Networks that transmit signals through the atmosphere via radio frequency (RF) waves.
A continuum of the electromagnetic waves used for data and voice communication. The _______ _______ (as defined by the FCC, which controls its use) spans frequencies between 9KHz and 300 GHz. each type of wireless service can be associated with one area of the wireless spectrum.
An antenna's _______ _______ describes the relative strength over a three-dimensional area of all the electromagnetic energy the antenna sends or receives.
A ______ ______ issues wireless signals along a single direction. This type of antenna is used when the source needs to communicate with one destination, as in a point to point link.
An ______ ______ issues and receives wireless signals with equal strength and clarity in all directions. This type of antenna is used when many different receivers must be able to pick up the signal, or when the receiver's location is highly mobile.
LOS (Line of Sight)
This type of propagation uses the least amount of energy and results in the reception of the clearest possible signal.
In the context of wireless, the phenomenon that occurs when an electromagnetic wave encounters an obstacle and bounces back toward its source. A wireless signal will bounce off objects whose dimensions are large compared to the signal's average wavelength.
When a wireless signal splits into secondary waves as it encounters an obstruction. The secondary waves continue to propagate in the direction in which they were split. (bending around an obstacle)
This is the diffusion, or the reflection in multiple different directions, of a signal. This occurs when a wireless signal encounters an object that has small dimensions compared to the signal's wavelength.
Because of reflection, diffraction, and scattering, wireless signals follow a number of different paths to their destination.
A change in a wireless signal's strength as a result of some of the electromagnetic energy being scattered, reflected, or diffracted after being issued by the transmitter.
2.4 GHz Band
The range of radio frequencies from 2.4 to 2.4835 GHz. This band allows for 11 unlicensed channels, and is used by WLANs that follow the popular 802.11b and 802.11g standards.
5 GHz Band
Used by newer types of WLANs. A range of frequencies that comprises four frequency bands: 5.1, 5.3, 5.4, and 5.8GHz. It consists of 24 unlicensed bands, each 20 MHz wide. This band is used by WLANs that follow the 802.11a and 802.11n standards.
In _____, a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies.
The use of multiple frequencies to transmit a signal. (because the signal is spread out over the wireless spectrum)
FHSS (Frequency Hopping Spread Spectrum)
In ________________, a signal jumps between several different frequencies within a band in a synchronization pattern known only to the channel's receiver and transmitter.
DSSS (Direct-Sequence Spread Spectrum)
Another type of Spread-Spectrum signaling. In __________, a signal's bits are distributed over an entire frequency band at once. Each bit is coded so that the receiver can reassemble the original signal upon receiving the bits.
The locations of the transmitter and receiver do not move. The transmitting antenna focuses its energy directly toward the receiving antenna. This results in a point to point link. (Advantage: receiver's location is predictable, energy need not be wasted issuing signals across a large geographical area. Thus more energy can be used for the signal.
In ________ wireless, the receiver can be located anywhere within the transmitter's range. This allows the receiver to roam from one place to another while continuing to pick up its signal.
A type of wireless LAN in which stations communicate directly with each other (rather than using an access point)
An end node on a network; used most often in the context of wireless networks.
A device used on wireless LANs that transmits and receives wireless signals to and from multiple nodes and retransmits them to the rest of the network segment. Access points can connect a group of nodes with a network or two networks with each other. They may use directional or omnidirectional antennas.
A method used by wireless stations to detect the presence of an access point. In _____ _____, the station issues a probe to each channel in its frequency range and waits for the access point to respond.
In the context of wireless networking, the communication that occurs between a station and an access point to enable the station to connect to the network via that access point.
In the context of wireless networking, a frame issued by an access point to alert other nodes of its existence.
A wireless networking standard that uses FHSS signaling in the 2.4GHz band to achieve a maximum throughput of either 723 Kbps or 2.1 Mbps, depending on the version. Bluetooth was designed for use primarily with small office or home networks in which multiple devices are connected.
Bluetooth Special Interest Group (SIG)
A consortium of companies, including Sony Ericsson, Intel, Nokia, Toshiba, and IBM, that formally banded together in 1998 to refine and standardize Bluetooth technology.
