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In A Nutshell: What Is 3G?


Part of being a good user and consumer is understanding how technology works, why we use it the way we do, and what that barrage of acronyms and PR jargon means. We're here to help you make sense of it all, and to give you a better appreciation of how those transistors, pixels, and antennae work together to deliver the conveniences of the modern world to your living room or office.

What is 3G?

3G is an umbrella term for a collection of technologies that make up the third generation of cellular data networks. These standards allow cell phones (and other devices capable of connecting to a cellular network) to send and receive data at speeds comparable to cable or DSL. There are two major families of cellular tech, commonly called CDMA (code division multiple access) and GSM (global system for multiple access), each having their own confusing array of specific sub-technologies, that qualify as "3G."


So what qualifies as 3G?

Well, there are quite a number of different mobile standards that fall under the guise of 3G. CDMA-based carriers, such as Sprint and Verizon, use EV-DO or Evolution-Data Optimized. EV-DO comes in three distinct flavors: Rev.0, Rev.A and Rev.B. No carriers in the U.S. use, or plan to upgrade to, the fastest of the three, Rev.B. Meanwhile, GSM carriers (T-Mobile and AT&T in the U.S.) use the much more confusing family of standards known as UMTS. In the U.S., UMTS is commonly called HSPA, or High Speed Packet Access. While there are actually differences between them (HSPA being a specific flavor of UMTS), for layman purposes the two are essentially interchangeable. HSPA, like EV-DO, comes in different varieties, with HSDPA, HSUPA and HSPA+ being the most popular of the bunch (and the ones used in the U.S.).

What's with all this Rev.A and HSPA+ stuff?

Let's start with the easy one. The different types of EV-DO are simply evolutionary upgrades. An improvement on Rev.0, Rev.A offers faster upload and download speeds, as well as lower latency (the time it takes to establish a connection, and to request and receive data). Rev.B offers similar improvements on Rev.A. The lower latency is especially important, since it improves responsiveness and perceived speed; which are essential for functions like VoIP.

HSPA (or UMTS) is a little more complex. HSDPA and HSUPA are actually components of the broader HSPA standard. HSDPA, or High Speed Downlink Packet Access, is the set of standards that govern download speeds over 3G GSM networks. HSUPA, on the other hand, defines upload speeds. HSPA, like EV-DO, comes in different speeds, but there are no naming conventions to differentiate the various upgrades. HSPA+ is sometimes called 3.5G, and effectively doubles the speed of HSPA.

So how do EV-DO and HSPA stack up against each other?

On paper, at least, this is a very lopsided battle. Even the top-of-the-line Rev.B version of EV-DO can't compete with HSPA. Sprint and Verizon use the mid-level Rev.A, which has download speeds of 3.1 Megabits (Mbits) per-second and 1.8 Mbits upload speeds. This is fine for e-mail and for light Web browsing or audio streaming, but a two-way video call over Skype might prove a bit frustrating.

The HSPA networks of T-Mobile and AT&T double the download rates of EV-DO, hitting 7.2 Mbits per-second. That's more than enough for VoIP calls, and is only half of HSPA's top speed. The GSM 3G standard's latency is lower than EV-DO's, its signals can travel six times as far, and it's capable of handling both voice and data traffic at the same time; Verizon and Sprint customers have to hang up a phone call before pulling up directions or checking their e-mail.

Of course, this is all theoretical. In theory, T-Mobile and AT&T should trounce their CDMA-based competitors. It should be easier and cheaper for those carriers to build their networks. But, as any iPhone owner can tell you, what works on paper doesn't always translate to real-world success. Regardless, when shopping around for a carrier or a phone, it helps to know the limits and potential perks of a chosen network's technology.

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