An iPhone User's Guide to 3G

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 f 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 support. (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