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Appendix D. Glossary

61200214L1-20 IQ Probe User Manual D-5

DDS

Digital data service. AT&T private line service for transmitting data

over a digital system. The digital transmission system transmits elec-

trical signals directly, instead of translating the signals into tone of

varied frequencies as with traditional analog transmission systems.

Digital techniques provide more efficient use of transmission facili-

ties, resulting in lower error rates and costs than analog systems.

Discard eligibility. A user-set bit indicating that a frame may be dis-

carded in preference to other frames if congestion occurs, to maintain

the committed quality of service within the network. Frames with

the DE bit set are considered Be excess data.

DLCI

Data link connection identifier. A unique number assigned to a PVC

end point in a frame relay network. Identifies a particular PVC end-

point within a user's access channel in a frame relay network and has

local significance only to that channel.

DSU

Data service unit. A device designed to transmit and receive digital

data on digital transmission facilities.

DTE

Data terminal equipment. The end-user terminal or computer that

plugs into the termination point (DCE) of a communications circuit.

The main difference between the DCE and the DTE is that pins two

and three are reversed.

encapsulation

A process by which an interface device places an end device's proto-

col-specific frames inside a frame rely frame. The network accepts

only frames formatted specifically for frame relay; therefore interface

devices acting as interfaces to a frame relay network must perform

encapsulation. See also interface device and frame-relay-capable interface

device.

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ADTRAN 1200214L1 Spezifikationen Seite 163