I don't understand how HDLC is encapsulated with PPP. Granted HDLC is a point-to-point protocol but what I don't understand is if you have 2 routers where one is Cisco and another is non-Cisco PPP can be used as an encapsualtion and HDLC you cannot be used. But like I mentioned HDLC is encapsulated in the PPP frame. Can someone answer this question. Thanks.