Working of Domain Name Servers

If you've ever used the Internet, it's a good bet that you've used the Domain Name System, or DNS, even without realizing it. DNS is a protocol within the set of standards for how computers exchange data on the Internet and on many private networks, known as the TCP/IP protocol suite. Its basic job is to turn a user-friendly domain name like "how-does-things-work.blogspot.com" into an Internet Protocol (IP) address like 70.42.251.42 that computers use to identify each other on the network. It's like your computer's GPS for the Internet.
Computers and other network devices on the Internet use an IP address to route your request to the site you're trying to reach. This is similar to dialing a phone number to connect to the person you're trying to call. Thanks to DNS, though, you don't have to keep your own address book of IP addresses. Instead, you just connect through a domain name server, also called a DNS server or name server, which manages a massive database that maps domain names to IP addresses.
Whether you're accessing a Web site or sending e-mail, your computer uses a DNS server to look up the domain name you're trying to access. The proper term for this process is DNS name resolution, and you would say that the DNS server resolves the domain name to the IP address. For example, when you enter "http://www.how-does-things-work.blogspot.com" in your browser, part of the network connection includes resolving the domain name "how-does-things-work.blogspot.com" into an IP address, like 70.42.251.42, for HowStuffWorks' Web servers.
You can always bypass a DNS lookup by entering 70.42.251.42 directly in your browser (give it a try). However, you're probably more likely to remember "how-does-things-work.blogspot.com" when you want to return later. In addition, a Web site's IP address can change over time, and some sites associate multiple IP addresses with a single domain name.
Without DNS servers, the Internet would shut down very quickly. But how does your computer know what DNS server to use? Typically, when you connect to your home network, Internet service provider (ISP) or WiFi network, the modem or router that assigns your computer's network address also sends some important network configuration information to your computer or mobile device. That configuration includes one or more DNS servers that the device should use when translating DNS names to IP address.
So far, you've read about some important DNS basics. The rest of this article dives deeper into domain name servers and name resolution. It even includes an introduction to managing your own DNS server. Let's start by looking at how IP addresses are structured and how that's important to the name resolution process.

Finding Your IP Address

The following are tips on how to find your computer's IP address. Note that the address will change periodically unless you've chosen to use a static IP (rare for end-users):

• Windows -- Though you can click through the user interface to find your network interface settings, one quick way to find your IP address is to open the Command Prompt application from Accessories and enter this command: ipconfig
• Mac -- Open your System Preferences, click Network, be sure your current network connection (with the green dot beside it) is selected, click Advanced, and click the TCP/IP tab.
• Linux or UNIX -- If don't already have a command prompt, open a terminal application, such as XTERM or iTerm. At the command prompt, enter this command: ifconfig
• Smartphones using WiFi -- Look at your phone's network settings. This will vary depending on the phone the version of its operating system.

Note that if you're on a home or small local network, your address will probably be in the form 192.168.x.x, 172.16.x.x or 10.x.x.x (where x is a number between 0 and 255). These are reserved addresses used on each local network, and a router on that network then connects you to the Internet.

DNS Servers and IP Addresses

You just learned that the primary job of a domain name server, or DNS server, is to resolve (translate) a domain name into an IP address. That sounds like a simple task, and it would be, except for the following points:

• There are billions of IP addresses currently in use, and most machines have a human-readable name as well.
• DNS servers (cumulatively) are processing billions of requests across the Internet at any given time.
• Millions of people are adding and changing domain names and IP addresses each day.

With so much to handle, DNS servers rely on network efficiency and Internet protocols. Part of the IP's effectiveness is that each machine on a network has a unique IP address in both the IPV4 and IPV6 standards managed by the Internet Assigned Numbers Authority (IANA). Here are some ways to recognize an IP address:

• An IP address in the IPV4 standard has four numbers separated by three decimals, as in: 70.74.251.42
• An IP address in the IPV6 standard has eight hexadecimal numbers (base-16) separated by colons, as in 2001:0cb8:85a3:0000:0000:8a2e:0370:7334. Because IPV6 is still a very new standard, we'll concentrate on the more common IPV4 for this article.
• Each number in an IPV4 number is called an "octet" because it's a base-10 equivalent of an 8-digit base-2 (binary) number used in routing network traffic. For example, the octet written as 42 stands for 00101010. Each digit in the binary number is the placeholder for a certain power of two from 2⁰ to 2⁷, reading from right to left. That means that in 00101010, you have one each of 2¹, 2³ and 2⁵. So, to get the base-10 equivalent, just add 2¹ + 2³ + 2⁵ = 2 + 8 + 32 = 42.
• There are only 256 possibilities for the value of each octect: the numbers 0 through 255.
• Certain addresses and ranges are designated by the IANA as reserved IP addresses, which means they have a specific job in IP. For example, the IP address 127.0.0.1 is reserved to identify the computer you're currently using. So, talking to 127.0.0.1 is just talking to yourself!

Where does your computer's IP address come from? If we're talking about your desktop or laptop computer, it probably comes from a Dynamic Host Configuration Protocol (DHCP) server on your network. The job of a DHCP server is to make sure your computer has the IP address and other network configuration it needs whenever you're online. Because this is "dynamic," the IP address for your computer will probably change from time to time, such as when you shut down your computer for a few days. As the user, you'll probably never notice all this taking place. See the sidebar on this page for hints on where to find the IP address assigned to your computer or mobile device.
Web servers and other computers that need a consistent point of contact use static IP addresses. This means that the same IP address is always assigned to that system's network interface when it's online. To make sure that interface always gets the same IP address, IP associates the address with the Media Access Control (MAC) address for that network interface. Every network interface, both wired and wireless, has a unique MAC address embedded in it by the manufacturer.
For more information on IP addresses, see the IANA, operated by the Internet Corporation for Assigned Names and Numbers (ICANN). Now, though, let's look at the other side of the DNS equation: domain names.

