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Table of Contents

Chapter One: An Introduction to RFID

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In Twelfth Night, Shakespeare wrote, "Some are born great, some achieve greatness, and some have greatness thrust upon them." RFID is one of the more recent four-letter abbreviations to have greatness thrust upon it in a flurry of industry mandates, governmental legislation, and hyperbole. RFID stands for Radio Frequency Identification, a term that describes any system of identification wherein an electronic device that uses radio frequency or magnetic field variations to communicate is attached to an item. The two most talked-about components of an RFID system are the tag, which is the identification device attached to the item we want to track, and the reader, which is a device that can recognize the presence of RFID tags and read the information stored on them. The reader can then inform another system about the presence of the tagged items. The system with which the reader communicates usually runs software that stands between readers and applications. This software is called RFID middleware . Figure 1-1 shows how the pieces fit together.

Much of the recent interest surrounding RFID has arisen from mandates and recommendations by government agencies such as the U.S. Department of Defense (DoD) and the Food and Drug Administration (FDA), and from a few private sector megacorporations. For instance, in an effort to improve efficiency, Wal-Mart called for its top 100 suppliers to begin providing RFID tags by early 2005 on pallets shipped to its stores. This mandate caused the companies in Wal-Mart's supply chain to focus on implementing RFID solutions. Companies worked to decide which tags and readers to use, how to attach tags to (or embed them in) containers or products, and how to test the read rates for RF tags on pallets as they moved through doors and onto trucks. Several companies have announced their support for what are now commonly known as tag and ship applications, which tag a product just before shipping it somewhere else, but few of these companies have moved beyond minimum compliance with the mandates to using the information on RFID tags to increase efficiency in their own internal processes.

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The Case for RFID

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RFID technologies offer practical benefits to almost anyone who needs to keep track of physical assets. Manufacturers improve supply-chain planning and execution by incorporating RFID technologies. Retailers use RFID to control theft, increase efficiency in their supply chains, and improve demand planning. Pharmaceutical manufacturers use RFID systems to combat the counterfeit drug trade and reduce errors in filling prescriptions. Machine shops track their tools with RFID to avoid misplacing tools and to track which tools touched a piece of work. RFID-enabled smart cards help control perimeter access to buildings. And in the last couple of years, owing in large part to Wal-Mart and DoD mandates, many major retail chains and consumer goods manufacturers have begun testing pallet- and case-level merchandise tagging to improve management of shipments to customers.

Part of what made the growth in RFID technologies possible were the reductions in cost and size of semiconductor components. Some of the earliest RFID tags were as big as microwave ovens, and the earliest readers were buildings with large antennas, as described in Chapter 3. Figure 1-2 shows a modern RFID tag (in the clear applicator) and a reader.

Figure 1-2: A tag and reader (image courtesy of Merten G. Pearson, D.V.M.)

Note how the bar code on the applicator matches the code read on the reader. The tag is inside the applicator in this picture and is about the size of a grain of rice. It's very similar to the glass capsule tag shown in Figure 1-3.

Figure 1-3: The VeriChip is smaller than a dime (image courtesy of Applied Digital)

Like RFID tags, the size of tag readers is shrinking. While most tag readers are still the size of a large book, smaller and less expensive readers may open up opportunities for many new RFID applications that, over the coming years, could become a normal and mostly unnoticed part of our lives. Figure 1-4 shows one of the smallest readers currently available.

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The Eras of RFID

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The progress of RFID adoption divides naturally into eras: the Proprietary era, the Compliance era, the RFID-Enabled Enterprise era , the RFID-Enabled Industries era, and the Internet of Things era. In Figure 1-5, you can see when some of the capabilities of RFID technology became, or will become, available.

In the beginning, during the Proprietary era, businesses and governmental entities created systems designed to track one particular type of item, and this tracking information typically remained within the same business or governmental entity. In the Compliance era (the present era), businesses implement RFID to meet mandates for interoperability with important customers or regulatory agencies but often don't use the RFID data themselves. The future will bring the era of the RFID-Enabled Enterprise, where organizations will use RFID information to improve their own processes. The era of RFID-Enabled Industries will see RFID information shared among partners over robust and secure networks according to well-established standards. The final RFID era that is currently foreseeable is the era of the Internet of Things. By this time, the ubiquity of RFID technology and other enabling technologies, combined with high standards and customer demand for unique products based on this infrastructure, will lead to a revolutionary change in the way we perceive the relationship between information and physical objects and locations. More and more, we will expect most objects in our daily lives to exist both in a particular place, with particular properties, and in the information spaces we inhabit. For instance, a park bench has a particular shape, color, and location, but with a tag, it can also have a list of notes left by people who have stopped there to rest. The list is just as real as the color of the paint, and just as much an attribute of the bench. This is now a green metal bench on the north end of Shaker Park with "a great view of the sunrise," according to "pigeon-guy."

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Application Types

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Certain broad types of RFID applications characterize whole approaches to this technology and are different enough in considerations and implementation to warrant a separate discussion. The tree in Figure 1-6 shows RFID's relationship to other identity systems, as well as the relationships between different types of RFID.

The term "autoid," short for automatic ID, describes any automated system for attaching an identity to an item. Real-Time Location Systems (RTLSs) are automated systems for tracking the location of an item. Notice that RFID is related only indirectly to RTLSs and that RFID is only one type of automated identity system. We will discuss RTLSs and how they can complement RFID in Chapter 11.

