1) PAP (Packet-Level Procedure) is a full-duplex protocol for transferring packets between parties in an X.25 network. PAP supports data sequencing, flow control, accountability, and error detection and recovery.
2) PAP (Password Authentication Procedure) is a procedure used by Point-to-Point Protocol servers to validate a connection request. PAP works as follows:
- After the link is established, the requestor sends a password and an id to the server.
- The server either validates the request and sends back an acknowledgement, terminates the connection, or offers the requestor another chance.
Passwords are sent without security and the originator can make repeated attempts to gain access. For these reasons, a server that supports Challenge-Handshake Authentication Protocol will offer to use that protocol before using PAP. PAP protocol details can be found in RFC 1334.