Domain Names

If we had to remember the IP addresses of all our favorite Web sites, we'd probably go nuts! Human beings are just not that good at remembering strings of numbers. We are good at remembering words, however, and that is where domain names come in. You probably have hundreds of domain names stored in your head, such as:

• howstuffworks.com -- our favorite domain name
• google.com -- one of the most used domain names in the world
• mit.edu -- a popular EDU name
• bbc.co.uk -- a three-part domain name using the country code UK

You'll recognize domain names as having strings of characters separated by dots (periods). The last word in a domain name represents a top-level domain. These top-level domains are controlled by the IANA in what's called the Root Zone Database, which we'll examine more closely later. The following are some common top-level domains:

• COM -- commercial Web sites, though open to everyone
• NET -- network Web sites, though open to everyone
• ORG -- non-profit organization Web sites, though open to everyone
• EDU -- restricted to schools and educational organizations
• MIL -- restricted to the U.S. military
• GOV -- restricted to the U.S. government
• US, UK, RU and other two-letter country codes -- each is assigned to a domain name authority in the respective country

In a domain name, each word and dot combination you add before a top-level domain indicates a level in the domain structure. Each level refers to a server or a group of servers that manage that domain level. For example, "how does things work  " in our domain name is a second-level domain off the COM top-level domain. An organization may have a hierarchy of sub-domains further organizing its Internet presence, like "bbc.co.uk" which is the BBC's domain under CO, an additional level created by the domain name authority responsible for the UK country code.
The left-most word in the domain name, such as www or mail, is a host name. It specifies the name of a specific machine (with a specific IP address) in a domain, typically dedicated to a specific purpose. A given domain can potentially contain millions of host names as long as they're all unique to that domain.
Because all of the names in a given domain need to be unique, there has to be some way to control the list and makes sure no duplicates arise. That's where registrars come in. A registrar is an authority that can assign domain names directly under one or more top-level domains and register them with InterNIC, a service of ICANN, which enforces uniqueness of domain names across the Internet. Each domain registration becomes part of a central domain registration database known as the whois database. Network Solutions, Inc. (NSI) was one of the first registrars, and today companies like GoDaddy.com offer domain registration in addition to many other Web site and domain management services. [source: InterNIC]
Later, when we look at how to create a domain name, we'll see that part of registering a domain requires identifying one or more name servers (DNS servers) that have the authority to resolve the host names and sub-domains in that domain. Typically, you would do this through a hosting service, which has its own DNS servers. Next, we'll look at how these DNS servers manage your domain, and how DNS servers across the Internet work together to ensure traffic is routed properly between IP addresses.

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The Distributed System

Every domain has a domain name server handling its requests, and there is a person or IT team maintaining the records in that DNS server's database. No other database on the planet gets as many requests as DNS servers, and they handle all those queries while also processing data updates from millions of people every day. That's one of the most amazing parts of DNS -- it is completely distributed throughout the world on millions of machines, managed by millions of people, and yet it behaves like a single, integrated database!

Because managing DNS seems like such a big job, most people tend to leave it to the IT professionals. However, by learning a little bit about how DNS works and how DNS servers are distributed across the Internet, you can manage DNS with confidence. The first thing to know is what the purpose of a DNS server is on the network where it resides. A DNS server will have one of the following as its primary task:

• Maintain a small database of domain names and IP addresses most often used on its own network, and delegate name resolution for all other names to other DNS servers on the Internet.
• Pair IP addresses with all hosts and sub-domains for which that DNS server has authority.

DNS servers that perform the first task are normally managed by your Internet service provider (ISP). As mentioned earlier, the ISP's DNS server is part of the network configuration you get from DHCP as soon as you go online. These servers reside in your ISP's data centers, and they handle requests as follows:

• If it has the domain name and IP address in its database, it resolves the name itself.
• If it doesn't have the domain name and IP address in its database, it contacts another DNS server on the Internet. It may have to do this multiple times.
• If it has to contact another DNS server, it caches the lookup results for a limited time so it can quickly resolve subsequent requests to the same domain name.
• If it has no luck finding the domain name after a reasonable search, it returns an error indicating that the name is invalid or doesn't exist.

The second category of DNS servers mentioned above is typically associated with Web, mail and other Internet domain hosting services. Though some hardcore IT gurus set up and manage their own DNS servers, hosting services have made DNS management much easier for the less technical audience. A DNS server that manages a specific domain is called the start of authority (SOA) for that domain. Over time, the results from looking up hosts at the SOA will propagate to other DNS servers, which in turn propagate to other DNS servers, and so on across the Internet.
This propagation is a result of each DNS server caching the lookup result for a limited time, known as its Time To Live (TTL), ranging from a few minutes to a few days. People managing a DNS server can configure its TTL, so TTL values will vary across the Internet. So, each time you look up "www.how-does-things-work.blogspot.com," it's possible that the DNS server for your ISP will find the lookup results "70.42.251.42" in its own cache if you or someone else using that server looked for it before within the server's TTL.
This great web of DNS servers includes the root name servers, which start at the top of the domain hierarchy for a given top-level domain. There are hundreds of root name servers to choose from for each top-level domain. Though DNS lookups don't have to start at a root name server, they can contact a root name server as a last resort to help track down the SOA for a domain.
Now that you know how DNS servers are interconnected to improve the name resolution process, let's look at how you can configure a DNS server to be the authority for your domain.