Obviously, we can't fit all of the possible uses of RFID into five simple categories, so we've left out a few applications. For example, while we don't directly discuss payment systems, pay-at-the-pump systems based on RFID raise some (but not all) of the same concerns as access control systems. Refer to the "Access Control" section for information on considerations and implementation; although payment systems don't always have issues with tailgating , both types of system must overcome counterfeiting and require strong audit procedures. We've also left out some unique applications, such as using RFID tags on compatible pieces of equipment to coordinate assembly of mobile structures in the field for military deployments and trade shows. However, these five categories are inclusive enough to provide at least some sense of the issues and considerations involved in typical RFID applications. The future will bring even more varied applications, but they will raise many of the same concerns as the applications in these categories.

Figure 1-6: Relationships among the various types of RFID applications

Access control applications are RFID systems used to selectively grant access to certain areas—for example, RFID tags attached to an automobile or held in a person's hand as a card, key chain, or wristband may allow access to a road, building, or secure area.

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Summary

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In this chapter, we discussed the following:

• RFID is a technology that allows a small radio device attached to an item to carry an identity for that item
• RFID has been around a while—long enough that we can divide its history into eras and begin to predict future trends.
• In the current era (Compliance), cheap semiconductors and fast Internet connections have encouraged retailers and governmental agencies to require suppliers to place RFID tags on shipping units such as pallets and cartons. However, most suppliers are just tagging pallets and shipping them without using the information internally, and even retailers are simply breaking down the pallets on receipt
• As the components get cheaper and the information infrastructure becomes more defined and robust, RFID will be used for an increasingly broad array of tasks.
• There are five main categories of RFID applications. Knowing the type of application in question can tell us quite a bit about special considerations and implementation.
• This is a volatile time for RFID, so we must take a disciplined approach to both acquiring knowledge about it and adopting the technology within our organizations. Keep an eye on key players and standards as we move through this era to see which way the technology will shift.

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Chapter Two: RFID Architecture

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For our purposes, an architecture may be defined as a decomposition of a particular computer system into individual components to show how the components work together to meet the requirements for the entire system. With this definition in mind, we can confidently say that there is no such thing as a single, universal RFID architecture that fits all requirements for all systems. Likewise, there is no set number of variations on a single theme. Because of a recent confluence of technologies, RFID systems now offer some key functionalities that have a distinct and predictable impact on the architectures of systems that use it. In this chapter, we describe the components that RFID adds to the architectures of these systems and how RFID affects systemic qualities (i.e., nonfunctional requirements of the system, such as performance, security, scalability, and manageability). From these observations we will derive some architectural guidelines for systems that incorporate RFID.

RFID may be seen as the next logical step in the progression of tracking systems and sensor networks because of technological advances in several fields. Let's look at some of the developments that have made RFID possible.

Every so often a new technology is introduced that seemingly promises to solve a myriad of problems. In 2001, one of the authors was invited to participate in a technology roundtable on web services hosted by the Chief Technology Officer (CTO) of a Fortune 500 company. Each of the panel members was asked to make an opening remark about the very much hyped web services technologies. One of the vendor participants began by declaring web services "revolutionary" and likening their effects on the IT ecosystem to those of a tsunami. The CTO immediately interrupted and stressed that he wanted to have a pragmatic discussion about web services and did not want anyone to indulge in hype. Declaring web services revolutionary would mean that all learning thus far, including sound software development and architectural principles, does not apply to them.

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A Confluence of Technologies

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RFID may be seen as the next logical step in the progression of tracking systems and sensor networks because of technological advances in several fields. Let's look at some of the developments that have made RFID possible.

Every so often a new technology is introduced that seemingly promises to solve a myriad of problems. In 2001, one of the authors was invited to participate in a technology roundtable on web services hosted by the Chief Technology Officer (CTO) of a Fortune 500 company. Each of the panel members was asked to make an opening remark about the very much hyped web services technologies. One of the vendor participants began by declaring web services "revolutionary" and likening their effects on the IT ecosystem to those of a tsunami. The CTO immediately interrupted and stressed that he wanted to have a pragmatic discussion about web services and did not want anyone to indulge in hype. Declaring web services revolutionary would mean that all learning thus far, including sound software development and architectural principles, does not apply to them.

We have found that, in the early adoption phases of emerging technologies, the amount of caution, past learning, and pragmatism applied to projects that make use of those technologies is inversely proportional to the amount of hype that surrounds them.

History teaches us that hype is generally more profitable for sellers than buyers. We have all seen our share of failed projects in which caution and past learning were abandoned in the name of a new wave. The CTO's comment in 2001 about web services rings very true today for RFID systems. Therefore, instead of indulging in hype and issuing heady promises, we'll take a look at how today's RFID technologies have evolved from the advances we have seen over the past five decades in device, platform, and software technologies.

Advances in semiconductor technologies

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Key Functionalities

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What does an RFID system look like? Because there are many possible uses for RFID systems, there will naturally be differences in their architectures. For instance, as described in Chapter 1, a typical tag and ship application implemented by a consumer packaged goods manufacturer would focus primarily on automating RFID tagging of products and ensuring that the tags can be read by the specified readers at higher than the minimum acceptable read accuracy. Generally speaking, these systems focus on the physical side of the implementation, and outside of generating fairly simple reports such as advanced shipment notifications (ASNs) , they tend to have minimal data management/exchange requirements. (The ASN is a manifest indicating what items the receiver of a shipment should expect and what the identities of those items will be.) On the other hand, a pharmaceutical company that wants to track the movement of drugs from manufacturing plants to distributors to retail pharmacies would want up-to-the-minute information, including details on where a particular product is at any point in the process, how and where it was manufactured, and where it has been. It is very likely that both the manufacturer and the retailers will also need some of this tracking information. Thus, such a system will require not only item-level tracking capabilities, but also some degree of business-to-business (B2B) information exchange.

