Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor also used for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving information bearing signals over power lines to provide access to the Internet.

Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but some can cross between two levels (for example, both the distribution network and premises wiring).

All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.

Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles (kilometres) long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.

Internet access (broadband over powerlines)
Broadband over power lines (BPL), also known as power-line Internet or powerband, is the use of PLC technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL "modem" into any outlet in an equipped building to have high-speed Internet access. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.

BPL may offer benefits over regular cable or DSL connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up.

Home control (narrowband)
Power line communications technology can use the household electrical power wiring as a transmission medium. INSTEON and X10 are the two most popular,de facto standards using power line communications for home control. This is a technique used in home automation for remote control of lighting and appliances without installation of additional control wiring.

Home networking (broadband)
Power line communications can also be used to interconnect home computers, peripherals or other networked consumer peripherals. Proprietary specifications for power line home networking have been developed by a number of different companies within the framework of the HomePlug Powerline Alliance, the Universal Powerline Association and the HD-PLC Alliance.

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DSL or xDSL, is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop, although in recent years, the term digital subscriber line has been widely adopted as a more marketing-friendly term for ADSL, which is the most popular version of consumer-ready DSL. DSL can be used at the same time and on the same telephone line with regular telephone, as it uses high frequency, while regular telephone uses low frequency.

Typically, the download speed of consumer DSL services ranges from 256 kilobits per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line conditions and service level implemented. Typically, upload speed is lower than download

DSL (VDSL) typically works by dividing the frequencies used in a single phone line into two primary "bands". The ISP data is carried over the high-frequency band (25 kHz and above) whereas the voice is carried over the lower-frequency band (4 kHz and below).The user typically installs a DSL filter on each phone. This filters out the high frequencies from the phone line, so that the phone only sends or receives the lower frequencies (the human voice). The DSL modem and the normal telephone equipment can be used simultaneously on the line without interference from each other.

DSL technologies
The line length limitations from telephone exchange to subscriber are more restrictive for higher data transmission rates. Technologies such as VDSL provide very high speed, short-range links as a method of delivering "triple play" services (typically implemented in fiber to the curb network architectures). Technologies likes GDSL can further increase the data rate of DSL. Fiber Optic technologies exist today that allow the conversion of copper based IDSN, ADSL and DSL over fiber optics.

Example DSL technologies (sometimes called xDSL) include:

ISDN Digital Subscriber Line (IDSL), uses ISDN based technology to provide data flow that is slightly higher than dual channel ISDN.
High Data Rate Digital Subscriber Line (HDSL / HDSL2), was the first DSL technology that uses a higher frequency spectrum of copper, twisted pair cables.
Symmetric Digital Subscriber Line (SDSL / SHDSL), the volume of data flow is equal in both directions.
Symmetric High-speed Digital Subscriber Line (G.SHDSL), a standardised replacement for early proprietary SDSL.
Asymmetric Digital Subscriber Line (ADSL), the volume of data flow is greater in one direction than the other.
Asymmetric Digital Subscriber Line 2 (ADSL2), an improved version of ADSL
Asymmetric Digital Subscriber Line 2 Plus (ADSL2+), A version of ADSL2 that doubles the data rates by using twice the spectrum.
Asymmetric Digital Subscriber Line Plus Plus (ADSL++), technology developed by Centillium Communications for Japan market that extends downstream rates to 50 Mbit/s by using spectrum up to 3.75 MHz.
Rate-Adaptive Digital Subscriber Line (RADSL)
Very High Speed Digital Subscriber Line (VDSL)
Very High Speed Digital Subscriber Line 2 (VDSL2), an improved version of VDSL
Etherloop Ethernet Local Loop
Uni Digital Subscriber Line (UDSL), technology developed by Texas Instruments, backwards compatible with all DMT standards
Gigabit Digital Subscriber Line (GDSL), based on binder MIMO technologies[7].
(UHDSL) Universal Digital Subscriber Line using fiber optics. Developed in 2005 by RLH Industries, Inc. Converts HDSL-1, 2 or 4 copper service into fiber optic HDSL service.

