ISDN and PPP basic questions

Hi friends,

Just a few basic questions on ISDN and PPP:

1. When the ISDN BRI0:0 interface is up and line protocol is down, then is it because the ISDN NT1 box is not connected to the ISDN BRI port on router? Or is it that the NT1 box is off?

1. When ppp multilink is issued on the BRI interface, does it mean that both the BRI channels will come up?

2. Does PPP callback required PPP authentication? Or can the callback server callback without any authentication?

1. I saw that the BRI0:1 and BRI0:0 interfaces were administratively down? My understanding is that an interface can be administratively shut down only after issuing the command int BRI0:1 / 2 and executing the command shut on the router manually. But the BRI0:1 and BRI0:2 interfaces cannot be configured. Please help me understand this

Thanks a lot Gautam

Thanks and Regards Gautam