slcompress.h revision 13765 
1/*	slcompress.h	8.1	93/06/10	*/
2/*
3 * Definitions for tcp compression routines.
4 *
5 * Copyright (c) 1989, 1993
6 *	The Regents of the University of California.  All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
37 *	- Initial distribution.
38 * $Id: slcompress.h,v 1.8 1995/11/18 13:07:51 bde Exp $
39 */
40
41#ifndef _NET_SLCOMPRESS_H_
42#define _NET_SLCOMPRESS_H_
43
44#define MAX_STATES 16		/* must be > 2 and < 256 */
45#define MAX_HDR MLEN		/* XXX 4bsd-ism: should really be 128 */
46
47/*
48 * Compressed packet format:
49 *
50 * The first octet contains the packet type (top 3 bits), TCP
51 * 'push' bit, and flags that indicate which of the 4 TCP sequence
52 * numbers have changed (bottom 5 bits).  The next octet is a
53 * conversation number that associates a saved IP/TCP header with
54 * the compressed packet.  The next two octets are the TCP checksum
55 * from the original datagram.  The next 0 to 15 octets are
56 * sequence number changes, one change per bit set in the header
57 * (there may be no changes and there are two special cases where
58 * the receiver implicitly knows what changed -- see below).
59 *
60 * There are 5 numbers which can change (they are always inserted
61 * in the following order): TCP urgent pointer, window,
62 * acknowledgement, sequence number and IP ID.  (The urgent pointer
63 * is different from the others in that its value is sent, not the
64 * change in value.)  Since typical use of SLIP links is biased
65 * toward small packets (see comments on MTU/MSS below), changes
66 * use a variable length coding with one octet for numbers in the
67 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
68 * range 256 - 65535 or 0.  (If the change in sequence number or
69 * ack is more than 65535, an uncompressed packet is sent.)
70 */
71
72/*
73 * Packet types (must not conflict with IP protocol version)
74 *
75 * The top nibble of the first octet is the packet type.  There are
76 * three possible types: IP (not proto TCP or tcp with one of the
77 * control flags set); uncompressed TCP (a normal IP/TCP packet but
78 * with the 8-bit protocol field replaced by an 8-bit connection id --
79 * this type of packet syncs the sender & receiver); and compressed
80 * TCP (described above).
81 *
82 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
83 * is logically part of the 4-bit "changes" field that follows.  Top
84 * three bits are actual packet type.  For backward compatibility
85 * and in the interest of conserving bits, numbers are chosen so the
86 * IP protocol version number (4) which normally appears in this nibble
87 * means "IP packet".
88 */
89
90/* packet types */
91#define TYPE_IP 0x40
92#define TYPE_UNCOMPRESSED_TCP 0x70
93#define TYPE_COMPRESSED_TCP 0x80
94#define TYPE_ERROR 0x00
95
96/* Bits in first octet of compressed packet */
97#define NEW_C	0x40	/* flag bits for what changed in a packet */
98#define NEW_I	0x20
99#define NEW_S	0x08
100#define NEW_A	0x04
101#define NEW_W	0x02
102#define NEW_U	0x01
103
104/* reserved, special-case values of above */
105#define SPECIAL_I (NEW_S|NEW_W|NEW_U)		/* echoed interactive traffic */
106#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
107#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
108
109#define TCP_PUSH_BIT 0x10
110
111
112/*
113 * "state" data for each active tcp conversation on the wire.  This is
114 * basically a copy of the entire IP/TCP header from the last packet
115 * we saw from the conversation together with a small identifier
116 * the transmit & receive ends of the line use to locate saved header.
117 */
118struct cstate {
119	struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
120	u_short cs_hlen;	/* size of hdr (receive only) */
121	u_char cs_id;		/* connection # associated with this state */
122	u_char cs_filler;
123	union {
124		char csu_hdr[MAX_HDR];
125		struct ip csu_ip;	/* ip/tcp hdr from most recent packet */
126	} slcs_u;
127};
128#define cs_ip slcs_u.csu_ip
129#define cs_hdr slcs_u.csu_hdr
130
131/*
132 * all the state data for one serial line (we need one of these
133 * per line).
134 */
135struct slcompress {
136	struct cstate *last_cs;	/* most recently used tstate */
137	u_char last_recv;	/* last rcvd conn. id */
138	u_char last_xmit;	/* last sent conn. id */
139	u_short flags;
140#ifndef SL_NO_STATS
141	int sls_packets;	/* outbound packets */
142	int sls_compressed;	/* outbound compressed packets */
143	int sls_searches;	/* searches for connection state */
144	int sls_misses;		/* times couldn't find conn. state */
145	int sls_uncompressedin;	/* inbound uncompressed packets */
146	int sls_compressedin;	/* inbound compressed packets */
147	int sls_errorin;	/* inbound unknown type packets */
148	int sls_tossed;		/* inbound packets tossed because of error */
149#endif
150	struct cstate tstate[MAX_STATES];	/* xmit connection states */
151	struct cstate rstate[MAX_STATES];	/* receive connection states */
152};
153/* flag values */
154#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
155
156void	 sl_compress_init __P((struct slcompress *, int));
157u_int	 sl_compress_tcp __P((struct mbuf *,
158	    struct ip *, struct slcompress *, int));
159int	 sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
160int	 sl_uncompress_tcp_core __P((u_char *, int, int, u_int,
161	    struct slcompress *, u_char **, u_int *));
162
163#endif /* !_NET_SLCOMPRESS_H_ */
164