Glossary

Access Point (AP)
A wireless LAN transceiver that acts as a center point of an all-wireless network or as a connection point between wireless and wired networks.

Ad Hoc Mode
A client setting that provides independent peer-to-peer connectivity in a wireless LAN. An alternative setup is where PCs communicate with each other through an AP. See Infrastructure Mode.

Ad Hoc Network
A wireless network composed only of network clients in peer-to-peer mode (without access points).

Antenna
A device for transmitting or receiving a radio frequency (RF). Antennas are designed for specific and relatively tightly defined frequencies and are quite varied in design. An antenna designed for 2.4 GHz 802.11b devices will not work with 2.5 GHz devices.

Antenna Gain
The measure of antenna performance relative to a theoretical antenna called an isotropic antenna. Certain antenna designs feature higher performance relative to beamwidth and frequencies.

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 an antenna. Beamwidth typically decreases as antenna gain increases.

Bootstrap Protocol (BOOTP)
Allows a network device to configure itself by obtaining required parameters over the network from a host device.

Broadband
In general, a RF system is deemed broadband if it has a constant data rate at or in excess of 1.5 Mbps. Its corresponding opposite is narrowband.

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
Wireless LAN media access method as specified by IEEE 802.11. It is a listen before talk method of minimalizing collisions caused by simultaneous transmission by multiple radios.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
LAN access method used by Ethernet. When a device wants to gain access to the network, it checks to see if the network is available. If the network is occupied, the device waits a random amount of time before retrying.

Channel
A communications path wide enough to permit a single RF transmission.

Client
Any computer, bar-code scanner, wireless camera, or other device that wirelessly connects to a network to access network services (files, printing, etc.).

Client Adapter

Network interface card that provides devices with wireless connectivity.

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

dB
Decibel; a unit for measuring relative power ratios in terms of gain or loss. Units are expressed in terms of the logarithm to base 10 of a ratio and are typically expressed in watts. A decibel is not an absolute value; rather it is the measure of power loss or gain between two devices.

dBi
A ratio, measured in decibels, of the effective gain of an antenna compared to an isotropic antenna. The greater the dBi value, the higher the gain and, as such, the more acute the angle of coverage.

dBd
A ratio, measured in decibels, of the effective gain of an antenna compared to a dipole antenna (see dipole). The greater the dBd 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 1 Mbps.

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

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.

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

Diversity Antenna Systems
A system using two antennas and an intelligent radio that continually senses incoming radio signals, or a transmitted signals success rate, and automatically selects the antenna best positioned to receive or transmit.

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.

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.

Fresnel Effect
A phenomenon whereby a transmitted radio signal is degraded by physical objects surrounding the line of sight.

Gain
The ratio of the output amplitude of a signal to the input amplitude of a signal. This ratio is typically expressed in decibels (dB).

Gateway
A network point that acts as an entrance to another network.

Hertz (Hz)
The international unit for measuring frequency, equivalent to cycles per second. One megahertz (MHz) is one million hertz. One gigahertz (GHz) is one billion hertz. The standard U.S. electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55-1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, and wireless 802.11 LANs operate at 2.4 GHz.

Hidden Node
A station on a wireless LAN that attempts to transmit data to another station but, because of 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 are the result. A packet retry at the radio protocol level may occur.

IEEE 802.X
A set of specifications for local-area networks (LANs) from the IEEE. Most wired networks conform to 802.3, the specification for CSMA/CD-based Ethernet networks. The 802.11 committee completed a standard for 1- and 2-Mbps wireless LANs in 1997 that has a single Media Access Control (MAC) layer for the following physical-layer technologies: Frequency Hopping Spread Spectrum, Direct Sequence Spread Spectrum, and Infrared. IEEE 802.11b, an 11 Mbps version of the standard, and IEEE 802.11a, a 5 GHz, 54 Mbps version of the standard, were both ratified in 1999.

Independent Network
A network that provides (usually temporarily) peer-to-peer connectivity without relying on a complete network infrastructure.

