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第一台 HJD-31(400门)程控交换机于1992年12月20日在河北永年县刘营邮电所正式开通,投入试运行.HJD-31(200门、400门、600门、800门、1000门系列)空分程控交
The first HJD-31 (400-gate) program-controlled switch was officially put into trial operation at the Liuying Post and Telecommunication Office of Yongnian County in Hebei on December 20, 1992. The HJD-31 (200, 400, 600, 800, 1000 series) Air separation program-controlled pay