Creating a New Domain Name

When you want to create a new domain name, you need to do the following:

• Use the Whois database to find a unique domain name that isn't yet registered. There are several sites that offer free Whois database searches, such as Network Solutions. If the search comes up empty, you know the domain name is available.
• Register the domain name with a registrar. There are a lot of registrars to choose from, and some offer special prices for registering the COM, NET, and ORG versions of a domain at the same time, for registering for two or more years, or for hosting the domain with the same company.
• If you're hosting the domain at a different company than your registrar, configure the registrar to point your domain name to the correct host name or IP address for your hosting company (see information below about A records).

Using the DNS servers from your registrar or hosting company means that you have a parked domain. This means that someone else owns the computer hardware for the DNS servers, and your domain is just part of that company's larger DNS configuration. Alternatively, if you're passionate about hosting your own DNS, you can set up your own server, either as a physical or virtual machine. Whichever DNS setup you decide on, that DNS server (or group of servers) becomes the SOA for your domain, as described earlier.
Whether your SOA is somewhere else or on your own system, you can extend and modify your DNS settings to add sub-domains, redirect e-mail and control other services. This information is kept in a zone file on the DNS server [source: GoDaddy.com]. If you're running your own server, you'll probably need to manually edit the zone file in a text editor. Many registrars today have a Web interface you can use to manage DNS for your domain. Each new configuration you add is called a record, and the following are the most common types of records you can configure for your DNS server:

• Host (A) -- This is the basic mapping of IP address to host name, the essential component for any domain name.
• Canonical Name (CNAME) -- This is an alias for your domain. Anyone accessing that alias will be automatically directed to the server indicated in the A record.
• Mail Exchanger (MX) -- This maps e-mail traffic to a specific server. It could indicate another host name or an IP address. For example, people who use Google for the e-mail for their domain will create an MX record that points to ghs.google.com.
• Name Server (NS) -- This contains the name server information for the zone. If you configure this, your server will let other DNS servers know that yours is the ultimate authority (SOA) for your domain when caching lookup information on your domain from other DNS servers around the world.
• Start of Authority (SOA) -- This is one larger record at the beginning of every zone file with the primary name server for the zone and some other information. If your registrar or hosting company is running your DNS server, you won't need to manage this. If you're managing your own DNS, Microsoft's support information has a helpful article on the structure of a DNS SOA Record.

The following is an example of what a zone file might look like for those who are editing it directly in a text editor. Note that the center column (second item on each line) includes a record type from those listed above. When you see an "@" in the left column, it means that the record applies in all cases not otherwise specified:
@ NS auth-ns1.how-does-things-work.blogspot.com
@ NS auth-ns2.how-does-things-work.blogspot.com
@ MX 10 mail
mail A 209.170.137.42
vip1 A 216.183.103.150
www CNAME vip1
Typical users will probably get the most use out of MX and CNAME records. The MX records allows you to point your mail services somewhere other than your hosting company if you choose to use something like Google Apps for your domain. The CNAME records let you point host names for your domain to various other locations. This could include setting google.example.com to redirect to google.com, or setting up a dedicated game server with its own IP address and pointing it to something like gameserver.example.com. HowStuffWorks' parent company, Discovery, does this: dsc.discovery.com is the main Web site, science.discovery.com is The Science Channel Web site, and so on.

Working of Night Vision Technology

How Night Vision Works

Gyro-stabilized day/night binoculars manufactured by B.E. Meyers Company.

­ The first thing you probably think of when you see the words night vision is a spy or action movie you've seen, in which someone straps on a pair of night-vision goggles to find someone else in a dark building on a moonless night. And you may have wondered "Do those things really work? Can you actually see in the dark?"


The answer is most definitely yes. With the proper night-vision equipment, you can see a person standing over 200 yards (183 m) away on a moonless, cloudy night! Night vision can work in two very different ways, depending on the technology used.

• Image enhancement - This works by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.
• Thermal imaging - This technology operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.

Here, you will learn about the two major night-vision technologies. We'll also discuss the various types of night-vision equipment and applications. But first, let's talk about infrared light.

Infrared Light

In order to understand night vision, it is important to understand something about light. The amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible light spectrum is the infrared spectrum.

Infrared light is a small part of the light spectrum.

Infrared light can be split into three categories:

• Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengths that range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of a meter.
• Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1.3 to 3 microns. Both near-IR and mid-IR are used by a variety of electronic devices, including remote controls.
• Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3 microns to over 30 microns.

The key difference between thermal-IR and the other two is that thermal-IR is emitted by an object instead of reflected off it. Infrared light is emitted by an object because of what is happening at the atomic level.
Atoms
Atoms are constantly in motion. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around. Solids are actually in motion! Atoms can be in different states of excitation. In other words, they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and move to an excited level. The level of excitation depends on the amount of energy applied to the atom via heat, light or electricity.
An atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. Think of the electrons in this cloud as circling the nucleus in many different orbits. Although more modern views of the atom do not depict discrete orbits for the electrons, it can be useful to think of these orbits as the different energy levels of the atom. In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower energy orbitals would transition to higher energy orbitals, moving farther from the nucleus.

An atom has a nucleus and an electron cloud.

