slcompress.h revision 8876 
1/*
2 * Definitions for tcp compression routines.
3 *
4 * $Header: /home/ncvs/src/usr.sbin/ppp/slcompress.h,v 1.2 1995/02/26 12:17:58 amurai Exp $
5 *
6 * Copyright (c) 1989 Regents of the University of California.
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms are permitted
10 * provided that the above copyright notice and this paragraph are
11 * duplicated in all such forms and that any documentation,
12 * advertising materials, and other materials related to such
13 * distribution and use acknowledge that the software was developed
14 * by the University of California, Berkeley.  The name of the
15 * University may not be used to endorse or promote products derived
16 * from this software without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
19 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 *
21 * $Id: slcompress.h,v 1.2 1995/02/26 12:17:58 amurai Exp $
22 *
23 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
24 *	- Initial distribution.
25 */
26#include "cdefs.h"
27
28#define MAX_STATES 16		/* must be > 2 and < 256 */
29#define MAX_HDR 128		/* XXX 4bsd-ism: should really be 128 */
30
31/*
32 * Compressed packet format:
33 *
34 * The first octet contains the packet type (top 3 bits), TCP
35 * 'push' bit, and flags that indicate which of the 4 TCP sequence
36 * numbers have changed (bottom 5 bits).  The next octet is a
37 * conversation number that associates a saved IP/TCP header with
38 * the compressed packet.  The next two octets are the TCP checksum
39 * from the original datagram.  The next 0 to 15 octets are
40 * sequence number changes, one change per bit set in the header
41 * (there may be no changes and there are two special cases where
42 * the receiver implicitly knows what changed -- see below).
43 *
44 * There are 5 numbers which can change (they are always inserted
45 * in the following order): TCP urgent pointer, window,
46 * acknowlegement, sequence number and IP ID.  (The urgent pointer
47 * is different from the others in that its value is sent, not the
48 * change in value.)  Since typical use of SLIP links is biased
49 * toward small packets (see comments on MTU/MSS below), changes
50 * use a variable length coding with one octet for numbers in the
51 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
52 * range 256 - 65535 or 0.  (If the change in sequence number or
53 * ack is more than 65535, an uncompressed packet is sent.)
54 */
55
56/*
57 * Packet types (must not conflict with IP protocol version)
58 *
59 * The top nibble of the first octet is the packet type.  There are
60 * three possible types: IP (not proto TCP or tcp with one of the
61 * control flags set); uncompressed TCP (a normal IP/TCP packet but
62 * with the 8-bit protocol field replaced by an 8-bit connection id --
63 * this type of packet syncs the sender & receiver); and compressed
64 * TCP (described above).
65 *
66 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
67 * is logically part of the 4-bit "changes" field that follows.  Top
68 * three bits are actual packet type.  For backward compatibility
69 * and in the interest of conserving bits, numbers are chosen so the
70 * IP protocol version number (4) which normally appears in this nibble
71 * means "IP packet".
72 */
73
74/* packet types */
75#define TYPE_IP 0x40
76#define TYPE_UNCOMPRESSED_TCP 0x70
77#define TYPE_COMPRESSED_TCP 0x80
78#define TYPE_ERROR 0x00
79
80/* Bits in first octet of compressed packet */
81#define NEW_C	0x40	/* flag bits for what changed in a packet */
82#define NEW_I	0x20
83#define NEW_S	0x08
84#define NEW_A	0x04
85#define NEW_W	0x02
86#define NEW_U	0x01
87
88/* reserved, special-case values of above */
89#define SPECIAL_I (NEW_S|NEW_W|NEW_U)		/* echoed interactive traffic */
90#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
91#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
92
93#define TCP_PUSH_BIT 0x10
94
95/*
96 * "state" data for each active tcp conversation on the wire.  This is
97 * basically a copy of the entire IP/TCP header from the last packet
98 * we saw from the conversation together with a small identifier
99 * the transmit & receive ends of the line use to locate saved header.
100 */
101struct cstate {
102	struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
103	u_short cs_hlen;	/* size of hdr (receive only) */
104	u_char cs_id;		/* connection # associated with this state */
105	u_char cs_filler;
106	union {
107		char csu_hdr[MAX_HDR];
108		struct ip csu_ip;	/* ip/tcp hdr from most recent packet */
109	} slcs_u;
110};
111#define cs_ip slcs_u.csu_ip
112#define cs_hdr slcs_u.csu_hdr
113
114/*
115 * all the state data for one serial line (we need one of these
116 * per line).
117 */
118struct slcompress {
119	struct cstate *last_cs;	/* most recently used tstate */
120	u_char last_recv;	/* last rcvd conn. id */
121	u_char last_xmit;	/* last sent conn. id */
122	u_short flags;
123	struct cstate tstate[MAX_STATES];	/* xmit connection states */
124	struct cstate rstate[MAX_STATES];	/* receive connection states */
125};
126
127struct slstat {
128  int sls_packets;		/* outbound packets */
129  int sls_compressed;		/* outbound compressed packets */
130  int sls_searches;		/* searches for connection state */
131  int sls_misses;		/* times couldn't find conn. state */
132  int sls_uncompressedin; 	/* inbound uncompressed packets */
133  int sls_compressedin; 	/* inbound compressed packets */
134  int sls_errorin;		/* inbound unknown type packets */
135  int sls_tossed;		/* inbound packets tossed because of error */
136};
137
138/* flag values */
139#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
140
141extern void sl_compress_init __P((struct slcompress *));
142extern u_char sl_compress_tcp __P((struct mbuf *, struct ip *,
143				struct slcompress *, int compress_cid_flag));
144extern int sl_uncompress_tcp __P((u_char **, int,  u_int, struct slcompress *));
145