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802.11: A term often used for 802.11a, 802.11b, and 802.11g or for wireless in general. But it properly refers to a 2Mbps wireless protocol in the 2.4Ghz band which is no longer in wide use.
802.11b: A wireless protocol in the 2.4Ghz band which achieves 11Mbps raw throughput. 802.11b is the first technology to be widely implemented by home users and is still one of the most popular.
802.11g: A wireless protocol in the 2.4Ghz band which can provide up to 54Mbps raw throughput. 802.11g is designed and marketed as a faster direct replacement for 802.11b, and is backward compatible with it, though at some cost in performance.
802.11a: A wireless protocol in the 5.4Ghz and 5.8Ghz band which achieves 54Mbps raw throughput. 802.11a has less range than 802.11b or 802.11g, and is marketed to the office/commercial market. It is incompatible with 802.11b and 802.11g.
AP: An Access Point in its simplest form is essentially a wireless hub. It serves to allow wireless clients to connect to a wired LAN as well as to each other. An AP in Access Point Mode cannot wirelessly negotiate its own connection to the LAN; it must be hardwired to a switch or other node. Many access points can be configured for use as an Access Point, Bridge, Multi-point Bridge, Repeater, or Wireless Client.
Bridge: An AP mode in which two access points form a dedicated wireless link between two separate LAN segments. Bridging is commonly used to join two spatially separated networks within a limited proximity. When set to bridge mode, the AP cannot serve any wireless clients; its sole function becomes to complete the link with the other AP in bridge mode. Each AP in bridge mode must be wired to a switch or other network node.
Multi-point Bridge: A scenario in which three or more access points form a dedicated wireless link between themselves. Serves to wirelessly join separate LAN segments. Each access point must be set to multi-point bridge mode.
Repeater: An AP set to repeater mode serves to extend the range of a wireless network. The repeater receives a wireless signal from an access point and in turn broadcasts it out to wireless clients. Throughput for wireless clients of the repeater is cut in half.
Wireless Router: A wireless router combines the functions of an access point with those of a router. Thus it will have both a WAN and LAN interface. The WAN interface is most often used for connection to a broadband modem. The router uses NAT to allow the computers on the LAN to share the one WAN connection.
Client (Station): An AP in client mode serves to wirelessly connect a separate LAN segment to the rest of the LAN. Its function is similar to that of a bridge, however in this scenario, one AP is set to access point mode, and the other AP is set to client mode. This allows other wireless clients to also connect to the first AP.
Infrastructure Mode: A situation in which wireless adapters associate with an access point rather than directly with each other.
Ad-Hoc Mode: A situation in which two wireless adapters form a peer-to-peer network with each other. Useful for situations in which a network infrastructure is not available, or is not needed.
IBSS: Independent Basic Service Set. Same as an Ad-Hoc network. A direct connection between two wireless adapters.
dB: decibels. A measurement of power difference, defined so that increasing the power by a factor of 10 gives an increase of 10 dB.
dBm: decibels relative to one milliwatt. An absolute measurement of power, where 0dBm = 1 milliwatt. SO 10dBm = 10mw, 20dBm = 100mW, 30dBm = 1W.
Receive sensitivity: The power level below which a connection cannot be maintained. Typically expressed in dBm. This will often be qualified by a data rate -- to say that a wireless card has a receive sensitivity of -80dBm at 11Mbps means that if there is less signal available than -80dBm, an 11Mbps connection cannot be maintained.
Transmit power: The power level a wireless card emits. Usually expressed in either dBm or milliwatts. Typical values are 15dBm (~33mW), 100mW (20dBm), and 200mW(~23dBm). Note that transmit power is always in _positive_ dBm (greater than 1mW) whereas receive sensitivity is in _negative_ dBm (less than 1 mW)
SNR (Signal to Noise ratio: The ratio between the power level of the desired signal at the receiver, and the power level of noise (any undesired RF energy) at the reciever. This is usually expressed in decibels, and when expressed in decibels is the _difference_ between the signal and the noise.
AES: Advanced Encryption Standard. The United States Department of Commerce (DOC) Federal Information Processing Standard (FIPS) 197 standard to replace Data Encryption Standard (DES). AES is currently considered the most robust encryption algorithm available. 802.11 devices that support AES require faster and more current hardware technology (manufactured in or since 2003). When choosing to use AES, you must also choose a key exchange technology, such as WPA with a Radius Server, WPA-PSK, or TKIP.
