F

 < Day Day Up > 



FCC

See Federal Communications Commission (FCC).

FEC

See Forward Error Correction (FEC).

FDMA

See Frequency Division Multiple Access (FDMA).

Federal Communications Commission (FCC)

The government agency responsible for regulating telecommunications in the United States.

FHSS

See Frequency Hopping Spread Spectrum (FHSS).

File Transport Protocol (FTP)

This Internet protocol is used to copy files between computers. FTP is also the standard method for downloading and uploading files over the Internet. FTP allows users to transfer files to and from a distant or local computer, list directors, and to delete and rename files on the distant computer.

Firewall

Hardware and/or software that sit between two networks, such as an internal network and an Internet service provider. It protects the network by refusing access by unauthorized users. It can even block messages to specific recipients outside the network.

Firmware

The basic instructions that equipment needs to function properly. Firmware is actually software that is constantly called upon by a computer so it is stored in semipermanent memory called PROM (Programmable Read Only Memory) or EPROM (Electrical PROM) where it cannot be "forgotten" when the power is shut off. It is used in conjunction with hardware and software and shares the characteristics of both. When there is a firmware upgrade it is to modify these instructions in order to adapt to new software releases, environments, or new hardware. It may also resolve potential bugs and may increase reliability or performance.

Flash card

See CompactFlash.

Flash Memory

This term refers to nonvolatile memory that does not need a constant power supply to retain its data. It offers extremely fast access times, low power consumption, and relative immunity to severe shock or vibration. Flash memory is similar to EPROM (Electronic Programmable Read Only Memory) with the exception that it can be electrically erased, whereas EPROM must be exposed to ultra-violet light to erase. These qualities combined with its compact size, make it perfect for portable devices like PDAs, barcode scanners digital cameras, cellular phones, etc.

FM

See Frequency Modulation (FM).

Forward Error Correction (FEC)

This term refers to a methodology that uses error correction coding to improve the proper transmission of digital data. This is the opposite of ARQ (automatic repeat request), which uses retransmission of data to improve the accuracy of digital data.

FreeSpot

Places where free Wi-Fi networks exist. They are usually put up around public spaces by local governments, in local venues by the venue operator, or by individuals whose philosophy is to share their high-speed Net connections with neighbors.

Frequency

As used in this book, frequency refers to the rate at which an electromagnetic waveform (electrical current) alternates, i.e., the number of complete cycles of energy (electrical current) that occurs in one second. It's usually measured in Hertz.

See also Hertz (Hz).

Frequency Division Multiple Access (FDMA)

A technique used in cellular communications in which channels are assigned specific frequencies. This digital radio technology divides the available spectrum into separate radio channels. It is generally used in conjunction with Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA).

Frequency Hopping Spread Spectrum (FHSS)

One of two types of spread spectrum radio technology used in Wi-Fi networks. FHSS modulates the data signal with a narrowband carrier signal that "hops" in a predictable sequence from frequency to frequency as a function of time over a wide band of frequencies. Interference is reduced, because a narrowband interferer affects the spread spectrum signal only if both are transmitting at the same frequency at the same time. The transmission frequencies are determined by a spreading (hopping) code. The receiver must be set to the same hopping code and must listen to the incoming signal at the proper time and frequency to receive the signal. Compare with Direct Sequence Spread Spectrum.

Frequency Modulation (FM)

This term refers to a method used to add voice or data to a radio frequency transmission by varying the carrier frequency. Both broadcast stations in the 88–108 MHz "FM" band and television station sound channels use this modulation technique. FM has grown in popularity because of its relatively insensitivity to the static sources.

Fresnel Zone

Pronounced "fre-nel," this term refers to the area around the visual line-of-sight that radio waves spread into after they leave the antenna. When designing 802.11 networks, this area must be 80% clear or else signal strength will weaken.

FTP

See FTP.



 < Day Day Up > 



Going Wi-Fi. A Practical Guide to Planning and Building an 802.11 Network
Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network
ISBN: 1578203015
EAN: 2147483647
Year: 2003
Pages: 273

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net