An iPhone User’s Guide to 3G

The iPhone 3G’s name immediately raises an obvious question, even to people who already own 3G phones: What the heck does 3G mean, beyond its abbreviation expansion to “third generation.”

A 3G cellular telephone network offers something akin to wired broadband while away from a wire, whether you’re anchored to a table, walking, or traveling at driving or train speeds. The 3G part refers to the evolution of the cell telephone network.

First-generation (1G) networks were all analog. If you’re too young to remember the giant bricks of phones—which at one point required shoulder-harness cases, even—you might laugh to think of minutes, not hours of talk time, poor reception, and very crackly speech. 1G networks could handle very low-speed data on a good day.

Second-generation (2G) networks were all digital, but were developed just early enough that the Internet wasn’t part of the thinking. 2G networks weren’t optimized to move data around, just to reduce the network capacity needed to carry voice packets. Squeezing analog voice into data allowed networks to carry an order of magnitude more calls, which meant much more money in the days before unlimited plans of any kind.

2G networks can carry data, though. The CDMA (Code Division Multiple Access) technology that drives Sprint and Verizon Wireless’s networks—and which is used in few other countries—offers dial-up modem speeds with 1xRTT, the slowest CDMA data standard. GSM (Global System for Mobile communication) networks offer both GSM (data transfer speeds of 9,600 to 1,4400 bps) and GPRS (General Packet Radio Services, up to dial-up modem speeds).

This brings us to 3G. (You may ask, what about 2.5G? I’ll touch on that soon.) 3G was designed to deliver data as part of its very nature. It’s optimized to carry bits that may or may not be voice bits. Verizon and Sprint chose a standard on the CDMA path called EVDO (Evolution Data Only). So far, it’s gone through two revisions, from Rev. 0 (zero) to Rev. A. Rev. A is deployed almost everywhere that has 3G service on both networks.

AT&T chose to stick with GSM, and picked HSPA (High Speed Packet Access), a faster flavor in harmony with GSM equipment and networks. HSPA comes in separately organized standards as downlink (HSDPA) and uplink (HSUPA) flavors that are paired for service. AT&T initially deployed HSDPA with a slow uplink, but will finish upgrading its HSPA network to full HSUPA service this month.

AT&T’s HSPA network is designed and enabled to allow simultaneous voice and data calls. Apple confirmed in a briefing with me that the iPhone 3G can browse the Web, retrieve e-mail, and find maps, all while you’re talking (via speakerphone or Bluetooth headset, presumably). While Verizon and Sprint’s EVDO Rev. A network can technically handle both tasks, too, the companies have focused on service-at-a-time: either data or voice, not both. A Verizon spokesperson said that the company is moving towards allowing both voice and data at once.

You might wonder why I haven’t mentioned T-Mobile: the distant fourth among American carriers, T-Mobile didn’t own spectrum capable of 3G services until a relatively recent spectrum auction. The company has just started to roll out a slow 3G standard in New York City, and expects to offer HSPA in the near future more broadly.

Now as to 2.5G, that 200 Kbps to 400 Kbps flavor bridges between 2G and 3G networks—which is primarily represented by the EDGE network the current iPhone uses—and was developed to accelerate 2G networks to be faster without the new technology and spectrum required for 3G networks. Second-and-a-half-generation doesn’t make much sense grammatically, but it was a way for carriers to save money and have something faster when 3G deployments were delayed. (Future versions of EDGE are expected to be four times as fast through software updates to carrier base stations, although new chips are required for adapters and smartphones.)

The three 3G carriers claim their networks work in average ranges, where you would typically see somewhere in this range depending on a variety of factors. Verizon says its networks offers a range of 600 Kbps to 1.4 Mbps downstream, and 500 to 800 Kbps upstream. Sprint cites the same downstream rate, but just 350 to 500 Kbps upstream.

