February 13, 2013


Wi-Fi Offloading: A Better Way To Decongest Wireless Networks

Let’s start with some numbers. In January 2013, the average traffic in bps (bits per second) was a mindboggling 2.4Terabits per second, i.e. 2.4 x 1,000,000,000,000 (1Terabit = 1000Gigabits/1 Trillion bits) with an all-time high of 2.7Tbps reached on 27/01/2013. The average traffic has risen from 1.75Terabits to 2.4 Terabits in one year. If that isn’t enough, average data traffic has risen from 0.3Tbps to 2.4Tbps in five years. That’s an astonishing 800% rise in data traffic. This data consists of both desktop and mobile Internet traffic. If we specifically look at mobile Internet traffic, different sources spill out different numbers, but the writing on the wall is very clear – mobile internet usage is going to overtake desktop Internet traffic in the next few years. It’s already done so in India. Data usage is increasing, and mobile phones and tablets are seeding this storm. Our devices are getting smarter, faster; the networks are becoming more and more congested, even though they are using cutting edge technologies. With the advent of 4G and LTE-Advanced, the move to all IP networks is the mantra for all the service providers. While all this data bombardment isn't bad for mankind, with newer and more efficient technologies such as 4G, Super Wi-fi coming into picture, there is a complementary concept gaining cognizance. It’s called Data Offloading.

With mobile internet traffic set to scale higher traffic data generation, it is obvious the current networks will get clogged; this will strain the networks, badly hurting the QoS of the delivery networks, resulting in an unacceptable QoE to the user. Mobile data offloading is currently the most viable solution for operators to alleviate network congestion. Per Wikipedia, data offloading is defined as the use of complementary network technologies for delivering data. Today, small cell technologies such as Wi-fi and Femtocells are the most preferred mobile data offloading candidates. In this blog, I will talk about wi-fi offloading specifically.

Most of the smartphones and tablets prevailing in the market today have Wi-fi capabilities, hence Wi-fi by default becomes a suitable offloading medium. It’s a very cost-effective means, with large deployments around the globe, globally available spectrum, and flexibility in connecting to devices without the use of a SIM. Most residential homes in the large metro cities (I say large metro cities as these cities are the main source of generating the humungous mobile Internet traffic) today boast a residential wi-fi gateway backhauled over either the cable networks or the very popular DSL lines. So, to cite a simple data offloading example, say on the way home from work, I was browsing the internet in the car using either a 3G or 4G service provided by my ISP. I reach home after some time. I have two options now to continue to browse the Internet. One, to continue using the 3G/LTE services offered by my ISP, or two, to use the wi-fi broadband residential gateway in my home. If I choose the latter, this process is called mobile data offloading.

There are three main components of a wi-fi based mobile data offloading system. They consist of the wi-fi RAN, wi-fi gateway and the packet network. The Radio Access Network (RAN) is the RF-based physical media (airwaves) to send the data between the user equipment and the wi-fi gateway. The gateway is responsible for user authentication, securing the channel and acting as a gateway for the data to flow back and forth from the Internet. Hence, in a true seamless Wi-fi offloading system, as soon as I walk into my home from my car, my phone would get connected to the wi-fi gateway, the credentials stored on the phone would be authenticated by the gateway using protocols such as RADIUS/AAA (portal-based authentication vs. EAP-based authentication), an IP address would be assigned to the phone, and the browsing would work as if nothing had changed, but importantly, now the mobile internet data is travelling through a wi-fi based access network rather than the 3G/LTE network. This frees up extremely valuable spectrum for other users on the road.

Although a very simple yet highly effective means of de-clogging airwaves, the process is much more complicated than described above. One of the key challenges is what is known as Policy Charging and Control (PCC). The Service Provider (SP) applies security and bandwidth policies on each of the subscribers. As part of the end-to-end experience and quality of service guarantee, the SP would want to enforce these policies transparently, irrespective of whether the user is using the 3G/LTE spectrum or has offloaded his data to the wi-fi access network. Moreover, how he is billed for using these services is also an integral part of the whole exercise. The PCC is responsible for enforcing the process of usage of identical policies for each subscriber. Another key challenge to any mobile data off-loading technique is the handover of the radio frequencies from one radio type to another, i.e. 3G/LTE to wi-fi. The trick here is to keep the user experience seamless and transparent when switching radio types. Since the physical interface changes, the TCP/UDP sockets and the IP addresses bound to the network interface could get disrupted. Radio handover could take place either through the UE using the same IP address which it was using while it was connected to the 3G/LTE network, or being assigned a different IP address. Although the preferred case would be for the same IP address to be given back to the UE, it would also depend on the TCP/IP stack implementation in the UE. If the sockets are closely bound to the physical layer, then in spite of the reuse of the IP address, the socket would have to be closed and reopened again, causing a disruption of service.

We have seen one example of intelligent wi-fi offloading when the user walks into his home-based wi-fi RAN and continues a seamless Internet browsing experience. Wi-fi networks are of two types – namely trusted and untrusted. Trusted networks are operator built and maintained with an over-the-air encryption and a secure authentication method. Untrusted networks are those where there are not sufficient security policies enforced, such as a public open hotspot or a subscriber's home WLAN. The example we showed earlier was data offloading to an untrusted network, namely the subscriber’s home WLAN. In case of data offloading to trusted networks, other mechanisms to move to such a network can be built in. A couple of ways of doing this could be:

  1. Based on current capacity handling of the 3G/LTE network –

    If network intelligence can indicates there is pressure on the network due to a large amount of data traffic flowing, and that the user is in an area where his own SP is operating a trusted wi-fi network, then the user could be moved to the wi-fi network operated by the SP.

  2. Based on location intelligence –

    Trusted networks can be made more intelligent by remembering users who visit them on some kind of periodic basis, if not regularly. This information could be used to seamlessly switch the user to the operator controlled Wi-fi network the next time the user visits the same location.

Mobile data offloading has arrived. It is just a matter of time for it to become a reality in the true sense through widespread embrace by service providers. It is certainly one of the most cost-efficient ways of reducing the workload of the 3G/LTE networks. 2013 could be the year for it to show its true potential.Visit HCL Tech's enterprise wireless solutions section to know more about its wireless services.


[1] http://www.de-cix.net/about/statistics/