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.