Wi-Fi acronyms, wireless buzzwords, WLAN nomenclature, wireless terms
Before we dive headlong into the actual art and science of Wi-Fi, I am going to present a glossary of terms that are used to define the technology. WLANs have a language, an "alphabet soup" of acronyms and buzzwords that serve, ironically, to facilitate the deeper discussions of the technology that will follow. This list is by no means exhaustive, but these terms will be used extensively in the rest of this series, so I urge you to bookmark this entry and share it with co-workers for future reference.
Access Point (AP): A wireless infrastructure device connected to a distribution system allowing wireless LAN client devices to access computer network resources. At least two network interfaces are required: Ethernet (usually) and RF (wireless).
Active site survey: A type of manual wireless LAN site survey that requires an association to an access point.
ad hoc: Another term for independent basic service set (IBSS), a wireless network in which no access points are used and only device-to-device communication takes place. This type of network is also called peer-to-peer.
Authentication, Authorization, and Accounting (AAA): A protocol that provides a framework to allow secure access and authorization as well as keep track of the user’s activities on a computer network, including wireless networks.
Basic Service Area (BSA): The area of radio frequency coverage surrounding an access point or other wireless infrastructure device and the associated wireless LAN client devices.
Basic Service Set (BSS): One access point connected to a distribution system.
Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA): Protocol using mechanisms that attempt to avoid collisions. This protocol is required with IEEE 802.11 wireless networking because the wireless devices have no way of detecting a collision. Instead, devices will use a method that may involve reserving the wireless medium for a specified period of time, attempting to avoid collisions.
Carrier Sense Multiple Access/Collision Detection (CSMA/CD): A method used with IEEE 802.3 Ethernet networking; it is a contention-based media access control method that Ethernet devices use to share the medium. This method allows for only one device to transmit at any one time. If a collision is detected, the transmitting devices will need to back off for a random period of time and retransmit.
Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP): A security protocol that is a mandatory part of the IEEE 801.11i amendment to the standard and part of Wi-Fi Protected Access 2.0 (WPA2) certification from the Wi-Fi Alliance, providing strong security.
dB: Decibel (dB) is a relative expression representing a change in radio frequency power.
dBd: A decibel referenced to a dipole antenna, representing the passive gain of a dipole antenna and a relative expression of radio frequency power.
dBi: A decibel referenced against an isotropic radiator, representing the passive gain of an antenna as an increase in power and a relative expression of radio frequency power.
dBm: A decibel referenced to 1 milliwatt (mW), and an absolute measure of radio frequency power.
Direct-Sequence Spread Spectrum (DSSS): A spread-spectrum technology used in IEEE 802.11 and IEEE 802.11b/g with data rates of 1 and 2 Mbps set on a specific radio frequency channel.
Extended Service Set (ESS): One or more interconnected basic service sets connected to a common distribution system.
Extensible Authentication Protocol (EAP): Used in IEEE 802.11 wireless networks as an authentication process to allow access to network resources. EAP is available in various types, which include user and certificate authentication.
Fresnel zone: The area of usable RF coverage between a transmitter and receiver in outdoor point-to-point wireless links. The area cannot be obstructed by more than 40% for reliable communication. The Fresnel zone diameter is calculated using distance between endpoints and the frequency in use.
Gain: An increase in signal strength of an RF signal, caused by an increase in amplitude.
Half-duplex: Two-way communication that occurs in only one direction at a time.
Hidden node: In wireless networking, the hidden node problem is the result of wireless client devices associated to an access point and not able to "hear" each other prior to starting an RF transmission. Hidden node results in excessive collisions at the access point.
High Rate/Direct-Sequence Spread Spectrum (HR/DSSS): A spread-spectrum technology used in IEEE 802.11b and IEEE 802.11b/g with data rates of 5.5 and 11 Mbps.
IBSS: Independent basic service set, another term for an ad hoc network.
ISM: Radio bands that are reserved internationally for industrial, scientific, and medical (ISM) purposes.
Loss: A decrease in radio frequency power or energy, resulting in lower signal strength and throughput.
MAC (Medium Access Control) address: The unique identifier or hardware address of each device on a computer network. It is also referred to as the physical address and takes the form: xx:xx:xx:xx:xx:xx.
Milliwatt (mW): An absolute measure of radio frequency power that is equal to 1/1000 W.
Modulation and Coding Scheme (MCS): Describes various HT-OFDM data rates depending on the wireless LAN configuration in use such as modulation, bandwidth, and guard intervals.
Multipath: A phenomenon resulting from various wavefronts of reflected signals arriving at a receiver at slightly different times. Multipath causes corruption of the received signal, resulting in less overall throughput.
Multiple-channel architecture (MCA): A wireless network design in which access points are set to different nonoverlapping channels to minimize interference.
Multiple input/multiple output (MIMO): A technology using multiple radio chains and multiple antennas, allowing for high throughput up to 600 Mbps in IEEE 802.11 wireless networks.
Multiple user – MIMO (Mu-MIMO): A technology utilizing multiple data streams and multiple radio chains to allow the simultaneous use of spectrum by multiple users, allowing for throughput up to 6 Gbps.
