|  |  | CHAP is another authentication protocol that is run over serial links. PPP is established. The server sends a CHAP challenge to the client. The client sends a response back to the server. The server sends an "accept" or "reject" back to the client. CHAP provides more security than PAP by sending an MD5-encrypted password. CHAP may also periodically verify the connection, and the server may issue a challenge to the client on a periodic basis.