单项选择题 You have just obtained a modular Cisco router with 2 serial connections and a BRI/U interface. What other physical piece of hardware is required in order to establish an ISDN connection?（）

多项选择题 Which of the following can LCP successfully negotiate during the establishment of a PPP connection?（）

多项选择题 You are about to configure PPP n the interface of a Cisco router. Which authentication methods could you use?（）