1 /* $NetBSD: slcompress.h,v 1.9 1995/07/04 06:28:29 paulus Exp $ */
2 /* Id: slcompress.h,v 1.1 1995/12/11 05:17:12 paulus Exp */
5 * Copyright (c) 1989, 1993
6 * The Regents of the University of California. All rights reserved.
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9 * modification, are permitted provided that the following conditions
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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.
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36 * @(#)slcompress.h 8.1 (Berkeley) 6/10/93
40 * Definitions for tcp compression routines.
42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
43 * - Initial distribution.
46 #define MAX_STATES 16 /* must be > 2 and < 256 */
47 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */
50 * Compressed packet format:
52 * The first octet contains the packet type (top 3 bits), TCP
53 * 'push' bit, and flags that indicate which of the 4 TCP sequence
54 * numbers have changed (bottom 5 bits). The next octet is a
55 * conversation number that associates a saved IP/TCP header with
56 * the compressed packet. The next two octets are the TCP checksum
57 * from the original datagram. The next 0 to 15 octets are
58 * sequence number changes, one change per bit set in the header
59 * (there may be no changes and there are two special cases where
60 * the receiver implicitly knows what changed -- see below).
62 * There are 5 numbers which can change (they are always inserted
63 * in the following order): TCP urgent pointer, window,
64 * acknowlegement, sequence number and IP ID. (The urgent pointer
65 * is different from the others in that its value is sent, not the
66 * change in value.) Since typical use of SLIP links is biased
67 * toward small packets (see comments on MTU/MSS below), changes
68 * use a variable length coding with one octet for numbers in the
69 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
70 * range 256 - 65535 or 0. (If the change in sequence number or
71 * ack is more than 65535, an uncompressed packet is sent.)
75 * Packet types (must not conflict with IP protocol version)
77 * The top nibble of the first octet is the packet type. There are
78 * three possible types: IP (not proto TCP or tcp with one of the
79 * control flags set); uncompressed TCP (a normal IP/TCP packet but
80 * with the 8-bit protocol field replaced by an 8-bit connection id --
81 * this type of packet syncs the sender & receiver); and compressed
82 * TCP (described above).
84 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
85 * is logically part of the 4-bit "changes" field that follows. Top
86 * three bits are actual packet type. For backward compatibility
87 * and in the interest of conserving bits, numbers are chosen so the
88 * IP protocol version number (4) which normally appears in this nibble
94 #define TYPE_UNCOMPRESSED_TCP 0x70
95 #define TYPE_COMPRESSED_TCP 0x80
96 #define TYPE_ERROR 0x00
98 /* Bits in first octet of compressed packet */
99 #define NEW_C 0x40 /* flag bits for what changed in a packet */
106 /* reserved, special-case values of above */
107 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
108 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
109 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
111 #define TCP_PUSH_BIT 0x10
115 * "state" data for each active tcp conversation on the wire. This is
116 * basically a copy of the entire IP/TCP header from the last packet
117 * we saw from the conversation together with a small identifier
118 * the transmit & receive ends of the line use to locate saved header.
121 struct cstate *cs_next; /* next most recently used cstate (xmit only) */
122 u_int16_t cs_hlen; /* size of hdr (receive only) */
123 u_char cs_id; /* connection # associated with this state */
126 char csu_hdr[MAX_HDR];
127 struct ip csu_ip; /* ip/tcp hdr from most recent packet */
130 #define cs_ip slcs_u.csu_ip
131 #define cs_hdr slcs_u.csu_hdr
134 * all the state data for one serial line (we need one of these
138 struct cstate *last_cs; /* most recently used tstate */
139 u_char last_recv; /* last rcvd conn. id */
140 u_char last_xmit; /* last sent conn. id */
143 int sls_packets; /* outbound packets */
144 int sls_compressed; /* outbound compressed packets */
145 int sls_searches; /* searches for connection state */
146 int sls_misses; /* times couldn't find conn. state */
147 int sls_uncompressedin; /* inbound uncompressed packets */
148 int sls_compressedin; /* inbound compressed packets */
149 int sls_errorin; /* inbound unknown type packets */
150 int sls_tossed; /* inbound packets tossed because of error */
152 struct cstate tstate[MAX_STATES]; /* xmit connection states */
153 struct cstate rstate[MAX_STATES]; /* receive connection states */
156 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
158 void sl_compress_init __P((struct slcompress *, int));
159 u_int sl_compress_tcp __P((struct mbuf *,
160 struct ip *, struct slcompress *, int));
161 int sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
162 int sl_uncompress_tcp_core __P((u_char *, int, int, u_int,
163 struct slcompress *, u_char **, u_int *));