2 * Definitions for tcp compression routines.
4 * $Header: /home/paulus/ppp/samba.org/ppp/include/net/slcompress.h,v 1.1 1994/02/23 03:49:22 paulus Exp $
6 * Copyright (c) 1989 Regents of the University of California.
9 * Redistribution and use in source and binary forms are permitted
10 * provided that the above copyright notice and this paragraph are
11 * duplicated in all such forms and that any documentation,
12 * advertising materials, and other materials related to such
13 * distribution and use acknowledge that the software was developed
14 * by the University of California, Berkeley. The name of the
15 * University may not be used to endorse or promote products derived
16 * from this software without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
19 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
21 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
22 * - Initial distribution.
25 #define MAX_STATES 16 /* must be > 2 and < 256 */
26 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */
29 * Compressed packet format:
31 * The first octet contains the packet type (top 3 bits), TCP
32 * 'push' bit, and flags that indicate which of the 4 TCP sequence
33 * numbers have changed (bottom 5 bits). The next octet is a
34 * conversation number that associates a saved IP/TCP header with
35 * the compressed packet. The next two octets are the TCP checksum
36 * from the original datagram. The next 0 to 15 octets are
37 * sequence number changes, one change per bit set in the header
38 * (there may be no changes and there are two special cases where
39 * the receiver implicitly knows what changed -- see below).
41 * There are 5 numbers which can change (they are always inserted
42 * in the following order): TCP urgent pointer, window,
43 * acknowlegement, sequence number and IP ID. (The urgent pointer
44 * is different from the others in that its value is sent, not the
45 * change in value.) Since typical use of SLIP links is biased
46 * toward small packets (see comments on MTU/MSS below), changes
47 * use a variable length coding with one octet for numbers in the
48 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
49 * range 256 - 65535 or 0. (If the change in sequence number or
50 * ack is more than 65535, an uncompressed packet is sent.)
54 * Packet types (must not conflict with IP protocol version)
56 * The top nibble of the first octet is the packet type. There are
57 * three possible types: IP (not proto TCP or tcp with one of the
58 * control flags set); uncompressed TCP (a normal IP/TCP packet but
59 * with the 8-bit protocol field replaced by an 8-bit connection id --
60 * this type of packet syncs the sender & receiver); and compressed
61 * TCP (described above).
63 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
64 * is logically part of the 4-bit "changes" field that follows. Top
65 * three bits are actual packet type. For backward compatibility
66 * and in the interest of conserving bits, numbers are chosen so the
67 * IP protocol version number (4) which normally appears in this nibble
73 #define TYPE_UNCOMPRESSED_TCP 0x70
74 #define TYPE_COMPRESSED_TCP 0x80
75 #define TYPE_ERROR 0x00
77 /* Bits in first octet of compressed packet */
78 #define NEW_C 0x40 /* flag bits for what changed in a packet */
85 /* reserved, special-case values of above */
86 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
87 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
88 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
90 #define TCP_PUSH_BIT 0x10
94 * "state" data for each active tcp conversation on the wire. This is
95 * basically a copy of the entire IP/TCP header from the last packet
96 * we saw from the conversation together with a small identifier
97 * the transmit & receive ends of the line use to locate saved header.
100 struct cstate *cs_next; /* next most recently used cstate (xmit only) */
101 u_short cs_hlen; /* size of hdr (receive only) */
102 u_char cs_id; /* connection # associated with this state */
105 char csu_hdr[MAX_HDR];
106 struct ip csu_ip; /* ip/tcp hdr from most recent packet */
109 #define cs_ip slcs_u.csu_ip
110 #define cs_hdr slcs_u.csu_hdr
113 * all the state data for one serial line (we need one of these
117 struct cstate *last_cs; /* most recently used tstate */
118 u_char last_recv; /* last rcvd conn. id */
119 u_char last_xmit; /* last sent conn. id */
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 */
131 struct cstate tstate[MAX_STATES]; /* xmit connection states */
132 struct cstate rstate[MAX_STATES]; /* receive connection states */
135 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */
137 extern void sl_compress_init(/* struct slcompress * */);
138 extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *,
139 struct slcompress *, int compress_cid_flag */);
140 extern int sl_uncompress_tcp(/* u_char **, int, u_char, struct slcompress * */);