Sprint Mobile Broadband (EV-DO)

I finally decided to get a cellular data service, Sprint Mobile Broadband (EVDO). Short summary: I’ve only tried using it at my office so far, but the performance is great. I’m getting over 500 Kbps downstream, with round-trip ping times of less than 100 ms. The latency is low enough that interactive sessions like SSH and NX work fine. I hope it performs this well in the other locations in which I want to use it, particularly in the Denver metro area.

When I vacation in Denver, I stay at a friend’s house. It’s very generous of him to put me up, and I’m not at all inclined to complain, but the one thing that could be better is that he doesn’t have a broadband internet connection. He uses a 56K modem, though he does have his Windows machine set up with “Internet Connection Sharing”, so I can take advantage of the dialup link.

I offered to pay for a DSL line for him, but he’s happy with his ISP and doesn’t want to mess with it. I’ll readily agree that “if it ain’t broke, don’t fix it.”

Back when the Metricom Ricochet service was a going concern, I tried that, but it usually didn’t work very well in the places I needed it. Although Ricochet service is available in Denver (from Terabeam), it isn’t available anywhere else I go. And the performance isn’t really any better than a 56K modem anyhow.

On the other hand, “broadband wireless” is now available from cellular carriers. Verizon and Sprint offer EV-DO, and Cingular offers HSDPA, with T-Mobile to follow. I currently use Cingular for my cellular telephone service, but after comparing the service offerings in terms of price, coverage areas, and terms of service, I decided to sign up for the Sprint EV-DO service.

A friend who has done some work in the cellular industry warned me not to get my hopes up about the performance, but as I stated earlier, for my single sample point it works great. I think that may be because Sprint has deployed “Rev A” service here, which is supposed to offer much better latency than the original “Rev 0″ service. It’s necessary to have a “Rev A” compatible modem to take advantage of that.

I chose the Novatel U720 modem, which has a USB interface, rather than the S720 PCMCIA card. My laptop has an ExpressCard slot rather than PCMCIA, so the latter wouldn’t help me. I also want to use the modem with a Shuttle small form factor PC as a router, and USB was more suited for that.

I installed the supplied Windows software to get the service going. It went fairly smoothly. The “Sprint PCS Connection Manager” software downloaded a software update, installed a new PRL in the modem, and updated the modem’s firmware. It worked fine with Windows, but what I really needed was for it to work with Linux.

I’m running Fedora Core 6. I had to manually issue a modprobe command for the usbserial driver, because the driver does not yet know that it should claim vendor 0×1410 product 0×2110. The command is

/sbin/modprobe usbserial vendor=0×1410 product=0×2110

Once that was done, the modem appeared as /dev/ttyUSB0 and /dev/ttyUSB1. I think the latter is a management and diagnostic interface; the former is used for the PPP connection. I’ll submit a patch for usbserial so that future releases will work automatically.
I used the Fedora network administration tool to configure a PPP interface on ttyUSB0. It did not work the first time I tried it, so I had to screw around with it a bit. Eventually I manually changed the “serial” bit rate in the configuration files from 430800 bps to 961600 bps, and it started working. I’m not sure if that was the real problem. The Fedora network administration tool does not offer 961600 as a choice, so I will file a bug report.

Now I can start the ppp connection with the command

/sbin/ifup sprint

Sometimes the first attempt gives an error message “RTNETLINK answers: No such process”. I’m not sure what that’s all about, but giving the command a second time usually seems to work OK.