Making Things Talk

262 MAKING THINGS TALK

Network Location and Physical Location

Locating things is one of the most common tasks people want to achieve with sensor

systems. Once you understand the wide range of things that sensors can detect, it’s

natural to get excited about the freedom this affords. All of a sudden, you don’t have to

be confined to a chair to interact with computers. You’re free to dance, run, jump — and

it’s still possible for a computer to read your action and respond in some way.

The downside of this freedom is the perception that in a

networked world, you can be located anywhere. Ubiqui-

tous surveillance cameras and systems like Wireless E911,

a system for locating mobile phones on a network, make

it seem as if anyone or anything can be located anywhere

and at any time, whether you want to be located or not.

The reality of location technologies lies somewhere in

between these extremes.

Locating things on a network is different than locating

things in physical space. As soon as a device is connected

to a network, you can get a general idea of its location

using a variety of means, from address lookup to

measuring its signal strength, but that doesn’t mean that

you know its physical location. You just know its relation-

ship to other nodes of the network. You might know that

a cell phone is closest to a given cell transmitter tower, or

that a computer is connected to a particular ...