"Making Wi-Fi as easy as cellular” is a popular maxim when engineers, marketeers, and journalists talk about Hotspot 2.0. And it’s not hard to understand why. The cellular connectivity experience is well understood in virtually every culture, while, except to those involved with its development and testing, Hotspot 2.0 remains a big unknown. Therefore to say Hotspot 2.0 makes Wi-Fi connectivity like cellular puts it in terms that most people can understand. In fact, if you look back, you’ll find a few Ruckus press releases and presentations that use this very analogy.
However, as we approach the launch of production Hotspot 2.0 networks and begin using this technology in our daily lives, it is important to have a more precise understanding of what it is and how it works.
It’s at this point that the comparison with cellular connectivity and roaming falls short of conveying what people need to know. For context, it’s best to start examining some of the similarities and differences between cellular and Wi-Fi with Hotspot 2.0 relative to connecting automatically, authentication, and roaming. Airlink encryption aside, users can be assured that robust security is given for both cellular and Wi-Fi (wih Hotspot 2.0) connections.
To connect to any type of network, a client device must support the same physical interface and medium access mechanisms (Layers 1 and 2) as the access network.
Sometimes the compatibility cues are obvious. For example, plugging a token ring hermaphroditic connector into a 10BASE-T hub would have been quite an accomplishment, even if futile in terms of passing data. But in the wireless world, there are no visible cables or connectors and the end users need to have a fuller understanding in order to ensure that her device will connect to an available network.
The first consideration is the frequency band. Does the device “talk” on the same frequency that the network is operating. Wi-Fi currently operates in swaths of unlicensed 2.4 GHz and 5 GHz spectrum that are largely harmonized globally. The first 11 channels (3 non-overlapping) in the 2.4GHz band are de facto “world bands” as they are approved in virtually all regulatory domains. The picture in 5 GHz is currently less uniform, but there are sections (5.15-5.25 and 5.725-5.85 especially) that have been, or soon will be, adopted for unlicensed use in most parts of the world. 5 GHz is the current focus of regulatory bodies since 802.11ac requires it, and commissioners are endeavoring to open more common frequencies there.
So for Wi-Fi at least, a dual-band (2.4 GHz and 5 GHz) device bought in the US today will definitely connect to a 2.4 GHz Wi-Fi network in Europe, Africa, or Asia, and can connect to 5 GHz Wi-Fi networks in most areas of the world.
In the cellular world, the situation with device support is not nearly as straightforward.
Because licensed spectrum is exclusively allocated in much ‘thinner’ slices to individual mobile operators at the national or regional level. And because the 2G, 3G, and LTE bands vary from country to country, it is impractical to implement a single radio access front end that can support all of the possible RF bands.
One aspect of this is the so-called LTE “band fragmentation” issue. This means that even the most sophisticated handsets have to be produced in a large range of models, which are often specific to a region, country, and/or operator. Even the “international” models can’t hope to support all of the possible operating bands for each generation of technology. At last glance there were 19 different models of the Samsung Galaxy S4s in production to support this collection of different cellular bands.
The difference between Wi-Fi’s harmonized bands and cellular’s fragmented bands is underscored by the fact that all of the 19 different models of the Galaxy S4 use the same Broadcom BCM4335 Wi-Fi chipset.
Meanwhile cellular chipset manufacturers are hard at work creating advanced chipsets and RF frontend solutions that can support large numbers of licensed bands, such as the Qualcomm RF360. As Qualcomm SVP of Product Management, Alex Katouzian, recently pointed out, "The wide range of radio frequencies used to implement 2G, 3G and 4G LTE networks globally presents an ongoing challenge for mobile device designers.”
This severe band fragmentation issue doesn’t exist for Wi-Fi connectivity.
Another challenge that the cellular industry faces with ubiquitous device support is technology schisms. With 2G, 2.5G, and 3G most of the world settled on GSM/UMTSbased coding and modulation, but big (and globally significant) operators in the US and Korea chose CDMA solutions. A similar split is occurring with LTE. In LTE land, the world is standardizing on the Frequency Division Duplexing (FDD) implementation. Meanwhile China is deploying a version based on Time Division Duplexing (TDD).
The bottom line being that a 3G CDMA handset can’t connect to a UMTS Node B, nor can an FDD LTE handset connect to a TDD LTE eNB.
In contrast to the technology factions that exist within the cellular industry, Wi-Fi modulation and coding implementations have effectively remained uniform as standardized by the IEEE and certified by the Wi-Fi Alliance.
The reality is that Wi-Fi devices are able to connect to just about any Wi-Fi network in the world (and Hotspot 2.0 makes it even easier), while cellular band and technology fragmentation has led to a complex mix of often incompatible devices and networks, especially when traveling outside of the home operator’s coverage area.
Where the cellular user experience truly excels, is in the automatic authentication of the device to the network. Each device is provisioned with a unique identifier that is known, and can be verified, by its home operator’s subscriber database (Home Location Register or Home Subscriber Server – HLR / HSS). The identifier is known as an International Mobile Subscriber Identity or IMSI, and can be embedded in a SIM, USIM, or sometimes in the device itself.
