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NAME

     ng_pred1 - Predictor-1 PPP compression (RFC 1978) netgraph node type

SYNOPSIS

     #include <sys/types.h>
     #include <netgraph/ng_pred1.h>

DESCRIPTION

     The pred1 node type implements the Predictor-1 sub-protocols of the
     Compression Control Protocol (CCP).

     The node has two hooks, comp for compression and decomp for
     decompression.  Only one of them can be connected at the same time,
     specifying node’s operation mode.  Typically that hooks would be
     connected to the ng_ppp(4) node type hook of the same name.

HOOKS

     This node type supports the following hooks:

     comp    Connection to ng_ppp(4) compress hook.  Incoming frames are
             compressed and sent back out the same hook.
     decomp  Connection to ng_ppp(4) decompress hook.  Incoming frames are
             decompressed and sent back out the same hook.

     Only one hook can be connected at the same time, specifying node’s
     operation mode.

CONTROL MESSAGES

     This node type supports the generic control messages, plus the following:

     NGM_PRED1_CONFIG (config)
          This command resets and configures the node for a session (i.e., for
          compression or decompression).  This command takes a struct
          ng_pred1_config as an argument:

          struct ng_pred1_config {
                  u_char          enable;                 /* node enabled */
          };
          The enable field enables traffic flow through the node.

     NGM_PRED1_RESETREQ (resetreq)
          This message contains no arguments, and is bi-directional.  If an
          error is detected during decompression, this message is sent by the
          node to the originator of the NGM_PRED1_CONFIG message that
          initiated the session.  The receiver should respond by sending a PPP
          CCP Reset-Request to the peer.

          This message may also be received by this node type when a CCP
          Reset-Request or Reset-Ack is received by the local PPP entity.  The
          node will respond by flushing its compression state so the sides can
          resynchronize.

     NGM_PRED1_GET_STATS (getstats)
          This control message obtains statistics for a given hook.  The
          statistics are returned in struct ng_pred1_stats:

          struct ng_pred1_stats {
                  uint64_t        FramesPlain;
                  uint64_t        FramesComp;
                  uint64_t        FramesUncomp;
                  uint64_t        InOctets;
                  uint64_t        OutOctets;
                  uint64_t        Errors;
          };

     NGM_PRED1_CLR_STATS (clrstats)
          This control message clears statistics for a given hook.

     NGM_PRED1_GETCLR_STATS (getclrstats)
          This control message obtains and clears statistics for a given hook.

SHUTDOWN

     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when hook have been disconnected.

SEE ALSO

     netgraph(4), ng_ppp(4), ngctl(8)

     D. Rand, PPP Predictor Compression Protocol, RFC 1978.

     W. Simpson, The Point-to-Point Protocol (PPP), RFC 1661.

AUTHORS

     Alexander Motin 〈mav@alkar.net

BUGS

     Due to nature of netgraph PPP implementation there are possible race
     conditions between data packet and ResetAck CCP packet in case of packet
     loss. As result, packet loss can produce bigger performance degradation
     than supposed by protocol.