Figure 2-3 lists the five eras of RFID described in Chapter 1 and shows the corresponding capabilities required of the RFID systems in each.

As you can imagine, RFID systems will continue to evolve to meet a wide spectrum of needs and thus will require various architectures. As we stated at the beginning of this chapter, it would be impossible to define a general-purpose RFID system architecture or implementation suitable for all the uses of RFID. However, certain capabilities are required of almost every RFID system. In this chapter, we'll focus on those broad underpinnings. Once we've covered the basics, we'll provide some guidelines for developing architectures that will help you get started.

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RFID System Components

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Figure 2-5 shows the primary components of an RFID system. We will explain each of these components in detail soon, but first let's look at the big picture, starting with the components typically present at the edges.

Figure 2-5 shows the typical components found in a retail store. In the bottom-left corner of the diagram, there is a set of RFID tags that represent the tagged merchandise. The store also has readers stationed within the shelves and at the checkout lanes. These readers may read tags hundreds or even thousands of times per minute, but most of these reads will not be interesting to our application. The readers must also be configured and managed and must know how to work together to cover blind spots should a reader fail. The box marked RFID middleware represents one or more software modules that handle these responsibilities. The box marked Edge applications represents any enterprise applications that have components running inside the store—for instance, POS system components. The box marked RFID information service represents a mechanism to store RFID events and related data at the edge. As you can see, we are showing similar RFID information service boxes in the enterprise's data center and in its business partners' data center. This is because RFID information is stored at various points in the infrastructure: at the edges, within the data center, and with business partners. We will provide more detail on what this information looks like later in this section. For an in-depth discussion of RFID information networks, see Chapter 8.

Figure 2-5: RFID system components

The two other components shown inside the enterprise data center in Figure 2-5 are the enterprise service bus and enterprise applications . The enterprise service bus is any mechanism that your company may have selected for application integration. Standards-based products that facilitate this are now available. Enterprise applications are any applications that are clients of, or are otherwise affected by, RFID data in your enterprise.

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Systemic Quality Considerations

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As we know, a system's requirements come in two flavors: functional and nonfunctional. The functional requirements define what the system does, while nonfunctional requirements involve systemic qualities such as privacy and security, performance, scalability, manageability, extensibility, and maintainability. RFID systems demand vastly increased data-processing capabilities at the edges of corporate environments. The volume of raw RFID data that is captured and available for filtering, coupled with the need to automatically monitor and manage RFID devices (such as antennas and readers), requires a level of sophistication that was generally absent from the bar code-type systems that RFID systems replace.

Some of the most important systemic qualities for RFID systems are covered in the following sections.

Privacy and security considerations are a core part of the design and architecture of any RFID solution. Ironically, even though RFID solutions are sometimes offered as enhancements to security, the technology itself presents certain vulnerabilities. As in any enterprise system, security considerations for an RFID system—ensuring the authenticity of the information stored on the tags themselves, securing the transmission of information between tags and readers, and ensuring overall application and infrastructure security—permeate the various layers of its architecture.

Physical security measures involve efforts to prevent both corruption of tag data and interception of communication between tags and readers. For instance, a malicious tag reader that is not part of an RFID system can attempt to read tags in its vicinity. Wireless security focuses on securing the communication pipe between readers and tags since this communication can be intercepted using wireless sniffing and spoofing devices. Any security-sensitive application must carefully weigh the risks of both interception or alteration of tag-to-reader and reader-to-tag communications.

Of course, security considerations vary depending on business needs. For example, using an RFID-enabled credit card to purchase goods can be done securely as long as the fulfillment systems on the backend are prepared to handle and detect fraudulent data (as credit card systems are), but a ticketing system that depends on the authenticity of every tag read might be more easily compromised.

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Architecture Guidelines

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The infrastructure for RFID edge components must be incredibly robust. Ideally, the readers, RFID middleware, and so on should support effortless plug-and-play functioning. In other words, they should be the edge equivalents of telephones in terms of ease of use, provisioning, monitoring, and management. A human operating a bar code scanner will be able to tell if the scanner goes down, but you'll need to employ automated means to monitor and manage RFID readers. Also, you'll want to shield your applications from the large number of readers deployed in a store or other location. To support all this, your edge architectures will need to be more flexible, scalable, robust, secure, and manageable than ever before.

As is always the case in a technology's early adoption phase, RFID standards and products are rapidly evolving. It is very likely that you will encounter a highly heterogeneous infrastructure, whereas types of RFID tags, readers, and other sensors will vary. Event managers based on standards such as ALE will have to coexist with other vendor-specific extensions to vertical applications such as point-of-sale and warehouse-management systems. When developing your RFID architecture roadmap, it is very important to take a close look at both your business and systemic quality requirements and how they might evolve over time. RFID systems are no different than any other distributed system in that you should plan for performance, scalability, security, manageability, maintainability, ease of use, and failover early on. The following section cover some important principles to consider when devising an RFID architecture roadmap for your company.

