How Bluetooth Works

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Introduction to How Bluetooth Works

Photo courtesy DealTime Jabra FreeSpeak BT250 Bluetooth headset. Check out our mobile technology image gallery.

There are lots of different ways that electronic devices can connect to one another. For example:

• Component cables
• Electrical wires
• Ethernet cables
• WiFi
• Infrared signals

When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light beams, and an even greater variety of connectors, plugs and protocols.

The art of connecting things is becoming more and more complex every day. In this article, we will look at a method of connecting devices, called Bluetooth, that can streamline the process. A Bluetooth connection is wireless and automatic, and it has a number of interesting features that can simplify our daily lives.

How Bluetooth Creates a Connection

Bluetooth takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power. Picture this: You're on your Bluetooth-enabled cell phone, standing outside the door to your house. You tell the person on the other end of the line to call you back in five minutes so you can get in the house and put your stuff away. As soon as you walk in the house, the map you received on your cell phone from your car's Bluetooth-enabled GPS system is automatically sent to your Bluetooth-enabled computer, because your cell phone picked up a Bluetooth signal from your PC and automatically sent the data you designated for transfer. Five minutes later, when your friend calls you back, your Bluetooth-enabled home phone rings instead of your cell phone. The person called the same number, but your home phone picked up the Bluetooth signal from your cell phone and automatically re-routed the call because it realized you were home. And each transmission signal to and from your cell phone consumes just 1 milliwatt of power, so your cell phone charge is virtually unaffected by all of this activity.

Bluetooth is essentially a networking standard that works at two levels:

• It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.

• It provides agreement at the protocol level, where products have to agree on when bits are sent, how many will be sent at a time, and how the parties in a conversation can be sure that the message received is the same as the message sent.

Photo courtesy Bluetooth SIG Bluetooth wireless PC card

The big draws of Bluetooth are that it is wireless, inexpensive and automatic. There are other ways to get around using wires, including infrared communication. Infrared (IR) refers to light waves of a lower frequency than human eyes can receive and interpret. Infrared is used in most television remote control systems. Infrared communications are fairly reliable and don't cost very much to build into a device, but there are a couple of drawbacks. First, infrared is a "line of sight" technology. For example, you have to point the remote control at the television or DVD player to make things happen. The second drawback is that infrared is almost always a "one to one" technology. You can send data between your desktop computer and your laptop computer, but not your laptop computer and your PDA at the same time. (See How Remote Controls Work to learn more about infrared communication.)

These two qualities of infrared are actually advantageous in some regards. Because infrared transmitters and receivers have to be lined up with each other, interference between devices is uncommon. The one-to-one nature of infrared communications is useful in that you can make sure a message goes only to the intended recipient, even in a room full of infrared receivers.

Bluetooth is intended to get around the problems that come with infrared systems. The older Bluetooth 1.0 standard has a maximum transfer speed of 1 megabit per second (Mbps), while Bluetooth 2.0 can manage up to 3 Mbps. Bluetooth 2.0 is backward-compatible with 1.0 devices.

Let's find out how Bluetooth networking works.

How Bluetooth Operates

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.

One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.

When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn't have to press a button or give a command -- the electronic conversation happens automatically. Once the conversation has occurred, the devices -- whether they're part of a computer system or a stereo -- form a network. Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass no more distance than that between the cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that may be operating in the same room. Let's check out an example of a Bluetooth-connected system.

Bluetooth Piconets

Let’s say you have a typical modern living room with typical modern stuff inside. There’s an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television; there's also a cordless telephone and a personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between the main unit and peripheral.

The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer has programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in the range, it responds, and a tiny network is formed. Now, even if one of these devices should receive a signal from another system, it will ignore it since it’s not from within the network. The computer and entertainment system go through similar routines, establishing networks among addresses in ranges established by manufacturers. Once the networks are established, the systems begin talking among themselves. Each piconet hops randomly through the available frequencies, so all of the piconets are completely separated from one another.

Now the living room has three separate networks established, each one made up of devices that know the address of transmitters it should listen to and the address of receivers it should talk to. Since each network is changing the frequency of its operation thousands of times a second, it’s unlikely that any two networks will be on the same frequency at the same time. If it turns out that they are, then the resulting confusion will only cover a tiny fraction of a second, and software designed to correct for such errors weeds out the confusing information and gets on with the network’s business.

