PPP (Point-to-point protocol) is a WAN protocol that is often used on point-to-point links. Originally, PPP was often used for dial-up connections. Nowadays it's still used for DSL with PPPoE (PPP over Ethernet) and PPPoA (PPP over ATM). PPP has stronger protections, such as encryption of passwords and IP address validation. This makes it less likely that an intruder can establish a network connection in the first place.