ssid:wlandscape[net]

:: Glossary

10BASE-T: Part of the IEEE 802.3 (Ethernet) standard for transmission over Cat-3 (or better) twisted-pair cable. The term signifies a 10 Mbps transmission rate using baseband transmission over unshielded twisted-pair.
802.3: The official IEEE standard employing CSMA/CD access technology. 802.3 (10M), 802.3u (100M), 802.3z (1000M).
802.11: refers to a family of specifications developed by the IEEE for WLAN technology. 802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. 802.11 per se provides 1 or 2 Mbps transmission in the 2.4 GHz ISM band using either FHSS or DSSS.
802.11b: A revision of 802.11 standard allowing data rates up to 11Mbps in the 2.4GHz ISM band. Also known as 802.11 High-Rate and Wi-Fi. 802.11b only uses DSSS, the maximum speed of 11Mbps has fallbacks to 5.5, 2 and 1Mbps.
802.11a: A revision of 802.11 that operates in the unlicensed 5 GHz band and allows transmission rates of 54Mbps. 802.11a uses orthogonal frequency division multiplexing as opposed to FHSS or DSSS. Higher data rates possible by combining channels. Due to higher frequency, range is less than lower frequency systems (i.e., 802.11b and 802.11g) and can increase the cost of the overall solution because a greater number of access points may be required. 802.11a is not directly compatible with 802.11b or 802.11g networks. In other words, a user equipped with an 802.11b or 802.11g radio card will not be able to interface directly to an 802.11a access point. Multi-mode NICs will solve this problem.
802.11g: is an extension to 802.11b. 802.11g will broaden 802.11b's data rates to 54 Mbps within the 2.4 GHz band using OFDM (orthogonal frequency division multiplexing) technology. An 802.11b radio card will interface directly with an 802.11g access point (and vice versa) at 11 Mbps or lower depending on range. Range at 54 Mbps is less than 802.11b access points operating at 11 Mbps.
Ad-hoc mode: An 802.11 framework in which devices communicate directly with each other, without the use of an Access Point. Ad-hoc mode is also referred to as peer-to-peer mode or an Independent Basic Service Set (IBSS).
AP access point: A transceiver device serving as an interface between a wired LAN and wireless LAN clients. APs can improve aspects of wireless security and extend the physical range of service.
ATM: Asynchronous Transfer Mode (Cell Relay). ATM is a layer-2 connection oriented protocol offering a comprehensive Quality-of-Service mechanism and is designed to carry all traffic profiles including ? packet, circuit emulation and isochronous traffic. ATM allows negotiation of bandwidth on demand. Cell size is 53 bytes with a maximum usable payload of 48 bytes.
Authentification: The process of identifying an individual in order for other processes to confer appropriate access rights to system facilities. Authentication merely ensures that the individual is who he or she claims to be.
Backbone network: A network used as a transmission path between other networks. Usually high speed.
Bandwidth: A figure stated for a communications device (specified in Hz, kHz, MHz, GHz) that ultimately dictates the amount of information that it can convey.
Baseband: A transmission system in which information signals are transmitted in their core frequency spectrum without resource to modulation.
Baud rate: The number of symbols/sec transmitted. In binary transmission a symbol has 2-states and represents a bit. A system using the same baud rate but employing quaternary transmission (4-states) encodes 2-bits/symbol and therefore transmits at twice the bit-rate.
Bit: Stands for "Binary digIT." The smallest unit of information. (True/False ? Yes/No - Hot/Cold ? On/Off etc.)
Bluetooth: Bluetooth is a wireless person area networking technology initially proposed by Ericsson. It uses FHSS in the 2.4GHz ISM band at approx 1600 hops/s. Data rates of up to 1Mbit/s over a range of 10m can be achieved (range can be extended). Bluetooth is the "cableless" technology intended to allow radio interfacing of peripheral devices and will be seen in many consumer devices such as PDAs. See 802.15 standards on WPAN.
Bridge: A device used to partition a LAN into multiple access domains based upon MAC (layer-2) information. There are two common forms of bridge Transparent Bridges (Ethernet systems) and Source Routing Bridges (Token Ring), the former being the most common. Partitioning a network using bridges offers several advantages. 1. Access concurrency. 2. Reduced contention. 3. Speed matching 4. Increased distance 5. Increased node count.
Broadband: A transmission system involving modulation techniques in which several data streams are each modulated onto a different frequency, the frequencies are mixed to create a composite, and the composite signal containing all component data streams placed on the transmission medium.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD): The media access control method used by Ethernet and 802.3 standards. Devices first Carrier Sense (i.e. listen) and only transmit if the channel is clear. If two devices see a clear channel and transmit at the same time a collision will occur. This is resolved by the Collision Detection mechanism of the protocol in which devices continuously read data off the channel and compare with their own contribution; if a difference is detected a collision is assumed and they terminate transmission. A new attempt at transmission is made after waiting a random amount of time.
Client/server architecture: An environment in which applications are distributed between a host server and a remote client. Processing may be shared between client and server, the nature of this sharing will effect the bandwidth utilisation of the communications channel.