The IMSI contains the Mobile Country Code (MCC) and Mobile Network Code (MNC) for the home mobile operator, which together comprise the Public Land Mobile Network (PLMN) ID. A device capable of communicating with a cellular access network can examine the PLMN ID(s) being advertised by the network, and if they match its IMSI, be assured that authentication is possible.
Wi-Fi authentication historically has been quite fragmented primarily due to the diversity of its use (residential, enterprise, hotspot, etc.) and the resulting need for different security requirements. With 802.11, authentication can be open system, based on a static shared code (WEP, WPA-PSK, and WPA2-PSK), or on more sophisticated mechanisms like 802.1X and the Extensible Authentication Protocol (WPA-Enterprise and WPA2 Enterprise). Also, portal-based authentication is often the method of choice for public access Wi-Fi networks, usually in conjunction with 802.11 open auth. These various authentication options are also related to the type of encryption, if any that is used over the air.
Hotspot 2.0 fixes this by standardizing Public Wi-Fi authentication and security.
With Hotspot 2.0, 802.1X is mandated with EAP-SIM/AKA, EAP-TLS, or EAP-TTLS and AES 256-bit encryption required. The authentication credential can be a cellular IMSI, an X.509 client certificate, or a username/password pair.
The inclusion of non-cellular credentials opens up Hotspot 2.0 services to Wi-Fi only devices like tablets, iPod Touches, laptop computers, and even client devices within the worldwide Internet of Things. Supporting a wide range of credential types also provides for a much broader pool of authentication providers, including mobile operators, cable operators, social media companies, hotel chains, and corporations.
Through the use of the 802.11u protocol, a Hotspot 2.0 Access Point (AP) advertises the PLMN IDs, network access identifier (NAI) Realms (think domain name), and Roaming Consortiums (a 3 or 5-byte hexadecimal identifier issued by the IEEE) for which it can authenticate credentials.
The client device examines these various markers being advertised by the AP, and if there is a match with one of its provisioned credentials, it knows that automatic authentication is possible, and proceeds to connect and begin the EAP process.
Cellular network roaming is often portrayed as a successful model that Hotspot 2.0 should attempt to emulate. But is it really?
Even when consumers have devices that are compatible with a visited cellular network, it turns out they are quite hesitant to connect. Rightly or wrongly, cellular roaming has become synonymous with “bill shock”,“highway robbery”, and “OMG” in the minds of the general public and especially CEOs.
This issue was highlighted
by the European Commission in a recent survey report showing that a large percentage of Europeans either disable cellular roaming, turn off their mobiles altogether, or drastically curtail their usage when traveling abroad within the region.
Cellular roaming charges are perceived to be such an issue that some upstart carriers are seeking to gain market share by promoting low, or no, cost roaming plans, seeing this as a significant differentiator from the status quo.
Another symptom is the growing abundance of airport vending machines and kiosks waiting to provide local SIMs and prepaid plans to arriving visitors with unlocked devices. The calculation for the consumer is simple.
Option 1: spend $20-30, and perhaps a little time hassling with APN settings, to get a generous amount of voice/text/data from a local operator, or
Option 2: roam at will using your home IMSI, make a call or two, but be sure you don’t let GMail, Facebook, or Twitter use any cellular data for the duration of your trip, risking the potential $1,000+ bill you can’t seem to expense.
Harbingers for Hotspot 2.0?
Admittedly still in its infancy, Hotspot 2.0 may create radically different models for roaming, or authentication peering. Some precursor services like Eduroam and the Cable Wi-Fi alliance provide some indication as to how it may likely evolve.
Eduroam, like Hotspot 2.0, is an 802.1X-based automatic connection and authentication network that has come from the higher education community. It started in Europe and Asia, but increasingly has a global presence. Individual institutions join Eduroam in order for their users (students and faculty) to automatically connect at any other Eduroam college or university, and so that visiting users can likewise automatically connect to the locally hosted network. It’s a reciprocally beneficial arrangement, and each institution that joins broadens the reach for the other participants. Even retail and hospitality businesses near Eduroam campuses are starting to offer the service as an enhanced benefit to their student customers. It’s common to see a social media post from an Eduroam user surprised to see that their device has connected in some unexpected venue or location.
In the U.S., the Cable WiFi alliance is a consortium of 5 of the largest MSOs (cable operators). Each company had independently deployed large-scale Wi-Fi hotspot networks in their coverage areas as a service to their residential broadband subscribers. They then decided to join together and advertise a single “CableWiFi” SSID across their combined footprint (between 200,000 and 250,000 hotspots across the country), which can be accessed by any of their subscribers. Again, another mutually beneficial arrangement.
Both Eduroam and the Cable WiFi alliance currently utilize SSID-based solutions, but they are also actively investigating Hotspot 2.0 as the next logical development for their service.
So, while it has been helpful up till now to describe Hotspot 2.0 in terms of making Wi-Fi work like cellular, a fuller understanding of the nuances and differences between the technologies and models shows that Wi-Fi can effectively be made easier to use and more pervasive than today’s cellular technologies.
Hotspot 2.0 enabled Public Wi-Fi will offer a service that will be available to all Wi-Fi devices, allow authentication by a number of types of providers, and support roaming consortiums with diverse business arrangements and models. Hotspot 2.0, wherever you may roam. And roam you will.