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data service unit
See DSU.
dB
decibel. A unit of measure of signal strength; usually the relation between a
transmitted signal and a standard signal source.
DCE
data communications equipment. Device that provides all the functions required
for connection to telephone company lines and for converting signals between
telephone lines and DTE. Also see DTE.
DDS
digital data service. A private line digital service for transmitting data end-to-
end at speeds of 2.4, 4.8, 9.6, and 56 kbps (and in some cases 19.2, 38.4, or 64
kbps). The systems can use central hub offices for obtaining test access, bridging
legs of multi-point circuits, and cross connecting equipment. DDS is offered on
an inter-LATA basis by AT&T and on an intra-LATA basis by the Bell operating
companies.
delay
The amount of time by which a signal is delayed. A round-trip transmission
delay measurement helps detect possible causes of protocol timeouts.
DLCI
datalink communications identifier. A unique number assigned to a PVC end
point in a frame relay network. Identifies a particular PVC endpoint within a
user's access channel in a frame relay network and has local significance only to
that channel.
DS1
digital signal level one. Twenty-four DS0 channels make up one DS1 (total band-
width is 1.544 Mbps).
DS3
digital signal level three. Equivalent of 28 DS1s and 672 DS0s (total bandwidth is
44.736 Mbps).
DSU
data service unit. A device designed to transmit and receive digital data on digi-
tal transmission facilities.
61200217L1-1
T3SU 300 User Manual
Appendix D. Glossary
D-5
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