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Diagnostics in the Time of Disconnectedness: The MicroCell, Under a Microscope

Summer is one of the few times that I'm off the road, which of course means that it's time for ... network upgrades! (What, had you guessed something else?) So one of my recent projects has been to solve my, "No cell signal at my house" problem by installing one of AT&T's MicroCells. How'd it go? In short, remember last month when I bemoaned the lack of built-in troubleshooting tools and the uselessness of vendor tech support in streaming video devices like the Roku and the Sony Bravia TVs? Well, believe it or not, AT&T topped them with the MicroCell. When you can get it working, however, it's quite useful, so let me pass along what I found, and how to work around its installation problems.

In case you haven't heard of them, MicroCells are AT&T's implementation of a "femtocell"—a device offered by wireless providers wanting to provide wider coverage area and/or greater bandwidth to customers. In my case, I wanted iPhone coverage at my house in rural Virginia, a part of the country which has never felt the touch of a single AT&T microwave. To get signal in my house, I was told, I merely needed to buy a MicroCell ($159 with tax), plug it into my Internet connection (AT&T says the MicroCell needs a minimum of 1.5 mbps upstream, 256 kbps downstream), and in no time my cell phone would be reporting five bars, even out in the hinterland.

The MicroCell comes with a small pamphlet explaining how to set it up. You get online, punch its serial number into AT&T's site, tell AT&T your physical location (so emergency services get the right address if anyone dials 911 from a cell phone connected to the MicroCell), hook the MicroCell up to your Internet connection, and plug it in. It sports five lights, four of which need to be lit and steady (that is, not blinking) in order for the thing to be working. (The superfluous fifth indicates that a PC's directly connected to the MicroCell.) The first two indicate that the MicroCell has power and an IP address.

The MicroCell must also be close enough to a window (AT&T recommends four feet, I found that eight worked fine) to acquire a GPS signal. If having the MicroCell near a window isn't practical, the unit has an unexplained socket labeled "antenna" that turns out to work fine with an external GPS antennafind one by Googling "mcx connector" and "garmin," which led me to several remote GPS antenna/extension cable products for sale. The unit uses the GPS to check that you are indeed at the address that you told AT&T when you registered the MicroCell online. (Isn't it sad how high-tech companies don't trust their customers? Microsoft makes us register our copies of Windows and AT&T thinks we'll lie about our locations. I mean, what's next, Google snooping on our wireless access points or something?)

Where I got into trouble was the fourth LED—the one that that AT&T tech support folks called the "3G light." It comes on once AT&T's communications protocols sync up. Mine didn't, even after the 90 minutes that AT&T requires that we wait before giving up. Now, telling me to expect that it might take an Internet-based protocol 90 minutes to establish a handshake made me assume that they'd spent way too much time reading RFC 1149 (look it up, it's fun), but I waited, and after 90 joyless minutes I unplugged the errant MicroCell, plugged it back in and waited another 90 minutes before calling AT&T's tech support. (AT&T won't talk to you until you've done that.) I'll spare you the details, but basically for the next two weeks I'd call AT&T's MicroCell tech support, have someone tell me to unplug the thing and plug it back in, and I'd say okay, but why not just tell me exactly what the thing needs in terms of TCP and UDP ports so I can just dig in and figure it out myself? (Everyone I talked to said that they didn't know and couldn't find out.)

I finally got the answer: just Google "MicroCell Troubleshooting Guide - SMT-i8100," and work your way in a few pages to the "Advanced" troubleshooting section to find the port and connectivity requirements. In short, the router that connects your Internet router must not block fragmented packets (many to head off some old exploits involving fragmented packets), must be configured to enable IPSec pass-through (it's a checkbox on most small router's Web UIs), and—at least according to AT&T—its MTU size must be set to 1492 bytes in length. (At least, that's what the AT&T manual says; I think they mean that it must have at least an MTU of 1492, as mine runs at 1500 without trouble.)

I finally got things worked out and the MicroCell now lets me use the iPhone in the house, but it'd have been nicer if I could have gotten that network configuration information earlier or, better, if AT&T would either scrap the four idiot lights in favor of a web interface, or add more idiot lights—one for MTU, another for IPSec pass-through, and so on.

Unfortunately AT&T didn't do that, and instead opted for what most folks do nowadays when building an attach-to-the-Internet doodad: they left out any valuable troubleshooting assistance, and probably did it in the name of saving money. But over the course of two weeks, I must have had AT&T people on the phone for at least two hours a day, and it's easy to do the math. The bottom line is, to quote an old Fram oil filter ad, "you can pay me now... or you can pay me later." A cautionary tale for makers of all Internet-attached appliances, wouldn't you say?

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