The answer to question 01: A layer 2 protocol is the Point-to-Point Protocol (PPP). IP packets are encased in PPP frames and sent via the dial-up link to the ISP's router. The answer to question 02: In contrast to Ethernet's variable-size frames, ATM uses fixed-size cells and includes traffic shaping and policing techniques. The answer to question 03: IP routing is "best effort," whereas MPLS enables traffic shaping by allowing constraint-based routing.