RFC 1134 (rfc1134) - Page 3 of 38

Point-to-Point Protocol: A proposal for multi-protocol transmission of datagrams over Point-to-Point links

RFC 1134                          PPP                      November 1989


   every host supports point-to-point connections.  For example,
   asynchronous RS-232-C [1] interfaces are essentially ubiquitous.

   One reason for the small number of point-to-point IP links is the
   lack of a standard encapsulation protocol.  There are plenty of non-
   standard (and at least one defacto standard) encapsulation protocols
   available, but there is not one which has been agreed upon as an
   Internet Standard.  By contrast, standard encapsulation schemes do
   exist for the transmission of datagrams over most popular LANs.

   One purpose of this memo is to remedy this problem.  But even more
   importantly, the Point-to-Point Protocol proposes more than just an
   encapsulation scheme.  Point-to-Point links tend to exacerbate many
   problems with the current family of network protocols.  For instance,
   assignment and management of IP addresses, which is a problem even in
   LAN environments, is especially difficult over switched point-to-
   point circuits (e.g., dialups).

   Some additional issues addressed by PPP include asynchronous
   (start/stop) and bit-oriented synchronous encapsulation, network
   protocol multiplexing, link configuration, link quality testing,
   error detection, and option negotiation for such capabilities as
   network-layer address negotiation and data compression negotiation.

   PPP addresses these issues by providing an extensible Link Control
   Protocol (LCP) and a family of Network Control Protocols (NCP) to
   negotiate optional configuration parameters and facilities.

1.2.  Overview of PPP

   PPP has three main components:

      1. A method for encapsulating datagrams over serial links.  PPP
         uses HDLC as a basis for encapsulating datagrams over point-
         to-point links.

      2. An extensible Link Control Protocol (LCP) to establish,
         configure, and test the data-link connection.

      3. A family of Network Control Protocols (NCP) for establishing
         and configuring different network-layer protocols.  PPP is
         designed to allow the simultaneous use of multiple network-
         layer protocols.

   In order to establish communications over a point-to-point link, the
   originating PPP would first send LCP packets to configure and test
   the data link.  After the link has been establish and optional
   facilities have been negotiated as needed by the LCP, the originating



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