RFC 1973 (rfc1973) - Page 2 of 8

PPP in Frame Relay

RFC 1973                     PPP in Frame Relay                June 1996


      Because PPP does not normally require the use of control signals,
      the failure of such signals MUST NOT affect correct operation of
      PPP.  Implications are discussed in [2].

   Encoding

      The definition of various encodings is the responsibility of the
      DTE/DCE equipment in use, and is outside the scope of this
      specification.

      While PPP will operate without regard to the underlying
      representation of the bit stream, Frame Relay requires NRZ
      encoding.



3.  The Data Link Layer

   This specification uses the principles, terminology, and frame
   structure described in "Multiprotocol Interconnect over Frame Relay"
   [4].

   The purpose of this specification is not to document what is already
   standardized in [4].  Instead, this document attempts to give a
   concise summary and point out specific options and features used by
   PPP.



3.1.  Frame Format

   As described in [4], Q.922 header address and control fields are
   combined with the Network Layer Protocol Identifier (NLPID), which
   identifies the encapsulation which follows.  The fields are
   transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |  Flag (0x7e)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Q.922 Address         |    Control    |  NLPID(0xcf)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         PPP Protocol          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The PPP Protocol field and the following Information and Padding
   fields are described in the Point-to-Point Protocol Encapsulation



Simpson                      Standards Track