本文主要介绍了大客户专线电路中常见的故障，并通过实际中的故障案例提供了解决方法和思路。
This paper introduces a major customer of the common green circuit failures, and through actual cases of failure to provide the solutions and ideas.
WAN连接类型包括专线、电路交换和分封交换。
WAN connection types include leased line, circuit-switched, and packet-switched.
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