以下是配置PPP认证时通过debug ppp authentication得到的信息，请问该协议是几路握手？%UPDOWN：Interface Serial0，changed state to upPPP Serial0：Send CHAP challenge id=2 to remotePPP Serial0：CHAP response id=2 received from user1PPP Serial0：Send CHAP success id=2 to remotePPP Serial0：remote passed CHAP authentication.%UPDOWN：Line protocol on Interface Serial0，changed state to up ( )