ADTRAN ISU 512 user manual Dds

Glossary

DDS

Dataphone digital service. AT&T private line service for transmitting data over a digital system. The digital transmission system transmits electrical signals direct- ly, instead of translating the signals into tone of varied frequencies as with tradi- tional analog transmission systems. Digital techniques provide more efficient use of transmission facilities, resulting in lower error rates and costs than analog sys- tems.

digital loopback

Technique for testing the digital processing circuitry of a communications device. May be initiated locally or remotely via a telecommunications circuit. Device be- ing tested will echo back a received test message after first decoding and then en- coding it. The results are compared with the original message (compare with analog loopback).

DSU

Data service unit. A device providing an interface between a data terminal or oth- er data communications device and a digital access line.

DTE

Data terminal equipment. The portion of a data terminal that interfaces to the end- user’s equipment. The main difference between DCE and DTE is that pins 2 and 3 are reversed on the RS-232.

frame

A group of bits sent serially over a communications channel. Generally a local transmission unit sent between data-link-layer entities that contains its own con- trol information for addressing and error checking. The basic data transmission unit is employed with bit-oriented protocols, similar to blocks. In video transmis- sion, a set of electron scan lines that comprise a television picture (usually 525 in the U.S.).

four-wire circuits

Telephone lines using two wires for transmitting and two wires for receiving of- fering much higher quality than a 2-wire circuit. All long distance circuits are 4- wire. Almost all local phone lines and analog phones are 2-wire.

in-band signaling

Signaling made up of tones which pass within the voice frequency band and are carried along the same circuit as the talk path being established by the signals. Vir- tually all signaling (request for service, dialing, disconnect, etc.) in the U.S. is in- band signaling. Most of that signaling is MF (multi-frequency) dialing. The more modern form of signaling is out-of-band.

information element

The name for the data fields within an ISDN Layer 3 message.

61202.086L1-1 ISU 512 User Manual 101