While researching this book, we approached many experts in RFID technologies and asked them what aspect was most overlooked when designing RFID systems. The almost unanimous response was business processes. In our experience as system architecture consultants, which has spanned several new waves of technologies, we have often seen people forget that technology's ultimate purpose is to solve business problems. This is the case even more so with promising new technologies, as the newness and buzz surrounding these technologies drive a bottom-up way of thinking. While you're defining the business requirements and capturing functional requirements, pay careful attention to accounting for exception processing. These are the "what if" situations, such as what to do if a reader goes down, or a tag falls off a package, or you are not able to read a particular tag. The exception scenarios should provide capabilities to use alternate means to accomplish the task. For example, if a read registers only 50 packages of a product when an operator visually determines that the number should be closer to 100, you could create alternate workflows to obtain the inventory count manually.

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System Management

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The level and scale of automation for some RFID systems poses significant challenges for system administrators and managers. As stated earlier, if a manual bar code scanner is down, a human operator will immediately pick up on it and call for service. The automated processing capabilities that RFID technologies offer make automated detection of system faults and stoppages indispensable. Similarly, we need to provide novel solutions for provisioning, monitoring, and managing our silently ticking antennas, readers, and other RFID infrastructure components.

Think ease of configuring, provisioning, managing, and monitoring when deciding on infrastructure components such as readers, sensors, event managers, servers, storage, and networks. Build redundancy into the architecture. Have a plan in place for what should happen when an antenna, a reader, or an event manager malfunctions. Consider using RFID middleware and other system management solutions to stay ahead of the difficulties that come with a fast-growing edge infrastructure.

Much of the time, enterprise architecture grows out of its selection of products. With minor exceptions, over time, a proprietary architecture that is locked into a particular product and vendor develops. Begin with well-defined interfaces between different layers, such as event managers, applications, and integration servers, and then choose products that fit your architecture. Later, this will pay in greater flexibility and independence.

As explained earlier in this chapter, you will find it necessary to use RFID middleware for all but trivial implementations. RFID middleware helps decouple your enterprise applications from the physical architecture of your RFID systems; those applications don't need to know about the reader vendors, their APIs, or the physical configuration of readers and antennas. In addition to this, RFID middleware provides the important function of filtering the highly fragmented data that comes from the readers. By cutting down the volume of data that passes over wide area networks, event filtering also allows you to define application-level events and pass more meaningful information to your enterprise applications.

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Summary

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RFID and other, similar technologies are pushing increasingly more network intelligence toward the network's edge, where RFID readers, temperature and light sensors, and smart middleware manage events without requiring guidance from massive, central servers. This movement toward edge computing is changing the way companies think about their data and computing resources. We shouldn't underestimate how disruptive this will be to the way we design, deploy, and manage our enterprise systems. In large part, how we design systems for RFID now will shape the way we deal with other edge devices for many years to come.

In this chapter, we covered the following important points about RFID:

• A confluence of factors has led us to the tipping point, where RFID seems primed for widespread adoption. Technological factors include advances in semiconductor technologies, the advent of intelligent devices, widely available broadband networks, and web services standards available under the umbrella of service-oriented architecture. Nontechnological factors include the interest of leading government agencies such as the FDA and the DoD, coupled with megacorporations such as Wal-Mart and Tesco, in RFID technology.
• When planning the architecture of an RFID system, the key processes include selecting an item numbering scheme, encoding RFID tags, attaching RFID tags to items you want to track, reading the RFID-tagged items as they move through the physical environment, integrating RFID information into enterprise applications and business processes, and, finally, sharing RFID information within and between companies.
• As with most enterprise systems, RFID systems are multi-layered. The physical layer components include RFID tags, antennas, readers, and sensors.
• RFID middleware provides many important services, including decoupling the physical layer components from the application layer components, managing and monitoring physical layer components, and filtering raw RFID observations and generating high-level events that are more meaningful to applications. The Application Level Events (ALE) standard is the EPCglobal standard that is gaining momentum for RFID middleware. There are already several vendor products available that implement ALE. (ALE is explained in detail in Chapter 7.)

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Chapter Three: Tags

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The purpose of an RFID tag is to physically attach data about an object (item) to that item. Each tag has some internal mechanism for storing data and a way of communicating that data. Figure 3-1 shows diagrams of several representative RFID tags .

Not every sort of RFID tag has a microchip or a built-in power source, but every RFID tag has a coil or antenna of some sort.

While it is important to realize what all tags have in common, classifying tags helps in understanding how they work. In this chapter, we will categorize RFID tags by those criteria most likely to affect the capabilities of the tag within our applications. We will divide tags based on their physical characteristics, their air interfaces (how they communicate with readers), and their information storage and processing capacity. With these criteria in mind, we will then explore some of the standards that define these variations and talk about guidelines for matching tags to applications. We'll start by looking at some basic tag capabilities before launching into the discussion of tag categories.

Many basic operations can be performed with an RFID tag, but only two of them are universal.

Figure 3-1: Typical RFID tags

Attaching the tag

Any RFID tag must be attachable to an item in some way.

Reading the tag

Any RFID tag must be able to communicate information over some radio frequency in some way.

Many tags also offer one or more of the following features and capabilities:

Kill/disable

Some tags allow a reader to command them to cease functioning permanently. After a tag receives the correct "kill code," it will never respond to a reader again.