Once an electron moves to a higher-energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon -- a particle of light. You see atoms releasing energy as photons all the time. For example, when the heating element in a toaster turns bright red, the red color is caused by atoms excited by heat, releasing red photons. An excited electron has more energy than a relaxed electron, and just as the electron absorbed some amount of energy to reach this excited level, it can release this energy to return to the ground state. This emitted energy is in the form of photons (light energy). The photon emitted has a very specific wavelength (color) that depends on the state of the electron's energy when the photon is released.
Anything that is alive uses energy, and so do many inanimate items such as engines and rockets. Energy consumption generates heat. In turn, heat causes the atoms in an object to fire off photons in the thermal-infrared spectrum. The hotter the object, the shorter the wavelength of the infrared photon it releases. An object that is very hot will even begin to emit photons in the visible spectrum, glowing red and then moving up through orange, yellow, blue and eventually white. Be sure to read How Light Bulbs Work, How Lasers Work and How Light Works for more detailed information on light and photon emission.
In night vision, thermal imaging takes advantage of this infrared emission. Next, we'll see just how it does this.

Thermal Imaging

Here's how thermal imaging works:

1. A special lens focuses the infrared light emitted by all of the objects in view.
2. The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the thermogram. This information is obtained from several thousand points in the field of view of the detector array.
3. The thermogram created by the detector elements is translated into electric impulses.
4. The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.
5. The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.

The basic components of a thermal-imaging system

Types of Thermal Imaging Devices
Most thermal-imaging devices scan at a rate of 30 times per second. They can sense temperatures ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C), and can normally detect changes in temperature of about 0.4 F (0.2 C).

It is quite easy to see everything during the day...

...but at night, you can see very little.

Thermal imaging lets you see again.

There are two common types of thermal-imaging devices:

• Un-cooled - This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the battery built right in.
• Cryogenically cooled - More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 32 F (zero C). The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can "see" a difference as small as 0.2 F (0.1 C) from more than 1,000 ft (300 m) away, which is enough to tell if a person is holding a gun at that distance!

While thermal imaging is great for detecting people or working in near-absolute darkness, most night-vision equipment uses image-enhancement technology.

Image Enhancement

Image-enhancement technology is what most people think of when you talk about night vision. In fact, image-enhancement systems are normally called night-vision devices (NVDs). NVDs rely on a special tube, called an image-intensifier tube, to collect and amplify infrared and visible light.

The image-intensifier tube changes photons to electrons and back again.

Here's how image enhancement works:

1. A conventional lens, called the objective lens, captures ambient light and some near-infrared light.
2. The gathered light is sent to the image-intensifier tube. In most NVDs, the power supply for the image-intensifier tube receives power from two N-Cell or two "AA" batteries. The tube outputs a high voltage, about 5,000 volts, to the image-tube components.
3. The image-intensifier tube has a photocathode, which is used to convert the photons of light energy into electrons.
4. As the electrons pass through the tube, similar electrons are released from atoms in the tube, multiplying the original number of electrons by a factor of thousands through the use of a microchannel plate (MCP) in the tube. An MCP is a tiny glass disc that has millions of microscopic holes (microchannels) in it, made using fiber-optic technology. The MCP is contained in a vacuum and has metal electrodes on either side of the disc. Each channel is about 45 times longer than it is wide, and it works as an electron multiplier. When the electrons from the photo cathode hit the first electrode of the MCP, they are accelerated into the glass microchannels by the 5,000-V bursts being sent between the electrode pair. As electrons pass through the microchannels, they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. Basically, the original electrons collide with the side of the channel, exciting atoms and causing other electrons to be released. These new electrons also collide with other atoms, creating a chain reaction that results in thousands of electrons leaving the channel where only a few entered. An interesting fact is that the microchannels in the MCP are created at a slight angle (about a 5-degree to 8-degree bias) to encourage electron collisions and reduce both ion and direct-light feedback from the phosphors on the output side.
   
   
   
   
   

   Night-vision images are known for their eerie green tint.

5. At the end of the image-intensifier tube, the electrons hit a screen coated with phosphors. These electrons maintain their position in relation to the channel they passed through, which provides a perfect image since the electrons stay in the same alignment as the original photons. The energy of the electrons causes the phosphors to reach an excited state and release photons. These phosphors create the green image on the screen that has come to characterize night vision.
6. The green phosphor image is viewed through another lens, called the ocular lens, which allows you to magnify and focus the image. The NVD may be connected to an electronic display, such as a monitor, or the image may be viewed directly through the ocular lens.

Working of RFID

How RFID Works

An RFID tag.

Long checkout lines at the grocery store are one of the biggest complaints about the shopping experience. Soon, these lines could disappear when the ubiquitous Universal Product Code (UPC) bar code is replaced by smart labels, also called radio frequency identification (RFID) tags. RFID tags are intelligent bar codes that can talk to a networked system to track every product that you put in your shopping cart.
Imagine going to the grocery store, filling up your cart and walking right out the door. No longer will you have to wait as someone rings up each item in your cart one at a time. Instead, these RFID tags will communicate with an electronic reader that will detect every item in the cart and ring each up almost instantly. The reader will be connected to a large network that will send information on your products to the retailer and product manufacturers. Your bank will then be notified and the amount of the bill will be deducted from your account. No lines, no waiting.

