2 * Definitions for tcp compression routines.
4 * Copyright (c) 1989, 1993
5 * The Regents of the University of California. All rights reserved.
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17 * This product includes software developed by the University of
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21 * without specific prior written permission.
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35 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
36 * - Initial distribution.
37 * $FreeBSD: src/sys/net/slcompress.h,v 1.14.2.1 2000/05/05 13:37:06 jlemon Exp $
38 * $DragonFly: src/sys/net/slcompress.h,v 1.2 2003/06/17 04:28:48 dillon Exp $
41 #ifndef _NET_SLCOMPRESS_H_
42 #define _NET_SLCOMPRESS_H_
44 #define MAX_STATES 16 /* must be > 2 and < 256 */
48 * Compressed packet format:
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).
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.)
73 * Packet types (must not conflict with IP protocol version)
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).
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
92 #define TYPE_UNCOMPRESSED_TCP 0x70
93 #define TYPE_COMPRESSED_TCP 0x80
94 #define TYPE_ERROR 0x00
96 /* Bits in first octet of compressed packet */
97 #define NEW_C 0x40 /* flag bits for what changed in a packet */
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)
109 #define TCP_PUSH_BIT 0x10
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.
119 struct cstate *cs_next; /* next most recently used cstate (xmit only) */
120 u_int16_t cs_hlen; /* size of hdr (receive only) */
121 u_char cs_id; /* connection # associated with this state */
124 char csu_hdr[MAX_HDR];
125 struct ip csu_ip; /* ip/tcp hdr from most recent packet */
128 #define cs_ip slcs_u.csu_ip
129 #define cs_hdr slcs_u.csu_hdr
132 * all the state data for one serial line (we need one of these
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 */
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 */
150 struct cstate tstate[MAX_STATES]; /* xmit connection states */
151 struct cstate rstate[MAX_STATES]; /* receive connection states */
154 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
156 void sl_compress_init __P((struct slcompress *, int));
157 u_int sl_compress_tcp __P((struct mbuf *,
158 struct ip *, struct slcompress *, int));
159 int sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *));
160 int sl_uncompress_tcp_core __P((u_char *, int, int, u_int,
161 struct slcompress *, u_char **, u_int *));
163 #endif /* !_NET_SLCOMPRESS_H_ */