One of the most ever-present and ancient uses of the Internet and networking has been to provide remote access to networks or network resources. Since the early 1980's, different remote access protocols have existed to allow users to remotely dial in to a network of choice; while some of these protocols have come and gone, many of them remain widely in use even today in dial-up WAN access and business VPN networks.
RAS, or Remote Access Service, is a rarely-used, unsecure, and outdated Microsoft offering in the area of remote access technology. You should know for the exam that RAS provides dial-up access and once was the protocol of choice for connecting to the Internet.
RAS was eventually replaced by PPP, the most common dial-up networking protocol today. PPP, or point-to-point protocol, utilizes a direct connection from a client to WAN over TCP/IP.
This is advantageous for dial-up networking services as most people today wish to be able to use the Internet, which of course requires TCP/IP networking. When you think dial-up access, think PPP.