RFID tags, a technology once limited to tracking cattle, are tracking consumer products worldwide. Many manufacturers use the tags to track the location of each product they make from the time it's made until it's pulled off the shelf and tossed in a shopping cart.
Outside the realm of retail merchandise, RFID tags are tracking vehicles, airline passengers, Alzheimer's patients and pets. Soon, they may even track your preference for chunky or creamy peanut butter. Some critics say RFID technology is becoming too much a part of our lives -- that is, if we're even aware of all the parts of our lives that it affects.
In this article, you'll learn about the types of RFID tags and how these tags can be tracked through the entire supply chain. We'll also look at the non-commercial uses of RFID tags and how the Departments of State and Homeland Security are using them. Lastly, we'll examine what some critics consider an Orwellian application of RFID tags in animals, humans and our society.

Reinventing the Bar Code

Barcodes, like this one found on a soda can, are found on almost everything we buy.

­Almost everything that you buy from retailers has a UPC bar code printed on it. These bar codes help manufacturers and retailers keep track of inventory. They also give valuable ­information about the quantity of products being bought and, to some extent, by whom the products are being bought. These codes serve as product fingerprints made of machine-readable parallel bars that store binary code.
Created in the early 1970s to speed up the check out process, bar codes have a few disadvantages:

• In order to keep up with inventories, companies must scan each bar code on every box of a particular product.
• Going through the checkout line involves the same process of scanning each bar code on each item.
• Bar code is a read-only technology, meaning that it cannot send out any information.

RFID tags are an improvement over bar codes because the tags have read and write capabilities. Data stored on RFID tags can be changed, updated and locked. Some stores that have begun using RFID tags have found that the technology offers a better way to track merchandise for stocking and marketing purposes. Through RFID tags, stores can see how quickly the products leave the shelves and who's buying them.

In addition to retail merchandise, RFID tags have also been added to transportation devices like highway toll passcards and subway passes. Because of their ability to store data so efficiently, RFID tags can tabulate the cost of tolls and fares and deduct the cost electronically from the amount of money that the user places on the card. Rather than waiting to pay a toll at a tollbooth or shelling out coins at a token counter, passengers use RFID chip-embedded passes like debit cards.

But would you entrust your medical history to an RFID tag? How about your home address or your baby's safety? Let's look at two types of RFID tags and how they store and transmit data before we move past grocery store purchase­s to human lives.
­

Bar Code HistoryAt 8:01 a.m. on June 26, 1974, a customer at Marsh's supermarket in Troy, OH, made the first purchase of a product with a barcode, a 10-pack of Wrigley's Juicy Fruit Gum. This began a new era in retail that sped up checkout lines and gave companies a more efficient method for inventory control. That pack of gum took its place in American history and is currently on display at the Smithsonian Institution's National Museum of American History. That historical purchase was the culmination of nearly 30 years of research and development. The first system for automatic product coding was patented by Bernard Silver and Norman Woodland, both graduate students at the Drexel Institute of Technology (now Drexel University). They used a pattern of ink that glowed under ultraviolet light. This system was too expensive and the ink wasn't very stable. The system we use today was unveiled by IBM in 1973 and uses readers designed by NCR.

 

Working of GPS Receivers

A GPS receiver uses satellites to pinpoint locations.

How GPS Receivers Work

Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.
Things are much, much easier today. For less than $100, you can get a pocket-sized gadget that will tell you exactly where you are on Earth at any moment. As long as you have a GPS receiver and a clear view of the sky, you'll never be lost again.
In this article, we'll find out how these handy guides pull off this amazing trick. As we'll see, the Global Positioning System is vast, expensive and involves a lot of technical ingenuity, but the fundamental concepts at work are quite simple and intuitive.
­When people talk about "a GPS," they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites(24 in operation and three extras in case one fails). The U.S. military developed and implemented this satellite network as a military navigation system, but soon opened it up to everybody else.
Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky.
A GPS receiver's job is to locate four or more of these satellites, figure out the distanc­e to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration. Trilateration in three-dimensional space can be a little tricky, so we'll start with an explanation of simple two-dimensional trilateration.

2-D Trilateration

Imagine you are somewhere in the United States and you are TOTALLY lost -- for whatever reason, you have absolutely no clue where you are. You find a friendly local and ask, "Where am I?" He says, "You are 625 miles from Boise, Idaho."
This is a nice, hard fact, but it is not particularly useful by itself. You could be anywhere on a circle around Boise that has a radius of 625 miles, like this:

You ask somebody else where you are, and she says, "You are 690 miles from Minneapolis, Minnesota." Now you're getting somewhere. If you combine this information with the Boise information, you have two circles that intersect. You now know that you must be at one of these two intersection points, if you are 625 miles from Boise and 690 miles from Minneapolis.

If a third person tells you that you are 615 miles from Tucson, Arizona, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points. You now know exactly where you are -- Denver, Colorado.

This same concept works in three-dimensional space, as well, but you're dealing with spheres instead of circles. Next, we'll look at this type of trilateration.

Working of Location Tracing Mechanism

How Location Tracking Works

These days, even traffic lights are keeping an eye on you.

As children playing hide and seek, there seemed to be so many places where we could hide and never be found. With the world bec­oming ever smaller through technology, hiding is increasingly difficult. Cameras peer down on us at red lights, in our workplace, in stores and even at home. Now, those cameras are being augmented by new technologies that track our cars, cell phones and possibly any product we buy.
This location-tracking technology also is being used to streamline supply chains for corporations, seeking to move products to the market faster, and to monitor assets and prevent inventory loss.
­Soon, companies also will be able to track your location. Imagine walking through your local supermarkets, and as you pass through the aisle, an electronic coupon for your favorite cereal is beamed to your phone.
However, many privacy advocates are worried about the implications of these new surveillan­ce systems. Such technology means that marketers and others could know your whereabouts at any time.

