THE WHATIS.COM WEEKLY WORDSET April 27, 2001 STRIKE UP THE BANDWIDTH ______________ THIS WEEK'S SPONSOR: VeriSign - The Internet Trust Company Protect your servers with 128-bit SSL encryption! Get VeriSign's FREE guide, "Securing Your Web Site for Business". You will learn everything you need to know about using SSL to encrypt your e-commerce transactions. Click here! http://www.verisign.com/cgi-bin/go.cgi?a=n016035170014000 _____________ THIS WEEK'S WORDSET: STRIKE UP THE BANDWIDTH These are shortened versions of definitions at whatis.com. bandwidth - the width of a band of electromagnetic frequencies. Bandwidth is used to mean (1) how fast data flows on a given transmission path, and (2), the width of the range of frequencies that an electronic signal occupies on a given transmission medium. Every digital or analog signal has a bandwidth that is directly proportional to the amount of data transmitted or received per unit time. In a qualitative sense, bandwidth is proportional to the complexity of the data for a given level of system performance. Large sound files, computer programs, and animated videos require more bandwidth for acceptable system performance. Virtual reality (VR) and full-length three-dimensional audio/visual presentations require the most bandwidth of all. http://whatis.techtarget.com/definition/0,289893,sid9_gci211634,00.html Fast Reference / The Speed of... - engineers use the phrase "data rate" rather than "speed", but speed (as in "Why isn't my Web page getting here faster?") seems more meaningful for the less technically inclined. Many of us tend to think that the number of bits getting somewhere over a period of time (bandwidth) is their speed of travel. Data speed is not, however, the same thing as bandwidth. For instance, a modem operating at a speed of 28,800 bps has a nominal frequency of 28.8 kHz but the bandwidth is generally much smaller because it depends on variations in the individual data characters, not on the number of data bits per unit time. http://whatis.techtarget.com/definition/0,289893,sid9_gci214198,00.html bandwidth test - a program that sends one or more files of known size over a network to a distant computer (for example, your own computer), measures the time required for the file(s) to successfully download at the destination, and thereby obtains a theoretical figure for the data speed between two or more points, usually in kilobits per second (Kbps) or megabits per second (Mbps). In order to get a reasonable estimate of bandwidth (sometimes referred to as throughput), experts suggest that three or more different test sites be used, and that each test be conducted six times at each site. The top and bottom 1/3 of the figures should be disregarded and the middle 1/3 of the results should be averaged. http://whatis.techtarget.com/definition/0,289893,sid9_gci529674,00.html bits per second (abbreviated bps) - a common measure of data speed for computer modem and transmission carriers. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second. The bandwidth of a signal depends on the speed in bps. http://whatis.techtarget.com/definition/0,289893,sid9_gci213820,00.html hertz - a unit of frequency (of change in state or cycle in a sound wave, alternating current, or other cyclical waveform) of one cycle per second. It replaces the earlier term of "cycle per second (cps)." The unit of measure is named after Heinrich Hertz, German physicist. http://whatis.techtarget.com/definition/0,289893,sid9_gci212244,00.html megahertz (abbreviated MHz) - a unit of alternating current (AC) or electromagnetic (EM) wave frequency equal to one million hertz (1,000,000 Hz). The unit is used in measurements of bandwidth for high-speed digital data, analog and digital video signals, and spread spectrum signals. http://whatis.techtarget.com/definition/0,289893,sid9_gci212562,00.html spread spectrum - a form of wireless communications in which the frequency of the transmitted signal is deliberately varied. This results in a much greater bandwidth than the signal would have if its frequency were not varied. The frequency of a conventional wireless signal is kept as constant as the state-of-the-art will permit so that the bandwidth can be kept within certain limits, and like a station on the radio, the signal can be easily located by someone who wants to retrieve the information. http://whatis.techtarget.com/definition/0,289893,sid9_gci213041,00.html electromagnetic radiation spectrum - the complete range of the wavelengths of electromagnetic radiation, beginning with the longest radio waves (including those in the audio range) and extending through visible light (a very small part of the spectrum) all the way to the extremely short gamma rays that are a product of radioactive atoms. In the electromagnetic radiation spectrum, there is only so much available bandwidth to go around. This contrasts with hard-wired systems, where available bandwidth can literally be constructed without limit by installing more and more cables. http://whatis.techtarget.com/definition/0,289893,sid9_gci211634,00.html Integrated Services Digital Network (ISDN) - a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. Home and business users who install an ISDN adapter (in place of a modem) can see highly-graphic Web pages arriving very quickly (up to 128 Kbps). ISDN requires adapters at both ends of the transmission so your access provider also needs an ISDN adapter. ISDN is generally available from your phone company in most urban areas in the United States and Europe. http://whatis.techtarget.com/definition/0,289893,sid9_gci212399,00.html bottleneck - a stage in a process that causes the entire process to slow down or stop. In data transmission, for instance, if your dial-up Internet service provider (ISP) promises you Internet access at 56 Kbps, but your modem can only handle 14.4 Kbps, your modem's slow performance would be a bottleneck. The term bottleneck is derived from the narrow part of a bottle used to slow down the flow of liquid. http://whatis.techtarget.com/definitionsSearchResults/1,289878,sid9,00.html?query=bottleneck Fast Guide to DSL (Digital Subscriber Line) - a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines. A DSL line can carry both data and voice signals and the data part of the line is continuously connected. Assuming your home or small business is close enough to a telephone company central office that offers DSL service, you may be able to receive data at rates up to 6.1 megabits (millions of bits) per second (of a theoretical 8.448 megabits per second), enabling continuous transmission of motion video, audio, and even 3-D effects. http://whatis.techtarget.com/definition/0,289893,sid9_gci213915,00.html cable modem - a device that enables you to hook up your PC to a local cable TV line and receive data at about 1.5 Mbps. This data rate far exceeds that of the prevalent 28.8 and 56 Kbps telephone modems and the up to 128 Kbps of Integrated Services Digital Network (ISDN) and is about equal to the data rate available to subscribers of Digital Subscriber Line (DSL) telephone service. The actual bandwidth for Internet service over a cable TV line is up to 27 Mbps on the download path to the subscriber with about 2.5 Mbps of bandwidth for interactive responses in the other direction. However, since the local provider may not be connected to the Internet on a line faster than a T-carrier system at 1.5 Mpbs, a more likely data rate will be close to 1.5 Mpbs. http://whatis.techtarget.com/definition/0,289893,sid9_gci211726,00.html _____________________ TECHTARGET FEATURE: McGraw-Hill Illustrated Telecom Dictionary , 3rd Edition By: Jade Clayton This annually updated collection of to-the-minute definitions helps you decipher telecom and data terminology, concepts, insider jargon, and acronyms. This third edition moves beyond traditional telecom and networking topics to embrace and explain the fast moving world of Internet telephony (VoIP). The accompanying CD lets you search the entire book. http://www.digitalguru.com/dgstore/product.asp?isbn=0071372016&ac_id=76 __________________________ SUPPORT OUR SPONSOR! 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