| 单词 | DDD (Direct Distance Dialing) |
| 释义 | DDD (Direct Distance Dialing) A feature of the public switched telephone network (PSTN) that allows a subscriber to dial a long distance telephone number directly, i.e., without the intervention of an operator. DDD was introduced by the Bell System in 1951, and is virtually ubiquitous today. See also long distance and PSTN. |
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