Tracking Technology

­ Location tracking is not one, single technology. Rather, it is the convergence of several technologies that can be merged to create systems that track inventory, livestock or ­vehicle fleets. Similar systems can be created to deliver location-based services to wireless devices.
Current technologies being used to create location-tracking and location-based systems include:

• Geographic Information Systems (GIS) - For large-scale location-tracking systems, it is necessary to capture and store geographic information. Geographic information systems can capture, store, analyze and report geographic information.
• Global Positioning System (GPS) - A constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). A GPS receiver, like the one in your mobile phone, can locate four or more of these satellites, figure out the distance to each, and deduce your location through trilateration. For trilateration to work, it must have a clear line of sight to these four or more satellites. GPS is ideal for outdoor positioning, such as surveying, farming, transportation or military use (for which it was originally designed). See How GPS Receivers Work for more information.
  
  
  

  Artist's concept of the GPS satellite constellation ­

• Radio Frequency Identification (RFID) - Small, battery-less microchips that can be attached to consumer goods, cattle, vehicles and other objects to track their movements. RFID tags are passive and only transmit data if prompted by a reader. The reader transmits radio waves that activate the RFID tag. The tag then transmits information via a pre-determined radio frequency. This information is captured and transmitted to a central database. Among possible uses for RFID tags are a replacement for traditional UPC bar codes. See How RFIDs Work for more information.
• Wireless Local Area Network (WLAN) - Network of devices that connect via radio frequency, such as 802.11b. These devices pass data over radio waves and provide users with a network with a range of 70 to 300 feet (21.3 to 91.4 meters).

­ Any location tracking or location-based service system will use one or a combination of these technologies. The system requires that a node or tag be placed on the object, animal or person being tracked. For example, the GPS receiver in a cell phone or an RFID tag on a DVD can be used to track those devices with a detection system such as GPS satellites or RFID receivers.
Next , we'll take a look at how location tracking can be used to streamline supply chains and track fleets of trucks, ships and planes.

Types of Tracking

­Companies are finding location-tracking technologies ideal for better managing inventories or fleets of vehicles. Knowing the exact location of each piece of inventory helps to control the supply chain and saves money by not losing those assets that are in transit. Companies, such as retailers, must consider how to track inventory across a wide area, either country or state, and in a smaller area, such as the warehouse or store.
Wide-Area Tracking
On a large scale, companies must track their vehicle fleets across the country or the world. GPS is the ideal tracking technology for tracking over large areas. To do this, every vehicle needs to be equipped with a GPS receiver. As the vehicle crosses the country, the GPS satellites track the truck's position. With GPS, the operator can request positioning at anytime. However, GPS is limited in smaller areas or indoors.
Local-Area and Indoor Tracking
A good example of where GPS would not be suitable for tracking items is in a warehouse or hospitals. The accuracy provided by GPS is not sufficient for such a small scale. Consider all of the medical equipment, wheelchairs, gurneys and even patients that need to be tracked. GPS is not a practical or cost-effective solution.


­For smaller areas, companies and healthcare organizations would likely use a network of RFID tags and readers to monitor the location of assets or inventory. A wireless LAN also would be more suitable. In such a system, each asset would be tagged with an RFID tag, and readers would be placed in strategic locations to be able to accurately read those tags within a matter of inches. A hospital worker would be able to find the exact room a wheelchair is located and retailers would be able to locate an item on any given shelf.
Another example of how this technology is already being deployed is in tracking children in some amusement parks. A child can wear a wristband with an embedded RFID tag. Park staff can track that tag through location receivers positioned around the park. One system in use at Legoland in Denmark even allows for the tag identification number to be registered with the parents' mobile phone.
Location tracking isn't limited to just allowing an organization to know where its assets are, these technologies also will help retailers and marketers find you to better target their key markets.

Working of Facial Recognition Systems

How Facial Recognition Systems Work

Anyone who has seen the TV show "Las Vegas" has seen facial recognition software in action. In any given episode, the security department at the fictional Montecito Hotel and Casino uses its video surveillance system to pull an image of a card counter, thief or blacklisted individual. It then runs that image through the database to find a match and identify the person. By the end of the hour, all bad guys are escorted from the casino or thrown in jail. But what looks so easy on TV doesn't always translate as well in the real world.

In 2001, the Tampa Police Department installed police cameras equipped with facial recognition technology in their Ybor City nightlife district in an attempt to cut down on crime in the area. The system failed to do the job, and it was scrapped in 2003 due to ineffectiveness. People in the area were seen wearing masks and making obscene gestures, prohibiting the cameras from getting a clear enough shot to identify anyone.
Boston's Logan Airport also ran two separate tests of facial recognition systems at its security checkpoints using volunteers. Over a three month period, the results were disappointing. According to the Electronic Privacy Information Center, the system only had a 61.4 percent accuracy rate, leading airport officials to pursue other security options.
Humans have always had the innate ability to recognize and distinguish between faces, yet computers only recently have shown the same ability. In the mid 1960s, scientists began work on using the computer to recognize human faces. Since then, facial recognition software has come a long way.
In this article, we will look at the history of facial recognition systems, the changes that are being made to enhance their capabilities and how governments and private companies use (or plan to use) them.

Facial Recognition Technology

FaceIt software compares the faceprint with other images in the database.

