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+Network Working Group                                            D. Rand
+Request for Comments: 1962                                        Novell
+Category: Standards Track                                      June 1996
+
+
+               The PPP Compression Control Protocol (CCP)
+
+Status of this Memo
+
+   This document specifies an Internet standards track protocol for the
+   Internet community, and requests discussion and suggestions for
+   improvements.  Please refer to the current edition of the "Internet
+   Official Protocol Standards" (STD 1) for the standardization state
+   and status of this protocol.  Distribution of this memo is unlimited.
+
+Abstract
+
+   The Point-to-Point Protocol (PPP) [1] provides a standard method for
+   transporting multi-protocol datagrams over point-to-point links.  PPP
+   also defines an extensible Link Control Protocol.
+
+   This document defines a method for negotiating data compression over
+   PPP links.
+
+Table of Contents
+
+   1.     Introduction ..........................................    1
+   2.     Compression Control Protocol (CCP) ....................    2
+      2.1       Sending Compressed Datagrams ....................    3
+   3.     Additional Packets ....................................    4
+      3.1       Reset-Request and Reset-Ack .....................    4
+   4.     CCP Configuration Options .............................    5
+      4.1       Proprietary Compression OUI .....................    7
+      4.2       Other Compression Types .........................    8
+   SECURITY CONSIDERATIONS ......................................    9
+   REFERENCES ...................................................    9
+   ACKNOWLEDGEMENTS .............................................    9
+   CHAIR'S ADDRESS ..............................................    9
+   AUTHOR'S ADDRESS .............................................    9
+
+1.  Introduction
+
+   In order to establish communications over a PPP link, each end of the
+   link must first send LCP packets to configure and test the data link
+   during Link Establishment phase.  After the link has been
+   established, optional facilities may be negotiated as needed.
+
+
+
+
+
+Rand                        Standards Track                     [Page 1]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+   One such facility is data compression.  A wide variety of compression
+   methods may be negotiated, although typically only one method is used
+   in each direction of the link.
+
+   A different compression algorithm may be negotiated in each
+   direction, for speed, cost, memory or other considerations, or only
+   one direction may be compressed.
+
+2.  Compression Control Protocol (CCP)
+
+   The Compression Control Protocol (CCP) is responsible for
+   configuring, enabling, and disabling data compression algorithms on
+   both ends of the point-to-point link.  It is also used to signal a
+   failure of the compression/decompression mechanism in a reliable
+   manner.
+
+   CCP uses the same packet exchange mechanism as the Link Control
+   Protocol (LCP).  CCP packets may not be exchanged until PPP has
+   reached the Network-Layer Protocol phase.  CCP packets received
+   before this phase is reached should be silently discarded.
+
+   The Compression Control Protocol is exactly the same as the Link
+   Control Protocol [1] with the following exceptions:
+
+   Frame Modifications
+
+      The packet may utilize any modifications to the basic frame format
+      which have been negotiated during the Link Establishment phase.
+
+   Data Link Layer Protocol Field
+
+      Exactly one CCP packet is encapsulated in the PPP Information
+      field, where the PPP Protocol field indicates type hex 80FD
+      (Compression Control Protocol).
+
+      When individual link data compression is used in a multiple link
+      connection to a single destination, the PPP Protocol field
+      indicates type hex 80FB (Individual link Compression Control
+      Protocol).
+
+   Code field
+
+      In addition to Codes 1 through 7 (Configure-Request, Configure-
+      Ack, Configure-Nak, Configure-Reject, Terminate-Request,
+      Terminate-Ack and Code-Reject), two additional Codes 14 and 15
+      (Reset-Request and Reset-Ack) are defined for this protocol.
+      Other Codes should be treated as unrecognized and should result in
+      Code-Rejects.
+
+
+
+Rand                        Standards Track                     [Page 2]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+   Timeouts
+
+      CCP 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
+
+      CCP has a distinct set of Configuration Options.
+
+2.1.  Sending Compressed Datagrams
+
+   Before any compressed packets may be communicated, PPP must reach the
+   Network-Layer Protocol phase, and the Compression Control Protocol
+   must reach the Opened state.
+
+   One or more compressed packets are encapsulated in the PPP
+   Information field, where the PPP Protocol field indicates type hex
+   00FD (Compressed datagram).  Each of the compression algorithms may
+   use a different mechanism to indicate the inclusion of more than one
+   uncompressed packet in a single Data Link Layer frame.
+
+   When using multiple PPP links to a single destination, there are two
+   methods of employing data compression.  The first method is to
+   compress the data prior to sending it out through the multiple links.
+   The second is to treat each link as a separate connection, that may
+   or may not have compression enabled.  In the second case, the PPP
+   Protocol field MUST be type hex 00FB (Individual link compressed
+   datagram).
