Glossary: Mostlyabreviations and acronyms:
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X.25: Interface between data terminal equipment(DTE) and data circuit-terminating equipment (DCE)for terminals operating in the packet mode on public data networks. X.75:Terminal and transit call control procedures and data-transfer system oninternational circuits between packet-switched data networks.

X11: X Windows version 11; a network basedwindowing system developed at MIT. Releases are designatedas X11R6 meaning version 11 release 6.

XA: eXtended Architecture, (IBM)

xbm: X11 Bit-Map

xDSL: Any of the various 'Digital SubscriberLine' technologies; HDSL,ADSL, SDSL,RADSL, VDSL. Digital Subscriber Lines are a technology for bringing high-bandwidth informationto homes and small businesses over ordinary telephone lines.  Assumingyour home or small business is close enough to a telephone company centraloffice that offers DSL service, you may soon be able to receive data atrates up to 6.1 megabits (millions of bits) per second (of a theoretical8.448 megabits per second), enabling continuous transmission of motionvideo, audio, and even 3-D effects. More typically, individual connectionswill provide either 512 kilobits (thousands of bits) per second or 1 megabitsper second. During 1998, DSL will be installed in a number of communitiesin the U.S. and elsewhere. Compaq, Intel, and Microsoft are among companiesworking with manufacturers to accelerate deployment of an easier-to-installform of DSL called "DSL Lite." Within a few years,
DSL is expected to replace ISDN in many areas andto compete with the cable modem in bringing multimedia and 3-D to homesand small businesses. Dataquest, a market research firm, forecasts 5.8million lines installed by the end of the century.

Traditional phone service (sometimes called "Plain Old Telephone Service"or POTS) connects your home or small business to atelephone company office over copper wires that are wound around each otherand called twisted pair. Traditional phone service was created to let youexchange voice information with other phone users and the type of signalused for this kind of
transmission is called an analog signal. An input device such as aphone set takes an acoustic signal (which is a natural analog signal) andconverts it into an electrical equivalent in terms of volume (signal amplitude)and pitch (frequency of wave change). Since the telephone company's signallingis already set up for this analog wave transmission, it's easier for itto use that as the way to get information back and forth between your telephoneand the telephone company. That's why your computer has to have a modem- so that it can demodulate the analog signal and turn its values intothe string of 0 and 1 values that is called digital information.

Because analog transmission only uses a small portion of the availableamount of information that could be transmitted over copper wires, themaximum amount of data that you can receive using ordinary modems is about56 Kbps (thousands of bits per second). (With ISDN,which one might think of as a limited precursor to DSL, you can receiveup to 128 Kbps.) The ability of your computer to receive information isconstrained by the fact that the telephone company filters informationthat arrives as digital data, puts it into analog form for your telephoneline, and requires your modem to change it back into digital. In otherwords, the analog transmission between your home or business and the phonecompany is a bandwidth bottleneck.

Digital Subscriber Line is a technology that assumes digital data doesnot require change into analog form and back. Digital data is transmittedto your computer directly as digital data and this allows the phone companyto use a much wider bandwidth for transmitting it to you. Meanwhile, ifyou choose, the signal can be separated so that some of the bandwidth isused to transmit an analog signal so that you can use your telephone andcomputer on the same line and at the same time.

Splitter-based vs. Splitterless DSL; most DSL technologies require thata signal splitter be installed at a home or business, requiring the expenseof a phone company visit and installation. However, it is possible to managethe splitting remotely from the central office. This is known as splitterlessDSL or "DSL Lite."

DSL Modulation Technologies:  The modulation technology that isused for the various kinds of DSL is likely to be settled late in 1998by the International Telecommunication Union (ITU).Meanwhile, different DSL modem makers are using either Discrete MultitoneTechnology (DMT) or Carrierless Amplitude Modulation(CAP). A third technology, known as Multiple VirtualLine (MVL), is another possibility.

XDR: eXernal Data Representation

XFN: X/Open Federated Naming

XFS: eXtended File System; 64-bit journaledfilesystem, (SGI)

XIWT: Cross Industry Working Team; a multi-industrycoalition defining the architecture and key technical requirements fora powerful, sustainable information infrastructure.  (

XIWT aims

XIWT willXIWT Members

     Participate actively in working teams, Plenarymeetings, seminars and by other means to identify issues and
     solutions and work towards consensus on recommendations.

XNS: Xerox Network Services, (PARC)

XTP: eXpress Transfer Protocol

xwd: X11 Window Dump

Last Update:12/13/03
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