| 单词 | Class 3 |
| 释义 | Class 3 In the traditional public switched telephone network (PSTN) hierarchy, a primary toll center. Class 3 offices served to connect Class 4 offices for intrastate toll calling, and to interconnect independent telcos and the Bell operating companies (BOCs). Approximately 200 Class 3 offices existed prior to the breakup of the Bell System. It is doubtful that any remain. See also Bell System, BOC, Class 4, independent telephone company, and PSTN. |
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