Serial line protocol (SLIP) is an older protocol used to handle TCP/IP traffic over a dial-up or other serial connection. SLIP is a physical layer protocol that doesn't provide error checking. Such as modem error checking. It only supports the transmission of one protocol, TCP/IP.
A later version of SLIP, called compressed SLIP (CSLIP), became available though the name says compressed; the protocol actually just reduces the amount of information in the headers, and does not compress the transmission.
Point to point protocol (PPP) is much more robust than its earlier cousin, SLIP.PPP provides a physical and data link layer functionality that fixes many problems with SLIP.At the data link layer, PPP provides error checking to ensure the accurate delivery of the frames that it sends and receives. PPP also keeps a logical link control communication between the two connect devices by using the Link Control Protocol (LCP).PPP also supports the dynamic configuration of the dialled-in computer. Unlike STIP, where your addresses and other information have to be hard-coded ahead of time, PPP allows the client computer to receive its information from the host it dials into. Most internet dial-up connections today are made using PPP over modem or ISDN.