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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8 * modification, are permitted provided that the following conditions
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19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
32 * - Initial distribution.
37 #define MIN_VJ_STATES 3
38 #define MAX_VJ_STATES 255
39 #define DEF_VJ_STATES 16 /* must be > 2 and < 256 */
43 * Compressed packet format:
45 * The first octet contains the packet type (top 3 bits), TCP
46 * 'push' bit, and flags that indicate which of the 4 TCP sequence
47 * numbers have changed (bottom 5 bits). The next octet is a
48 * conversation number that associates a saved IP/TCP header with
49 * the compressed packet. The next two octets are the TCP checksum
50 * from the original datagram. The next 0 to 15 octets are
51 * sequence number changes, one change per bit set in the header
52 * (there may be no changes and there are two special cases where
53 * the receiver implicitly knows what changed -- see below).
55 * There are 5 numbers which can change (they are always inserted
56 * in the following order): TCP urgent pointer, window,
57 * acknowlegement, sequence number and IP ID. (The urgent pointer
58 * is different from the others in that its value is sent, not the
59 * change in value.) Since typical use of SLIP links is biased
60 * toward small packets (see comments on MTU/MSS below), changes
61 * use a variable length coding with one octet for numbers in the
62 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
63 * range 256 - 65535 or 0. (If the change in sequence number or
64 * ack is more than 65535, an uncompressed packet is sent.)
68 * Packet types (must not conflict with IP protocol version)
70 * The top nibble of the first octet is the packet type. There are
71 * three possible types: IP (not proto TCP or tcp with one of the
72 * control flags set); uncompressed TCP (a normal IP/TCP packet but
73 * with the 8-bit protocol field replaced by an 8-bit connection id --
74 * this type of packet syncs the sender & receiver); and compressed
75 * TCP (described above).
77 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
78 * is logically part of the 4-bit "changes" field that follows. Top
79 * three bits are actual packet type. For backward compatibility
80 * and in the interest of conserving bits, numbers are chosen so the
81 * IP protocol version number (4) which normally appears in this nibble
87 #define TYPE_UNCOMPRESSED_TCP 0x70
88 #define TYPE_COMPRESSED_TCP 0x80
89 #define TYPE_ERROR 0x00
91 /* Bits in first octet of compressed packet */
92 #define NEW_C 0x40 /* flag bits for what changed in a packet */
99 /* reserved, special-case values of above */
100 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
101 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
102 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
104 #define TCP_PUSH_BIT 0x10
107 * "state" data for each active tcp conversation on the wire. This is
108 * basically a copy of the entire IP/TCP header from the last packet
109 * we saw from the conversation together with a small identifier
110 * the transmit & receive ends of the line use to locate saved header.
113 struct cstate *cs_next; /* next most recently used cstate (xmit only) */
114 u_short cs_hlen; /* size of hdr (receive only) */
115 u_char cs_id; /* connection # associated with this state */
118 char csu_hdr[MAX_HDR];
119 struct ip csu_ip; /* ip/tcp hdr from most recent packet */
123 #define cs_ip slcs_u.csu_ip
124 #define cs_hdr slcs_u.csu_hdr
127 * all the state data for one serial line (we need one of these
131 struct cstate *last_cs; /* most recently used tstate */
132 u_char last_recv; /* last rcvd conn. id */
133 u_char last_xmit; /* last sent conn. id */
135 struct cstate tstate[MAX_VJ_STATES]; /* xmit connection states */
136 struct cstate rstate[MAX_VJ_STATES]; /* receive connection states */
140 int sls_packets; /* outbound packets */
141 int sls_compressed; /* outbound compressed packets */
142 int sls_searches; /* searches for connection state */
143 int sls_misses; /* times couldn't find conn. state */
144 int sls_uncompressedin; /* inbound uncompressed packets */
145 int sls_compressedin; /* inbound compressed packets */
146 int sls_errorin; /* inbound unknown type packets */
147 int sls_tossed; /* inbound packets tossed because of error */
151 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
156 extern void sl_compress_init(struct slcompress *, int);
157 extern u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *,
158 struct slstat *, int);
159 extern int sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *,
160 struct slstat *, int);
161 extern int sl_Show(struct cmdargs const *);