What is Wi-Fi Offload?
Whether you call it Wi-Fi offload(ing), mobile data offloading, 3G data offloading or just offloading, it is all about relieving the congested mobile data networks with additional capacity from unlicensed Wi-Fi spectrum.
Just four years ago mobile operators could have asked, “what is offloading?” because the concept was not invented yet. In four years from now they will still ask the same question because 3G, 4G and Wi-Fi will all be integrated into one service where the devices intelligently and dynamically choose the best network available.
The concept of Wi-Fi offload has then been through four phases.
Several years ago, mobile operators already utilized a form of Wi-Fi offload, even if the concept did not yet have a name. In this first phase they built Wi-Fi hotspots as a separate network and then bundled the service with mobile subscriptions. Users had to login manually so the offloading effect was very modest: well below 10% of the data traffic went through the Wi-Fi network. Simultaneously, on the other side of the network, most operators were building Wi-Fi as a complement to indoor coverage rather than for offloading.
It was the rapid growth of data-hungry smartphones and tablet computers that created the need for what we today refer to as seamless Wi-Fi offload, the second phase of offloading. Since these devices are designed to prefer connecting to Wi-Fi (rather than 3G/4G) if available, it was just a question of making the login process to the Wi-Fi network as secure and seamless as it was for the mobile network.
Mobile operators that had existing Wi-Fi networks introduced SIM authentication (EAP-SIM/AKA) to automatically login the users to their Wi-Fi network. An additional benefit with SIM authentication is that it requires that the Wi-Fi network be encrypted (802.1x).
Since then, mobile operators around the world have aggressively deployed Wi-Fi networks and SIM authentication has become the best practice for authentication. Mobile networks that do not utilize SIM cards e.g. CDMA have the same type of authentication implemented through clients in the device. With this automatic login, the offloading effect has increased to 20-30% and in some cases as high as 50%. So far (October 2013), integration with the mobile core has been relatively limited. This will change in the two next phases of offloading further described in the “Trends for Wi-Fi Offload” section.
Why Wi-Fi Offload?
Seamless Wi-Fi offload is the new mass-market business opportunity for mobile operators (MNOs): MNOs can provision combined carrier-class Wi-Fi and mobile services today and profit from offering consumers a vast service improvement with convenient ‘always-on’ data connectivity.
Many of the world’s biggest carriers already recognize Wi-Fi as a business-critical, strategic technology.
The drivers for Wi-Fi offload are well known: Wi-Fi-capable devices are everywhere and more than a billion of them are equipped with SIM cards. For many users of tablets, smartphones and laptops, studies indicate that Wi-Fi has become the preferred wireless technology. Razor-sharp competition is forcing many MNOs to cut spending while looking for new ways to stand out in the market.
Some models  show that carrier-class Wi-Fi deployments allow MNOs to save 30-40% on network CAPEX while gaining several thousand percent in radio network capacity in typical indoor deployments.
Carrier-class Wi-Fi is also a business opportunity for MNOs in its own right. Whether MNOs choose to partner with existing Wi-Fi service providers (WISPs) or build their own carrier-class Wi-Fi networks, Wi-Fi gives MNOs the opportunity to address a vast market for connectivity of general Wi-Fi enabled devices. Since 2009 more than 9 billion Wi-Fi devices have been shipped and in 2012 alone this number exceeded 1.5 billion, which is nearly twice the number of devices shipped in 2011 .
Today’s mobile broadband subscriber typically owns three or four Wi-Fi enabled devices and a couple of these probably do not include SIM cards. By offering Wi-Fi services for all devices the subscriber is more likely to be loyal to the service and the MNO may as a result reduce churn.
Trends for Wi-Fi Offload?
A strong trend currently is 3GPP Wi-Fi access with mobile core integration. This is the third phase of offloading that literally no mobile operator has implemented yet but most are interested in. Some or all of the data traffic is backhauled to the mobile core through GTP tunnels. A GTP tunnel is set up for the individual user session between the Wireless Access Gateway (WAG) and the GGSN in the mobile core. This means that the Wi-Fi traffic will be treated as mobile broadband and the mobile operator can then utilize all existing policy control and charging mechanisms. An alternative to this is to integrate policy and charging with the Wi-Fi service management system which handles these tasks for local traffic breakout. In reality both options may be required as it may not make sense to backhaul all traffic, for instance traffic from laptops or tablets, to the mobile core. Local traffic breakout will also offload the whole 3G / 4G network and not just the radio network.
The rollout of Hotspot 2.0 technology will enable compatible mobile devices to automatically and silently discover Wi-Fi access points that have roaming agreements with the user’s home network, and then automatically and securely connect. The user experience will be similar to when you enter a new mobile network. You just have to turn on your device and the services will work instantly and be billed by your home operator through roaming.
In the fourth and final phase of offloading which most likely is 3-5 years in-front of us, the 3G / 4G and Wi-Fi services are fully integrated as one service where the devices intelligently select the best network at any given time. This requires more intelligence in the devices to measure the connection quality and to actively interact with the ANDSF node in the mobile core to decide which network to connect to. One could argue that the term “offloading” will no longer be relevant at this point. When Wi-Fi is just another radio network (RAN) and maybe even used simultaneously with the 3G /4G network, and with 50% of traffic going through Wi-Fi, then the question of who is offloading to whom becomes purely academic.
 White paper from Aptilo Networks SEAMLESS WI-FI OFFLOAD:
A BUSINESS OPPORTUNITY TODAY