slcompress.h revision 1.1 
1/*	$NetBSD: slcompress.h,v 1.9 1995/07/04 06:28:29 paulus Exp $	*/
2
3/*
4 * Copyright (c) 1989, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. All advertising materials mentioning features or use of this software
16 *    must display the following acknowledgement:
17 *	This product includes software developed by the University of
18 *	California, Berkeley and its contributors.
19 * 4. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 *
35 *	@(#)slcompress.h	8.1 (Berkeley) 6/10/93
36 */
37
38/*
39 * Definitions for tcp compression routines.
40 *
41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
42 *	- Initial distribution.
43 */
44
45#define MAX_STATES 16		/* must be > 2 and < 256 */
46#define MAX_HDR MLEN		/* XXX 4bsd-ism: should really be 128 */
47
48/*
49 * Compressed packet format:
50 *
51 * The first octet contains the packet type (top 3 bits), TCP
52 * 'push' bit, and flags that indicate which of the 4 TCP sequence
53 * numbers have changed (bottom 5 bits).  The next octet is a
54 * conversation number that associates a saved IP/TCP header with
55 * the compressed packet.  The next two octets are the TCP checksum
56 * from the original datagram.  The next 0 to 15 octets are
57 * sequence number changes, one change per bit set in the header
58 * (there may be no changes and there are two special cases where
59 * the receiver implicitly knows what changed -- see below).
60 *
61 * There are 5 numbers which can change (they are always inserted
62 * in the following order): TCP urgent pointer, window,
63 * acknowlegement, sequence number and IP ID.  (The urgent pointer
64 * is different from the others in that its value is sent, not the
65 * change in value.)  Since typical use of SLIP links is biased
66 * toward small packets (see comments on MTU/MSS below), changes
67 * use a variable length coding with one octet for numbers in the
68 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
69 * range 256 - 65535 or 0.  (If the change in sequence number or
70 * ack is more than 65535, an uncompressed packet is sent.)
71 */
72
73/*
74 * Packet types (must not conflict with IP protocol version)
75 *
76 * The top nibble of the first octet is the packet type.  There are
77 * three possible types: IP (not proto TCP or tcp with one of the
78 * control flags set); uncompressed TCP (a normal IP/TCP packet but
79 * with the 8-bit protocol field replaced by an 8-bit connection id --
80 * this type of packet syncs the sender & receiver); and compressed
81 * TCP (described above).
82 *
83 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
84 * is logically part of the 4-bit "changes" field that follows.  Top
85 * three bits are actual packet type.  For backward compatibility
86 * and in the interest of conserving bits, numbers are chosen so the
87 * IP protocol version number (4) which normally appears in this nibble
88 * means "IP packet".
89 */
90
91/* packet types */
92#define TYPE_IP 0x40
93#define TYPE_UNCOMPRESSED_TCP 0x70
94#define TYPE_COMPRESSED_TCP 0x80
95#define TYPE_ERROR 0x00
96
97/* Bits in first octet of compressed packet */
98#define NEW_C	0x40	/* flag bits for what changed in a packet */
99#define NEW_I	0x20
100#define NEW_S	0x08
101#define NEW_A	0x04
102#define NEW_W	0x02
103#define NEW_U	0x01
104
105/* reserved, special-case values of above */
106#define SPECIAL_I (NEW_S|NEW_W|NEW_U)		/* echoed interactive traffic */
107#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
108#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
109
110#define TCP_PUSH_BIT 0x10
111
112
113/*
114 * "state" data for each active tcp conversation on the wire.  This is
115 * basically a copy of the entire IP/TCP header from the last packet
116 * we saw from the conversation together with a small identifier
117 * the transmit & receive ends of the line use to locate saved header.
118 */
119struct cstate {
120	struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
121	u_int16_t cs_hlen;	/* size of hdr (receive only) */
122	u_char cs_id;		/* connection # associated with this state */
123	u_char cs_filler;
124	union {
125		char csu_hdr[MAX_HDR];
126		struct ip csu_ip;	/* ip/tcp hdr from most recent packet */
127	} slcs_u;
128};
129#define cs_ip slcs_u.csu_ip
130#define cs_hdr slcs_u.csu_hdr
131
132/*
133 * all the state data for one serial line (we need one of these
134 * per line).
135 */
136struct slcompress {
137	struct cstate *last_cs;	/* most recently used tstate */
138	u_char last_recv;	/* last rcvd conn. id */
139	u_char last_xmit;	/* last sent conn. id */
140	u_int16_t flags;
141#ifndef SL_NO_STATS
142	int sls_packets;	/* outbound packets */
143	int sls_compressed;	/* outbound compressed packets */
144	int sls_searches;	/* searches for connection state */
145	int sls_misses;		/* times couldn't find conn. state */
146	int sls_uncompressedin;	/* inbound uncompressed packets */
147	int sls_compressedin;	/* inbound compressed packets */
148	int sls_errorin;	/* inbound unknown type packets */
149	int sls_tossed;		/* inbound packets tossed because of error */
150#endif
151	struct cstate tstate[MAX_STATES];	/* xmit connection states */
152	struct cstate rstate[MAX_STATES];	/* receive connection states */
153};
154/* flag values */
155#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
156
157void	 sl_compress_init __P((struct slcompress *, int));
158u_int	 sl_compress_tcp __P((struct mbuf *,
159	    struct ip *, struct slcompress *, int));
160int	 sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
161int	 sl_uncompress_tcp_core __P((u_char *, int, int, u_int,
162	    struct slcompress *, u_char **, u_int *));
163