Nonoverlapping channels: Radio frequency channels that do not occupy the same part of the radio spectrum.
Open Systems Interconnection (OSI) model: Theoretical networking model describing seven layers that perform unique functions on transmitted data. Each layer is built upon a set of protocols and act upon data passed from adjacent layers.
Orthogonal Frequency Division Multiplexing (OFDM): A technology designed to transmit many signals simultaneously over one transmission path in a shared medium; it is orthogonal in the sense that subcarriers are 90 deg out of phase with adjacent subcarriers.
Parabolic dish antenna: A highly directional and high-gain antenna typically used for long-range point-to-point links.
Passive gain: The result of an antenna focusing RF energy into a specific radiation pattern.
Patch/Panel antenna: A semidirectional antenna providing coverage over a predetermined area less than an omnidirectional, but more than a directional antenna, such as a Yagi or Parabolic type.
Power over Ethernet (PoE): A means of supplying dc voltage and data together over an Ethernet cable.
Predictive survey: A software-based wireless LAN site survey in which a floor plan or drawing of the area to be surveyed is imported into the program. RF propagation from access points is simulated by the program to predict coverage.
Protocol: A set of rules that defines the method of exchanging data between devices. The TCP/IP protocol suite is an example of a protocol commonly used in data communication.
Radio frequency (RF): The section of the electromagnetic spectrum between XX Hz and XX Hz.
Reflection: A phenomenon that occurs when an RF signal bounces off a smooth, nonabsorptive surface resulting in the original signal changing direction.
Refraction: A phenomenon that occurs when an RF signal passes between mediums of different densities. As with light, the signal will change direction and speed, and experience loss.
Remote Authentication Dial-In User Service (RADIUS): A remote server used to provide authentication services, authorization, and accounting for users requiring access to network resources.
Role-Based Access Control (RBAC): A method of restricting access to network resources to only those associated with that network segment as defined by their specific roles, regardless of user identities.
Sector antenna: A semidirectional antenna that can be configured in a group to provide omnidirectional coverage. Useful in communities and campuses, or for wireless ISPs.
Semidirectional antenna: An antenna used to focus the isotropic energy into a specific radiation pattern. Available in various types, including patch/panel, sector, and Yagi.
Service Set Identifier (SSID): The name of a wireless network that identifies a basic service set and is used for segmentation. It can be broadcast in beacon frames as part of the passive scanning process to allow wireless LAN client devices to locate and join the network.
Signal-to-noise ratio (SNR): The RF noise value in dBm minus the received signal strength in dBm. The minimum recommended value for wireless networking is 20dB to 25dB or higher.
Single-channel architecture (SCA): A wireless network design in which all access points operate on the same channel and are managed by a centralized controller to avoid interference.
Spread spectrum: A signal spread over a frequency range, which results in a wider bandwidth.
Subcarrier: A separate signal carried on a main radio frequency transmission.
Temporal Key Integrity Protocol (TKIP): A firmware upgrade designed to enhance security issues with Wired Equivalent Privacy (WEP); TKIP is an enhancement to WEP.
Throughput: The actual rate at which information is transferred, taking into consideration factors such as overhead, interference, and contention between devices.
Unlicensed National Information Infrastructure (U-NII): U-NII is a radio frequency range used by IEEE-802.11a/n devices and for point-to-point or point-to-multipoint connections. The U-NII band consists of a lower, middle, and upper band with four frequency ranges and is used for IEEE wireless LANs.
Virtual local area networks (VLANs): A logical separation of ports to define broadcast domains in a Layer 2 network, independent of their physical location.
Voltage standing wave ratio (VSWR): Disruption common in a wireless LAN system, caused by a mismatch in the impedance.
Watt (W): The basic unit of measurement for radio frequency power.
Wavelength: The distance of one complete cycle or one oscillation of an ac signal. Wavelength is typically identified by the Greek symbol lambda.
Wi-Fi: A trademark term from the Wi-Fi Alliance identifying interoperability testing certifications.
Wired Equivalent Privacy (WEP): An optional authentication and/or encryption mechanism defined in the IEEE 802.11 standard designed to prevent casual eavesdropping. A weak and compromised legacy form of wireless security.
Wireless Intrusion Prevention System (WIPS): A software and/or hardware solution designed to monitor wireless networking RF signals using sensors or access points and to record events to a centralized database. It has the capability to react and prevent intrusion.
Wireless Network Management System (WNMS): A software-based, hardware-based, or cloud-based solution that allows for centralized management and control of a wireless network and may allow work with wired networks.
Yagi antenna: A semidirectional antenna typically used outdoors for short-range bridging or indoors for long hallways and corridors to provide RF coverage to a specific area.
– Daniel E. Capano, owner and president, Diversified Technical Services Inc. of Stamford, Conn., is a certified wireless network administrator (CWNA). Edited by Chris Vavra, content specialist, CFE Media, Control Engineering, firstname.lastname@example.org.
www.controleng.com/blogs has other wireless tutorials from Capano on the following topics:
Wireless propagation fundamentals
Wi-Fi and the OSI model
www.controleng.com/webcasts has wireless webcasts, some for PDH credit.
Control Engineering has a wireless page.