BSSID (Basic Service Set Identifier)
In IEEE terminology, the identifier for a BSS (basic service set)
In the context of 802.11n wireless technology, the combination of two 20-MHz frequency band to create one 40-MHz frequency band that can carry more than twice the amount of data that a single 20-MHz band could. It's recommended for use only in the 5-GHz range, because this band has more available channels and suffers less interference than the 2.4 GHz band.
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
A network access method used on 802.11 wireless networks. In CSMA/CA, before a node begins to send data it checks the medium. If it detects no transmission activity, it waits a brief, random amount of time, and then sends its transmission. If the node does detect activity, it waits a brief period of time before checking the channel again. CSMA/CA does not eliminate, but minimizes, the potential for collisions.
A method of satellite Internet access in which a subscriber receives data via a satellite downlink transmission, but sends data to the satellite via an analog modem (dial-up) connections.
A connection from an orbiting satellite to an Earth -based receiver.
ESS (Extended Service Set Identifier)
A group of access points and associated stations (or basic service sets) connected to the same LAN.
ESSID (Extended Service Set Identifier)
A special identifier shared by BSSs that belong to the same ESS.
GEO (Geosynchronous Orbit or Geostationary Orbit)
The term used to refer to a satellite that maintains a constant distance from a point on the equator at every point in its orbit. Geosynchronous orbit satellites are the type used to provide satellite Internet access.
An area covered by a wireless access point that provides visitors with wireless services, including Internet access.
A type of WLAN in which stations communicate with an access point and not directly with each other.
A command-line utility for viewing and setting wireless interface parameters on Linux and UNIX workstations.
LEO (Low Earth Orbiting)
A type of satellite that orbits the Earth with an altitude between 100 and 900 miles, closer to the Earth's poles than the orbits of either GEO or MEO satellites. LEO satellites cover a smaller geographical range than GEO satellites and require less power.
MEO (Medium Earth Orbiting)
A type of satellite that orbits the Earth roughly 6000 to 12,000 miles above its service, positioned between the equator and the poles. MEO satellites can cover a larger area of the Earth's surface than LEO satellites while using less power and causing less signal delay than GEO satellites.
MIMO (Multiple Input-Multiple Output)
In the context of 802.11n wireless networking, the ability for access points to issue multiple signals to stations, thereby multiplying the signal's strength and increasing their range and data-carrying capacity. Because the signals follow multipath propagation, they must be phase-adjusted when they reach their destination.
PAN (Personal Area Network)
A small (usually home) network composed of personal communications devices.
In the context of wireless networking, the process in which a station listens to several channels within a frequency range for a beacon issued by an access point.
In 802.11 wireless networking, a type of frame issued by a station during active scanning to find nearby access points.
The relative strength over a three dimensional area of all the electromagnetic energy an antenna sends or receives.
The geographical area in which signals issued from an antenna or wireless system can be consistently and accurately received.
In the context of wireless networking, the process of a station establishing a connection (or associating) with a different access point.
In wireless networking, the process that describes a station moving between BSSs without losing connectivity.
RTS/CTS (Request to Send/Clear to Send)
an exchange in which a wireless station requests the exclusive right to communicate with an access point and the access point confirms that it has granted that request.
A type of satellite Internet access service in which a subscriber sends and receives data to and from the Internet over the satellite link. This is a symmetrical technology, in which both upstream and downstream throughputs are advertised to reach 400-500 Kbps; in reality, throughput is often higher.
The process a wireless station undergoes to find an access point.
In the context of wireless networking, an assessment of client requirements, facility characteristics, and coverage areas to determine an access point arrangement that will ensure reliable wireless connectivity within a given area.
SSID (Service Set Identifier)
A unique character string used to identify an access point on an 802.11 network.
The equipment on a satellite that receives an uplinked signal from Earth, amplifies the signal, modifies its frequency, then retransmits it (in a downlink) to an antenna on Earth.
The signals made of electromagnetic energy that travel through the atmosphere.
The term used to describe the recently released standards for high thoughput, long-distance digital data exchange over wireless connections. WiMAX (IEEE 802.16) is one example of a wireless broadband technology.
An access point that provides routing functions and is used as a gateway.
An access point that provides routing functions.