While AT&T used to claim similar numbers, the HSUPA update for its network quietly contained a major downlink update as well. As of June 4, 2008, the company says that by the end of June its network will run at rates from 700 to 1.7 Mbps downstream and 500 to 1.2 Mbps upstream. This is a big selling point for customers uploading photos or video from the field. (AT&T says that hardware with HSUPA built in is required; for phones, it’s certain that the iPhone 3G has this technology, and AT&T sells four models of mobile broadband adapters in USB, PC Card, and ExpressCard form factors that include HSUPA hardware.)

Verizon, Sprint, and AT&T now also claim low latency, which wasn’t the case with some of the first 3G standards. Latency is to bandwidth like water flow is to water pipes: just as the former measures how long it takes after you open a tap for the water to start flowing, the latter indicates how long it takes for data to start moving over a connection once opened. High latency makes video jitter, makes even quick Web page loads seem to take a long time before they show up, and disrupts voice calls and video chats.

The top rates of each of these networks isn’t precisely a cap. The HSPA network, for instance, has a nominal top speed of 3.6 Mbps, although that’s a raw rate and shared among users in a given cell area using the same set of frequencies. EVDO Rev. A has a nominal top rate of 3.1 Mbps. For both networks, you can see peak rates for sustained transfers that go far above the 1.4 Mbps or 1.7 Mbps top of the typical range. I’ve measured well over 2 Mbps in a recent test of Sprint’s network and gear. In cities at peak usage times, you won’t see the peak speeds. And the carriers may lack fast enough connections at some of their 3G cell towers to handle the full capability of their 3G networks, too.

If you listened to Steve Jobs during his WWDC keynote, you’ll note that the 1.7 Mbps top downstream rate, about 8 times faster than the 200 Kbps or so top EDGE downstream rate, is nowhere near the 2 to 3 times improvement the Apple CEO cited for Web-page browsing and email attachment downloads. He also said that the iPhone’s 3G performance would be very close to Wi-Fi.

Stats comparing browser and attachment loading in 3G, 2G and Wi-Fi are sort of red herrings; not inaccurate, but not revealing. It’s the network processing speed and the iPhone 3G’s main and graphics processors that determine how fast data can be relayed and rendered on the device. You could stick gigabit Ethernet into an iPhone 3G, and it still might take 26 seconds to render the National Geographic home page that Jobs showed in his side-by-side comparison.

Likewise, the iPhone 3G should be able to communicate as fast as about 25 Mbps over an 802.11g Wi-Fi network, the fastest standard the phone supports. (The as-fast-as-100 Mbps Draft N or 802.11n Wi-Fi flavor isn’t available yet in chips small and low power enough for a compact phone.)

What Jobs was comparing 3G to was a typical Wi-Fi hotspot, which normally has about 1.5 Mbps of backhaul—bandwidth to the Internet—and is comparable to AT&T’s nearly upgraded network’s highest downstream rate. It’s increasingly the case that high-end hotspots in airports, cafes, and hotels are boosting their service well above 1.5 Mbps—San Jose’s airport just noted that it was adding 15 Mbps service at no cost in several terminals. And my home DSL gives me about 2.5 Mbps of real downstream service. While 3G is fast, Wi-Fi can be faster. Wi-Fi typically tethers you, and 3G does not.

The future of 3G is pretty grand, based on what’s already known about new and evolving standards. AT&T’s network will likely jump to 7.2 Mpbs in the not-too-distant future, and there are leaps to double and quadruple that on the current roadmap. AT&T plans to move to a fourth-generation network—all Internet protocol as opposed to today’s networks—using LTE (Long Term Evolution), which may offer 50 to 100 Mbps of downstream service as early as 2012. Verizon and T-Mobile are also on track for LTE, while Sprint is pursuing the near-term deployment of an incompatible standard (backed by Intel) called WiMax that might offer 5 to 15 Mbps downstream as early as late this year in certain markets in the U.S.

Apple’s move to 3G with the iPhone is part of a larger trend for wireless devices: giving those devices not just the freedom to move about, but the power of real broadband, extending their usefulness for downloading and streaming video, as well as providing a real alternative to a laptop.

[Glenn Fleishman writes daily about wireless networking at his site Wi-Fi Networking News. He also runs the Glenn Fleishman on Hardware blog at PC World.]

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