Write once

Many tags are manufactured with their data permanently set at the factory, but a write-once tag may be set to a particular value by an end user one time. After that, the tag cannot be changed except, possibly, to be disabled.

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Basic Tag Capabilities

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Many basic operations can be performed with an RFID tag, but only two of them are universal.

Figure 3-1: Typical RFID tags

Attaching the tag

Any RFID tag must be attachable to an item in some way.

Reading the tag

Any RFID tag must be able to communicate information over some radio frequency in some way.

Many tags also offer one or more of the following features and capabilities:

Kill/disable

Some tags allow a reader to command them to cease functioning permanently. After a tag receives the correct "kill code," it will never respond to a reader again.

Write once

Many tags are manufactured with their data permanently set at the factory, but a write-once tag may be set to a particular value by an end user one time. After that, the tag cannot be changed except, possibly, to be disabled.

Write many

Some tags can be written and rewritten with new data over and over.

Anti-collision

When many tags are in close proximity, a reader may have difficulty telling where one tag's response ends and another's begins. Anti-collision tags know how to wait their turn when responding to a reader.

Security and encryption

Some tags are able to participate in encrypted communications, and some will respond only to readers that can provide a secret password.

Standards compliance

A tag may comply with one or more standards, enabling it to talk to readers that also comply with those standards; or, in the case of standards for physical characteristics, a tag may fit in a particular standard receptacle.

With these basics in mind, we can begin to explore the various categories of tags.

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Physical Characteristics

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Because RFID tags must physically attach data to items of different shapes and sizes in different environments, they come in a wide assortment of shapes and sizes. Furthermore, they may be housed in many different kinds of materials. Some of the physical characteristics of various tags include:

• PVC or plastic buttons and disks, usually including a central hole for fasteners. These tags are durable and reusable.
• RFID tags shaped like credit cards, which are called "contactless smart cards ."
• Tags made into the layers of paper in a label, called "smart labels ." These may be applied with automated applicators similar to those used for bar code labels.
• Small tags embedded in common objects such as clothing, watches, and bracelets. These small tags may also come in the form of keys and key chains.
• Tags in glass capsules, which can survive even in corrosive environments or in liquids.

Figure 3-2 shows just a few types of tag housings.

Figure 3-2: Tags come in many shapes and sizes (image courtesy of Texas Instruments)

Packaging may be the most obvious way to divide tags into categories, and this is the property of a tag that most directly affects how the tag can be attached to an item. We've already mentioned that buttons typically attach with a fastener through a central hole. Keys and key chains attach as you would expect, and smart labels attach with an adhesive backing. A plastic medicine bottle may contain a glass capsule in its lid or base, and smaller capsules can be injected for tracking pets and livestock.

Any new RFID application should be tested in candidate systems, with tags in the same packaging and attached in just the same way as they would be in the production system.

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Power Source

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A common way of categorizing tags is by their source of power. This is also one of the main determining factors for the cost and longevity of a tag. Passive tags obtain all of their energy by some method of transmission from the reader. Active tags use an on-board battery to power communications, a processor, memory, and possibly sensors. Traditionally, tags that use battery power for some functions but still allow the reader to power communications have been termed "active" as well, but for clarity, we will use the more recent terminology for them: semi-passive. One additional type of tag is not only capable of supplying power for itself but is also able to initiate communications with other tags of its own kind without the aid of a reader. These tags are called two-way tags.

As you might expect, having a battery on board makes for a more expensive chip, but semi-passive and active tags have several advantages over passive tags . In the case of semi-passive tags , the read range may be longer because the passive communications can use all of the power provided by the reader for communications rather than sharing some of the power with the chip. An active tag may have an extremely long read range and may perform some functions in the absence of a reader—for example, using battery power for environmental sensors. This capability can be very useful for tags that identify items such as perishable goods.

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Air Interface

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The air interface describes the way in which a tag communicates with a reader. By knowing a tag's air interface, we can determine the tag's read range and identify readers compatible with the tag. The following sections describe the attributes that comprise the definition of an air interface. The major attributes include the tag's power source, operating frequency, communication mode, keying, encoding, and coupling.

RFID has been in use longer than most people realize. It first appeared in the air war during WWII. British pilots noticed that sometimes, inexplicably, all of the German planes in sight would roll in unison. British intelligence later learned that German pilots were participating in a sort of manual RFID to help identify their planes to the newly invented German radar systems. By changing their radar images in response to a ground challenge, the pilots identified themselves as Luftwaffe.

The British later developed an automated system for their own aircraft that caused their planes to appear to pulse according to a preset rhythm when illuminated by the British "Chain Home" (CH) air defense radar. This new system was known as the MK I and was the predecessor of all Identify Friend or Foe (IFF) and aircraft transponder systems in use to this day.

Like RFID systems today, the most important components of the system were an interrogator and a transponder. In early IFF systems, the interrogator was the radar system itself and the transponder was an unwieldy box of tubes with dials and switches. The term "interrogator" gives us a clue as to how the system worked: the ground station sent out a radar signal, and the transponder receiving this signal reflected it back, causing the radar antenna to receive a stronger return than it otherwise would have. The transponder also "swept" the frequency of its return back and forth over a small range as it responded, causing the radar return to pulsate according to a specific rhythm.

The operating frequency is the electromagnetic frequency the tag uses to communicate or to obtain power. The electromagnetic spectrum in the range in which RFID typically operates is usually broken up into low frequency (LF) , high frequency (HF), ultra-high frequency (UHF), and microwave (see Table 3-1). Because RFID systems broadcast electromagnetic waves, they are regulated as radio devices. RFID systems must not interfere with other, protected applications, such as emergency service radios or television transmissions.