­Identix®, a company based in Minnesota, is one of many developers of facial recognition technology. Its software, FaceIt®, can pick someone's face out of a crowd, extract the face from the rest of the scene and compare it to a database of stored images. In order for this software to work, it has to know how to differentiate between a basic face and the rest of the background. Facial recognition software is based on the ability to recognize a face and then measure the various features of the face.
Every face has numerous, distinguishable landmarks, the different peaks and valleys that make up facial features. FaceIt defines these landmarks as nodal points. Each human face has approximately 80 nodal points. Some of these measured by the software are:

• Distance between the eyes
• Width of the nose
• Depth of the eye sockets
• The shape of the cheekbones
• The length of the jaw line

These nodal points are measured creating a numerical code, called a faceprint, representing the face in the database.In the past, facial recognition software has relied on a 2D image to compare or identify another 2D image from the database. To be effective and accurate, the image captured needed to be of a face that was looking almost directly at the camera, with little variance of light or facial expression from the image in the database. This created quite a problem.
In most instances the images were not taken in a controlled environment. Even the smallest changes in light or orientation could reduce the effectiveness of the system, so they couldn't be matched to any face in the database, leading to a high rate of failure.

Working of Fingerprint Scanners

How Fingerprint Scanners Work

A computer mouse with a built-in fingerprint scanner

Computerized fingerprint scanners have been a mainstay of spy thrillers for decades, but up until recently, they were pretty exotic technology in the real world. In the past few years, however, scanners have started popping up all over the place -- in police stations, high-security buildings and even on PC keyboards. You can pick up a personal USB fingerprint scanner for less than $100, and just like that, your computer's guarded by high-tech biometrics. Instead of, or in addition to, a password, you need your distinctive print to gain access. In this article, we'll examine the secrets behind this exciting development in law enforcement and identity security. We'll also see how fingerprint scanner security systems stack up to conventional password and identity card systems, and find out how they can fail.

 

Fingerprint Basics

Fingerprints are one of those bizarre twists of nature. Human beings happen to have built-in, easily accessible identity cards. You have a unique design, which represents you alone, literally at your fingertips. How did this happen? People have tiny ridges of skin on their fingers because this particular adaptation was extremely advantageous to the ancestors of the human species. The pattern of ridges and "valleys" on fingers make it easier for the hands to grip things, in the same way a rubber tread pattern helps a tire grip the road.

The other function of fingerprints is a total coincidence. Like everything in the human body, these ridges form through a combination of genetic and environmental factors. The genetic code in DNA gives general orders on the way skin should form in a developing fetus, but the specific way it forms is a result of random events. The exact position of the fetus in the womb at a particular moment and the exact composition and density of surrounding amniotic fluid decides how every individual ridge will form.
So, in addition to the countless things that go into deciding your genetic make-up in the first place, there are innumerable environmental factors influencing the formation of the fingers. Just like the weather conditions that form clouds or the coastline of a beach, the entire development process is so chaotic that, in the entire course of human history, there is virtually no chance of the same exact pattern forming twice.
Consequently, fingerprints are a unique marker for a person, even an identical twin. And while two prints may look basically the same at a glance, a trained investigator or an advanced piece of software can pick out clear, defined differences.
This is the basic idea of fingerprint analysis, in both crime investigation and security. A fingerprint scanner's job is to take the place of a human analyst by collecting a print sample and comparing it to other samples on record. Next , we'll find out how scanners do this.

Working of CAPTCHA

How CAPTCHA Works

 

You're using your computer to purchase tickets to see They Might Be Giants play a concert at a local venue. Before you can buy the tickets, you first have to pass a test. It's not a hard test -- in fact, that's the point. For you, the test should be simple and straightforward. But for a computer, the test should be almost impossible to solve.
This sort of test is a CAPTCHA, an acronym that stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart. They're also known as a type of Human Interaction Proof (HIP). You've probably seen CAPTCHA tests on lots of Web sites. The most common form of CAPTCHA is an image of several distorted letters. It's your job to type the correct series of letters into a form. If your letters match the ones in the distorted image, you pass the test.

Google's Gmail service requires new users to enter a CAPTCHA before creating an account.

Why would anyone need to create a test that can tell humans and computers apart? It's because of people trying to game the system -- they want to exploit weaknesses in the computers running the site. While these individuals probably make up a minority of all the people on the Internet, their actions can affect millions of users and Web sites. For example, a free e-mail service might find itself bombarded by account requests from an automated program. That automated program could be part of a larger attempt to send out spam mail to millions of people. The CAPTCHA test helps identify which users are real human beings and which ones are computer programs.

Greetings, Program! One of the ironies of the CAPTCHA program is that a CAPTCHA application can generate a test that even it can't solve without already knowing the answer.

­One interesting thing about CAPTCHA tests is that the people who design the tests aren't always upset when their tests fail. That's because for a CAPTCHA test to fail, someone has to find a way to teach a computer how to solve the test. In other words, every CAPTCHA failure is really an advance in artificial intelligence.
Let's take a closer look at exactly what a CAPTCHA .­

CAPTCHAs and the Turing Test

CAPTCHA technology has its foundation in an experiment called the Turing Test. Alan Turing, sometimes called the father of modern computing, proposed the test as a way to examine whether or not machines can think -- or appear to think -- like humans. The classic test is a game of imitation. In this game, an interrogator asks two participants a series of questions. One of the participants is a machine and the other is a human. The interrogator can't see or hear the participants and has no way of knowing which is which. If the interrogator is unable to figure out which participant is a machine based on the responses, the machine passes the Turing Test.
Of course, with a CAPTCHA, the goal is to create a test that humans can pass easily but machines can't. It's also important that the CAPTCHA application is able to present different CAPTCHAs to different users. If a visual CAPTCHA presented a static image that was the same for every user, it wouldn't take long before a spammer spotted the form, deciphered the letters, and programmed an application to type in the correct answer automatically.

