slcompress.h revision 58982 
1/*
2 * Definitions for tcp compression routines.
3 *
4 * Copyright (c) 1989 Regents of the University of California.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms are permitted
8 * provided that the above copyright notice and this paragraph are
9 * duplicated in all such forms and that any documentation,
10 * advertising materials, and other materials related to such
11 * distribution and use acknowledge that the software was developed
12 * by the University of California, Berkeley.  The name of the
13 * University may not be used to endorse or promote products derived
14 * from this software without specific prior written permission.
15 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
17 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
18 *
19 * $FreeBSD: head/usr.sbin/ppp/slcompress.h 58982 2000-04-03 19:54:33Z gj $
20 *
21 *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
22 *	- Initial distribution.
23 */
24
25#define MIN_VJ_STATES 3
26#define MAX_VJ_STATES 255
27#define DEF_VJ_STATES 16		/* must be > 2 and < 256 */
28#define MAX_HDR 128
29
30/*
31 * Compressed packet format:
32 *
33 * The first octet contains the packet type (top 3 bits), TCP
34 * 'push' bit, and flags that indicate which of the 4 TCP sequence
35 * numbers have changed (bottom 5 bits).  The next octet is a
36 * conversation number that associates a saved IP/TCP header with
37 * the compressed packet.  The next two octets are the TCP checksum
38 * from the original datagram.  The next 0 to 15 octets are
39 * sequence number changes, one change per bit set in the header
40 * (there may be no changes and there are two special cases where
41 * the receiver implicitly knows what changed -- see below).
42 *
43 * There are 5 numbers which can change (they are always inserted
44 * in the following order): TCP urgent pointer, window,
45 * acknowlegement, sequence number and IP ID.  (The urgent pointer
46 * is different from the others in that its value is sent, not the
47 * change in value.)  Since typical use of SLIP links is biased
48 * toward small packets (see comments on MTU/MSS below), changes
49 * use a variable length coding with one octet for numbers in the
50 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
51 * range 256 - 65535 or 0.  (If the change in sequence number or
52 * ack is more than 65535, an uncompressed packet is sent.)
53 */
54
55/*
56 * Packet types (must not conflict with IP protocol version)
57 *
58 * The top nibble of the first octet is the packet type.  There are
59 * three possible types: IP (not proto TCP or tcp with one of the
60 * control flags set); uncompressed TCP (a normal IP/TCP packet but
61 * with the 8-bit protocol field replaced by an 8-bit connection id --
62 * this type of packet syncs the sender & receiver); and compressed
63 * TCP (described above).
64 *
65 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
66 * is logically part of the 4-bit "changes" field that follows.  Top
67 * three bits are actual packet type.  For backward compatibility
68 * and in the interest of conserving bits, numbers are chosen so the
69 * IP protocol version number (4) which normally appears in this nibble
70 * means "IP packet".
71 */
72
73/* packet types */
74#define TYPE_IP 0x40
75#define TYPE_UNCOMPRESSED_TCP 0x70
76#define TYPE_COMPRESSED_TCP 0x80
77#define TYPE_ERROR 0x00
78
79/* Bits in first octet of compressed packet */
80#define NEW_C	0x40		/* flag bits for what changed in a packet */
81#define NEW_I	0x20
82#define NEW_S	0x08
83#define NEW_A	0x04
84#define NEW_W	0x02
85#define NEW_U	0x01
86
87/* reserved, special-case values of above */
88#define SPECIAL_I (NEW_S|NEW_W|NEW_U)	/* echoed interactive traffic */
89#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
90#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
91
92#define TCP_PUSH_BIT 0x10
93
94/*
95 * "state" data for each active tcp conversation on the wire.  This is
96 * basically a copy of the entire IP/TCP header from the last packet
97 * we saw from the conversation together with a small identifier
98 * the transmit & receive ends of the line use to locate saved header.
99 */
100struct cstate {
101  struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
102  u_short cs_hlen;		/* size of hdr (receive only) */
103  u_char cs_id;			/* connection # associated with this state */
104  u_char cs_filler;
105  struct ip cs_ip;		/* ip/tcp hdr from most recent packet */
106};
107
108/*
109 * all the state data for one serial line (we need one of these
110 * per line).
111 */
112struct slcompress {
113  struct cstate *last_cs;	/* most recently used tstate */
114  u_char last_recv;		/* last rcvd conn. id */
115  u_char last_xmit;		/* last sent conn. id */
116  u_short flags;
117  struct cstate tstate[MAX_VJ_STATES];	/* xmit connection states */
118  struct cstate rstate[MAX_VJ_STATES];	/* receive connection states */
119};
120
121struct slstat {
122  int sls_packets;		/* outbound packets */
123  int sls_compressed;		/* outbound compressed packets */
124  int sls_searches;		/* searches for connection state */
125  int sls_misses;		/* times couldn't find conn. state */
126  int sls_uncompressedin;	/* inbound uncompressed packets */
127  int sls_compressedin;		/* inbound compressed packets */
128  int sls_errorin;		/* inbound unknown type packets */
129  int sls_tossed;		/* inbound packets tossed because of error */
130};
131
132/* flag values */
133#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
134
135struct mbuf;
136struct cmdargs;
137
138extern void sl_compress_init(struct slcompress *, int);
139extern u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *,
140                              struct slstat *, int);
141extern int sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *,
142                             struct slstat *, int);
143extern int sl_Show(struct cmdargs const *);
144