Flexible Transmission Most of the time, a network or communications method either works in one direction at a time, called half-duplex communication, or in both directions simultaneously, called full-duplex communication. A speakerphone that lets you either listen or talk, but not both, is an example of half-duplex communication, while a regular telephone handset is a full-duplex device. Because Bluetooth is designed to work in a number of different circumstances, it can be either half-duplex or full-duplex.

The cordless telephone is an example of a use that will call for a full-duplex (two-way) link, and Bluetooth can send data at more than 64 kilobits per second (Kbps) in a full-duplex link -- a rate high enough to support several voice conversations. If a particular use calls for a half-duplex link -- connecting to a computer printer, for example -- Bluetooth can transmit up to 721 Kbps in one direction, with 57.6 Kbps in the other. If the use calls for the same speed in both directions, Bluetooth can establish a link with 432.6-Kbps capacity in each direction.

Bluetooth Security

In any wireless networking setup, security is a concern. Devices can easily grab radio waves out of the air, so people who send sensitive information over a wireless connection need to take precautions to make sure those signals aren't intercepted. Bluetooth technology is no different -- it's wireless and therefore susceptible to spying and remote access, just like WiFi is susceptible if the network isn't secure. With Bluetooth, though, the automatic nature of the connection, which is a huge benefit in terms of time and effort, is also a benefit to people looking to send you data without your permission.

Bluetooth offers several security modes, and device manufacturers determine which mode to include in a Bluetooth-enabled gadget. In almost all cases, Bluetooth users can establish "trusted devices" that can exchange data without asking permission. When any other device tries to establish a connection to the user's gadget, the user has to decide to allow it. Service-level security and device-level security work together to protect Bluetooth devices from unauthorized data transmission. Security methods include authorization and identification procedures that limit the use of Bluetooth services to the registered user and require that users make a conscious decision to open a file or accept a data transfer. As long as these measures are enabled on the user's phone or other device, unauthorized access is unlikely. A user can also simply switch his Bluetooth mode to "non-discoverable" and avoid connecting with other Bluetooth devices entirely. If a user makes use of the Bluetooth network primarily for synching devices at home, this might be a good way to avoid any chance of a security breach while in public.

Still, early cell-phone virus writers have taken advantage of Bluetooth's automated connection process to send out infected files. However, since most cell phones use a secure Bluetooth connection that requires authorization and authentication before accepting data from an unknown device, the infected file typically doesn't get very far. When the virus arrives in the user's cell phone, the user has to agree to open it and then agree to install it. This has, so far, stopped most cell-phone viruses from doing much damage. See How Cell-phone Viruses Work to learn more.

Other problems like "bluejacking," "bluebugging" and "Car Whisperer" have turned up as Bluetooth-specific security issues. Bluejacking involves Bluetooth users sending a business card (just a text message, really) to other Bluetooth users within a 10-meter (32-foot) radius. If the user doesn't realize what the message is, he might allow the contact to be added to his address book, and the contact can send him messages that might be automatically opened because they're coming from a known contact. Bluebugging is more of a problem, because it allows hackers to remotely access a user's phone and use its features, including placing calls and sending text messages, and the user doesn't realize it's happening. The Car Whisperer is a piece of software that allows hackers to send audio to and receive audio from a Bluetooth-enabled car stereo. Like a computer security hole, these vulnerabilities are an inevitable result of technological innovation, and device manufacturers are releasing firmware upgrades that address new problems as they arise.

To learn more about Bluetooth security issues and solutions, see Bluetooth.com: Wireless Security.

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Can't Robots Get a Break?

Science fiction author Isaac Asimov created the three laws of robotics in his short story "Runaround." But these are mainly aimed at protecting humans from robots. Do robots have rights, too?

Asimov's Three Laws of Robotics 1. A robot may not injure a human being or, through inaction, allow a human being to come to harm. 2. A robot must obey orders given it by human beings except where such orders would conflict with the First Law. 3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

But what happens if robots become a large part of society? How will people treat them? Will humans hold themselves superior to their creations? Will they balk at the idea of robots taking the place of one of the partners in a romantic relationship? Many roboticists believe that now is the time to begin thinking about the moral and ethical questions posed by humanity's development of robots. South Korea, after all, plans to have a robot in every house by 2020. This is a far cry from the chicken in every pot envisioned by Herbert Hoover's campaign during the 1928 United States presidential election.

