RFC 1548 (rfc1548) - Page 3 of 53

The Point-to-Point Protocol (PPP)

RFC 1548              The Point-to-Point Protocol          December 1993


1. Introduction

   Encapsulation

      The PPP encapsulation provides for multiplexing of different
      network-layer protocols simultaneously over the same link.  It is
      intended that PPP provide a common solution for easy connection of
      a wide variety of hosts, bridges and routers [1].

      The PPP encapsulation has been carefully designed to retain
      compatibility with most commonly used supporting hardware.

      Only 8 additional octets are necessary to form the encapsulation
      when used with the default HDLC framing.  In environments where
      bandwidth is at a premium, the encapsulation and framing may be
      shortened to 2 or 4 octets.

      To support high speed implementations, the default encapsulation
      uses only simple fields, only one of which needs to be examined
      for demultiplexing.  The default header and information fields
      fall on 32-bit boundaries, and the trailer may be padded to an
      arbitrary boundary.

    Link Control Protocol

      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
      companion documents.






Simpson