Page 229 - Electrical Engineering Dictionary

acterized by the appearance in the output distributedcomputingenvironment(DCE)
of frequencies equal to the sum and differ- an industry-standard, comprehensive, and
ence of the desired carrier’s frequency and integrated set of services that supports the
the unwanted cross modulating carrier’s fre- development, use, and maintenance of dis-
quency. Although harmonic components are tributed computing technologies. DCE is in-
also caused to be present, they are not usually dependent of the operating systems and net-
a part of measurements of this effect. work types. It provides interoperability and
portability across heterogeneous platforms,
distortion factor See total harmonic dis- and provides security services to protect and
tortion. control access to data. DCE also provides
services that make it easy to find distributed
distortion-rate theory See rate-distortion resources; for instance, directory service, a
theory. DCE component, is a central repository for
information about resources in a distributed
distributed amplifier (1) composed of system. Distributed time service (DTS), an-
two main artificial transmission-line sections other DCE component, provides a way to
consisting of series inductors and shunt ca- synchronize the times on different hosts in
pacitors, which are usually supplied by the a distributed system. DCE gives a model for
FET transistor. Excellent bandwidth per- organizing widely scattered users, services,
formers are obtainable and the amplifier can and data. It runs on all major computing plat-
be designed as wideband low-noise ampli- forms and is designed to support distributed
fiers and are relatively easy to simulate and applications in heterogeneous hardware and
fabricate. software environments. Particularly impor-
(2) the input and output capacitance of tant for the World Wide Web and security of
the active devices can be absorbed into dis- distributed objects.
tributed circuits (i.e., transmission lines) to
obtain a very broad bandwidth.
distributed computing system a system
distributed antenna typically consists of whose different parts can run on different
a set of discrete radiators fed by a common processors.
cable from a single signal source.
distributed control a control technique
distributed arbitration a scheme used
whereby portions of a single control process
for bus arbitration where multiple bus mas-
are located in two or more places.
ters can access the bus. Arbitration is not
done centrally (by a bus arbiter), but instead
done in a distributed fashion. A mechanism distributed element a circuit element in
to detect when more than one master tries to which dimension is not negligible relative to
transmit on the bus is included. When this the wavelength. The characteristics of a dis-
happens, one (or all) stops transmitting and tributed element depend upon a dimension
will reattempt the transmission after a short such as a length.
(e.g., random) time delay.
Compare with centralized arbitration.
distributed feedback laser (DFB) a laser
distributed computing an environment source where the optical feedback is dis-
in which multiple computers are networked tributed throughout the length of the gain
together and the resources from more than medium. Feedback then occurs through
one computer are available to a user. See Bragg diffraction, and the laser operates in
also distributed computing environment. only one optical mode.

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2000 by CRC Press LLC