It's a good thing, then, that South Korea is at the forefront of thinking about robot ethics. In fact, the country announced in March 2007 that it had assembled a panel to develop a Robot Ethics Charter, a set of guidelines for future robotic programming. It will deal with the human aspects of human-robot interaction -- like safeguards against addiction to robot sex -- as well as explore ways to protect humans and robots from suffering abuse at the hands of one another [source: National Geographic].

Courtesy Yoshikazu Tsuno/AFP/Getty Images As robots become more life-like, the challenges of integrating them into human society are expected to increase.

The South Koreans aren't the only ones who are thinking about robots' rights. In 2006, future robot issues were brought up as part of a conference on the future commissioned by the British government. Among the issues discussed were the potential need for government-subsidized healthcare and housing for robots, as well as robots' role in the military [source: BBC].

These considerations do not need to be addressed immediately, but as robots become increasingly life-like, these issues will almost certainly come into play. Designers are already working on robotic skin that can produce life-like facial expressions. Others are developing robots that can hold conversations and mimic human emotions.

It may be very difficult for many people to overcome the idea of a human-robot couple. In 1970, Dr. Masahiro Mori wrote an article for Energy magazine in which he describes the "uncanny valley," a phenomenon where people grow uncomfortable with technological beings the more human-like they become. People build robots that have human qualities to help them complete human tasks, but once these robots start to look and act like humans, people start to be turned off by them [source: Mori].

With these and other features, robots of the future will present a great many challenges as they integrate into human society. And in the face of such challenges, perhaps the idea of human-robot marriages isn't so scandalous after all. That is, if the robot is just as willing to get married as the human.

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Will robots get married?

You've known each another for many years now, and you've come to truly understand each another. You share a home, pay bills and putter around the garden together. The two of you look forward to your Sunday morning ritual of working on The New York Times crossword puzzle together. You are truly and deeply in love.

You'd like to get married, but unfortunately, you live in a society where your relationship is considered unnatural and immoral. Despite the breadth of your love for each other, marriage is against the law. If your beloved were a human and not a robot, society might be more tolerant.

Robot Image Gallery

Courtesy Choi Won-Suk/AFP/Getty Images Artificial intelligence researcher David Levy predicts that in 50 years, this robot could be the groom rather than master of ceremonies. See more robot images.

While the idea of human-robot marriage may seem far-fetched now, it may one day come to pass if artificial intelligence researcher David Levy's theory is correct.

Levy, a British researcher who recently earned a Ph.D. from the University of Maastricht in the Netherlands, believes that by 2050, robots and humans will be able to marry legally in the United States. He predicts that Massachusetts will lead the way as it did in 2004, when it became the first state to allow same-sex marriages between humans.

As robots become increasingly humanoid in appearance, Levy and other roboticists believe that people will begin to have sex with robots -- as soon as 2011, says at least one artificial intelligence theorist [source: Economist]. Physical attractiveness, coupled with the advances in robot programming that will allow human-like emotions and intellect in robots, could produce artificial mates that some humans will want to marry.

In fact, Levy told one reporter, it's "inevitable" [source: LiveScience].

Why is he so confident? For his doctoral thesis, Levy researched sociology, sexology, robotics, artificial intelligence and other fields related to marriage, love and robots. He concluded that all of the most important factors that cause humans to fall in love with one another could be programmed into robots. Do you like your women to be coquettish? Your robot will be programmed to be demure and to flirt. Does a strong, sensitive man who likes to build premium furniture light your fire? In the not-too-distant future, say some researchers, your perfect man will be available for purchase.

We’ve already had a peek at everyday life within a human-robot marriage. Remember the Geek Squad “Mandroid” commercial featuring the robot husband with the whistling lisp?

Levy isn't predicting that human couples will stop falling in love and reproducing. He doesn't even think a lot of people will opt for a robotic mate. Instead, Levy thinks that robots will offer a few people a viable alternative to being unable to find their ideal partner. Shy people who are uncomfortable meeting others could potentially benefit from marriage to a robot. So, too, could the mentally ill and people who "have unpleasant personalities" [source: LiveScience].