Code Division Multiple Access (CDMA): A spread-spectrum digital cellular radio system in which different codes are used to distinguish sources.
Data link layer: Layer-2 of the OSI model. Split into two sub-layers called LLC and MAC. The MAC layer is responsible for accessing a shared media and implements some form of access technique such as CSMA/CD/CA or token passing, performs error detection, and requires the use of physical addressing. LLC comes in different flavours but can if required implement error correction and flow-control.
Decibel: a logarithmic measure used to represent a gain or loss relative to some reference point. The overall gain(loss) of a network may be found by adding or subtracting the gains (losses) of each cascaded stage, this is the benefit of logarithmic measure. dBm represents a power level relative to 1milliwatt.
Direct Sequence Spread Spectrum (DSSS): A type of spread spectrum that spreads its signal continuously over a wide frequency band. DSSS is a transmission technology in which a data signal at the sending station is mapped into a higher data rate bit sequence using a "chipping" code. The chipping code (also known as processing gain) introduces redundancy which allows data recovery if certain bit errors occur during transmission. The FCC rules the minimum processing gain should be 10, typical systems use processing gains of 20.
Dwell Time: In a FHSS systems this is the amount of time (dwell) a device is allowed to spend transmitting on any one of the frequencies.
Extension point: A base-station 2-radio transceiver that bridges the gap between a wireless client and an access point or between a wireless client and another extension point.
File Transfer Protocol (FTP): A reliable connection oriented application layer protocol, part of the TCP/IP suite, it is used for reliable file transfers.
Frame Relay: A Connection-oriented Layer-2 protocol used to connect LANs. FR offers a rudimentary quality-of-service in the form of CIR and EIR. Fundamental to the use of FR is good quality (low error rate) medium.
Frequency Division Multiple Access (FDMA): A digital radio technology that divides the available spectrum into separate radio channels. FMDA is normally used in conjunction with Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA).
Frequency Hopping Multiple Access (FHMA): A system using frequency hopping spread spectrum to permit multiple, simultaneous conversations or data sessions by assigning different hopping patterns to each.
Frequency Hopping Spread Spectrum: (FHSS): A type of radio communications in which the transmitter and receiver hop in synchronisation through a pre-arranged pattern of frequencies. This reduces the effect of narrow band noise. FHSS modulates information onto a narrowband carrier signal that "hops" in a pseudo-random but predictable sequence from frequency to frequency. This technique reduces interference because a signal from a narrowband system will only affect part of the spectrum. Transmission frequencies are determined by a so-called spreading, or hopping, code. Receivers must be set to the same hopping code and must listen to the incoming signal at the right time and correct frequency in order to properly decode the signal. FCC regulations require manufacturers to use 75 or more frequencies per transmission channel with a maximum dwell time (the time spent at a particular frequency) of 400 ms.
Frequency Shift Keying (FSK): A modulation scheme for data communications using a limited number of discrete frequencies to convey binary information. Used by earlier modems V.21, V.22 etc.
Fresnel Zone: The area around the visual line-of-sight between transmitter and receiver. Radio waves disperse as they leave the antenna. Obstructions in this zone of dispersion (Fresnel Zone) attenuate the signal. In the 2.4GHz ISM band this is particularly true of objects with a large moisture content such as trees.
Gigahertz (GHz): One billion hertz
Hand-off: In a cellular network, refers to the process of terminating communications with one cell and establishing communications with an adjacent cell when a mobile user travels between cells. Hand-offs normally involve switching from one pair of frequencies to another.
Hertz (Hz): Cycles per second. Used to measure frequency.
HomeRF: Is a specification for wireless digital communication between PCs and consumer electronic devices used within the home environment. Based on frequency hopping for the transmission of voice and data. HomeRF has a range of up to 150 feet and uses the Shared Wireless Access Protocol.
HyperLAN/HiperLAN: A wireless LAN protocol developed by ETSI (European Telecommunications Standards Institute) akin to 802.11. There are two types of HiperLAN, both operating in the 5GHz band. HiperLAN/1 provides data-rates up to 20 Mbps, and HiperLAN/2 data-rates up to 54 Mbps.
IEEE (Institute of Electrical and Electronics Engineers): A professional society serving electrical engineers through its publications, conferences and standards development activities.
Infrastructure Mode: Refers to an 802.11 framework in which communication takes place via an Access Point. In infrastructure mode, wireless devices use the AP to communicate with each other and with devices on a wired network. Most corporate WLANs operate in infrastructure mode in order to access to the wired LAN.
Internet Protocol (IP): A connectionless network-layer protocol from the TCP/IP suite It provides a best-efforts (fire and forget) datagram delivery service. The reliability of the Internet comes from TCP which is (CO) and implements time-outs and auto-retransmission.
Internetwork Packet Exchange (IPX): The network-layer protocol from the Novell NetWare protocol stack.
Local Area Network (LAN): A network interconnecting devices in the same office, floor or building, or areas inside buildings with areas just outside.
Media Access Control (MAC): Protocols used to control access to a shared network medium. Common MAC techniques include ? CSMA/CD, CSMA/CA, Token Passing, and polling.
