Which carrier had the best data network at CES?

Anyone who's attended CES knows that getting a cell phone signal during the show's peak hours is never a sure bet. With 140,000 phone-wielding people crammed into a square half mile, you can go several hours without making a call, accessing your e-mail, or even sending a tweet.

Since it's rather ironic that you can't use your cell phone at a gadget show, we made a point this year of seeing just how bad the conditions were. So we brought along RootMetrics, a company that powers our cell phone coverage maps, to test the average and maximum data speeds for the four national wireless carriers.

For more about RootMetrics' methodology, see CNET's cell phone coverage map tool.

To gather that information, RootMetrics stationed four smartphones--one each for Verizon Wireless, Sprint, T-Mobile, and AT&T--right behind CNET's stage in one of the busiest areas of the Las Vegas Convention Center. The testing period spanned the four days of CES (January 6 to January 9) and concentrated on the 3G networks of each provider, as well as 4G networks from T-Mobile and Sprint.

The findings covered four areas: the overall reliability of a carrier's network, hourly aggregations of each carrier's average data speeds, the maximum speeds achieved each day, and the rate at which consumers could access a carrier's data network successfully (also called success rate). You can click over to RootMetrics' online report (PDF) to read the full details, but we're happy to offer the meatiest information here.

According to RootMetrics, T-Mobile and Verizon Wireless offered the best 3G data networks for show attendees, but they did so in different ways. Throughout the show, T-Mobile had the advantage in the area of overall 3G speeds, followed by Verizon, AT&T, and Sprint. Verizon, on the other hand, took the prize for the most reliable 3G network with the fewest data failure rates. Sprint and AT&T tied for second place and T-Mobile brought up the rear. On the 4G side, Sprint beat T-Mobile by offering both the fastest data speeds and the most reliable network.

Keep in mind that reliability and speed for all networks dipped considerably during the middle of the day when most CES attendees were roaming the show floor. On the chart above, for example, notice the big dip in performance starting around 11:00 a.m. and ending around 6:00 p.m. Indeed, this matches my experience during my time at CES. Though things were fine in the morning, CNET's iPhone was pretty much unusable by lunch time, even if I went across the street to our hotel. A T-Mobile phone behaved better, but it wasn't until nightfall that I really got either handset back.

Average speeds during CES show hours (Jan 6-9)