which the group said "provides a framework for operators to customize network steering policies and distribute those policies down to devices." 4G Americas said there are ongoing efforts in 3GPP Release 12 to align ANDSF with the HotSpot 2.0 capabilities.

Importantly, 4G America said the combination of ANDSF, SaMOG, HotSpot 2.0 and other technologies could lead to "simplified roaming, seamless handovers, and more intelligent network steering, are designed to enable users to continue using data services as they pass between cellular macro cells, small cells and Wi-Fi hotspots, with no need for further authentication or user intervention."

Of course, integration between unlicensed Wi-Fi networks and licensed cellular networks presents a wide range of challenges. Indeed, the WBA recently said that its ongoing collaboration with the GSMA to facilitate roaming between Wi-Fi and cellular networks has revealed that there are a couple of additional issues the industry needs to address: authentication signaling optimization and session continuity.

4G Americas also highlighted challenges to Wi-Fi/cellular roaming, including:

  • Premature Wi-Fi Selection, which the group said happens when devices connect to a known Wi-Fi network without first checking for better cellular and Wi-Fi options.
  • Unhealthy choices, which 4G Americas said can happen when devices select Wi-Fi connections even though those Wi-Fi networks are already straining under heavy loads. "Real-time, load-based traffic steering can be used to mitigate this," the group said.
  • Lower capabilities, which the group said can lead to poor performance if a device connects to a Wi-Fi network with a lower bandwidth in the backhaul than the cellular base station presently serving the device.
  • And Ping-Pong, which 4G Americas said happens when a user ping-pongs between Wi-Fi and cellular networks.

4G Americas' white paper seeks to address some of these problems and outlines future technological options for vendors and operators.

Of course, ANDSF and HotSpot 2.0 are just the latest technologies aimed at addressing the cellular/Wi-Fi roaming problem. For example, T-Mobile US (NYSE:TMUS) continues to offer its Wi-Fi Calling service, which allows users to place and receive calls and texts via Wi-Fi. The operator said the service is available on a range of its phones, including the new iPhone 5s. And MVNO Republic Wireless recently boasted that "where other attempts have failed or abandoned, our team has succeeded--we've invented new technology that enables seamless Wi-Fi to cellular handover, vastly improved Wi-Fi call quality, and MMS capabilities as well as some great new features such as visual voicemail."

For more:
- see this 4G Americas press release and white paper (PDF)

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