Modulation: Used to impress an information source (intelligence) onto a transmitter's carrier signal. Carriers are used to match the transmitted signal to the bandpass characteristics of the transmission medium.
Multipath fading: A type of fading caused by signals taking different paths from the transmitter to the receiver and, consequently, interfering with each other.
Network Interface Card (NIC): A circuit board installed in each network station to allow communications with other stations.
Node: Any network station.
Open Systems Interconnection (OSI) model: A seven-layer protocol model developed to facilitate interconnection of disparate computer networks. Describes a 'model' as opposed to a protocol suite and provides a useful framework to classify protocols old and new.
Packet: Refers to the data-unit of the Network-Layer (layer-3). A packet usually includes a logical address to be used by routing devices. Messages are segmented and segments placed in packets with a logical address header. Packetising data allows greater throughput through noisy or congested communications environments. Sending a 1,000,000 bit message through an environment with a 1-in-10^6 error rate will result in zero throughput. Transmitting 10 packets of 100,000 bit will result in a 90% throughput.
Packet-switched: A communications network that uses shared facilities to route data packets from and to different users. Unlike a circuit-switched network, a packet-switched network does not set up dedicated circuits for each session.
PAN: A personal area network. Eg Bluetooth
Peer-to-peer network: A network design in which each computer shares and uses devices on an equal basis.
Physical layer: Layer-1 of the OSI model that establishes protocols for voltage, data transmission timing, speed, operation mode (FDX, HDX), transmission formatting asych vs synch, and connector pin-outs.
Protocol: The generic name used to describe communications structured according to a strict set of predefined rules.
Radio frequency (RF): A generic term for radio-based technology.
Repeater: A device used to extend cabling distances by regenerating signals. Signal regeneration is not simply amplification but involves three R's ? Re-shape, Re-time, Retransmit.
Roaming: refers to the ability to move from one Access Point coverage area to another without interruption in service or loss in connectivity.
Shared Wireless Access Protocol (SWAP): is a specification for wireless voice and data networking in the home. SWAP integrates with the PSTN and Internet using existing cordless telephony and WLAN. SWAP operates in the 2.4G ISM band at 50 hops per second at a data-rate of between 1 and 2 Mbps. A SWAP based network will allow cordless handheld devices to voice activate home electronic systems and access the Internet.
Simple Network Management Protocol (SNMP): A connectionless applications services protocol from the TCP/IP suite. It may also be used directly over Ethernet. SNMP provided the mechanism to retrieve MIB information from device agents. Three versions of SNMP are available v1, v2 and v3.
Spread spectrum: A radio transmission technology that spreads the user information (intelligence) over a much wider bandwidth but at reduced power. The principal benefits are improved tolerance to interference and allowing unlicensed operation.
Telnet: An application services protocol from TCP/IP protocol suite. Allows a remote PC, equipped with terminal emulator software, to take console control over a distant (IP addressable) device. Telnet is reliable since it is carried over TCP (Port 23).
Time Division Multiple Access (TDMA): A digital radio technology that divides each frequency channel into separate time slots for separate conversations or sessions.
Token Bus: A network that uses a logical token passing access method. Unlike a token passing ring, permission to transmit is usually based on the node address rather than the position in the network. A token bus network uses a common cable set with all signals broadcast across the entire LAN.
Token Ring: A Local Area Network (LAN) standard developed by IBM that uses tokens to control access to the communication medium. Token are received from physical upstream neighbours.
Transmission Control Protocol/ Internet Protocol (TCP/IP): A de facto, industry-standard protocol for interconnecting networks. TCP/IP is the basis of the Internet and corporate intranets.
Wired Equivalent Privacy (WEP): A security protocol for wireless local area networks. WEP was intended to provide the same level of security as that of a wired LAN. However, it has been found that WEP is not as secure as once believed. WEP is used at the two lowest layers of the OSI it therefore does not offer end-to-end security.
Wide Area Network (WAN): WAN implementation usually involves the use of a Telco service such as ISDN, F-Relay, X.25, ATM, SMDS. Data rates for WAN have traditionally been lower than that of LAN due to noise factors and the cost of leasing high-bandwidth links. One normally associates WAN implementations with a greater communications throw (distance); however a WAN service can equally be used to traverse a few hundred metres!
Wi-Fi: Wireless Fidelity; Wireless Ethernet Compatibility Alliance's (WECA) brand identity for the IEEE 802.11b standard; WECA certification that ensures products' compatibility.
Wi-Fi5: Refers to WLAN products based upon the 802.11a specification operating in the 5 GHz radio frequency band. Only products that have passed WECA'A interoperability testing are allowed to display the Wi-Fi5 certification logo.
Wireless: Describes any computing device that can access a network without a wired connection.
X.25: The original connection oriented packet switching protocol (layer-3). X.25 is quite slow but exceptionally reliable, is used in high noise environments (where packets may pass though analogue links). Providers offer X.25 service up to 64kbps. X.25 utilises HDLC (LAP-B) at layer-2 and X.21 (X.21bis) at layer-1.