1 .\" Copyright (c) 1996-1999 Whistle Communications, Inc.
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6 .\" without modifications are expressly permitted by Whistle Communications;
7 .\" provided, however, that:
8 .\" 1. Any and all reproductions of the source or object code must include the
9 .\" copyright notice above and the following disclaimer of warranties; and
10 .\" 2. No rights are granted, in any manner or form, to use Whistle
11 .\" Communications, Inc. trademarks, including the mark "WHISTLE
12 .\" COMMUNICATIONS" on advertising, endorsements, or otherwise except as
13 .\" such appears in the above copyright notice or in the software.
15 .\" THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
16 .\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
17 .\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
18 .\" INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
19 .\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
20 .\" WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
21 .\" REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
22 .\" SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
23 .\" IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
24 .\" RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
25 .\" WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
26 .\" PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
35 .\" $FreeBSD: src/share/man/man4/ng_vjc.4,v 1.17.2.1 2001/12/21 09:00:51 ru Exp $
36 .\" $DragonFly: src/share/man/man4/ng_vjc.4,v 1.4 2006/05/26 21:39:39 swildner Exp $
37 .\" $Whistle: ng_vjc.8,v 1.4 1999/01/25 23:46:28 archie Exp $
44 .Nd Van Jacobson compression netgraph node type
47 .In netgraph/vjc/ng_vjc.h
51 node type performs Van Jacobson compression, which is used
52 over PPP, SLIP, and other point-to-point IP connections to
53 compress TCP packet headers. The
55 hook represents the uncompressed side of the node, while the
60 hooks represent the compressed side of the node. Packets received on the
62 will be compressed or passed through as appropriate. Packets received
63 on the other three hooks will be uncompressed as appropriate.
64 This node also supports
65 .Dq always pass through
66 mode in either direction.
68 Van Jacobson compression only applies to TCP packets.
71 (i.e., common case) TCP packets are actually compressed.
72 These are output on the
74 hook. Other TCP packets are run through the state machine but not
75 compressed; these appear on the
78 Other non-TCP IP packets are forwarded unchanged to
89 hooks should be connected to the
99 This node type supports the following hooks:
101 .Bl -tag -width foobarbazi
103 Upstream (uncompressed) IP packets.
105 Downstream compressed TCP packets.
107 Downstream uncompressed TCP packets.
109 Downstream uncompressed IP packets.
112 This node type supports the generic control messages, plus the following:
114 .It Dv NGM_VJC_SET_CONFIG
115 This command resets the compression state and configures it according
117 .Dv "struct ngm_vjc_config"
118 argument. This structure contains the following fields:
119 .Bd -literal -offset 4n
120 struct ngm_vjc_config {
121 u_char enableComp; /* Enable compression */
122 u_char enableDecomp; /* Enable decompression */
123 u_char maxChannel; /* Number of outgoing channels - 1 */
124 u_char compressCID; /* OK to compress outgoing CID's */
130 is set to zero, all packets received on the
132 hook are forwarded unchanged out the
134 hook. Similarly, when
136 is set to zero, all packets received on the
138 hook are forwarded unchanged out the
140 hook, and packets are not accepted on the
145 When a node is first created,
146 both compression and decompression are disabled and the node is
147 therefore operating in bi-directional
151 When enabling compression,
153 should be set to the number of outgoing compression channels minus one,
154 and is a value between 3 and 15, inclusive. The
156 field indicates whether it is OK to compress the CID header field for
157 outgoing compressed TCP packets. This value should be zero unless
158 either (a) it is not possible for an outgoing frame to be lost, or
159 (b) lost frames can be reliably detected and immediately
160 reported to the peer's decompression engine (see
161 .Dv NGM_VJC_RECV_ERROR
163 .It Dv NGM_VJC_GET_STATE
164 This command returns the node's current state described by the
165 .Dv "struct slcompress"
166 structure, which is defined in
167 .In net/slcompress.h .
168 .It Dv NGM_VJC_CLR_STATS
169 Clears the node statistics counters. Statistics are also cleared whenever the
173 fields are changed from zero to one by a
174 .Dv NGM_VJC_SET_CONFIG
176 .It Dv NGM_VJC_RECV_ERROR
177 When the peer has CID header field compression enabled,
178 this message must be sent to the local
181 after detecting that a received frame has been lost, due to a bad
182 checksum or for any other reason. Failing to do this can result
183 in corrupted TCP stream data.
186 This node shuts down upon receipt of a
188 control message, or when all hooks have been disconnected.
196 .%T "Compressing TCP/IP Headers"
201 .%T "The PPP Internet Control Protocol (IPCP)"
207 node type was implemented in
210 .An Archie Cobbs Aq archie@FreeBSD.org
212 Because the initialization routine in the kernel implementation of
213 Van Jacobson compression initializes both compression and decompression
214 at once, this node does not allow compression and decompression to
215 be enabled in separate operations. In order to enable one when
216 the other is already enabled, first both must be disabled, then
217 both enabled. This of course resets the node state. This restriction
218 may be lifted in a later version.
220 When built as a loadable kernel module, this module includes the file
221 .Pa net/slcompress.c .
222 Although loading the module should fail if
224 already exists in the kernel, currently it does not, and the duplicate
225 copies of the file do not interfere.
226 However, this may change in the future.