Not all CAPTCHAs require you to type in text. This version asks users to use a mouse to trace certain shapes found in photographs.

Most, but not all, CAPTCHAs rely on a visual test. Computers lack the sophistication that human beings have when it comes to processing visual data. We can look at an image and pick out patterns more easily than a computer. The human mind sometimes perceives patterns even when none exist, a quirk we call pareidolia. Ever see a shape in the clouds or a face on the moon? That's your brain trying to associate random information into patterns and shapes.

I'm Sorry, I'll Read That Again

Now and then, a CAPTCHA presents an image or sound that's so distorted, even humans can't decipher it. That's why many CAPTCHA applications provide users with an option to generate a new CAPTCHA and try again. Hopefully the second time around won't be as confusing as the first.

But not all CAPTCHAs rely on visual patterns. In fact, it's important to have an alternative to a visual CAPTCHA. Otherwise, the Web site administrator runs the risk of disenfranchising any Web user who has a visual impairment. One alternative to a visual test is an audible one. An audio CAPTCHA usually presents the user with a series of spoken letters or numbers. It's not unusual for the program to distort the speaker's voice, and it's also common for the program to include background noise in the recording. This helps thwart voice recognition programs.
Another option is to create a CAPTCHA that asks the reader to interpret a short passage of text. A contextual CAPTCHA quizzes the reader and tests comprehension skills. While computer programs can pick out key words in text passages, they aren't very good at understanding what those words actually mean.

Next , we'll take a closer look at the kinds of sites that use CAPTCHA to verify whether or not you have a pulse.

Working of Code Breakers

How Code Breakers Work

Information is an important commodity. Nations, corporations and individuals protect secret information with encryption, using a variety of methods ranging from substituting one letter for another to using a complex algorithm to encrypt a message. On the other side of the information equation are people who use a combination of logic and intuition to uncover secret information. These people are cryptanalysts, also known as code breakers.

Binary code is the basis for many modern ciphers.

A person who communicates through secret writing is called a cryptographer. Cryptographers might use codes, ciphers or a combination of both to keep messages safe from others. What cryptographers create, cryptanalysts attempt to unravel.
Throughout the history of cryptography, people who created codes or ciphers were often convinced their systems were unbreakable. Cryptanalysts have proven these people wrong by relying on everything from the scientific method to a lucky guess. Today, even the amazingly complex encryption schemes common in Internet transactions may have a limited useful lifetime -- quantum computing might make solving such difficult equations a snap.

You Say Cryptology, I Say CryptographyIn English, the words cryptology and cryptography are often interchangeable -- both refer to the science of secret writing. Some people prefer to differentiate the words, using cryptology to refer to the science and cryptography to refer to the practice of secret writing.

In this article, we'll look at some of the most popular codes and cipher systems used throughout history. We'll learn about the techniques cryptanalysts use to break codes and ciphers, and what steps cryptographers can take to make their messages more difficult to figure out. At the end, you'll get the chance to take a crack at an enciphered message.

To learn how code breakers crack secret messages, you need to know how people create codes. we'll learn about some of the earliest attempts at hiding messages.

Polybius Squares and Caesar Shifts

Although historical findings show that several ancient civilizations used elements of ciphers and codes in their writing, code experts say that these examples were meant to give the message a sense of importance and formality. The person writing the message intended for his audience to be able to read it.
The Greeks were one of the first civilizations to use ciphers to communicate in secrecy. A Greek scholar named Polybius proposed a system for enciphering a message in which a cryptographer represented each letter with a pair of numbers ranging from one to five using a 5-by-5 square (the letters I and J shared a square). The Polybius Square (sometimes called the checkerboard) looks like this:

	1	2	3	4	5
1	A	B	C	D	E
2	F	G	H	I/J	K
3	L	M	N	O	P
4	Q	R	S	T	U
5	V	W	X	Y	Z

A cryptographer would write the letter "B" as "12". The letter O is "34". To encipher the phrase "How Stuff Works," the cryptographer would write "233452 4344452121 5234422543." Because he replaces each letter with two numbers, it's difficult for someone unfamiliar with the code to determine what this message means. The cryptographer could make it even more difficult by mixing up the order of the letters instead of writing them out alphabetically.
Julius Caesar invented another early cipher -- one that was very simple and yet confounded his enemies. He created enciphered messages by shifting the order of the alphabet by a certain number of letters. For example, if you were to shift the English alphabet down three places, the letter "D" would represent the letter "A," while the letter "E" would mean "B" and so forth. You can visualize this code by writing the two alphabets on top of one another with the corresponding plaintext and cipher matching up like this:

Plaintext

a

b

c

d

e

f

g

h

i

j

k

l

m

Cipher

D

E

F

G

H

I

J

K

L

M

N

O

P

Plaintext

n

o

p

q

r

s

t

u

v

w

x

y

z

Cipher

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

Notice that the cipher alphabet wraps around to "A" after reaching "Z." Using this cipher system, you could encipher the phrase "How Stuff Works" as "KRZ VWXII ZRUNV."
Both of these systems, the Polybius Square and the Caesar Shift, formed the basis of many future cipher systems.
In the next section, we'll look at a few of these more advanced methods of encryption.

Deciphering the LanguageTo encipher a message means to replace the letters in the text with the replacement alphabet. The readable message is called the plaintext. The cryptographer converts the plaintext into a cipher and sends it on. The recipient of the message uses the proper technique, called the key, to decipher the message, changing it from a cipher back into a plaintext.