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Information Storage and Processing Capacity

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Information storage and processing capacity is the final major consideration when dividing tags into categories. RFID tags range widely in their capability to store information. The simplest tags store only 1 bit. Systems based on these tags, such as those commonly used in libraries and clothing stores for theft prevention, can only recognize the presence or absence of a tag; they cannot identify individual items. On the other hand, some tags may store kilobytes of data. Larger capacities usually require active tags, and even among passive tags, larger memory capacity directly increases the cost per tag.

Some of the latest active tags ordered by the U.S. Department of Defense will be able to store as much as 256 bytes of information. How much storage do you need for your application? To get an idea, let's look at some numbers:

• Number of people on Earth: 6.3 * 10^9
• Number of grains of sand on Earth's beaches: 7.5 * 10^17
• Number of photons in the visible universe: 1 * 10^88

This means we can count everyone in the world in 33 bits (2^33 = 8,589,934,592). We can count all of the grains of sand on the world's beaches (not counting deserts) in 60 bits, and we can count every photon in the observable universe in 293 bits (less than 37 bytes).

For less tangible things such as license keys or electronic message IDs, there may be some value in going to a larger number, but probably not. A 256-byte RFID tag must be storing much more than a number. Larger capacities allow tags to store location IDs for every place they have visited, or sensor readings that have either come from on-board sensors or been sent to the tag by a reader. Electronic signatures or encryption keys might take up more room and so make use of larger memory sizes. At some point, tags may carry entire user manuals and item-care instructions for automated handling systems. But for now, to uniquely identify tangible items, most applications will not need more than 96 bits.

This section examines storage and processing capacities for 1-bit EAS tags, surface acoustic wave (SAW) tags, and state machines and microprocessors.

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Standards

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Some RFID applications need to interoperate only with the procedures and systems of a single company. Others must share information with a global consortium of partners. No matter where in this spectrum an individual application falls, standards will affect the choice of tags for that application—if only because large manufacturing runs of tags fitting a particular standard may make those tags less expensive than equivalent proprietary tags, even though the latter may be more simply designed. Choosing a tag is, to a large extent, choosing the type of RFID system you intend to build, and tag standards often involve much more than the physical characteristics and air interface of a tag.

EPCglobal, Inc., a collaboration between GS1 and industry partners, defines a combined method of classifying tags that specifies frequencies, coupling methods, types of keying and modulation, information storage capacity, and modes of interoperability. As described in Chapter 2, EPC tags are intended to carry EPC numbers, which are assigned by the specific management entities who own the object classes involved. (We will talk in detail in Chapter 4 about encoding and decoding EPC numbers from tag bitstreams.)

The European Article Number and Uniform Code Council groups, formerly known as "EAN.UCC," chose the new name "GS1 " in 2005. "GS1" is not an abbreviation, but instead stands for "one global standard, one global system and one global organisation." We will use "EAN.UCC" and "GS1" interchangeably in this and other chapters, as some of the specifications predate the name change.

Table 3-3 shows the different classifications of tags recognized by ECPglobal. These classifications, which began with the Auto-ID Center, have mutated as actual standards developed and vendors made suggestions. For instance, Class 0+ is a slightly modified (but still compliant) implementation of the Class 0 standard offered by a particular manufacturer. Version 1.1 of the EPC Tag Data Standard defines the contents and encoding for all EPC data carriers (tags) regardless of their class, but the air interfaces (that is, the coupling, frequencies, and communications protocols) are, at the time of this writing, specified only for Class 0 and Class I tags .

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Summary

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If you have an understanding of the different types of tags, choosing a tag for a particular application becomes easier. Tags with durable physical characteristics are available for harsh environments, and paper tags are available for controlled environments where the application calls for rapid, automated tag application. The air interface determines which tags may communicate with which readers, and the type of coupling defined for that air interface determines how far away a reader can be and still read a tag. Tags come in a variety of data storage capacities, and some even have additional information processing capabilities, but these additional capabilities come at a cost. By studying the standards, we also now know what EPC and ISO tags are and why (for now) they may need different readers.

With these characteristics and capabilities in mind, we can talk about guidelines for selecting the best tag for your application. We've only covered the essentials in this chapter, and the actual process of selecting tags for a given application still usually requires extensive testing and the help of a skilled RF engineer. However, here are some general rules of thumb to help match tags to applications:

• Use smart labels for automated application in a warehouse, but use PVC or glass for tougher environments.
• Use passive tags for the lowest cost, and semi-passive or active tags only as necessary for additional capabilities or greater read range.
• Use LF/HF tags for individual items.
• Use UHF tags for shipping units such as pallets.
• Use microwave tags for vehicles and long-distance reads.
• Where possible, to reduce cost, store only an identifier on the tag and look up the rest of the information. More storage capacity is more expensive.
• Follow the standards where you can, and watch what the largest adopters are doing.
• As always, don't reinvent the wheel!

This has been a complex chapter because the tag options are so numerous. As the Compliance era matures, the options in RFID systems will stabilize to the point where we can choose from a limited number of options with confidence that the elements will match.

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Chapter Four: Tag Protocols

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In the previous chapter, we discussed the "air interface ," the bedrock of tag communications, and the circuit designer's view of tag and reader interaction. In this chapter, we'll examine the protocols readers and tags use to exchange messages over that air interface as well as take a more detailed look into the information stored on tags.

