Guide To Networks Ch8 Terms

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2.4 GHz band

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The range of radio frequencies from 2.4 to 2.4835 GHz. The 2.4 GHz band, which allows for 11 unlicensed channels, is used by WLANs that follow the popular 802.11b and 802.11g standards. However, it is also used for cordless telephone and other transmissions, making the 2.4 GHz band more susceptible to interference than the 5-GHz band.

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5-GHz band

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A range of frequencies that comprises four frequency bands: 5.1 GHz, 5.3 GHz, 5.4 GHz, and 5.8 GHz. It consists of 24 unlicensed bands, each 20 MHz wide. The 5-GHz band is used by WLANs that follow the 802.11a and 802.11n standards.

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802.11a

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The IEEE standard for a wireless networking technique that uses multiple frequency bands in the 5-GHz frequency range and provides a theoretical maximum throughput of 54 Mbps. 802.11a’s high throughput, compared with 802.11b, is attributable to its use of higher frequencies, its unique method of encoding data, and more available bandwidth.

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802.11b

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The IEEE standard for a wireless networking technique that uses DSSS (direct sequence spread spectrum) signaling in the 2.4–2.4835-GHz frequency range (also called the 2.4-GHz band). 802.11b separates the 2.4-GHz band into 14 overlapping 22-MHz channels and provides a theoretical maximum of 11-Mbps throughput.

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802.11g

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The IEEE standard for a wireless networking technique designed to be compatible with 802.11b while using different encoding techniques that allow it to reach a theoretical maximum capacity of 54 Mbps. 802.11g, like 802.11b, uses the 2.4-GHz frequency band.

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802.11n

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The IEEE standard for a wireless networking technique that may issue signals in the 2.4- or 5-GHz band and can achieve actual data throughput between 65 and 600 Mbps. It accomplishes this through several means, including MIMO, channel bonding, and frame aggregation. 802.11n is backward compatible with 802.11a, b, and g.

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802.16

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An IEEE standard for wireless MANs. 802.16 networks may use frequencies between 2 and 66 GHz. Their antennas may operate in a line-of-sight or non-line-of-sight manner and cover 50 kilometers (or approximately 30 miles). 802.16 connections can achieve a maximum throughput of 70 Mbps, though actual throughput diminishes as the distance between transceivers increases. Several 802.16 standards exist. Collectively, they are known as WiMAX.

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802.16e

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Currently, the most popular version of WiMAX. With 802.16e, IEEE improved the mobility and QoS characteristics of the technology, making it better suited to VoIP and mobile phone users.

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access point

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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.

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active scanning

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A method used by wireless stations to detect the presence of an access point. In active scanning, the station issues a probe to each channel in its frequency range and waits for the access point to respond.

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ad hoc

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A type of wireless LAN in which stations communicate directly with each other (rather than using an access point).

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association

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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.

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beacon frame

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In the context of wireless networking, a frame issued by an access point to alert other nodes of its existence.

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Bluetooth

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A wireless networking standard that uses FHSS (frequency hopping spread spectrum) signaling in the 2.4-GHz 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 (including cordless phones, computers, and pagers) are connected.

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Bluetooth Special Interest Group (SIG)

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A consortium of companies, including Sony Ericsson, Intel, Nokia, Toshiba, and IBM, that formally banded together in 1998 to refine and standardize Bluetooth technology.

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BSS

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(basic service set) In IEEE terminology, a group of stations that share an access point.

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BSSID

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(basic service set identifier) In IEEE terminology, the identifier for a BSS (basic service set).

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channel bonding

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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.

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CSMA/CA

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(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.

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dial return

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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 (dialup) connection.

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diffraction

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In the context of wireless signal propagation, the phenomenon that occurs when an electromagnetic wave encounters an obstruction and splits into secondary waves. The secondary waves continue to propagate in the direction in which they were split. If you could see wireless signals being diffracted, they would appear to be bending around the obstacle. Objects with sharp edges—including the corners of walls and desks—cause diffraction.