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Step1
Read through Desktop Computer ::: How to . The "Before you shop" points and most of "The basics" also apply when shopping for a laptop.
Step2
Pick up the laptops at the store. (Ask to have them unlocked if necessary.) Choose one that feels sturdy, solid and not too heavy.
Step3
Try the keyboard. Since you can't replace it (except with the exact same item), make sure you're comfortable with its touch and responsiveness. Test it on a desk and on your lap.
Step4
Test the pointing device, track pad or track ball, the laptop alternatives to a mouse. Some of these can be hard to master. You'll be able to connect an external mouse, but the built-in device is more handy when you're mobile.
Step5
Check if the computer's bottom gets uncomfortably hot when it's running--a problem if you actually use the laptop on your lap.
Step6
Pay attention to screen size and resolution. Current liquid-crystal display (LCD) screens on laptops measure from 13 to 21 inches diagonally. Screen resolution may be as low as 800 x 600 pixels or as high as 1600 x 1200. The more pixels, the crisper the screen image. View the screen in a variety of settings: A screen that looks great in normal room lighting can look terrible in bright or dim light.
Step7
Choose a laptop with at least two USB 2 connections and at least one Firewire (IEEE1394) connection. USB 2 and Firewire are very popular and fast ways of connecting iPods, digital cameras and some phones to computers.
Step8
Check to see if the laptop has built in wireless capabilities, most do these days. A wireless network card (also called Wi-Fi or 802.11) will free you from having to be wired to your Internet connection (see How to Network Your Computers). Also, Bluetooth capability will let you share information wirelessly with other Bluetooth-equipped devices, such as your cell phone or personal digital assistant.
Step9
Check to see if the laptop has a DVD Burner. That makes backing up documents, music files and pictures a snap because of the high capacity of the discs.
Step10
Get an antitheft device. Hundreds of thousands of laptops are stolen every year. Look for cables that secure the laptop to a desk. Install software that disables a stolen laptop, or better yet, reports the laptop's location when it connects to the Internet.

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Before you shop
Step1
Decide if you're better served by the PC/Windows platform or the Macintosh. You can generally get a faster computer for your money by choosing a Windows machine, but Macs come with more easy-to-use built-in software. Top brands are Dell, Hewlett- Packard, IBM, Gateway and Toshiba. Apple, of course, makes the Macintosh.
Step2
Think about whether this machine will need to work with your office or school server. Exchanging files between platforms is less of an issue than it used to be, but it's still worth noting.
Step3
Ask your friends and co-workers in similar lines of work what machines they have, where they bought them, if there were any problems, and whether they're happy with their choices.
Step4
Expect to spend $1,000 to $2,000 for a general-purpose machine, although you can find desktop computers for anywhere from $400 to $10,000.

The basics
Step1
Realize that if you buy a super cheap computer at a warehouse store or discounter, you're going to be on your own. Technical support from the major manufacturers tends to be a lot better.
Step2
Buy as much random-access memory (RAM), or system memory, as you can afford. At a bare minimum, get 1024 megabytes (MB); 2048 MB or 4096 MB is preferable. (For a Macintosh, get at least 1024 MB.) Memory is more critical than a faster processor.
Step3
Get at least two universal serial bus (USB) connections and a FireWire (also called IEEE 1394) connection. These will connect peripheral devices, such as a printer, PDA, digital cameras and camcorders, scanners and game controllers.
Step4
Get a CD burner so you can back up valuable data and make your own music CDs. Look into a DVD burner too if you're involved in film making or editing, but remember that there are multiple competing standards; computer-burned DVDs might not play in your home DVD player. Make sure your machine has a DVD drive if you want to watch movies on your computer. Also look for an internal modem.
Step5
Ask about upgradability if you intend to use this computer for a long time, which is considered three or more years.
Step6
Choose any current computer model from the major manufacturers with a high degree of confidence if you simply want to send e-mail, surf the Web and do word-processing.
Special considerations
Step1
Get high-quality graphics and sound if you plan to play games. Look for a system that has a graphics card with a coprocessor, and 5.1 Surround sound. You'll want a broadband Internet connection to play online games, and to improve your Internet experience overall.
Step2
Buy the biggest hard drive you can afford--120 to 180 gigabytes (GB) is now commonplace. Get more than 200 GB if you're storing music and/or editing video. For video editing, you'll also need a video input/output card and a FireWire connection.
Step3
Add a TV capture card, and you can even have your computer function as a DVR.

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