| 摘要 |
PURPOSE:To omit a memory in common with respective exchange units by routining exchanging units in a prescribed order when the catch of a trunk in a routined exchange unit is failed, and requesting the catch of the trunk. CONSTITUTION:When the existence of a by-pass to a final terminating station is decided by a by-pass pattern table and a trunk 5 in the direction B is catched by an exchange unit X at the failure of trunk catching by a backword signal, an exchange unit Z is started and numerals are sent. The exchange unit Z detects that the 1st direction is a direction 1 on the basis of the numerals and catches a trunk 3 in the direction 1. When the trunk 3 is catched, the succeeding station is started and a series of numerals are sent, and when the trunk 3 is not catched, the status is informed to an exchange unit X.
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