Point-to-Point Protocol
SLIP
PPP (point-to-point protocol).
PPP (Point-to-Point Protocol)
PPP
Network Control Protocol is uses to identify the Network layer protocol used in the packet
HDLC
Point-to-Point Protocol (PPP) is the most commonly used protocol for dial-up connections.
PPP is point to point protocol. It does single channel network links, usually over a long distance, or a VPN. The program that sets up and manages PPP connections is pppd.
Network control protocol
The full form of PPP is Point-to-Point Protocol. It is a data link protocol used to establish a direct connection between two nodes in a network. PPP is commonly used in connecting computers to the internet via dial-up or dedicated connections.
there may be the issue with the layer 2 protocol like hdlc or ppp is not configured or wrongly configured if the interface is serial interface.
LCP sets up the PPP connection and its parameters. NCP handles higher layer protocol configurations.