+
+   Only one primary algorithm in each direction is in use at a time, and
+   that is negotiated prior to sending the first compressed frame.  The
+   PPP Protocol field of the compressed datagram indicates that the
+   frame is compressed, but not the algorithm with which it was
+   compressed.
+
+   The maximum length of a compressed packet transmitted over a PPP link
+   is the same as the maximum length of the Information field of a PPP
+   encapsulated packet.  Larger datagrams (presumably the result of the
+   compression algorithm increasing the size of the message in some
+   cases) may be sent uncompressed, using its standard form, or may be
+   sent in multiple datagrams, if the compression algorithm supports it.
+
+   Each of the compression algorithms must supply a way of determining
+   if they are passing data reliably, or they must require the use of a
+
+
+
+Rand                        Standards Track                     [Page 3]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+   reliable transport such as LAPB [3].  Vendors are strongly encouraged
+   to employ a method of validating the compressed data, or recognizing
+   out-of-sync compressor/decompressor pairs.
+
+3.  Additional Packets
+
+   The Packet format and basic facilities are already defined for LCP
+   [1].
+
+   Up-to-date values of the CCP Code field are specified in the most
+   recent "Assigned Numbers" RFC [2].  This specification concerns the
+   following values:
+
+      14      Reset-Request
+      15      Reset-Ack
+
+3.1.  Reset-Request and Reset-Ack
+
+   Description
+
+      CCP includes Reset-Request and Reset-Ack Codes in order to provide
+      a mechanism for indicating a decompression failure in one
+      direction of a compressed link without affecting traffic in the
+      other direction.  A decompression failure may be determined by
+      periodically passing a hash value, performing a CRC check on the
+      decompressed data, or other mechanism.  It is strongly suggested
+      that some mechanism be available in all compression algorithms to
+      validate the decompressed data before passing the data on to the
+      rest of the system.
+
+      A CCP implementation wishing to indicate a decompression failure
+      SHOULD transmit a CCP packet with the Code field set to 14
+      (Reset-Request), and the Data field filled with any desired data.
+      Once a Reset-Request has been sent, any Compressed packets
+      received are discarded, and another Reset-Request is sent with the
+      same Identifier, until a valid Reset-Ack is received.
+
+      Upon reception of a Reset-Request, the transmitting compressor is
+      reset to an initial state.  This may include clearing a
+      dictionary, resetting hash codes, or other mechanisms.  A CCP
+      packet MUST be transmitted with the Code field set to 15 (Reset-
+      Ack), the Identifier field copied from the Reset-Request packet,
+      and the Data field filled with any desired data.
+
+      On receipt of a Reset-Ack, the receiving decompressor is reset to
+      an initial state.  This may include clearing a dictionary,
+      resetting hash codes, or other mechanisms.  Since there may be
+      several Reset-Acks in the pipe, the decompressor MUST be reset for
+
+
+
+Rand                        Standards Track                     [Page 4]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+      each Reset-Ack which matches the currently expected identifier.
+
+   A summary of the Reset-Request and Reset-Ack packet formats is shown
+   below.  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
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |     Code      |  Identifier   |            Length             |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |    Data ...
+   +-+-+-+-+
+
+
+   Code
+
+      14 for Reset-Request;
+
+      15 for Reset-Ack.
+
+   Identifier
+
+      On transmission, the Identifier field MUST be changed whenever the
+      content of the Data field changes, and whenever a valid reply has
+      been received for a previous request.  For retransmissions, the
+      Identifier MAY remain unchanged.
+
+      On reception, the Identifier field of the Reset-Request is copied
+      into the Identifier field of the Reset-Ack packet.
+
+   Data
+
+      The Data field is zero or more octets and contains uninterpreted
+      data for use by the sender.  The data may consist of any binary
+      value and may be of any length from zero to the peer's established
+      MRU minus four.
+
+4.  CCP Configuration Options
+
+   CCP Configuration Options allow negotiation of compression algorithms
+   and their parameters.  CCP uses the same Configuration Option format
+   defined for LCP [1], with a separate set of Options.
+
+   Configuration Options, in this protocol, indicate algorithms that the
+   receiver is willing or able to use to decompress data sent by the
+   sender.  As a result, it is to be expected that systems will offer to
+   accept several algorithms, and negotiate a single one that will be
+   used.
+
+
+
+Rand                        Standards Track                     [Page 5]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+   There is the possibility of not being able to agree on a compression
+   algorithm.  In that case, no compression will be used, and the link
+   will continue to operate without compression.  If link reliability
+   has been separately negotiated, then it will continue to be used,
+   until the LCP is re-negotiated.
+
+   We expect that many vendors will want to use proprietary compression
+   algorithms, and have made a mechanism available to negotiate these
+   without encumbering the Internet Assigned Number Authority with
+   proprietary number requests.
