PPP (Point-to-Point Protocol)

PPP (Point-to-Point Protocol)

Point-to-Point Protocol (PPP) operates at the data link layer (from the OSI reference model perspective). It is typically used to establish a direct connection between two nodes. It is mainly used to connect two computers via serial ports, and is now also used for broadband computer connections. Many Internet Service Providers (ISPs) use PPPoE to provide access services to users (e.g., accessing the internet, largely replacing older standards like SLIP).

The PPP protocol was designed after the HDLC protocol and was intended to replace the non-standard SLIP protocol at the data link layer. Its designers included many additional features that were not considered in other data link layer protocols at the time on wide area networks. Therefore, it was designed to be very flexible: it serves as a data link layer (Layer 2) protocol supporting both synchronous and asynchronous link connections, and can support multiple network layer protocols (such as IP, IPX, and AppleTalk).

In addition to basic framing functions, the PPP protocol also includes two components: the Link Control Protocol (LCP) and the Network Control Protocol (NCP).

The PPP protocol uses Frame Check Sequence (FCS) to check each individual frame for errors. PPP can also monitor which frames consistently have errors when received and can configure to reduce the occurrence of errors on the interface.

The Link Control Protocol (LCP), as a part of the PPP protocol and defined in the same RFC, uses a special digit to identify itself as a feature to detect loops. When using the PPP protocol, endpoints send LCP information with a unique identifier that is different from other endpoints. If a loop exists in the line, the endpoint sending this information will receive information containing its identifier rather than another's.

The PPP protocol provides hooks for each endpoint user to automatically configure network interfaces (setting IP addresses and default gateways, etc.) and for authentication.

PPP provides hooks that allow each endpoint to automatically configure the network port and authentication (PAP and CHAP), compared to Dynamic Host Configuration Protocol.

The PPP Multilink Protocol allows multiple links between two systems to increase bandwidth. When accessing remote resources, the PPP Multilink Protocol allows the combination of two bandwidths or the merging of physical communication lines such as analog modems, ISDN, and other analog or digital links to improve overall throughput. The PPP Multilink Protocol is described in IETF RFC 1717.

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