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Glossary

8 A  B C D E F G H I  L M  O P  R S  W 

8 

802.11 - The IEEE standard that specifies a carrier sense media access control and physical layer specifications for 1 and 2 megabit per second wireless LANs. 

802.11b -The IEEE standard that specifies a carrier sense media access control and physical layer specifications for 5.5 and 11 megabit per second wireless LANs. 

802.3 -The IEEE standard that specifies carrier sense media access control and physical layer specifications for Ethernet LANs. 

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A 

Access Point - A wireless LAN transceiver that acts as a center point and bridges between wireless and wired networks. 

Ad Hoc Network - A wireless network composed only of stations without access points. 

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B 

Bandwidth - Specifies the amount of the frequency spectrum that is usable for data transfer. It identifies the maximum data rate that a signal can attain on the medium without encountering significant loss of power. 

Beamwidth - The angle of signal coverage provided by a radio. Beamwidth may by decreased by a directional antenna to increase gain. 

Boot Protocol (BOOTP) - The protocol used for the static assignment of IP addresses to devices on the network. 

Bridge - A device used to connect LANs by forwarding packets across connections at the Media Access Control (MAC) layer. 

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C 

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) - Wireless LAN media access method as specified by the IEEE 802.11 specification. 

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) - Ethernet media access method as specified by the IEEE 802.3 specification. 

Complementary Code Keying (CCK) - Modulation technique used by IEEE 802.11-compliant wireless LANs for transmission at 5.5 and 11Mbps. 

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D 

dBi - A ratio of decibels to an isotropic antenna that is commonly used to measure antenna gain. The greater the dBi value, the higher the gain and, as such, the more acute the angle of coverage. 

Differential Binary Phase Shift Keying (DBPSK) - Modulation technique used by IEEE 802.11-compliant wireless LANs for transmission at 1Mbps. 

Differential Quadrature Phase Shift Keying (DQPSK) - Modulation technique used by IEEE 802.11-compliant wireless LANs for transmission at 2Mbps.

Dipole - A type of low gain (2.2 dBi) antenna consisting of two (often internal) elements. 

Direct Sequence Spread Spectrum (DSSS) - A type of spread spectrum radio transmission that spreads its signal continuously over a wide frequency band. More.

Directional Antenna - An antenna that concentrates transmission power into a direction thereby increasing coverage distance at the expense of coverage angle. Directional antenna types include yagi, patch and parabolic dish. 

Diversity Antennas - An intelligent system of two antennas that continually senses incoming radio signals and automatically selects the antenna best positioned to receive it.  

Dynamic Host Configuration Protocol (DHCP) - A protocol available with many operating systems that automatically issues IP addresses within a specified range to devices on a network. The device retains the assigned address for a specific administrator-defined period.

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E 

Ethernet - The predominant wired LAN technology standardized in the IEEE 802.3 specification. 

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F 

Frequency Hopping Spread Spectrum (FHSS) - A type of spread spectrum radio transmission in which the transmitter and receiver hop in synchronization from one frequency to another according to a prearranged pattern.  More.

Fresnel Effect - A phenomenon related to line of sight whereby an object that does not obstruct the visual line of sight obstructs the line of transmission for radio frequencies. 

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G 

Gain - A method of increasing the transmission distance of a radio by the concentration its signal in a single direction, typically through the use of a directional antenna. Gain does not increase a radio's signal strength, but simply redirects it. Therefore, as gain increases, the decrease in angle of coverage is inversely proportional. 

Gigahertz (GHz) - One billion cycles per second. A unit of measure for frequency.

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H 

Hertz (Hz) - Cycles per second. A unit of measure for frequency.

Hidden Node - A station on a wireless LAN that attempts to transmit data to another station but, due to its location relative to the others, cannot sense that there is a third station simultaneously communicating with the intended recipient. Lost message and multiple retries is the result.

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I 

Institute of Electrical and Electronic Engineers (IEEE) - A professional society serving electrical engineers through its publications, conferences, and standards development activities. The body responsible for the Ethernet 802.3 and wireless LAN 802.11 specifications.

Isotropic - An antenna (or a theoretic construct of an antenna) that radiates its signal 360 degrees both vertically and horizontally - a perfect sphere.

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L 

Line of Sight - An unobstructed straight line between two transmitting devices. Line of sight is typically required for long-range directional radio transmission. Due to the curvature of the earth, the line of sight for devices not mounted on towers is limited to 16 miles (26km).