But does this mean that robots will be created just so jerks can have someone to push around? What happens when pushing people around leads to the "death" of the robot? It turns out that there are many people thinking today about the ethical implications robotic life will pose tomorrow. Read the next page to find out what they've concluded.

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How DSL Works

Introduction to How DSL Works

When you connect to the Internet, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line (DSL) connection. DSL is a very high-speed connection that uses the same wires as a regular telephone line.

Photo courtesy HowStuffWorks Shopper A DSL modem

­

Here are some advantages of DSL:

• You can leave your Internet connection open and still use the phone line for voice calls.
• The speed is much higher than a regular modem
• DSL doesn't necessarily require new wiring; it can use the phone line you already have.
• The company that offers DSL will usually provide the modem as part of the installation.

But there are disadvantages:

• A DSL connection works better when you are closer to the provider's central office. The farther away you get from the central office, the weaker the signal becomes.
• The connection is faster for receiving data than it is for sending data over the Internet.
• The service is not available everywhere.

In this article, we explain how a DSL connection manages to squeeze more information through a standard phone line -- and lets you make regular telephone calls even when you're online.

Telephone Lines
If you have read How Telephones Work, then you know that a standard telephone installation in the United States consists of a pair of copper wires that the phone company installs in your home. The copper wires have lots of room for carrying more than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to carry conversations. The entire plan is based on matching particular frequencies to specific tasks.

To understand DSL, you first need to know a couple of things about a normal telephone line -- the kind that telephone professionals call POTS, for Plain Old Telephone Service. One of the ways that POTS makes the most of the telephone company's wires and equipment is by limiting the frequencies that the switches, telephones and other equipment will carry. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz (cycles per second -- see How Telephones Work for a great demonstration of this). This range of frequencies is tiny. For example, compare this to the range of most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And the wires themselves have the potential to handle frequencies up to several million Hertz in most cases.

The use of such a small portion of the wire's total bandwidth is historical -- remember that the telephone system has been in place, using a pair of copper wires to each home, for about a century. By limiting the frequencies carried over the lines, the telephone system can pack lots of wires into a very small space without worrying about interference between lines. Modern equipment that sends digital rather than analog data can safely use much more of the telephone line's capacity. DSL does just that.

Asymmetric DSL
Most homes and small business users are connected to an asymmetric DSL (ADSL) line. ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit most of the time.

Photo courtesy Corning DSL signals can't pass through fiber-optic cables.

Precisely how much benefit you see from ADSL will greatly depend on how far you are from the central office of the company providing the ADSL service. ADSL is a distance-sensitive technology: As the connection's length increases, the signal quality decreases and the connection speed goes down. The limit for ADSL service is 18,000 feet (5,460 meters), though for speed and quality of service reasons many ADSL providers place a lower limit on the distances for the service. At the extremes of the distance limits, ADSL customers may see speeds far below the promised maximums, while customers nearer the central office have faster connections and may see extremely high speeds in the future. ADSL technology can provide maximum downstream (Internet to customer) speeds of up to 8 megabits per second (Mbps) at a distance of about 6,000 feet (1,820 meters), and upstream speeds of up to 640 kilobits per second (Kbps). In practice, the best speeds widely offered today are 1.5 Mbps downstream, with upstream speeds varying between 64 and 640 Kbps. Some vast improvements to ADSL are available in some areas through services called ASDL2 and ASDL2+. ASDL2 increases downstream to 12 Mbps and upstream to 1 Mbps, and ASDL2+ is even better -- it improves downstream to as much as 24 Mbps and upstream to 3 Mbps.­

You might wonder -- if distance is a limitation for DSL, why is it not also a limitation for voice telephone calls? The answer lies in small amplifiers called loading coils that the telephone company uses to boost voice signals. Unfortunately, these loading coils are incompatible with ADSL signals, so a voice coil in the loop between your telephone and the telephone company's central office will disqualify you from receiving ADSL. Other factors that might disqualify you from receiving ADSL include:

• Bridge taps - These are extensions, between you and the central office, that extend service to other customers. While you wouldn't notice the­se bridge taps in normal phone service, they may take the total length of the circuit beyond the distance limits of the service provider.
• Fiber-optic cables - ADSL signals can't pass through the conversion from analog to digital and back to analog that occurs if a portion of your telephone circuit comes through fiber-optic cables.
• Distance - Even if you know where your central office is (don't be surprised if you don't -- the telephone companies don't advertise their locations), looking at a map is no indication of the distance a signal must travel between your house and the office.

