NAME¶
ng_deflate —
Deflate PPP compression
(RFC 1979) netgraph node type
SYNOPSIS¶
#include <sys/types.h>
#include <netgraph/ng_deflate.h>
DESCRIPTION¶
The
deflate node type implements the Deflate 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. Corresponding
ng_ppp(4) node hook must be
switched to
NG_PPP_DECOMPRESS_FULL
mode to permit
sending uncompressed frames.
HOOKS¶
This node type supports the following hooks:
- comp
- Connection to ng_ppp(4)
comp hook. Incoming frames are compressed (if
possible) and sent back out the same hook.
- decomp
- Connection to ng_ppp(4)
decomp hook. Incoming frames are decompressed (if
they are compressed), 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_DEFLATE_CONFIG
(config
)
- This command resets and configures the node for a session
(i.e., for compression or decompression). This command takes a
struct ng_deflate_config as an argument:
struct ng_deflate_config {
u_char enable; /* node enabled */
u_char windowBits; /* log2(Window size) */
};
The enabled field enables traffic flow through the
node. The windowBits specify compression windows
size as negotiated by the Compression Control Protocol (CCP) in PPP.
NGM_DEFLATE_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_DEFLATE_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_DEFLATE_GET_STATS
(getstats
)
- This control message obtains statistics for a given hook.
The statistics are returned in struct
ng_deflate_stats:
struct ng_deflate_stats {
uint64_t FramesPlain;
uint64_t FramesComp;
uint64_t FramesUncomp;
uint64_t InOctets;
uint64_t OutOctets;
uint64_t Errors;
};
NGM_DEFLATE_CLR_STATS
(clrstats
)
- This control message clears statistics for a given
hook.
NGM_DEFLATE_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)
J. Woods, PPP
Deflate Protocol, RFC 1979.
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.