RFC 1331 (rfc1331) - Page 2 of 66

The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to-Point Links

RFC 1331                Point-to-Point Protocol                 May 1992


      implementations, and a software implementation is provided.

      By default, only 8 additional octets are necessary to form the
      encapsulation.  In environments where bandwidth is at a premium,
      the encapsulation may be shortened to as few as 2 octets.  To
      support high speed hardware implementations, PPP provides that the
      default encapsulation header and information fields fall on 32-bit
      boundaries, and allows the trailer to be padded to an arbitrary
      boundary.

   Link Control Protocol

      More importantly, the Point-to-Point Protocol defines more than
      just an encapsulation scheme.  In order to be sufficiently
      versatile to be portable to a wide variety of environments, PPP
      provides a Link Control Protocol (LCP).  The LCP is used to
      automatically agree upon the encapsulation format options, handle
      varying limits on sizes of packets, authenticate the identity of
      its peer on the link, determine when a link is functioning
      properly and when it is defunct, detect a looped-back link and
      other common misconfiguration errors, and terminate the link.

   Network Control Protocols

      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 circuit-switched
      point-to-point links (such as dial-up modem servers).  These
      problems are handled by a family of Network Control Protocols
      (NCPs), which each manage the specific needs required by their
      respective network-layer protocols.  These NCPs are defined in
      other documents.

   Configuration

      It is intended that PPP be easy to configure.  By design, the
      standard defaults should handle all common configurations.  The
      implementor may specify improvements to the default configuration,
      which are automatically communicated to the peer without operator
      intervention.  Finally, the operator may explicitly configure
      options for the link which enable the link to operate in
      environments where it would otherwise be impossible.

      This self-configuration is implemented through an extensible
      option negotiation mechanism, wherein each end of the link
      describes to the other its capabilities and requirements.
      Although the option negotiation mechanism described in this



Simpson