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M 

Management Information Base (MIB) - A collection of network operational information residing in a virtual store that may be accessed, typically through an SNMP-compliant system, for analysis.

Media Access Control (MAC) Layer - Provides media access services for IEEE 802 local area networks.

Megahertz (MHz) - One million cycles per second. A unit of measure for frequency.

Modulation - Any of several techniques for combining user information with a transmitter's carrier signal. 

Multipath - Multipath is the composition of a primary signal plus duplicate or echoed images caused by reflections of signals off objects between the transmitter and receiver. The receiver "hears" the primary signal sent directly from the transmission facility, but it also sees secondary signals that are bounced off nearby objects. These bounced signals will arrive at the receiver later than the incident signal. Because of this misalignment, the "out-of-phase" signals will cause intersymbol interference or distortion of the received signal. Although most of the multipath is caused by bounces of tall objects, multipath can also occur from bounces on low objects such as lakes and pavements.

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O 

Omni-Directional Antenna - An antenna that provides a 360 degree transmission pattern. These types of antennas are used when coverage in all directions is required.

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P 

Packet - A basic message unit for communication across a network. A packet usually includes routing information, data, and (sometimes) error detection information.

Parabolic - A concave or dish-shaped object. Often refers to dish antennas. Peer-to-Peer Network: A network design in which each computer shares and uses devices on an equal basis.

Physical Layer (PHY) - Provides for the transmission of data through a communications channel by defining the electrical, mechanical and procedural specifications for IEEE 802 local area networks. Protocol: Rules for communicating, particularly for the format and transmission of data.

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R 

Radio Frequency (RF) - A generic term for radio-based technology.

Range - A linear measure of the distance that a transmitter can send a signal.

Receiver Sensitivity - A measurement of the weakest signal a receiver can receive and still correctly translate it into data.

Reverse Polarity TNC (RP-TNC) - A connector type unique to Aironet radios and antennas. Part 15.203 of the FCC rules covering spread-spectrum devices limits the types of antennas that may be used with transmission equipment. In compliance with this rule, Aironet, like all other wireless LAN providers, equips its radios and antennas with a unique connector to prevent attachment of non-approved antennas to radios.

Roaming - A feature of some access points that allow users to move through a facility while maintaining unbroken connection to the LAN.

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S 

Simple Network Management Protocol (SNMP) - The network management protocol that defines the transfer of LAN operational data between Management Information Bases (MIBs).

Spread Spectrum - A radio transmission technology that "spreads" the user information over a much wider bandwidth than otherwise required in order to gain benefits such as improved interference tolerance and unlicensed operation.

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W 

WEP - WEP WEP (Wired Equivalent Privacy) is an optional IEEE 802.11 feature used to provide data confidentiality that is equivalent to the confidentiality of a wired LAN that does not employ crypto techniques to enhance privacy. WEP will only make the wireless LAN link in a system as secure as the wired link. As specified in the standard, WEP uses the RC4 algorithm with a 40-bit key. When WEP is enabled, each station (clients and Access Points) has a key. The key is used to scramble the data before it is transmitted through the airwaves. If a station receives a packet that is not scrambled with the appropriate key, the packet will be discarded and never delivered to the host. WEP will be available for the Aironet 3500, 4500, 4800, BR500 and BR100 Series products as a firmware upgrade. WEP will be released in phases. The first release will require the keys to be manually entered into each adapter, Bridge and AP. Improved key management and other features will be included in future releases. Key Features and Benefits Customers who are concerned about security can use WEP as a basis to build a comprehensive security system and be assured that the wireless link is not compromising the security of the network. Aironet can support longer keys—up to 128 bits—for customers who require security measures above and beyond what the standard specifies. In this mode, the product does not comply with the standard but the resulting system is more secure. Aironet’s WEP implementation is in the hardware, so there is minimal performance impact when WEP is used. Competition No other competitors will have better hardware support for WEP. Some competitors will do WEP encryption in their software, but the performance penalty for this type of implementation can be severe. Some competitors may have better management of keys and may also implement enhanced authentication. Future releases of Aironet’s WEP will include these improvements.

Wired Equivalent Privacy (WEP) - Optional security mechanism defined within the 802.11 standard designed to make the link integrity of the wireless medium equal to that of a cable.

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