Instead of using PPPoE for dialing-in, some DSL providers instead PPTP (Point-to-Point Tunneling Protocol). PPTP is a protocol extension of PPP and was primarily developed by Microsoft.
PPTP allows you to establish "tunnels" to a remote site via IP networks. A tunnel is a logically shielded connection that protects the transmitted data from unauthorized access by third parties. The RC4 encryption algorithm is used for this.