Thursday, August 27, 2009

Tethering AT&T Phones - As Fast as an Aircard?

We have been asked for several years if using a phone for tethering (aka "phone as modem") is as fast as using an aircard. In the case of Sprint and Verizon phones, the answer is pretty easy - if the phone is "EVDO Rev-A" capable, it can provide comparable performance as a USB/ExpressCard/PCMCIA modem (Sprint/Verizon EVDO Rev-0 phones won't be able to connect at the highest possible speeds, however).

Now that 3Gstore has recently started offering AT&T phones, many of which are tether-capable, this question has come up again. AT&T uses a different technology for their 3G network, so the "Rev-A vs Rev-0" factor that makes picking a Sprint/Verizon phone for tethering so easy is not applicable.

AT&T refers to their mobile broadband network simply as "3G", but not all AT&T devices that are labeled "3G" are capable of the same speeds! Let's take a look at a few definitions of terms associated with AT&T 3G that will help us better understand why some devices will be better choices than others:
  • EDGE: This is AT&T's 2G network (like Verizon/Sprint's "National Access"). AT&T has very widespread EDGE coverage, nearly as good as their voice coverage, but it is NOT 3G - upload and download speeds on the EDGE network average about 50Kbps - 100Kbps, just slightly faster than a standard 56K dial-up connection. If your AT&T phone is ONLY capable of connecting to the EDGE network, your tethering connection will be very, very slow (even if you are in an area where AT&T does have true 3G coverage, your phone won't be able to connect to it).
  • HSPA: HSPA is the technology used by AT&T for their 3G network. HSPA users theoretically can see average download speeds of 700-1700kbps and 500-1200kbps upload.... but there are two distinct types of HSPA:
    • HSDPA: The "D" stands for "download" and indicates that high-speed DOWNLOADS are possible, but UPLOAD speeds will be more like what you'd see on EDGE - even in a 3G area. If your device is HSDPA, you will never be able to take advantage of high-speed uploads.
    • HSUPA: The "U" stands for "upload" and indicates that high-speed uploads are possible. The best AT&T 3G devices are HSDPA/HSUPA, meaning they are capable of high-speed downloads AND uploads.
Obviously, to take advantage of the highest possible speeds from AT&T, users will want an "HSDPA/HSUPA" device. Unfortunately, AT&T doesn't make it easy to find a device with these capabilities - just because the 3G logo appears with a device on AT&T's site doesn't mean all 3G devices are created equal, and AT&T doesn't consistently label which technology each phone or aircard uses! In order to determine what your phone or aircard is capable of, you may have to do some digging (the manufacturer's website is a good place to start).

So can an AT&T phone be as fast as an AT&T aircard? Unlike Sprint and Verizon, who both offer a variety of phones that are capable of offering the same performance as an aircard, AT&T does not currently offer ANY phones that use both HSDPA and HSUPA. They DO offer some phones that are HSDPA, meaning they are capable of high-speed downloads, but NONE of their current lineup of phones uses HSUPA. If you are in the market for a tether-capable AT&T phone, you'll want to make sure you select one that uses HSDPA (avoid the EDGE-only phones, unless dial-up speeds are good enough for you) - but do not expect it to offer identical performance as an HSDPA/HSUPA aircard like the USB Mercury.

Of course, before diving into an AT&T contract for data (either for an aircard or if you plan on tethering), make sure you check your coverage - remember that while AT&T has good nationwide voice and EDGE coverage, their 3G coverage is limited mainly to metropolitan areas.