The Jargon File, a dictionary of technical jargon, defines a protocol as:

A set of formal rules describing how to transmit data, especially across a network. Low level protocols define the electrical and physical standards to be observed, bit- and byte-ordering, and the transmission and error detection and correction of the bit stream. High level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages, etc.

By this definition, the air interfaces described in Chapter 3 would be low-level protocols, while the protocols described here are the high-level protocols that define the actual syntax of messages and the structure of the dialog between a reader and a tag. The first part of this chapter covers some important terms and concepts for understanding tag protocols and explains more about the relationship between bar code standards and tag encodings, which should be helpful for developers building EPC applications. (These same encodings appear again in the APIs in Chapters 6 and 7.) We then discuss various types of singulation and anti-collision procedures in depth to illustrate how a reader can recognize a tag across a crowded room. The chapter closes with sections on tag features for security and privacy and some tips on troubleshooting tag communications.

The singulation protocols may seem esoteric at first, but they have been the focus of heated debate during recent months and are in many ways responsible (for better or worse) for critical decisions on the timing of technology purchases and for adoption of RFID technologies across many industries. In particular, the publication of the Gen2 specification in early 2005, was one of the most anticipated events in RFID in early 2005.

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Protocol Terms and Concepts

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Technical jargon develops around any new technology, and RFID is no exception. Some of these terms are quite useful, serving as a convenient way to communicate concepts needed to describe other concepts that will appear in the pages that follow. These terms include:

Singulation

This term describes a procedure for reducing a group of things to a stream of things that can be handled one at a time. For example, a subway turnstile is a device for singulating a group of people into a stream of individuals so that the system may count them or ask them for access tokens. This same singulation is necessary when communicating with RFID tags, because if there is no mechanism to enable the tags to reply separately, many tags will respond to a reader at once and may disrupt communications. Singulation also implies that the reader learns the individual IDs of each tag, thus enabling inventories. Inventories of groups of tags are just singulation that is repeated until no unknown tags respond.

Anti-collision

This term describes the set of procedures that prevent tags from interrupting each other and talking out of turn. Whereas singulation is about identifying individual tags, anti-collision is about both regulating the timing of responses and finding ways of randomizing those responses so that a reader can understand each tag amidst the plethora of responses.

Identity

As we discussed in Chapter 1, an identity is a name, number, or address that uniquely refers to a thing or place. "Malaclypse the Elder" is an identity referring to a particular person. "221b Baker Street London NW1 6XE, Great Britain" is an identity referring to a particular place, just as "urn:epc:id:sgtin:00012345.054322.4208" is an identity referring to a particular widget.

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How Tags Store Data

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The high-level tag communications protocols know about the ID types that can be stored on a tag and so know, at a general level, how data is stored on the tag. However, since a reader only communicates with a tag via the air protocol, the actual physical layout of memory on a tag is left to the tag manufacturer. A discussion of the physical layout is beyond the scope of this book, but the logical or apparent layout of tag memory is specified in the EPC Class 0 and Class I (Generation 1) standards. Figure 4-1 shows that layout.

Figure 4-1: Tag data layout

The CRC is a checksum (described in more detail in the sidebar "CCITT-CRC"), the EPC is the ID on the tag, and the password is the "kill code" to disable the tag. Note that for a tag to be EPC-compliant under Class 0 and Class I Generation 1 standards, it must never transmit the password under any circumstances—not even in response to proprietary diagnostic commands used only by the manufacturer.

This password is the same password described previously as a means of disabling (destroying) tags. (Under Gen2, this changed; we will describe Gen2 in more detail in the "EPC UHF Class I Gen2" section of this chapter.)

Version 1.1, Revision 1.26 of the EPC Tag Data Standards describes EPC as a "meta-coding scheme " because it allows existing identifiers to be encoded as EPC identifiers, as well as allowing for the creation of completely new identifiers. This standard defines one encoding for General Identifiers (GIDs), which is intended for creating new identification schemes, and five specific encodings—called System Identifiers —for particular uses. The System Identifiers are based on existing GS1 (EAN.UCC) identifiers.

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Singulation and Anti-Collision Procedures

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Our next topic concerns the way a reader and a tag use the air interface. There are many different ways for readers and tags to communicate, but the different methods can all be broadly categorized as Tag Talks First (TTF) or Reader Talks First (RTF). Logically, it would seem simplest for a tag arriving on the scene to announce its presence to all concerned. In practice, however, this is difficult unless tags are able to negotiate among themselves which tag will speak first. Some high-end active tags use TTF communications protocols, but the new crop of inexpensive smart labels and other passive tags exclusively use RTF protocols. In this section, we'll examine the most common of these protocols for RFID—Slotted Aloha, Adaptive Binary Tree, Slotted Terminal Adaptive Collection, and the new EPC Gen2 specification. In the later section "Tag Features for Security and Privacy," we'll look at how features of these protocols can affect security and data integrity in an application.

Slotted Aloha is derived from a procedure known simply as "Aloha," which was originally developed in the 1970s by Norman Abramson of Aloha Networks in Hawaii for packet radio communication. Aloha was the inspiration for the Ethernet protocol, and a variation of this procedure is still used for satellite communication as well as for ISO 18000-6 Type B and EPC Gen2 RFID tags.

