RFC 1762 (rfc1762) - Page 4 of 7

The PPP DECnet Phase IV Control Protocol (DNCP)

RFC 1762                        PPP DNCP                      March 1995


   Data Link Layer Protocol Field

      Exactly one DNCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame where the Protocol field indicates
      type hex 8027 (DNA Phase IV Control Protocol).

   Code field

      Only Codes 1 through 7 (Configure-Request, Configure-Ack,
      Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack
      and Code-Reject) are used.  Other Codes should be treated as
      unrecognized and should result in Code-Rejects.

   Timeouts

      DNCP packets may not be exchanged until PPP has reached the
      Network-Layer Protocol phase.  An implementation should be
      prepared to wait for Authentication and Link Quality Determination
      to finish before timing out waiting for a Configure-Ack or other
      response.  It is suggested that an implementation give up only
      after user intervention or a configurable amount of time.

   Configuration Option Types

      DNCP has no Configuration Options.

4.  Sending DNA Phase IV Routing Packets

      Before any DNA Phase IV Routing packets may be communicated, PPP
      must reach the Network-Layer Protocol phase, and the DNA Phase IV
      Routing Control Protocol must reach the Opened state.

      Exactly one length field and one DNA Phase IV Routing packet are
      encapsulated in the information field of a PPP Data Link Layer
      frame where the Protocol field indicates type hex 0027 (DNA Phase
      IV Routing).  The length field contains a count of the number of
      octets in the DNA Phase IV Routing packet.  It is two octets in
      length itself, and is stored in VAX byte ordering, to be more
      consistent with DNA Phase IV Routing over Ethernet (i.e. least
      significant byte first).  It is needed to disambiguate optional
      padding octets from real information.

      The maximum length of a DNA Phase IV Routing packet transmitted
      over a PPP link is the same as the maximum length of the
      Information field of a PPP data link layer frame minus 2 octets
      (for the Length field).





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