Infrastructure Mode
A client setting that provides connectivity to an AP. As compared to Ad Hoc Mode, where PCs or other client devices communicate directly with each other, clients set in Infrastructure Mode all pass data through a central AP. The AP not only mediates wireless network traffic in the immediate neighborhood, but also provides communication with the wired network. See AD Hoc Mode and Access Point.

Infrastructure Network
A wireless network centered about an access point. In this environment, the access point not only provides communication with the wired network but also mediates wireless network traffic in the immediate neighborhood.

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

Line of Sight
An unobstructed straight line between two transmitting devices. Line of sight is typically required for long-range directional radio transmission. Because of the curvature of the earth, the line of sight for devices not mounted on towers is limited to 6 miles (9.65 km). With certain wireless bridging technologies, there must be a clear, unobstructed path between the transmitters and the receivers.

Media Access Control (MAC)
In a wireless LAN (WLAN) network card, the MAC is radio controller protocol. It corresponds to the ISO Network Model Layer 2 data link layer. The IEEE 802.11 standard specifies the MAC protocol for medium sharing, packet formats and addressing, and error detection.

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

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

Microcell
A bounded physical space in which numerous wireless devices can communicate. Because it is possible to have overlapping cells as well as isolated cells, the boundaries of the cell are established by a predefined rule or convention.

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

Multipath
The echoes created as a radio signal bounces off of physical objects.

Network Address Translation (NAT)
The translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the internal network and it appears as one entity to the outside world. In the case of wireless LANs with an outside Internet connection, the NAT capability of Internet-sharing software allows the sharing of one Internet connection among all the wireless PCs connected.

Omnidirectional Antenna
An antenna that provides 360-degree transmission coverage along a horizontal plane.

Orthogonal Frequency Division Multiplexing (OFDM)
A radio modulation technique that provides 54 Mbps in the 5 GHz band.

OSI Network Model
The International Standards Organization has developed an Open Standards Interconnect (OSI) network model that consists of seven different levels, or layers. By standardizing these layers and the interfaces in between, different portions of a given protocol can be modified or changed as technologies advance, or systems requirements are altered. The seven layers follow:

• Physical
• Data Link
• Network
• Transport
• Session
• Presentation
• Application

The IEEE 802.11 standard encompasses the physical layer (PHY) and the lower portion of the data link layer. The lower portion of the data link layer is often referred to as the Medium Access Control (MAC) sublayer.

Parabolic
A concave or dish-shaped object; often refers to dish antennas. Parabolic dish antennas tend to provide the greatest gain and the narrowest beamwidth, making them ideal for point-to-point transmission over the longest distances.

Patch Antenna
A type of flat antenna designed for flush wall mounting that radiates a hemispherical coverage area.

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. The PHY is the lowest layer within the OSI Network Model. Itdeals primarily with transmission of the raw bit stream over the physical transport medium. In the case of wireless LANs, the transport medium is free space. The PHY defines parameters such as data rates, modulation method, signaling parameters, transmitter/receiver synchronization, and so on. Within an actual radio implementation, the PHY corresponds to the radio front-end and baseband signal-processing sections.

Radio Frequency (RF) Terms: GHz, MHz, and Hz
The international unit for measuring frequency is hertz (Hz), which is equivalent to cycles per second. One megahertz (MHz) is one million hertz. One gigahertz (GHz) is one billion hertz. For reference: the standard U.S. electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55-1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, and microwave ovens typically operate at 2.45 GHz.

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 Threaded Naval Connector (RP-TNC)
Unique connector for Cisco 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 and like all other wireless LAN providers, Cisco equips its radios and antennas with unique connectors to prevent attachment of nonapproved antennas to radios.

Roaming
Movement of a wireless node between two microcells. Roaming usually occurs in infrastructure networks built around multiple access points.

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.

Wide-Area Network (WAN)
A wide-area network connects local-area networks together. Typical WAN interfaces include plain old telephone service (POTS) lines, digital subscriber lines (DSL), cable, T1/T3, and ISDN.

Wireless Access Protocol
A language used for writing Web pages that uses far less overhead, making it more preferable for wireless access to the Internet by personal digital assistants (PDAs) and Web-enabled cellular phones.

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.

Wireless Node
A user computer with a wireless network interface card (adapter).

Yagi
A type of midrange-gain, directional antenna.

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