PPP stack
LCP
A method of establishing, configuring, maintaining, and terminating the point-to-point
connection.
NCP
A method of establishing and configuring different Network layer protocols. NCP is
designed to allow the simultaneous use of multiple Network layer protocols. Some examples
of protocols here are Internet Protocol Control Protocol (IPCP) and Internetwork Packet
Exchange Control Protocol (IPXCP).
Burn it into your mind that the PPP protocol stack is specified at the Physical and Data Link
layers only. NCP is used to allow communication of multiple Network layer protocols by
encapsulating the protocols across a PPP data link.