Your IP is:   


V92/90 (56K) FAQ's

56K Speed Limits

AT Commands


RS-232 Info

Telecom Certs

Modem Testing Stds

Layout Guidelines

Surge Protection

Common Pitfalls

Modems and VoIP

xDLS Stuff


Modem Consulting

Cool Stuff




Terms used as applied to Data (and some Voice) Transmission over Copper Wire

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

D Channel
D2 Channel Bank
D4 Channel Bank


























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


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

Broken Links?...  Suggestions?...   Please let us know...


Copyright 1997-2009 Floyd Kling 
- All Rights Reserved -