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D-4

(1) (D4) A framing format for T1 transmission that places 12 T1 frames into a superframe. See ESF.

(2) (Digital-4) There was never a D-4 videotape format because the Japanese believe 4 is unlucky. The pronunciation of the number sounds like the word for "death."



ESF

(1) (Extended SuperFrame) An enhanced T1 format that allows a line to be monitored during normal operation. It uses 24 frames grouped together (instead of the 12-frame D4 superframe) and provides room for CRC bits and other diagnostic commands.

(2) (External Source Format) A specification language for defining an application in IBM's CSP/AD application generator.



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D-3D/A preamp

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