+
+   The LCP option negotiation techniques are used.  If an option is
+   unrecognized, a Configure-Reject MUST be sent.  If all protocols the
+   sender implements are Configure-Rejected by the receiver, then no
+   compression is enabled in that direction of the link.
+
+   If an option is recognized, but not acceptable due to values in the
+   request (or optional parameters not in the request), a Configure-NAK
+   MUST be sent with the option modified appropriately.  The Configure-
+   NAK MUST contain only those options that will be acceptable.  A new
+   Configure-Request SHOULD be sent with only the single preferred
+   option, adjusted as specified in the Configure-Nak.
+
+   Up-to-date values of the CCP Option Type field are specified in the
+   most recent "Assigned Numbers" RFC [2].  Current values are assigned
+   as follows:
+
+      CCP Option      Compression type
+      0               OUI
+      1               Predictor type 1
+      2               Predictor type 2
+      3               Puddle Jumper
+      4-15            unassigned
+      16              Hewlett-Packard PPC
+      17              Stac Electronics LZS
+      18              Microsoft PPC
+      19              Gandalf FZA
+      20              V.42bis compression
+      21              BSD LZW Compress
+      255             Reserved
+
+      The unassigned values 4-15 are intended to be assigned to other
+      freely available compression algorithms that have no license fees.
+
+
+
+
+
+
+
+
+Rand                        Standards Track                     [Page 6]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+4.1.  Proprietary Compression OUI
+
+   Description
+
+      This Configuration Option provides a way to negotiate the use of a
+      proprietary compression protocol.
+
+      Since the first matching compression will be used, it is
+      recommended that any known OUI compression options be transmitted
+      first, before the common options are used.
+
+      Before accepting this option, the implementation must verify that
+      the Organization Unique Identifier identifies a proprietary
+      algorithm that the implementation can decompress, and that any
+      vendor specific negotiation values are fully understood.
+
+   A summary of the Proprietary Compression OUI Configuration Option
+   format is shown below.  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
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |     Type      |    Length     |       OUI ...
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         OUI       |    Subtype    |  Values...
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+
+
+   Type
+
+      0
+
+   Length
+
+      >= 6
+
+   IEEE OUI
+
+      The vendor's IEEE Organization Unique Identifier (OUI), which is
+      the most significant three octets of an Ethernet Physical Address,
+      assigned to the vendor by IEEE 802.  This identifies the option as
+      being proprietary to the indicated vendor.  The bits within the
+      octet are in canonical order, and the most significant octet is
+      transmitted first.
+
+
+
+
+
+
+Rand                        Standards Track                     [Page 7]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+   Subtype
+
+      This field is specific to each OUI, and indicates a compression
+      type for that OUI.  There is no standardization for this field.
+      Each OUI implements its own values.
+
+   Values
+
+      This field is zero or more octets, and contains additional data as
+      determined by the vendor's compression protocol.
+
+4.2.  Other Compression Types
+
+   Description
+
+      These Configuration Options provide a way to negotiate the use of
+      a publicly defined compression algorithm.  Many compression
+      algorithms are specified.  No particular compression technique has
+      arisen as an Internet Standard.
+
+      These protocols will be made available to all interested parties,
+      but may have certain licensing restrictions associated with them.
+      For additional information, refer to the compression protocol
+      documents that define each of the compression types.
+
+   A summary of the Compression Type Configuration Option format is
+   shown below.  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
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |     Type      |    Length     |  Values...
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+
+
+   Type
+
+      1 to 254
+
+   Length
+
+      >= 2
+
+   Values
+
+      This field is zero or more octets, and contains additional data as
+      determined by the compression protocol.
+
+
+
+Rand                        Standards Track                     [Page 8]
+
+RFC 1962                    PPP Compression                    June 1996
+
+
+Security Considerations
+
+   Security issues are not discussed in this memo.
+
+References
+
+   [1]   Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD
+         51, RFC 1661, July 1994.
+
+   [2]   Reynolds, J., and Postel, J., "Assigned Numbers", STD 2, RFC
+         1700, USC/Information Sciences Institute, October 1994.
+
+   [3]   Rand, D., "PPP Reliable Transmission", RFC 1663, July 1994.
+
+Acknowledgments
+
+   Bill Simpson helped with the document formatting.
+
+Chair's Address
+
+   The working group can be contacted via the current chair:
+
+      Karl Fox
+      Ascend Communications
+      3518 Riverside Drive, Suite 101
+      Columbus, Ohio 43221
+
+      EMail: karl@ascend.com
+
+Author's Address
+
+   Questions about this memo can also be directed to:
+
+      Dave Rand
+      Novell, Inc.
+      2180 Fortune Drive
+      San Jose, CA  95131
+
+      +1 408 321-1259
+
+      EMail: dlr@daver.bungi.com
+
+
+
+
+
+
+
+
+
+
+Rand                        Standards Track                     [Page 9]
+