What is PPP (Point-to-Point Protocol)?

Point-to-Point Protocol (PPP) is a data link layer (Layer 2) communication protocol used to establish a direct connection between two nodes in a network. It is commonly used to connect a computer to the Internet through a dial-up connection or to establish a direct link between two private networks. PPP is defined in the Internet Engineering Task Force (IETF) standard RFC 1661.

Here's a technical breakdown of PPP:

  1. Layer of Operation:
    • PPP operates at the data link layer of the OSI model, specifically Layer 2. It is designed to encapsulate network layer protocols, allowing data to be transmitted over a point-to-point link.
  2. Connection Establishment:
    • PPP is used to establish a connection between two devices, typically a user's computer and an Internet Service Provider's (ISP) network device. This connection is often made over a physical medium like telephone lines, fiber optics, or other point-to-point links.
  3. Encapsulation:
    • PPP encapsulates higher-layer network protocols. This means it takes the data from the network layer (Layer 3) and encapsulates it in its own frame format for transmission over the link.
  4. Frame Format:
    • PPP frames consist of a header and a trailer. The header includes information such as the protocol type being carried (e.g., IP, IPv6), control fields, and addressing information. The trailer contains an error-checking mechanism (FCS - Frame Check Sequence) for ensuring data integrity during transmission.
  5. Authentication:
    • PPP supports various authentication methods to verify the identity of the connecting parties. Common authentication protocols used with PPP include Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).
  6. Network Layer Protocol Support:
    • PPP is protocol-independent, meaning it can transport a variety of network layer protocols. It supports the encapsulation of IP, IPv6, IPX (Internetwork Packet Exchange), and others.
  7. Error Detection:
    • PPP uses a cyclic redundancy check (CRC) as part of its FCS in the frame trailer to detect errors that may occur during transmission.
  8. Multilink PPP (MLPPP):
    • MLPPP is an extension of PPP that allows the aggregation of multiple physical links into a single logical link, providing increased bandwidth and redundancy.
  9. LCP (Link Control Protocol):
    • PPP uses LCP to establish, configure, and test the data link connection. It negotiates options such as authentication, compression, and error detection during the link establishment phase.
  10. NCP (Network Control Protocol):
    • Once the link is established, NCP is used to negotiate and configure network layer protocols, such as IP, over the PPP link.