/vnd/media/agency_attachments/bGjnvN2ncYDdhj74yP9p.png)
Though the operators have been lamenting about 3G not taking off yet in India, it is a question of time before their networks are flooded with traffic, especially data and internet. With a meager amount of spectrum allocated for their 3G operations (viz, 2 × 5 MHz in 2,100 MHz), some operators are already scouting for alternative methods for balancing the traffic, especially in dense urban areas where the likelihood of congestion is very high. One of the widely deployed methods is Wi-Fi offloading.
Wi-Fi Offloading
Wi-Fi offloading is a method by which the traffic is diverted from the carrier's macro cellular network to a localized Wi-Fi network, installed typically in homes, enterprises or public locations, thus relieving the licensed spectrum used. Such Wi-Fi hot spots can be deployed by the owner of the venues as 'Private hotspots' (eg, homes, office premises, cafes and restaurants such as Starbuck, Costa Coffee, hotels) or by the Internet Service Providers (ISPs) as 'public hotspots' typically in areas such as airports and malls; or mobile operators either by themselves, or in partnership with ISPs as 'carrier Wi-Fi hotspots'.
Though deployment in the former two cases exists in plenty even in India (though lags behind much in terms of number of public Wi-Fi hotspots compared to other countries), the carrier Wi-Fi is yet to take off. One of the reasons is the failure in the growth of data traffic on 3G networks. However, a recent Cisco Visual Networking Index report shows that global mobile data traffic grew by more than 133% in 2011 to about 597 petabytes, which is about 8 times larger than the byte consumption of the entire global internet in 2000.
In case of private or public Wi-Fi, the hand-off from the carrier network often requires human or application intervention. Typically the hand-off requires authentication by the user or the application to the nearby hotspot. Moreover, since the carrier network and the Wi-Fi network do not necessarily collaborate in the hand-off, the IP address needs to be allocated when the device moves in to Wi-Fi zone and the connection needs to be reestablished either at the session layer level or at the data link layer level, leading to possible jitter and delay or even disconnects.
Moreover, when traffic is offloaded from the operator's cellular traffic to Wi-Fi network, the same level of security and integrity as applied in the cellular network needs to be applied on the Wi-Fi air interface as well. The Wi-Fi Protected Access (WPA) protocol deploys SIM based authentication as one of the options to achieve the cellular network level security and integrity along with the seamless mobility between the cellular and Wi-Fi networks. The SIM credentials are used for authentication in the Wi-Fi network, obviating the need for manual or application intervention. The architecture of the carrier Wi-Fi network elements has been defined in the latest 3GPP Release 10 specifications.
Architecture of Carrier Wi-Fi
The seamless mobility for all the mobile devices is supported with the help of a well-integrated infrastructure at the current cellular core network. This integration brings in a new node named Home Agent (HA) at the core network.
This HA is responsible for allocation of IP address for each subscriber based on the International Mobile Subscriber Identity (IMSI) from the respective SIM card. This termed as the HA-IP is bound with the Care-Of-Address assigned by the network based on the type of service. The HA provides the encryption keys retrieved from the Home Environment against each subscriber identity for each of the mobile devices after a proper device authentication procedure. These provide the required seamless mobility and security.
Carrier Wi-Fi vs Femtocells
There has been general reluctance by the operators to deploy any Wi-Fi solutions. For example in 2009, AT&T, the US mobile service provider who bundled Apple's iPhone 3G handsets along with its access service put restrictions on the use of “Skype over Wi-Fi” and made available only the restricted “Skype over 3G”, to protect their call revenues. However indications are that independent Over-The-Top (OTT) VoIP providers such as Microsoft-Skype dominate the VoIP market today. Carriers need to align themselves and get into VoIP offerings.
Carrier Wi-Fi provides them a viable alternative to do so. Similar is the famous case of AT&T banning the use of Sling Media player that streams the broadcast TV content over the internet on to mobile as it consumed its precious capacity. Though the operators cite insufficient bandwidth as the cause of such bans, options today are available to divert such traffic through the Wi-Fi network. In India, the conditions are worse as each operator gets roughly 1/4th of the spectrum block compared to their US and European counterparts. Hence, the importance of carrier Wi-Fi.
An alternative to carrier Wi-Fi of course is Femtocells-the pico cells that use licensed band and provide carrier based solutions for in-building offloading. Compared to carrier Wi-Fi, Femtocells are expensive propositions as indicated by the slow adoption. The Femtocells also require certain refarming of the spectrum by the operators and hence is not spectrally efficient and optimal compared to unlicensed Wi-Fi band. Moreover, today, Wi-Fi bandwidth and speeds are exploding thanks to the advancements in coding and multiplexing.
The recent IEEE 802.11 ac specifications provide a theoretical capacity of 1 Gbps much more than the Long Term Evolution (LTE) network speeds. The access points conforming to IEEE 802.11u onwards have carrier Wi-Fi specifications implemented and the devices are already available in the market. With US operators adopting them vigorously, the chipset and device prices are expected to drop dramatically making it a financially viable alternative compared to Femtocells or any other in-building solutions.
The obvious use case for carrier Wi-Fi is data roaming, both domestic and international. With free roaming already specified in the new National Telecom Policy 2012, there can be no surcharge on roaming. Carrier Wi-Fi is an option for offloading data roaming traffic to reduce the burden and hence the cost of carrying it on the macro cellular network. For international roaming, it makes more sense for operators to tie-up with ISP to do Wi-Fi offloading and hence bypass the local mobile operator networks, thus saving huge access fees.
The obvious concern is that will carrier Wi-Fi obliterate the otherwise fledgling Wi-Fi business of pure-play ISPs? There is definitely the possibility especially in dense urban areas. The ISPs need to be much proactive in their business plans to target the appropriate market segments and possibly partner with the mobile operators, given this new direction of technology and market movements. The operators on the other hand should loosen up their hold over the last mile access bottleneck facility (ie, the Radio Frequency access link) and embrace Wi-Fi and the internet more amicably.
V Sridhar and Chakravarthy Buchi
The authors are research fellow and senior architect,
Sasken Communication Technologies, respectively
vadmail@cybermedia.co.in