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1.1 root 1: /* slcompress.h 7.4 90/06/28 */
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 Regents of the University of California.
8: * All rights reserved.
9: *
10: * Redistribution is only permitted until one year after the first shipment
11: * of 4.4BSD by the Regents. Otherwise, redistribution and use in source and
12: * binary forms are permitted provided that: (1) source distributions retain
13: * this entire copyright notice and comment, and (2) distributions including
14: * binaries display the following acknowledgement: This product includes
15: * software developed by the University of California, Berkeley and its
16: * contributors'' in the documentation or other materials provided with the
17: * distribution and in all advertising materials mentioning features or use
18: * of this software. Neither the name of the University nor the names of
19: * its contributors may be used to endorse or promote products derived from
20: * this software without specific prior written permission.
21: * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
22: * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
23: * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
24: *
25: * Van Jacobson ([email protected]), Dec 31, 1989:
26: * - Initial distribution.
27: */
28:
29: #define MAX_STATES 16 /* must be > 2 and < 256 */
30: #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */
31:
32: /*
33: * Compressed packet format:
34: *
35: * The first octet contains the packet type (top 3 bits), TCP
36: * 'push' bit, and flags that indicate which of the 4 TCP sequence
37: * numbers have changed (bottom 5 bits). The next octet is a
38: * conversation number that associates a saved IP/TCP header with
39: * the compressed packet. The next two octets are the TCP checksum
40: * from the original datagram. The next 0 to 15 octets are
41: * sequence number changes, one change per bit set in the header
42: * (there may be no changes and there are two special cases where
43: * the receiver implicitly knows what changed -- see below).
44: *
45: * There are 5 numbers which can change (they are always inserted
46: * in the following order): TCP urgent pointer, window,
47: * acknowlegement, sequence number and IP ID. (The urgent pointer
48: * is different from the others in that its value is sent, not the
49: * change in value.) Since typical use of SLIP links is biased
50: * toward small packets (see comments on MTU/MSS below), changes
51: * use a variable length coding with one octet for numbers in the
52: * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
53: * range 256 - 65535 or 0. (If the change in sequence number or
54: * ack is more than 65535, an uncompressed packet is sent.)
55: */
56:
57: /*
58: * Packet types (must not conflict with IP protocol version)
59: *
60: * The top nibble of the first octet is the packet type. There are
61: * three possible types: IP (not proto TCP or tcp with one of the
62: * control flags set); uncompressed TCP (a normal IP/TCP packet but
63: * with the 8-bit protocol field replaced by an 8-bit connection id --
64: * this type of packet syncs the sender & receiver); and compressed
65: * TCP (described above).
66: *
67: * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
68: * is logically part of the 4-bit "changes" field that follows. Top
69: * three bits are actual packet type. For backward compatibility
70: * and in the interest of conserving bits, numbers are chosen so the
71: * IP protocol version number (4) which normally appears in this nibble
72: * means "IP packet".
73: */
74:
75: /* packet types */
76: #define TYPE_IP 0x40
77: #define TYPE_UNCOMPRESSED_TCP 0x70
78: #define TYPE_COMPRESSED_TCP 0x80
79: #define TYPE_ERROR 0x00
80:
81: /* Bits in first octet of compressed packet */
82: #define NEW_C 0x40 /* flag bits for what changed in a packet */
83: #define NEW_I 0x20
84: #define NEW_S 0x08
85: #define NEW_A 0x04
86: #define NEW_W 0x02
87: #define NEW_U 0x01
88:
89: /* reserved, special-case values of above */
90: #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
91: #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
92: #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
93:
94: #define TCP_PUSH_BIT 0x10
95:
96:
97: /*
98: * "state" data for each active tcp conversation on the wire. This is
99: * basically a copy of the entire IP/TCP header from the last packet
100: * we saw from the conversation together with a small identifier
101: * the transmit & receive ends of the line use to locate saved header.
102: */
103: struct cstate {
104: struct cstate *cs_next; /* next most recently used cstate (xmit only) */
105: u_short cs_hlen; /* size of hdr (receive only) */
106: u_char cs_id; /* connection # associated with this state */
107: u_char cs_filler;
108: union {
109: char csu_hdr[MAX_HDR];
110: struct ip csu_ip; /* ip/tcp hdr from most recent packet */
111: } slcs_u;
112: };
113: #define cs_ip slcs_u.csu_ip
114: #define cs_hdr slcs_u.csu_hdr
115:
116: /*
117: * all the state data for one serial line (we need one of these
118: * per line).
119: */
120: struct slcompress {
121: struct cstate *last_cs; /* most recently used tstate */
122: u_char last_recv; /* last rcvd conn. id */
123: u_char last_xmit; /* last sent conn. id */
124: u_short flags;
125: #ifndef SL_NO_STATS
126: int sls_packets; /* outbound packets */
127: int sls_compressed; /* outbound compressed packets */
128: int sls_searches; /* searches for connection state */
129: int sls_misses; /* times couldn't find conn. state */
130: int sls_uncompressedin; /* inbound uncompressed packets */
131: int sls_compressedin; /* inbound compressed packets */
132: int sls_errorin; /* inbound unknown type packets */
133: int sls_tossed; /* inbound packets tossed because of error */
134: #endif
135: struct cstate tstate[MAX_STATES]; /* xmit connection states */
136: struct cstate rstate[MAX_STATES]; /* receive connection states */
137: };
138: /* flag values */
139: #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
140:
141: extern void sl_compress_init(/* struct slcompress * */);
142: extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *,
143: struct slcompress *, int compress_cid_flag */);
144: extern int sl_uncompress_tcp(/* u_char **, int, u_char, struct slcompress * */);
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