Ricochet Modem

First a confession, I didn't have to buy a laptop computer to use the Ricochet modem radio. The reality is that these devices work quite nicely on desktop systems as well as on laptops.

I read of these modems in the local free computer newspaper, but since I was quite happy with my 56Kbps frame-relay connection, I didn't give them much consideration. Then one day my connection failed and I realized I had no backup for Internet access. After a quick trip to a local computer store and a few minutes configuring a PPP connect script, I was back in action. The frame relay was fixed shortly thereafter, but I still have my Ricochet modem. I use it when visiting client sites and when testing firewall configurations, and I used it on the one occasion when the frame went down again. I've also loaned it to friends suffering from phone noise and ISP mismanagement.

Plug it into your serial port. It has two connections: one for external power and one to connect to your computer. The computer sees it as a Hayes-compatible modem with a few additional AT (i.e., standard modem) commands.

I mentioned that I had to fiddle with the PPP connection scripts. As with most computer hardware, Metricom provides software for operation with the Apple and Microsoft operating systems. Since Linux comes with support for PPP dial up, there is no need to load their software. One has only to make some small but crucial changes to the scripts. The ppp-on-dialer script needs to send the strings:

ATZ
ATE0X4Q0V1&C1&D2&K3

to the modem to ensure that the configuration is correct. My ppp-on script needed the line:

route del default

First, the Ricochet is not a cell-phone modem. It is based on an infrastructure which is independent of the various telephone systems. Metricom has been in the wireless communication business since 1985—providing remote-access monitoring of meters to public utilities. The Ricochet division was started two years ago in order to offer wireless Internet connectivity to the public. They're currently offering service in the metropolitan areas of Seattle, San Francisco Bay, West Los Angeles and Washington, D.C. Metricom plans to extend coverage in the Los Angeles area by the end of this year and installation is underway in New York City.

If you pay attention, you'll see cell-phone antenna towers or roof-top clusters appearing everywhere. The Ricochet system is quite a bit harder to spot. There are three elements: the “modem radio” attached to your computer, a shoe box sized “microcell radio” attached to streetlamp poles at quarter mile intervals and “wired access points” to serve thirty or so microcell radios. (Seattle has 1800 microcell radios and 50 wired access points.) For instance, in this map of a Seattle neighborhood the small dots are the microcell radios, the red stars are wired access points, and the blue star is the home of Linux Journal. (The map is a product of a U.S. Census bureau server using the URL (without breaks) http://tiger.census.gov/cgi-bin/mapbrowser? lat=47.676&lon=-122.366&wid=0.10&ht=0.050& on=GRID&murl=http://www.aa.net/~bentson/tms& iwd=640&iht=720. (See Figure 1.)

Figure 1. Seattle Area Map

Just as the Internet uses a store-and-forward model to get data from one place to another, Ricochet packets are forwarded from pole to pole from the modem radio to the wired access point, at which point they enter the conventional Internet routing. Because this service is packet based, you don't consume resources when you're not sending or receiving bits. Therefore, you're welcome to establish a connection and leave it live for as long as you wish. This is a dramatic change from telephone-based Internet services.