slcompress.h revision 1542 
1/*	slcompress.h	8.1	93/06/10	*/
2/*
3 * Definitions for tcp compression routines.
4 *
5 * $Header: slcompress.h,v 1.10 89/12/31 08:53:02 van Exp $
6 *
7 * Copyright (c) 1989, 1993
8 *	The Regents of the University of California.  All rights reserved.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. All advertising materials mentioning features or use of this software
19 *    must display the following acknowledgement:
20 *	This product includes software developed by the University of
21 *	California, Berkeley and its contributors.
22 * 4. Neither the name of the University nor the names of its contributors
23 *    may be used to endorse or promote products derived from this software
24 *    without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * SUCH DAMAGE.
37 *
38 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
39 *	- Initial distribution.
40 */
41
42#define MAX_STATES 16		/* must be > 2 and < 256 */
43#define MAX_HDR MLEN		/* XXX 4bsd-ism: should really be 128 */
44
45/*
46 * Compressed packet format:
47 *
48 * The first octet contains the packet type (top 3 bits), TCP
49 * 'push' bit, and flags that indicate which of the 4 TCP sequence
50 * numbers have changed (bottom 5 bits).  The next octet is a
51 * conversation number that associates a saved IP/TCP header with
52 * the compressed packet.  The next two octets are the TCP checksum
53 * from the original datagram.  The next 0 to 15 octets are
54 * sequence number changes, one change per bit set in the header
55 * (there may be no changes and there are two special cases where
56 * the receiver implicitly knows what changed -- see below).
57 *
58 * There are 5 numbers which can change (they are always inserted
59 * in the following order): TCP urgent pointer, window,
60 * acknowlegement, sequence number and IP ID.  (The urgent pointer
61 * is different from the others in that its value is sent, not the
62 * change in value.)  Since typical use of SLIP links is biased
63 * toward small packets (see comments on MTU/MSS below), changes
64 * use a variable length coding with one octet for numbers in the
65 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
66 * range 256 - 65535 or 0.  (If the change in sequence number or
67 * ack is more than 65535, an uncompressed packet is sent.)
68 */
69
70/*
71 * Packet types (must not conflict with IP protocol version)
72 *
73 * The top nibble of the first octet is the packet type.  There are
74 * three possible types: IP (not proto TCP or tcp with one of the
75 * control flags set); uncompressed TCP (a normal IP/TCP packet but
76 * with the 8-bit protocol field replaced by an 8-bit connection id --
77 * this type of packet syncs the sender & receiver); and compressed
78 * TCP (described above).
79 *
80 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
81 * is logically part of the 4-bit "changes" field that follows.  Top
82 * three bits are actual packet type.  For backward compatibility
83 * and in the interest of conserving bits, numbers are chosen so the
84 * IP protocol version number (4) which normally appears in this nibble
85 * means "IP packet".
86 */
87
88/* packet types */
89#define TYPE_IP 0x40
90#define TYPE_UNCOMPRESSED_TCP 0x70
91#define TYPE_COMPRESSED_TCP 0x80
92#define TYPE_ERROR 0x00
93
94/* Bits in first octet of compressed packet */
95#define NEW_C	0x40	/* flag bits for what changed in a packet */
96#define NEW_I	0x20
97#define NEW_S	0x08
98#define NEW_A	0x04
99#define NEW_W	0x02
100#define NEW_U	0x01
101
102/* reserved, special-case values of above */
103#define SPECIAL_I (NEW_S|NEW_W|NEW_U)		/* echoed interactive traffic */
104#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
105#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
106
107#define TCP_PUSH_BIT 0x10
108
109
110/*
111 * "state" data for each active tcp conversation on the wire.  This is
112 * basically a copy of the entire IP/TCP header from the last packet
113 * we saw from the conversation together with a small identifier
114 * the transmit & receive ends of the line use to locate saved header.
115 */
116struct cstate {
117	struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
118	u_short cs_hlen;	/* size of hdr (receive only) */
119	u_char cs_id;		/* connection # associated with this state */
120	u_char cs_filler;
121	union {
122		char csu_hdr[MAX_HDR];
123		struct ip csu_ip;	/* ip/tcp hdr from most recent packet */
124	} slcs_u;
125};
126#define cs_ip slcs_u.csu_ip
127#define cs_hdr slcs_u.csu_hdr
128
129/*
130 * all the state data for one serial line (we need one of these
131 * per line).
132 */
133struct slcompress {
134	struct cstate *last_cs;	/* most recently used tstate */
135	u_char last_recv;	/* last rcvd conn. id */
136	u_char last_xmit;	/* last sent conn. id */
137	u_short flags;
138#ifndef SL_NO_STATS
139	int sls_packets;	/* outbound packets */
140	int sls_compressed;	/* outbound compressed packets */
141	int sls_searches;	/* searches for connection state */
142	int sls_misses;		/* times couldn't find conn. state */
143	int sls_uncompressedin;	/* inbound uncompressed packets */
144	int sls_compressedin;	/* inbound compressed packets */
145	int sls_errorin;	/* inbound unknown type packets */
146	int sls_tossed;		/* inbound packets tossed because of error */
147#endif
148	struct cstate tstate[MAX_STATES];	/* xmit connection states */
149	struct cstate rstate[MAX_STATES];	/* receive connection states */
150};
151/* flag values */
152#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
153
154void	 sl_compress_init __P((struct slcompress *));
155u_int	 sl_compress_tcp __P((struct mbuf *,
156	    struct ip *, struct slcompress *, int));
157int	 sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
158