Next, we'll look at how the signal is split and what equipment DSL uses.

Splitting the Signal

The CAP System
There are two competing and incompatible standards for ADSL. The official ANSI standard for ADSL is a system called discrete multitone, or DMT. According to equipment manufacturers, most of the ADSL equipment installed today uses DMT. An earlier and more easily implemented standard was the carrierless amplitude/phase (CAP) system, which was used on many of the early installations of ADSL.

CAP operates by dividing the signals on the telephone line into three distinct bands: Voice conversations are carried in the 0 to 4 KHz (kilohertz) band, as they are in all POTS circuits. The upstream channel (from the user back to the server) is carried in a band between 25 and 160 KHz. The downstream channel (from the server to the user) begins at 240 KHz and goes up to a point that varies depending on a number of conditions (line length, line noise, number of users in a particular telephone company switch) but has a maximum of about 1.5 MHz (megahertz). This system, with the three channels widely separated, minimizes the possibility of interference between the channels on one line, or between the signals on different lines.

The DMT System
DMT also divides signals into separate channels, but doesn't use two fairly broad channels for upstream and downstream data. Instead, DMT divides the data into 247 separate channels, each 4 KHz wide.

One way to think about it is to imagine that the phone company divides your copper line into 247 different 4-KHz lines and then attaches a modem to each one. You get the equivalent of 247 modems connected to your computer at once. Each channel is monitored and, if the quality is too impaired, the signal is shifted to another channel. This system constantly shifts signals between different channels, searching for the best channels for transmission and reception. In addition, some of the lower channels (those starting at about 8 KHz), are used as bidirectional channels, for upstream and downstream information. Monitoring and sorting out the information on the bidirectional channels, and keeping up with the quality of all 247 channels, makes DMT more complex to implement than CAP, but gives it more flexibility on lines of differing quality.

Filters
CAP and DMT are similar in one way that you can see as a DSL user.

If you have ADSL installed, you were almost certainly given small filters to attach to the outlets that don't provide the signal to your ADSL modem. These filters are low-pass filters -- simple filters that block all signals above a certain frequency. Since all voice conversations take place below 4 KHz, the low-pass (LP) filters are built to block everything above 4 KHz, preventing the data signals from interfering with standard telephone calls.

DSL Equipment

ADSL uses two pieces of equipment, one on the customer end and one at the Internet service provider, telephone company or other provider of DSL services. At the customer's location there is a DSL transceiver, which may also provide other services. The DSL service provider has a DSL Access Multiplexer (DSLAM) to receive customer connections.

The Transceiver
Most residential customers call their DSL transceiver a "DSL modem." The engineers at the telephone company or ISP call it an ATU-R. Regardless of what it's called, it's the point where data from the user's computer or network is connected to the DSL line.

Photo courtesy Allied Telesyn DSL modem

The transceiver can connect to a customer's equipment in several ways, though most residential installation uses USB or 10 base-T Ethernet connections. While most of the ADSL transceivers sold by ISPs and telephone companies are simply transceivers, the devices used by businesses may combine network routers, network switches or other networking equipment in the same platform.

The DSLAM
The DSLAM at the access provider is the equipment that really allows DSL to happen. A DSLAM takes connections from many customers and aggregates them onto a single, high-capacity connection to the Internet. DSLAMs are generally flexible and able to support multiple types of DSL in a single central office, and different varieties of protocol and modulation -- both CAP and DMT, for example -- in the same type of DSL. In addition, the DSLAM may provide additional functions including routing or dynamic IP address assignment for the customers.

The DSLAM provides one of the main differences between user service through ADSL and through cable modems. Because cable-modem users generally share a network loop that runs through a neighborhood, adding users means lowering performance in many instances. ADSL provides a dedicated connection from each user back to the DSLAM, meaning that users won't see a performance decrease as new users are added -- until the total number of users begins to saturate the single, high-speed connection to the Internet. At that point, an upgrade by the service provider can provide additional performance for all the users connected to the DSLAM.

For information on ADSL rates and availability in the United States, go to Broadband Reports. This site can provide information on ADSL service companies in your area, the rates they charge, and customer satisfaction, as well as estimating how far you are from the nearest central office.

