Logical failures occur when the frame relay link integrity verification protocol, sometimes called the local management interface (LMI), fails to successfully perform a protocol handshake between the switch and the CPE.

• 当帧中继链路完整性验证协议（有时也叫本地管理接口（LMI）不能成功地在交换机与CPE之间执行协议握手时，逻辑失效就出现。