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D Channel -- As
related to ISDN, a 16Kbps, full duplex channel, normally used for
supervisory support of the channel. This channel may be used to carry data
defined by the user (or manufacturer of the TA) See:
B Channel
D2 Channel Bank -
Analogue Multiplexer usually found at
the CO. Multiplexes 24 analogue(64K) channels (trunks) into a single
DS-1( T1)
port, usually for connection into a central office switch
D4 Channel Bank -
Analogue Multiplexer usually found at
the CO. Multiplexes up to 104 analogue(64K) channels (trunks) into a
single DS-3 port, usually for connection into a central office switch
DAC - See
DCS
Db (Decibel)
- A relative measure of strength. A Decibel is a ratio of the comparison of two signals. i.e. a
measurement of relative strength. Db in itself not a voltage (or
similar) measurement, it is a relationship between two signals.
Dbm (Decibel in milliwats)
- A definitive measure of power: A power level measurement referenced to
one milliwatt. (0 dBm = 1 milliwatt and -30 dBm = .001 milliwatt =
.775VRMS into 600 ohms)
DCE (Data Communications
Equipment) -- Refers to the
communications (analogue data link) side equipment. In the modem world,
refers to the analogue link <the phone line> between the two modems connection. See:
DTE
DCS (Digital Crossconnect
Switch - Pronounced "DACS") A time-slot
switch that electronically remaps( grooms)
DSO's(64Kbps) which are embedded into various DS1's(E1 or T1) and
moves(Routes) the DS0's to various other DS1's. Typically a DCS has
multiple DS1's connecting to a DS-3 or higher connection. Also called
DAC
or DXS.
Dial-up
- Usually refers to the telephone company's switched networks. Modems and
telephones are considered 'Dial-up' type equipment.
DLC (Digital Loop Carrier) --
A hardware 'box' that sits between a
CO and
CPE. Basically a
powerful Multiplexer that provides the services normally given directly
from the CO but is needed because the CO is too far from the customer
locations. A DLC is usually fed by fiber or DSX speeds (T1
/ E1 or
above). Capable of providing voice or data feeds to the CPE. The CPE
feeds may be in any form from straight twisted pair voice to any DSX
service. See BORSHT
functions
DMT (Discrete Multi-Tone) --
A modulation technique which explains several bands of low rate carrier
frequencies which are
QAM modulated at a low rate
that combine to transmit a single high rate data stream. DMT or
CAP are the two
main modulations used in ADSL.
DSX (Digital
Signal Level-X) -- A general
<non-specific> reference to speeds of a digital interface. More accurate
representations are DS-0 (64Kbps), DS-1 (1.544Mbps-T1) and DS-3
(45Mbps). Usually DSX refers to speeds above T1 (DS-1).
DS-0 (Digital Signal Level-0)
- An electrical translation of the
analogue (voice) or digital (data) on your standard phone lone DS-0
operates at a rates of 64Kbps. 28 DS-0 channels exist in a DS-1 (T1).
See:
SONET,
DSX
DS-1 (Digital Signal Level-1)
- Same as
T1.
Digital transmission facility capable of carrying data rates of
1.544Mbps. One DS-1 Combines 24 DS-0 channels. 28 DS-1's exist in one
OC-1
channel (approx. 50Mbps.)
DS-3 (Digital Signal Level-3)
- Same as
T3.
Digital transmission facility capable of carrying data rates of up to
44.736Mbps (45Mbps). Combines 28 DS-1 channels. Normally used in
connection to a Fiber Loop.
DSL (Digital Subscriber Line
<or Loop>) -- Refers to the wired
(copper) link from the telephone service company to the customer.
Usually misunderstood, DSL links are really analog signals which are
modulated to carry digital signals just like the familiar dial-up
modems.
DSL technology offers up to 'mega-bit' data
speeds over copper. It should be clearly noted that all DSL speeds vary
from their advertised speeds due to length, quality, gage of wire, S/N
ratios on wires, as well as manufacturers selection and implementation
of a modulation technology.
DSLAM (DSL Access
Multiplexer) -- A shelf of DSL
devices, usually installed at a CO, that combines several xDSL lines
into a single high speed link<usually ATM>. A DSLAM among other
features, could combine several individual xDSL lines into a single high
speed link such as a
DS-3
or OC-3
DSU/CSU (Data Service
Unit/Channel Service Unit) -- A type of
digital modem. Utilizes
2B1Q modulation
to speeds up to 128Kbps. Most units feature either
V.35 or
RS-232
DTE
interfaces.
DTE (Data Terminal Equipment)
- Refers to the data terminal
side equipment of an interface. Conventional modems have a DTE side and
a DCE side. The DTE side goes
to the PC or Host computing device via the serial port (i.e.
RS232).
The DCE side goes to the telephone line
interface such as the
modems DAA or RJ-11'
See: DCE,
Modem |