ADSL isn't the only type of DSL, and it's not the only way to get high-speed Internet access. Next, we'll look at ADSL alternatives.

Alternatives to ADSL

There are lots of variations in DSL technology -- many of them address DSL's distance limitations in one way or another. Other types of DSL include:

• Very high bit-rate DSL (VDSL) - This is a fast connection, but works only over a short distance. It is capable of handling Internet access, HDTV and on-demand services at rates of 52 Mbps downstream and 12 Mbps upstream.
• Symmetric DSL (SDSL) - This connection, used mainly by small businesses, doesn't allow you to use the phone at the same time, but the speed of receiving and sending data is the same.
• Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.
• ISDN DSL (IDSL) - This is a combination of the Integrated Services Digital Network (ISDN) and DSL technology. ISDN was the solution to dial-up Internet -- it allowed voice, text graphics, video and other data to share one telephone line. This made it possible to talk on the phone and use the Internet at the same time. IDSL is faster than ISDN connections but slower than DSL. It can travel a longer distance of 5 to 6 miles, so it is usually a good option for people who can't get DSL in their area.
• Universal DLS (Uni-DSL) - This emerging technology, developed by Texas Instruments, is backwards compatible with all existing versions of DSL. It offers somewhat of a middle ground between ASDL and VDSL -- at longer distances, it can reach the speeds of ASDL, but it can provide greater speeds than VDSL at shorter distances. In some locations, Uni-DSL can provide four times the amount of speed as VDSL.

Alternatives to DSL
With DSL's distance limitation and lower availability, what are some other options? There are two major alternatives to DSL -- cable and wireless.

Cable and DSL are the two big rivals in the world of broadband. Cable isn't limited by distance like DSL -- cable wires reach most neighborhoods, and signal strengths don't weaken over long distances. While DSL allows you to use the telephone and Internet simultaneously, cable lets users watch television and surf the Internet at the same time. Many cable companies are also beginning to bundle services with cable TV, Internet and digital telephone on one bill. Although cable and DSL speeds are about the same, the one disadvantage with cable is bandwidth -- connection speeds can slow down if too many people are using a cable service at the same time.

A new technology, known as WiMax or 802.16, looks to combine the benefits of broadband and wireless. WiMax will provide high-speed wireless Internet over very long distances and will most likely provide access to large areas such as cities. WiMax technology will be available in most American cities in 2008.

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How Batteries Work

Batteries are all over the place -- in our cars, our PCs, laptops, portable MP3 players and cell phones. A battery is essentially a can full of chemicals that produce electrons. Chemical reactions that produce electrons are called electrochemical reactions. In this article, you'll learn all about batteries -- the basic concept at work, the actual chemistry going on inside a battery, rechargeable versions, what the future holds for batteries and possible power sources that could replace them.

©2007 HowStuffWorks A 9-volt battery

If you look at any battery, you'll notice that it has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. In an AA, C or D cell (normal flashlight batteries), the ends of the battery are the terminals. In a large car battery, there are two heavy lead posts that act as the terminals.

Electrons collect on the negative terminal of the battery. If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can (and wear out the battery very quickly -- this also tends to be dangerous, especially with large batteries, so it is not something you want to be doing). Normally, you connect some type of load to the battery using the wire. The load might be something like a light bulb, a motor or an electronic circuit like a radio.

Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction (the battery's internal resistance) controls how many electrons can flow between the terminals. Electrons flow from the battery into a wire, and must travel from the negative to the positive terminal for the chemical reaction to take place. That is why a battery can sit on a shelf for a year and still have plenty of power -- unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. Once you connect a wire, the reaction starts. The ability to harness this sort of reaction started with the voltaic pile.

Next, we'll check out how a voltaic pile works and look at other types of batteries.

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FBI: Millions of computers roped into criminal 'robot networks'

WASHINGTON (CNN) -- More than 1 million computers in the last five months have become part of robot networks, or "botnets," in which hackers take over computers without their owners' knowledge and use them in criminal campaigns, the FBI said Thursday.

FBI Director Robert Mueller says botnets are "the Swiss Army knives of cyber crime."

The bureau in June announced Operation Bot Roast to stop this emerging type of cyber attack, which the FBI estimates has resulted in $20 million in losses and theft.

More than 1 million computers were infected with botnets when the FBI launched Bot Roast, and another million have been identified since then. Industry numbers suggest there are millions more.

