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.

Debian                                          December 24, 2006                                    NG_PRED1(4)