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Access Point (AP) A wireless LAN/WAN transceiver that acts as a center point of an all-wireless network or as a connection point between wireless and wired networks. ADSL Asymmetric Digital Subscriber Line. New technology to carry high speed data over ordinary phone lines. It is up to 70 times as fast as a 28.8 modem, and can be used concurrently with voice over the same line. It is gradually being offered to homes commercially now. It is called "asymmetric" because download speeds to the subscriber are faster than upload speeds from the subscriber. 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. 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. ATM Asynchronous Transfer Mode. A packet switching model for fast long distance communications that uses fixed packet size and allows for intelligent decisions on routing, handling, prioritization, and costing. This allows for special handling and routing for data that must be reassembled quickly and accurately, such as live Video. Backbone A central network connecting other networks together. Formerly a network run by the National Science Foundation for the US, there are now multiple backbones run by commercial providers such as MCI, Sprint, UUNET, and AT&T. Bandwidth Literally, the frequency width of a transmission channel in Hertz, kiloHertz, megaHertz, etc. Often used as an expression of the amount of data that can be sent through a circuit. The greater the bandwidth, the greater the amount of data that can travel in a given time period. Beamwidth The angle of signal coverage provided by an antenna. Beamwidth typically decreases as antenna gain increases. bit Short for binary digit (0 or 1). Lower case b is used in abbreviations to distinguish it from bytes. For example, KBps (thousand bytes per second) is 8 times as great as Kbps (thousand bits per second) Bps Bytes per second. bps Bits per second Bridge A bridge is a combination of hardware and software that connects local area networks (LANs) of similar types together. See router. Broadband When the bandwidth of a signal is large, it can simultaneously carry many channels of information. Fiber optic cable, in particular, has a very high bandwidth, and is referred to as broadband. Bus An electronic pathway. In networks, a configuration (topology) with a single linear cable, terminated at each end, to which computers and devices are connected. There are no loops or branches in the cable. Also called a daisy chain. Byte 8 bits of data. Capital B is used in abbreviations to distinguish it from bits. For example, KBps (thousand bytes per second) is 8 times as great as Kbps (thousand bits per second). CDSL Acronym for Consumer Digital Subscriber Line. Rockwell's new technology for digital modems that will use regular telephone lines and run at speeds up to 1 MBps. Channel A communications path wide enough to permit a single RF transmission. Client Any computer connected to a network that requests services (files, print capability) from another member of the network. Coax, coaxial cable A type of cable which contains two conductors, one inside and the other outside around it, separated by an insulating layer. They share the same axis, giving the cable its name co-axial. It is the same kind of cable that brings cable TV into your house. CRC Acronym for Cyclic Redundancy Check, a technique of providing a data string added to packets of information that can be used to detect errors in the data packets. In the OSI or TCP/IP network models, CRC is added to a packet frame at the Data Link Layer. 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 antenna). The greater the dBi value, the higher the gain and, as such, the more acute the angle of coverage. * differentiated services At present, all packets on the Internet are treated alike, regardless of their importance. If you want an important message to be delivered immediately or a streaming video signal to be distributed smoothly and without interruptions, there is no way to differentiate between immediate needs and routine transmissions which could be delayed for a long time without any problems. There are currently efforts under way to test and develop standards for differentiated services, where high priority data can be sent through or around clogged nodes ahead of low priority data. The high priority data transmission will cost more, of course. 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. DSL Acronym for Digital Subscriber Line or Digital Subscriber Loop, often referred to as xDSL. It refers to fast two-way data connections over ordinary telephone lines.. 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. Ethernet A LAN protocol developed by DEC, Intel, and Xerox as an outgrowth of Harvard graduate student Bob Metcalfe's dissertation on packet networks. Computers using TCP/IP often connect to the Internet via ethernet LANs. Ethernet typically uses a bus (daisy chain) topology. Firewall Firewall refers to the concept of a security interface or gateway between a closed system or network and the outside Internet that blocks or manages communications in and out of the system. The security may be provided by passwords, authentication techniques, software, and hardware. Frame relay A packet switching standard based on the older X.25 protocol that achieves greater speeds with fast, reliable networks. It lowers overhead by reducing the accounting and checking procedures used in X.25. 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 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. 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 Cycles per second. Used to describe the cycle rate in radio, electronics, and audio. Abbreviated Hz, and often combined with numeric prefixes, such KHz, MHz, GHz, and so on. Named for the German physicist Heinrich Hertz, who discovered electromagnetic waves. Hop A message or data packet travels a path among routers on a network through a series of hops from the source to the destination Hub A device that connects the cables from computers and other devices such as printers in an ethernet local area network. Traditionally, hubs are used for star topology networks, but they are often used with other configurations to make it easy to add and remove computers without bringing down the network. Smart hubs or switching hubs are often used to improve performance by managing traffic Isotropic An antenna (or a theoretic construct of an antenna) that radiates its signal 360 degrees both vertically and horizontally—a perfect sphere Intranet A network of networks that interconnects within a single widespread organization and uses the Internet Protocol (IP). The sites within an Intranet are generally closed to the Internet and are accessible to organization members only.. IP Internet Protocol. IP address IP addresses, together with domain addresses are the two forms of Internet addresses in common use. IP addresses consist of four numbers between 0 and 255, separated by dots. ISDN Integrated Services Digital Network. A technology that carries data over phone lines at up to 128Kbps for dialup users, but extends to fast broadband communications, too. It applies to the first three layers of the OSI and TCP/IP models. Slow to get started in the US, it is likely to be overtaken by the much faster DSL models over the next few years. ISP Internet Service Provider. 