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directional antenna

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A type of antenna that issues wireless signals along a single direction, or path.

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downlink

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A connection from an orbiting satellite to an Earth-based receiver.

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DSSS

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(direct-sequence spread spectrum) A transmission technique in which 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.

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ESS

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(extended service set) A group of access points and associated stations (or basic service sets) connected to the same LAN.

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ESSID

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(extended service set identifier) A special identifier shared by BSSs that belong to the same ESS.

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fading

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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.

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FHSS

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(frequency hopping spread spectrum) A wireless signaling technique in which a signal jumps between several different frequencies within a band in a synchronization pattern known to the channel’s receiver and transmitter.

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fixed

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A type of wireless system in which the locations of the transmitter and receiver are static. In a fixed connection, the transmitting antenna focuses its energy directly toward the receiving antenna. This results in a point-to-point link.

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GEO

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(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.

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hot spot

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An area covered by a wireless access point that provides visitors with wireless services, including Internet access.

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infrastructure WLAN

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A type of WLAN in which stations communicate with an access point and not directly with each other.

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iwconfig

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A command-line utility for viewing and setting wireless interface parameters on Linux and UNIX workstations.

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LEO

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(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.

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LOS

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(line-of-sight) A wireless signal or path that travels directly in a straight line from its transmitter to its intended receiver. This type of propagation uses the least amount of energy and results in the reception of the clearest possible signal.

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MEO

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(medium Earth orbiting) A type of satellite that orbits the Earth roughly 6000 to 12,000 miles above its surface, 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.

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MIMO

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(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.

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mobile

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A type of wireless system in which 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.

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multipath

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The characteristic of wireless signals that follow a number of different paths to their destination (for example, because of reflection, diffraction, and scattering).

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narrowband

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A type of wireless transmission in which signals travel over a single frequency or within a specified frequency range.

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omnidirectional antenna

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A type of antenna that 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.

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PAN

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(personal area network) A small (usually home) network composed of personal communications devices.

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passive scanning

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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.

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probe

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In 802.11 wireless networking, a type of frame issued by a station during active scanning to find nearby access points.

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radiation pattern

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The relative strength over a three-dimensional area of all the electromagnetic energy an antenna sends or receives.

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range

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The geographical area in which signals issued from an antenna or wireless system can be consistently and accurately received.

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reassociation

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In the context of wireless networking, the process of a station establishing a connection (or associating) with a different access point.

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reflection

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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.

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roaming

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In wireless networking, the process that describes a station moving between BSSs without losing connectivity.

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RTS/CTS

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(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.

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satellite return

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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.

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scanning

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The process a wireless station undergoes to find an access point. See also active scanning and passive scanning.

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scattering

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The diffusion of a wireless signal that results from hitting an object that has smaller dimensions compared to the signal’s wavelength. Scattering is also related to the roughness of the surface a wireless signal encounters. The rougher the surface, the more likely a signal is to scatter when it hits that surface.

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site survey

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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.

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spread spectrum

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A type of wireless transmission in which lower-level signals are distributed over several frequencies simultaneously. Spread-spectrum transmission is more secure than narrowband.

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SSID

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(service set identifier) A unique character string used to identify an access point on an 802.11 network.

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station

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An end node on a network; used most often in the context of wireless networks.

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transponder

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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.

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uplink

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A connection from an Earth-based transmitter to an orbiting satellite.

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wireless

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The signals made of electromagnetic energy that travel through the atmosphere.

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wireless broadband

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The term used to describe the recently released standards for high throughput, long-distance digital data exchange over wireless connections. WiMAX (IEEE 802.16) is one example of a wireless broadband technology.

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wireless gateway

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An access point that provides routing functions and is used as a gateway.

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wireless router

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An access point that provides routing functions.

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wireless spectrum

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A continuum of electromagnetic waves used for data and voice communication. The wireless spectrum (as defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300 GHz. Each type of wireless service can be associated with one area of the wireless spectrum.

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WLAN

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(wireless LAN) A LAN that uses wireless connections for some or all of its transmissions.