According to an FBI news release, New Zealand authorities in tandem with the FBI searched the home of an individual -- identified only by the cyber name, "AKILL" -- whose "elite international botnet coding group" is suspected of infecting more than 1 million computers.

Since the operation was launched, 13 search warrants have been served around the world, and eight individuals -- in Washington, Pennsylvania, Florida, California and Kentucky -- have been indicted or found guilty of crimes related to botnets. Such crimes include fraud, identity theft and denial of service attacks in which computer Web sites and other resources are made unavailable.

The schemes target more than individual computer users. The FBI in a news release said recent attacks have ensnared a major financial institution in the Midwest and the University of Pennsylvania.

FBI Director Robert Mueller noted in a speech earlier this month that there is potential to attack entire networks, send spam, infect computers and inject spyware -- not to mention more sinister crimes that threaten national security.

"Botnets are considered the Swiss Army knives of cyber crime. You name it, they can do it," Mueller said during a speech at Penn State University. "A botnet could shut down a power grid, flood an emergency call center with millions of spam messages or disable a military command post."

Here's how botnets work: A hacker known as a "botherder" takes over computers using viruses, worms or Trojan horses. A Trojan horse is software that appears to perform a harmless task while cloaking its true function.

Computer users unwittingly grant access to the botherder by clicking on an advertisement, opening an e-mail attachment or providing information to a "phishing" Web page, which is a phony site that mimics a legitimate site.

Once they have access, botherders use the computers for their criminal enterprise, making it difficult to trace.

According to a September report from Symantec Corp., China had the most infected computers at 29 percent, followed by the United States at 13 percent. However, Symantec said, 43 percent of all command-and-control servers -- which botherders use to relay commands to infected computers in their network -- were located in the United States.

Symantec reported that in the first half of 2007 it had detected more than 5 million computers that had been used to carry out at least one cyber attack a day.

The number represented a 17 percent drop since the previous reporting period, Symantec said.

The decrease is indicative of stronger computer security and law enforcement initiatives like Operation Bot Roast that are forcing botherders to abandon the technique, Symantec reported.

Protecting your computer is as easy as "putting locks on your doors and windows," according to an FBI news release. Make sure your anti-virus software is up to date, install a firewall, use complicated passwords and be careful opening e-mail attachments and advertisers' links on Web sites, the bureau advised.

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What is the Apple iPhone?

For several years, Apple enthusiasts have been asking each other the question, "Does it exist? Is Apple really making a cell phone?" Rumors came and went, but Apple, a company known for its secrecy about products in development, said nothing. In the last six months, those rumors began to take on a life of their own as industry analysts joined the blogosphere in predicting that Apple would produce a phone sometime in the first half of 2007. In mid-November, news broke that Apple had placed an order with Hon Hai Precision Industry, Co., a longtime Taiwanese manufacturing partner, for 12 million units of a new device believed to be the fabled "iPhone" [Forbes]. That news sent the rumor mill into overdrive, but Apple and Steve Jobs, the company's chief executive officer, again said nothing. Analysts began issuing predictions of cost, features and when the phone would be available, with many of them claiming to have inside information. Given Apple's extraordinary track record with the iPod and its recent innovations in desktop and laptop design, expectations were very high, perhaps impossibly so.

On January 9, at Apple's annual product showcase, Macworld Expo, Jobs finally revealed the already legendary phone, and it's beyond what anyone expected. Jobs briefly tricked his audience during his Macworld Expo keynote address, announcing three new Apple products: a widescreen iPod, a cell phone and an "Internet communicator." Each announcement drew thunderous applause from the crowd, but what Jobs then revealed was that these three products were actually all part of one device -- the Apple iPhone.

Image courtesy Apple/ ©2006 Apple Computer, Inc. All rights reserved.

Touted as a "revolutionary mobile phone," the iPhone can make calls, play music, navigate the Web, edit photos, play movies and text message, among many other capabilities. Although many of the iPhone's functions can be found in other devices, the iPhone appears to be unique in that it seamlessly blends these abilities together, while also throwing a bevy of innovations into the mix.