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. MAC address Media Access Control address, given to a device in a network. It consists of a 48-bit hexadecimal number (12 characters). The address is normally assigned to a device, such as a network card, when it is manufactured MAE Metropolitan Area Exchange or Metropolitan Area Ethernet. A major Internet Network Access Point (NAP) where different providers and networks hand off traffic to each other. The two main MAEs in the United States are MAE East in Washington, DC and MAE West in Silicon Valley. 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. NAP Network Access Point. A point where networks and service providers hand off traffic to each other. NAPs are typically the points with the worst congestion problems. When you encounter slow responses and run a traceroute, you will usually see the slowest connections occur where one network hands off to another. See MAE. Network A group of computers or devices that are connected together for the exchange of data and sharing of resources. 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. NIC Acronym for Network Interface Card, for example, an ethernet card in a network. Omnidirectional Antenna An antenna that provides a 360-degree transmission pattern. This type of antenna is used when coverage in all directions is required Packet A packet is a self-contained bundle of data sent over a packet switching network. Packets are typically less than 1500 bytes in size. Longer files are broken into multiple packets for transmission and reassembled at the other end. A packet includes a header with to and from addresses, relation to other packets (sequencing), and error checking information. On the Internet, datagram is a synonym for packet. 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. Port 1. A connection to a computer to enable other devices, such as printers, modems, monitors, keyboards, mice, etc. to interface with the computer. 2. A logical connection to a network. Different port numbers are used for different purposes, for example, HTTP usually uses port 80. POTS Acronym for Plain Old Telephone Service. Protocol A standard for the exchange of information. Different computers and operating systems and software are able to communicate with each other on the Internet, because of the adoption of protocols. RADSL Acronym for Rate Adaptive Digital Subscriber Line, currently being introduced by US West. RJ-11 The type of modular jack used with telephones. It connects one to three pairs of wires with a transparent connector that plugs into your phone on one end and a wall jack on the other. RJ-45 A modular jack that can connect up to four pairs of wires. It resembles the RJ-11 telephone jack, but is a bit larger. It is commonly used to connect twisted pairs of cable in a LAN. Ring A network configuration (topology) in which all computers and devices are connected to a circular pathway. Router A router connects networks together, controlling the routing of packets from source to destination and providing alternate paths when necessary. Routers are more sophisticated than bridges, connecting networks of different types (for example, star and token ring), and making logical routing decisions on the basis of available data. Typically a router hands off packets to another router along the path until the destination is reached. 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. Star A network configuration (topology) in which all computers and devices are connected by direct cables to a central hub. Streaming audio, streaming video Technologies which permit listening and watching continuously as the signal is transferred to your system from a remote web site. It requires a high degree of compression to transfer audio or video (or both) at 28.8 Kbps or 14.4 Kbps speeds and still retain quality music and non-jerky video. Faster connection speeds are needed to improve quality substantially, and the speed must be maintained over the entire path between the transmitting and receiving systems. The systems generally use a few seconds buffering, but signal slowdowns or interruptions longer than that break the flow. T-1 A digital communications circuit that transmits at 1.54 Mbps. T-3 A digital communications circuit that transmits at 45 Mbps. TCP/IP Transmission Control Protocol/Internet Protocol. The protocols that are the basis for transmitting and routing data packets on the Internet. The Internet Protocol is the one thing that all current Internet sites have in common. The basic TCP/IP model has five layers of interaction: Transmission Control Protocol (TCP) A protocol used along with the Internet Protocol (IP) to send data in the form of individual units (called packets) between computers over the Internet. Whereas IP handles the actual delivery of the data, TCP keeps track of the packets that a message is divided into for efficient routing through the Internet. For example, when a Web page is downloaded from a Web server, the TCP program layer in that server divides the file into packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, it may get routed differently through the network. At the other end, TCP reassembles the individual packets and waits until they have all arrived to forward them as a single file. Virtual Private Network (VPN) A private network within a public network, usually on the Internet. Privacy for the virtual network is achieved through encryption and provides a less expensive option than using dedicated lines. WAN Wide Area Network. 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. WAP Wireless Application Protocol. A protocol used with small handheld devices with small file sizes. X.25 An international standard for packet switching, typically used with older telephone networks for data communications. X.500 A directory access protocol to enable a common standard for directories of information over a network. It has never caught on as well as its designers intended. Yagi A type of midrange-gain, directional antenna. 10base2 An ethernet standard for cable. The 10 refers to its 10 Mbps bandwidth, the base to single channel baseband, and the 2 to its 200 meter effective range. It uses thin coaxial cable. 10baseT An ethernet standard for cable. The 10 refers to its 10 Mbps bandwidth, the base to single channel baseband, and the T to Twisted pair. The cable uses two pairs of unshielded twisted wires.
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