PPTP is an encapsulation protocol based on PPP that works at OSI layer 2 (Data Link) and that enables a single point-to-point connection, usually between a client and a server.
While PPTP depends on IP to establish its connection.
As currently implemented, PPTP encapsulates PPP packets using a modified version of the generic routing encapsulation (GRE) protocol, which gives PPTP to the flexibility of handling protocols other than IP, such as IPX and NETBEUI over IP networks.
PPTP does have some limitations:
It does not provide strong encryption for protecting data, nor does it support any token-based methods for authenticating users.
L2TP is derived from L2F and PPTP, not the opposite.