Jobs demonstrated many of the iPhone's features for the audience. One sequence began with a call from Phil Schiller, Apple's senior vice president of Worldwide Product Marketing. Jobs answered the call on his iPhone, added Schiller to his address book, and when Schiller asked for a photo, Jobs emailed it to him -- all while continuing the call. Later Jobs showed off the phone's ability to integrate multiple applications by using the integrated Google maps application, which knew his location, and typing in a search for Starbucks. Every Starbucks location in San Francisco showed up on screen. Jobs chose one and in a few minutes he was on the phone with Starbucks, ordering 4,000 lattes before abruptly hanging up.

In order to seamlessly integrate Web, phone, media and messaging features, the iPhone employs remarkable, groundbreaking technology. Unlike traditional smartphones that have small, finger-cramping keyboards, the iPhone has only one button for "home." Instead, its 3.5-inch high resolution, color screen, which occupies most of the phone's face, doubles as a "multi-touch" display. The display shows different controls based on what you're doing. If you're typing a text message or e-mail, a keyboard appears at the bottom of the screen, and you can easily type a message and send it to someone from your address book. The multi-touch technology also has an auto-corrective feature that accounts for unintentional taps and corrects misspellings. For music and video, volume and playback controls appear on the screen, and so on for other applications.

The iPhone's multi-touch interface also allows the opportunity for innovative uses of the touch display. When viewing a photo or surfing the Web, simply perform a pinching motion with two fingers, and the photo or Web page zooms in. Spread two fingers apart, and the display zooms out. Scrolling in any application is done by just brushing a finger up or down on the screen.

An intriguing innovation in the phone is what Apple calls visual voicemail. No longer will you have to listen to all of your voicemails if you don't want to. Instead, they will appear in a list, much like an e-mail inbox, and you can simply point to the voicemail you want to play.

Apple has also integrated three sensors into its phone. One is an accelerometer, and it senses when you turn the phone on its side, automatically shifting the display to a landscape mode. This feature is incredibly useful for viewing panoramic pictures, videos or shuffling through your albums, which you view by their cover art. A second sensor detects ambient light and adjusts the screen's brightness accordingly in order to save power. The third sensor deactivates the screen when you bring the phone towards your face, so you won't be dialing with your cheek while talking on the device.

Like many of Apple's products, iPhone syncs easily with a Mac or PC. The phone runs a version of Apple's reliable OSX operating system, and its programs and iPod connector (located on the bottom of the phone) will be familiar to many Mac users. Use the iPod connector or a docking station to connect the phone to your computer, the iPhone will automatically sync your address book, photos, movies, music and bookmarks between the computer and the phone.

Now, all of this may sound great, but there are a few catches. First, the iPhone isn't available until June -- Apple needs to get FCC approval before the iPhone can start using a radio band. Second, Apple has an exclusive contract with Cingular through 2009, so if you want a iPhone, you'll have to be a Cingular customer. And third, it's not cheap. A 4 GB iPhone will set you back $499 with a two year service plan, while an 8 GB iPhone will cost $599 with a two year plan. Still, when compared to other high end smartphones, you're getting a lot. This is essentially a small, powerful computer in the palm of your hand, and of course it has Apple's famous sleek, stylish, minimalist design.

Here's a quick rundown of some of the iPhone's other features:

• 802.11 b/g WiFi and Bluetooth 2.0 wireless capabilities
• Quad-band GSM and Cingular EDGE network
• 3.5-inch high resolution screen with 160 ppi (pixels per inch)
• 2.0 megapixel digital camera
• Battery life: 5 hours talk/video/browsing, 16 hours audio playback
• 11.6 mm thin, 4.8 ounces
• IMAP and POP email support, with integrated Yahoo! e-mail client
• Text messages are displayed like instant message conversations, making keeping track of many messages much easier
• Speaker and standard headphone jack

So will the iPhone change the cell phone industry forever? That depends on who you ask. Keep in mind that very few people have even used the iPhone. But given Jobs' impressive demonstration and Apple's recent track record -- over 100 million iPods and 3 billion songs sold -- it's difficult to doubt that this is an extraordinary and important product. Apple's stock surged 7 percent on the day of Jobs' announcement and appears headed for record prices.

In other news, Cisco has filed suit against Apple for infringing on Cisco's trademarked "iPhone" name. Apparently, Apple and Cisco were in talks to negotiate the licensing of the name "iPhone" for Apple's product, but they had not yet reached an agreement when Jobs announced the product at CES.

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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 History
At 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.

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