PPP (Point-to-Point Protocol) was designed to provide a managed data link connection between two devices, usually through some form of serial data link.
Before the development of PPP, many serial links used the HDLC (High Level Data Link Control) protocol. This was a simple protocol for no other purpose than to provide encapsulation at the data link layer.
In contrast, PPP comes with a number of options including encryption, authentication, and data compression. It is the authentication option that was identified as an ideal method to authenticate a user or client device over a network that had a service to provide. Being able to identify and authenticate a user by combining username and password became the common method used by service providers.
PPP really caught on with the advent of dial-up Internet services when the authentication function was used to authenticate a dial-up user to the network. A network RADIUS (Remote Access Dial-Up User Service) server would be placed on the network to perform the function of the authenticator. These days, PPP is used in many connections, including ADSL, Cable, and also for ISDN line authentication. PPP can be used with ATM like PPPoA or Ethernet like PPPoE. Next-generation networks that are designed and built to deliver voice, data, and multimedia will generally continue to use PPP.
When dial-up services were finally replaced by ADSL broadband services, PPPoA (Point-to-Point Protocol over ATM) became the method by which an ADSL user identified himself on the network. PPPoA quickly became the de facto standard for authentication on an ADSL network.
Some broadband services are delivered over an Ethernet connection rather than over a phone line. The user must still be authenticated, so PPP was adapted to run over Ethernet in a similar way to how it was used in an ATM connection. This was known as PPPoE (Point-to-Point Protocol over Ethernet) and it is this method that is proposed as the access authentication method for many next-generation network services.
PPPoE is often bundled with end-user software and operating systems and supports a simple and reliable method of end-user authentication. For broadband services to be economical for the end user, it is important that a simple method is used to identify and authenticate end user devices. Using this method will even mean that the existing authentication RADIUS servers can be used for the new services.
Using PPPoE has a number of distinct advantages over alternative access methods:
Simple authentication and access control
User accounting for billing purposes is simple
Streaming traffic is kept to a minimum, as PPP is not a streaming protocol.
PPP connections scale very well to allow thousands or tens of thousands of users
Therefore, PPPoe will continue to be used for some time, even in the next generation networks under development. PPPoA will largely disappear as standard ADSL services migrate to fiber and Ethernet. Service providers evolving next-generation networks don’t have to go back to the drawing board to create a new authentication and accounting system.
