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多项选择题

VoLTE网络中,ISUP消息REL消息中哪几个原因值对应于SIP错误响应值480?()……

VoLTE网络中,ISUP消息REL消息中哪几个原因值对应于SIP错误响应值480?()

A.17user busy
B.18no user responding
C.19no answer from the user
D.20subscriber absent