Aloha itself is as simple as an anti-collision procedure may reasonably be and doesn't really include the concept of singulation in the usual sense. With this procedure, tags begin broadcasting their IDs as soon as the reader's field energizes them. Each tag sends its entire ID and then waits for a pseudorandom period of time before broadcasting again. The reader simply receives the IDs, depending on chance to ensure that each tag will eventually broadcast during a period when all other tags are quiet. The reader doesn't respond to the tags in any way. The advantages of this procedure are speed and simplicity. Tag logic is minimal, and with such a low protocol overhead, this is the top performer for read rate where only a few tags are present.

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Tag Features for Security and Privacy

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There are justifiable privacy and security concerns with any sort of identification technology, and RFID, as much as biometrics, has raised popular concern because of its possible impact on personal privacy. A common concern is that an unauthorized person will be able to obtain information from, or possibly even change information stored on, an RFID tag. There is some legitimacy to these concerns. A tag that does not use a secure protocol might be read by anyone, just as a bar code or printed label might be read by anyone. A writable tag might also be maliciously altered if it does not implement a secure protocol for communication with a reader. This alteration might be less obvious than someone placing a false bar code or printed tag on a piece of merchandise. Unlike printed tags and bar codes, which will always remain at risk, future secure protocols will make RFID tags very difficult to forge or even read without authorization. The more secure the tag, however, the more expensive it is, and an unencrypted, read-only tag is no more risky in the right application than a bar code is now. For these reasons, many supply chain applications currently use less-secure RFID implementations. As overall RFID prices drop due both to wider adoption and standardization, the cost of more secure will also drop, and these in turn will become more widely adopted. Chapter 10 covers security and privacy for the entire RFID system, but because some of the implementation details of RFID security are specifically concerned with the tag protocols, we'll take a closer look at tag destruction and data encryption here.

A key concern of privacy advocates is the longevity of an identification mechanism such as RFID. Few privacy concerns arise from tracking pallets in a warehouse, or even from tracking individual items from the warehouse to the shelf. The point when an end user or customer first touches an item is the point where most privacy concerns arise. Within the store, expectations of privacy are tempered somewhat by the current precedent of surveillance from cameras and electronic anti-theft devices. But when RFID tags may still be attached and even active when a product leaves the store, there is a real possibility that tracking may continue outside the store, and this raises many concerns.

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Learn to Troubleshoot Tag Communications

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Troubleshooting tag and reader communications is the sort of subject that could (and probably someday will) fill up an entire book, but a few general techniques can solve the most common problems. Not many of us have spectrum analyzers, but RF questions can usually be approached indirectly. First, think of ways to halve the problem. In the usual case, where one reader fails to talk to one tag, we can halve the problem by asking, "Is it the reader or the tag?" Try another tag with the reader. If the new tag works, you have a faulty tag. If the new tag doesn't work, you have a faulty reader (or two faulty tags; in this case, it's best to try a few more tags just to be sure). The reader uses one or more antennas to talk to the tags. Can you swap antennas with another reader that works?

Be careful! Only swap antennas from identical readers and consult the reader manual first for more precautions.

Chances are that instead of being broken, the reader is simply misconfigured. Most readers these days support multiple tag types. Is the reader configured to speak to an ISO 18000-6 Type A tag only? If so, an EPC tag won't work (this week). Is it configured (or built) for HF or UHF? What about the tag? Was it tuned to work on a metal can or a rubber tire? Try it on the appropriate item.

A simple trick for testing packaging is to place a tag—one that you know to work—in different locations on the packaging of an item already in the field of a reader that provides a visible read light. Move the tag around and watch the read light come on and go off. In this way, one can develop a very good idea of the RF profile of an item and its packaging in just a few minutes. To "hide" a tag, place your body between the tag and the reader. Squishy humans are great RF shields.

In a story (possibly apocryphal) often told around the RFID camp, two technicians testing a reader and tag combination found that they could read the tag at a great distance in some cases but only at a short distance in others. To demonstrate, one technician would hold a portable reader near an item bearing the tag and then slowly step back. At roughly a half a meter, the tag would cease to register. This seemed to be the "dead zone." Another technician would then hold the end of a tape measure and the technician with the reader would step back to nearly 10 meters away. All the way from the outside of the dead zone to this limit, the reading was strong. An observer then pointed out that the metal tape measure might make an excellent antenna...

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Summary

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Understanding tag protocols, including singulation and encodings for identities, prepares the way for our discussion of readers in the next two chapters, as well as for understanding the reader protocols and RFID middleware discussed in Chapters 6 and 7. While these tag protocols have been the area most affected by what David P. Meany of Cisco Systems called the "tornado of obsolescence" that surrounds RFID technology, the much-anticipated Gen2 specifications from EPC have removed some of the uncertainty. Anyone working with RFID should keep up with at least the high points of the ongoing debate over adoption of this protocol, as well as some of the intellectual property issues currently in the news. The organizations and publications listed in Appendix B are a good place to start.

In this chapter we learned:

• That a protocol is a set of formal rules describing how to transmit data
• The meaning of the terms singulation, anti-collision, and identity
• How to encode identities for storage on an EPC RFID tag
• About singulation and anti-collision protocols, including Slotted Aloha, Adaptive Binary Tree, STAC, and the EPC Gen2 protocol
• About some of the features available in the tag protocols to increase security and privacy through encryption and careful planning
• A few tips on troubleshooting reader/tag communications

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Chapter Five: Readers and Printers

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