PPP (Point-to-Point Protocol) is a data link layer protocol used to establish a direct connection between two computer systems or network nodes. It can operate over various types of physical connections, including telephone lines, mobile communication networks, and direct serial connections. PPP is widely used to transport IP packets over serial links between a user and an Internet service provider.
There are several specialized variants of PPP:
- PPPoE (Point-to-Point Protocol over Ethernet) is used to establish PPP connections over Ethernet networks;
- PPPoA (Point-to-Point Protocol over ATM) is a PPP-based protocol used primarily with ATM-based DSL networks and was an alternative to PPPoE in such deployments.
PPP Characteristics
PPP is not a single protocol but a family of related protocols that perform different functions:
- LCP (Link Control Protocol) is used to establish, configure, test, and terminate the PPP link;
- NCP (Network Control Protocol) is a family of protocols used to configure network-layer protocols and negotiate their parameters over a PPP connection;
- PAP (Password Authentication Protocol) is a simple authentication protocol that transmits credentials without encryption. It is considered obsolete and insecure, although it is still supported in some legacy systems;
- CHAP (Challenge-Handshake Authentication Protocol) is another authentication protocol that uses a challenge-response mechanism instead of sending the password directly. It provides stronger protection than PAP and has traditionally been preferred for authentication between a customer and an ISP;
- MLPPP (Multilink PPP), also known as MPPP or MLP, allows a single logical PPP connection to use multiple physical links simultaneously. This can increase the available bandwidth and distribute traffic across several links.