TKIP: Temporal Key Integrity Protocol. A key exchange authentication technology drafted by the WiFi Alliance prior to ratifying the more complete 802.11i security standard. Implementing TKIP enhances the original Wired Equivalent Privacy (WEP) technology by by adding per-packet keying on all WEP encrypted data frames. Prior to TKIP, it was possible to break the WEP technology after collecting a large number of packets.
WPA: WiFi Protected Access. A key exchange authentication technology drafted by the WiFi Alliance prior to ratifying the more complete 802.11i security standard. Implementing WPA requires a RADIUS server to manage keys, which can then easily scale upwards to manage a large number of users.
WPA-PSK: WiFi Protected Access Pre-Shard Key. A key exchange authentication technology allowing the use of the AES encryption technology without requiring a RADIUS server. WPA-PSK is a viable solution to permit home users or small businesses the ability to implement AES or TKIP encryption technology.
Antenna: a device to transmit and/or receive electromagnetic wave (often referred to as radio waves). Antennas are resonant devices, which must be tuned to operate most efficiently at a given frequency. A single antenna can be constructed to operate on more than one frequency if required.
Omnidirectional Antenna: A omnidirectional antenna is designed to radiate and receive radio waves equally in all horizontal directions. Because of this, omnidirectional antennas typically have the lowest gain (or operational distance) when compared with other antenna types. An omnidirectional antenna with an increased gain is achieved by focusing the antenna's energy in a more narrow, donut-shaped pattern, decreasing it's effectiveness above and below the antenna. Most SOHO wireless networking products come standard with a low-gain omnidirectional antenna which will operate with a minimal amount of consideration given to the environment. Switching to a high-gain omnidirectional antenna may increase the effective gain or distance the product operate in a horizontal plane, while reducing it's effectiveness above and below this plane. For example, a 3 dB gain omnidirectional antenna may work better than a 5 dB gain omnidirectional antenna in a multi-story environment because it operates better above and below the horizontal plane. A 5 dB gain omnidirectional antenna may be best in a single-story environment because it will focus it's energy across the horizontal plane better than a 3dB gain omnidirectional antenna.
Yagi Antenna: A directional antenna, designed to radiate and receive radio waves in one focused direction, increasing the antenna's effectiveness in that direction. Different yagi antenna designs will determine how focused the beam width, or operational area, will be. Yagi antennas typically have a boom supporting a series of elements, which are spaced a precise distance apart, and precise lengths to cause the antenna to operate most efficiently for a given radio frequency. Wireless networking yagi antennas may have this appearance or may be contained in a long cylinder-like tube or pipe to protect it and make it easier to install. For wireless networking, yagi antennas are typically most effective for fixed, point-to-point installations, often between wireless access points. This antenna type gets it name from one of the Japanese inventors, Shuji Yagi.
Panel Antenna: A directional antenna, designed to radiate and receive radio waves in one general direction, increasing the antenna's effectiveness in that direction. Different panel antenna designs will determine how focused the beam width, or operational area, will be. Panel antennas, like their name implies, are often flat panel-like devices. Panel antennas are most useful when it is desired to have the operational area in one general direction as opposed to all directions (omnidirectional), but not to the degree that a yagi antenna would focus it. For wireless networking, a panel antenna may be useful when attaching it to a wireless router or access point that is placed off to one side of an operational area (e.g., one side of a home or office as opposed to centrally located). The beam width will be relatively wide (when compared with a yagi antenna beam width), so precise antenna aiming and device placement isn't necessary.
Antenna Polarization: The orientation of the electromagnetic waves radiating or being received by a given antenna. Antennas constructed with it's elements primarily in a vertical orientation will radiate and receive vertically-polarized electromagnetic waves most effectively, horizontally-polarized antennas will operate most effectively with horizontally-polarized electromagnetic waves. Environmental factors, such as metallic objects, can affect polarization of electromagnetic waves. Two similarly polarized antennas will inter-operate most effectively. For wireless networking products, it may be possible to increase effectiveness between devices by simply reorienting an antenna.
Antenna Gain: A term used to compare the effective range or distance of a given antenna. Gain is described in decibels (dB), with a higher dB gain antenna being more effective in it's designed radiation pattern.