RFC 1975 (rfc1975) - Page 2 of 6


PPP Magnalink Variable Resource Compression



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RFC 1975      PPP Magnalink Variable Resource Compression    August 1996


MVRCA Packets

   Before any MVRCA packets may be communicated, PPP must reach the
   Network-Layer Protocol phase[1], and the Compression Control Protocol
   must reach the Opened state.

   The text of a Packet to be compressed begins with PPP Protocol
   number.  The Packet header including the PPP Protocol number may have
   already been compressed when Protocol-Field-Compression has been
   negotiated.

Reliability and Sequencing

   MVRCA packets may be sent across an unreliable link or may use a
   reliable link as described in "PPP Reliable Transmission"[3] if the
   reliable link has been negotiated. If frames are delivered out of
   order or a frame is dropped, the decompressor will detect this and
   requests a resynchronization using the Reset-Req and Reset-Ack types
   of the CCP[2], with the compressor for the affected context.

Data Expansion

   Although the compression algorithm may occasionally expand a data
   packet, there is no expansion in MVRCA since any expanded data is
   instead sent uncompressed. Dictionary synchronization is maintained
   across uncompressed packets.

Encapsulation

   The encapsulation consists of the PPP Protocol Identifier, a bit to
   indicate if the data is compressed, the Context Identifier(CID), a
   proprietary flag bit (E), a Packet Integrity Byte(PIB), and the
   Compressed data.

       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PPP Protocol Identifier       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C|E|   CID     |     PIB       |  C compressed flag
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  1 data is compressed
      | Compressed data  ...             0 data is not compressed
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








Schremp, Black & Weiss       Informational