Some DSL providers enable dial-in over PPTP (Point-to-Point Tunneling Protocol) instead of PPPoE. PPTP is an extension of PPP, partly developed by Microsoft.
With PPTP it is possible to build up a “tunnel” over IP nets to a remote station. A tunnel is a logical shielded connection, that protects the transferred data from unauthorized access. For this purpose the encoding algorithm RC4 is used.