For those of us who grew up with a selection of cables, leads and analogue modems PPP was quite a common protocol. It was developed across the internet community to both encapsulate and transmit IP data across all sorts of links but initially serial point to point ones. The other popular scheme which to some extent where often interchangeable was SLIP (Serial Link Internet Protocol). Although SLIP was the original of these two protocols, there is little doubt that PPP was more common mainly because it offered the ability to interconnect with other protocols. The main advantage of this was the ability to work with IPX which enabled it to function in Novell networks for example.
PPP is extremely adaptable and allowed connections from routers and hosts between each other. In it’s earliest guise though it was most commonly used to enable internet connections over telephone dial up lines. Most modem software would offer the user the choice to connect via either SLIP or PPP however the latter was normally the default.
Using PPP the home user would dial into a server run by their ISP using the telephone line. After the modem has established the connection, the PPP session would allow user authentication to check the account. This part of the process would also assign an IP address to the user’s computer. This address is essential to communicate across the internet and essential to access any of the internet. In fact all web based activities from browsing a page to watching UK TV in USA need a valid IP address assigned to your computer or device.
When this exchange has taken place the user’s computer is effectively an extension of the ISP’s IP network in the same way as it might be connected using an ethernet cable plugged into a port. The serial port and modem have exactly the same functionality as any other network card plugged into the network.
In order to encapsulate high level protocol data and transmit them then PPP has to use a simple framing method. Using this method PPP can support data transmission using a physical cable in asynchronous and synchronous modes. This obviously operates over the physical layer and needs serial communication protocols to transmit too. The data link layer is managed on the same frame structure using HDLC, it uses a Link Control Protocol to establish and manage the links when established. This is also responsible for encapsulation methods and packet sizes, also the compression methods that might be available.
The other important function is of course user authentication primarily using simple usernames and passwords. LCP is able to verify or reject packets based on any of these criteria and can manage the configuration options. A network control protocol is used to further manage the type of protocol configuration and the data being transferred between the two hosts. Remember there is no client/server model both ends of the connection are considered equal and the protocol is responsible for managing the connection not either of the two connection end points.
BBC Blocking VPNs – http://www.iplayerabroad.com/2017/04/07/bbc-iplayer-blocking-vpn-2017/