Next: PPP on Up: The Point-to-Point Protocol Previous: The Point-to-Point Protocol . Just like SLIP, PPP is a protocol to send datagrams across a serial connection, but addresses a couple of deficiencies of the former. ... At the very bottom of PPP is the High-Level Data Link Control Protocol, abbreviated HDLC, which defines the boundaries around the individual PPP frames, and provides a 16-bit checksum. ... An important step at the configuration stage of a PPP link is client authorization. ...