Sidebar: Item-Level Identification Technologies
There are many technologies for identifying individual items. The most basic identification consists of a unique number or code associated with metadata about an object. This is how serial numbers on computers and cars work. More interesting effects appear when devices can read identifying codes without human intervention. Here is a sample of such machine-readable identification technologies.
• Barcodes. These are most commonly seen representing the UPC on most retail packaging. They are used to uniquely identify items in corporate inventory systems and in certain niche markets, such as wine storage.
• 2D barcodes. These come in many styles, from the Datamatrix code found on postal service package labels, to exotic fiducial markers used in motion sensing applications. QR Code markers (Figure 6-3), designed for easy reading using mobile device cameras, are increasingly popular.
Figure 6-3 QR Code that reads "Ubiquitous Computing User Experience Design" when decoded.
• Radio frequency IDs (RFIDs). These (Figure 6-4) come in many shapes and sizes — from subway access cards, to paper and metal stickers, to ceramic cylinders that sit in the stomachs of cows. Small radios inside them broadcast a unique identifying number. Because radio waves can transmit through solid materials, RFIDs can be embedded inside other objects (shipping palettes, clothing tags, and animals).
Figure 6-4 An RFID attached to a wine bottle. (Photo © 2007 by Tod E. Kurt, with permission)
Passive RFIDs, the most common kind, gather energy from radio broadcasts received from RFID readers and reflect that energy back to the readers in the form of a wireless stream of data communicating their unique identifier. They do not need their own source of power to function, but consequently work only within relatively short distances. Active RFIDs use their own power sources to transmit data farther, but are more expensive and often require batteries.
• Smart cards. SIM cards are small processors packaged inside plastic cards (Figure 6-5). They transmit a unique identifier when in direct contact with a reader. Because they contain an active processor (typically powered through contact with a reader), they are capable of more complex interaction. Thus, they can encrypt information, require authentication before transmitting their identifier, poll sensors, etc. Smart "buttons" that resemble coin cell batteries are a similar technology. These buttons also communicate through contact with a reader that also acts as a power source.
Figure 6-5 A standard telephone SIM card that uniquely identifies a subscriber to a phone network. (Author photo)
• Magnetic stripes are familiar from credit cards and hotel entry cards. They are an established technology, and are easily created or changed, but are neither as compact, convenient, or secure as some of the others on this list.
• IPv6. For devices that are actively communicating through a network, IPv6 is an extension to the familiar Internet Protocol standard designed to uniquely identify trillions of devices. It was formally defined in the mid-1990s, and while uncommon in current Internet devices, it will likely become an identification standard for smart devices communicating over a network.
It is important to remember that unique identification and machine-readability are different functions enabled by separate technical choices. The methods previously listed frequently combine the two, but readability and identification do not depend on each other. A single identification code can be either machine-readable or -unreadable and remain unique. An IPv6 address written on a Post-It and stuck to the side of a machine is still unique, but not easily machine-readable. Similarly, it is technically possible for multiple RFIDs to transmit the same identification code.