PPP is so versatile because it uses Network Control Protocols, which means WAN devices can use it to transfer multiple protocols such as IP, IPX, and AppleTalk all on a single link. This gives PPP an advantage over SLIP and HDLC because they don't support multiple protocols. PPP also have the ability to be used over several different physical interfaces, such as asynchronous serial, IDSN/synchronous serial and high-speed serial interface.
PPP features also include error detection, a method for testing links before transmission, and a way to monitor the quality of the link. PPP provides support for multiple authentication protocols, which makes it one of the most versatile and popular WAN technologies in use today.
PAP and CHAP are authentication methods used by the PPP Link Configuration Protocol. PAP stands for Password Authentication Protocol, whereas CHAP stands for Challenge Handshake Authentication Protocol. They are used to verify the identity of the device that initiates the link when a secure method of authentication is needed such as when dialing up to an ISP for a connection to the internet.
PAP sends the username and password all in one packet to the server. The server in turn sends the request to the server that holds the list of usernames and passwords. The server then validates the request, terminates the connection, or asks for re-verification.
CHAP works by sending a challenge message from the server to the client. The message contains a hash value and the client must calculate the value and the respond. The server checks to make sure the calculation matches its own calculation and then either approves or terminates the connection.
CHAP is more secure because the server can request the client to send a challenge message at any time. CHAP identifiers are also changed often so therefore there is less chance of an unauthorized user gaining access to the system.
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