RFC 1378 (rfc1378) - Page 3 of 16

The PPP AppleTalk Control Protocol (ATCP)

RFC 1378                        PPP ATCP                   November 1992


   Data Link Layer Protocol Field

      Exactly one ATCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame where the Protocol field indicates
      type hex 8029 (AppleTalk 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

      ATCP 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

      ATCP has a distinct set of Configuration Options, which are
      defined below.

2.1.  Sending AppleTalk Datagrams

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

   Unless otherwise negotiated (via option 4), exactly one AppleTalk
   packet is encapsulated in the Information field of a PPP Data Link
   Layer frame where the Protocol field indicates type hex 0029
   (AppleTalk).

   Note that the negotiation of compression may imply the use of
   different encapsulation and hence different protocol fields.  These
   different protocol fields imply packet types which are sub-protocols
   of the base AppleTalk NCP.

   An encapsulated AppleTalk packet begins with an extended DDP
   (Datagram Delivery Protocol) header -- also known as a Long DDP
   header.  The maximum length of a DDP datagram is 599 octets.

   Since there is no standard method for fragmenting and reassembling



Parker