Wi-Fi offload: Is your gateway ready?

-October 15, 2012

Studies of network analytics show that up to 80 percent of mobile data originates from indoor users who are more nomadic than truly mobile. Wi-Fi offers a solution to the problem of spectrum overload.

The Problem of Success
In response to a question about Ruggeri's, a St. Louis restaurant, Yogi Berra said, “Nobody goes there anymore. It’s too crowded.” Like Ruggeri’s, mobile broadband service suffers from the problem of success.

With the increase in customer access, hours of use, and high-bandwidth content, the mobile broadband network is also too crowded. Carriers are feeling the pressure to provide better performance and more bandwidth at a lower cost per bit.

As early iPhone adopters can attest, too many users in a service area can lead to saturation and degradation or loss of service. The number and range of mobile broadband devices grows hourly, from person-centric devices like smartphones, tablets, and notebooks to devices installed in vehicles.

It comes down to spectrum. Like land, they’re not making any more, and spectrum limitations have serious implications for carriers. Burgeoning demand for spectrum increases the number of unsatisfied customers. Lack of spectrum limits the ability to grow the subscriber base or expand into new markets. Increased demand accelerates the need for more towers, which are costly and time consuming to build. Leasing access and backhaul from another carrier can incur costs disproportionate to the added revenue.

Success in Search of a Solution
Thus far, many of the solutions are either expensive or nothing more than a bandage, and some solutions, like throttling high-usage customers, can add to customer churn.

One of the more obvious approaches to resolving spectrum issues for mobile wireless networks is to upgrade the network. While network upgrades may provide additional spectrum and use it more efficiently, they are also time consuming and expensive. Even when a network has been upgraded to the best and latest technologies, the fact remains that mobile wireless spectrum is finite.

Studies of network analytics show that up to 80 percent of mobile data originates from indoor users who are more nomadic than truly mobile. Too bad there’s not another wireless network out there that could share the load, allowing carriers to transparently and cost-effectively offload data traffic from the 3G/4G/LTE network via an alternative path to the core network and the Internet. Oh wait. There is.

The Solution for Success
Thanks to work by the 3rd Generation Partnership Project (3GPP), Wi-Fi offloading is a viable alternative for addressing spectrum overload. Because this approach offers lower CapEx and OpEx, many network equipment manufacturers (NEMs) have already integrated Wi-Fi offload gateways into their 3G/4G mobile gateway network products. See Figure 1.

Figure 1: Typical Wi-Fi offload test topology

Wi-Fi offloading can be enabled in mobile handsets with software updates, creating a large base of potential users. Wi-Fi gateways provide seamless mobility, security, mobile services, and more bandwidth at less cost to the subscriber, which in turn frees up the 3G/4G radio access network (RAN) and the mobile backhaul network (MBH) for subscribers outside of Wi-Fi range.

Typical wireless access for mobile devices travels through the RAN and MBH to the mobile packet core (MPC). Wi-Fi offload uses an access point (AP) talking to an access controller (AC), packet data network gateway (P-GW), or evolved packet data gateway (ePDG) depending on the technology in use to reach the MPC. Internet traffic directed through a Wi-Fi gateway can bypass the MPC altogether, bringing even greater efficiency to the core network.

The 3GPP proposal makes the user experience seamless–no searching for a Wi-Fi network and entering authentication information. Subscribers can roam from one Wi-Fi partner’s coverage to another without interrupting calls or reestablishing connections.

To achieve the fast authentication required to support the quality of experience mobile users expect, IEEE 802.11r and IETF protocols such as Control and Provisioning of Wireless Access Points (CAPWAP) and Handover Keying (HOKEY) reduce the amount of signaling required for Extensible Authentication Protocol (EAP) authentication during handoff to a neighboring AP.

Carrier Challenges
Wi-Fi offloading is set to become the ideal alternative for mobile data connectivity, but carriers face some significant challenges in delivering a solution that supports the quality of experience subscribers have come to expect.

First comes the question of what to offload and when. The ultimate goal is to handover everything to the Wi-Fi network when possible, but at the beginning data traffic is the priority, particularly for high-bandwidth applications such as video.

The exponential growth of signaling due to the proliferation of smartphones, which even without human intervention are continually checking for one kind of traffic or another—email, Facebook status messages, SMS messages—make signaling a prime candidate for Wi-Fi offload. Eventually the handoff will include voice calls, which will roll from VoLTE to VoIP.

Consider the case of a traveler checking her email while making a connection in an airport. She turns on her smartphone as soon as the wheels hit the ground, connecting to the 4G network, but as she exits the plane she comes in range of an AP. The handset authenticates with the AP through the gateway and is authorized by the mobile core before handing off the data traffic to the Wi-Fi offload network.
As she walks out of range of one AP and into range of another, the system performs an intra-SSID handoff, which requires authentication with each AP as she comes into range before the former AP hands off the traffic. Authentication must happen before the session times out and the handover of traffic must be seamless and transparent to the traveler.

Or consider the case of an apartment dweller using Wi-Fi to cable at home for Internet. He’s watching the highlights of last night’s game as he walks out of his building and into a coffee shop with Wi-Fi from a different carrier. The system performs an inter-SSID handoff, switching service from one AP and provider to another.

Once again, authentication and handover must be fast and seamless. Challenges abound, from supporting basic functionality per the specification to multi-vendor/multi-provider interoperability to achieving the performance and scalability required to deliver a high quality of experience.

>>Key Tests for Wi-Fi Offload
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