1 /* 2 * Definitions for tcp compression routines. 3 * 4 * Copyright (c) 1989 Regents of the University of California. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms are permitted 8 * provided that the above copyright notice and this paragraph are 9 * duplicated in all such forms and that any documentation, 10 * advertising materials, and other materials related to such 11 * distribution and use acknowledge that the software was developed 12 * by the University of California, Berkeley. The name of the 13 * University may not be used to endorse or promote products derived 14 * from this software without specific prior written permission. 15 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 17 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 18 * 19 * $FreeBSD$ 20 * 21 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 22 * - Initial distribution. 23 */ 24 25 #define MIN_VJ_STATES 3 26 #define MAX_VJ_STATES 255 27 #define DEF_VJ_STATES 16 /* must be > 2 and < 256 */ 28 #define MAX_HDR 128 29 30 /* 31 * Compressed packet format: 32 * 33 * The first octet contains the packet type (top 3 bits), TCP 34 * 'push' bit, and flags that indicate which of the 4 TCP sequence 35 * numbers have changed (bottom 5 bits). The next octet is a 36 * conversation number that associates a saved IP/TCP header with 37 * the compressed packet. The next two octets are the TCP checksum 38 * from the original datagram. The next 0 to 15 octets are 39 * sequence number changes, one change per bit set in the header 40 * (there may be no changes and there are two special cases where 41 * the receiver implicitly knows what changed -- see below). 42 * 43 * There are 5 numbers which can change (they are always inserted 44 * in the following order): TCP urgent pointer, window, 45 * acknowlegement, sequence number and IP ID. (The urgent pointer 46 * is different from the others in that its value is sent, not the 47 * change in value.) Since typical use of SLIP links is biased 48 * toward small packets (see comments on MTU/MSS below), changes 49 * use a variable length coding with one octet for numbers in the 50 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 51 * range 256 - 65535 or 0. (If the change in sequence number or 52 * ack is more than 65535, an uncompressed packet is sent.) 53 */ 54 55 /* 56 * Packet types (must not conflict with IP protocol version) 57 * 58 * The top nibble of the first octet is the packet type. There are 59 * three possible types: IP (not proto TCP or tcp with one of the 60 * control flags set); uncompressed TCP (a normal IP/TCP packet but 61 * with the 8-bit protocol field replaced by an 8-bit connection id -- 62 * this type of packet syncs the sender & receiver); and compressed 63 * TCP (described above). 64 * 65 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 66 * is logically part of the 4-bit "changes" field that follows. Top 67 * three bits are actual packet type. For backward compatibility 68 * and in the interest of conserving bits, numbers are chosen so the 69 * IP protocol version number (4) which normally appears in this nibble 70 * means "IP packet". 71 */ 72 73 /* packet types */ 74 #define TYPE_IP 0x40 75 #define TYPE_UNCOMPRESSED_TCP 0x70 76 #define TYPE_COMPRESSED_TCP 0x80 77 #define TYPE_ERROR 0x00 78 79 /* Bits in first octet of compressed packet */ 80 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 81 #define NEW_I 0x20 82 #define NEW_S 0x08 83 #define NEW_A 0x04 84 #define NEW_W 0x02 85 #define NEW_U 0x01 86 87 /* reserved, special-case values of above */ 88 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 89 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 90 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 91 92 #define TCP_PUSH_BIT 0x10 93 94 /* 95 * "state" data for each active tcp conversation on the wire. This is 96 * basically a copy of the entire IP/TCP header from the last packet 97 * we saw from the conversation together with a small identifier 98 * the transmit & receive ends of the line use to locate saved header. 99 */ 100 struct cstate { 101 struct cstate *cs_next; /* next most recently used cstate (xmit only) */ 102 u_short cs_hlen; /* size of hdr (receive only) */ 103 u_char cs_id; /* connection # associated with this state */ 104 u_char cs_filler; 105 union { 106 char csu_hdr[MAX_HDR]; 107 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 108 } slcs_u; 109 }; 110 111 #define cs_ip slcs_u.csu_ip 112 #define cs_hdr slcs_u.csu_hdr 113 114 /* 115 * all the state data for one serial line (we need one of these 116 * per line). 117 */ 118 struct slcompress { 119 struct cstate *last_cs; /* most recently used tstate */ 120 u_char last_recv; /* last rcvd conn. id */ 121 u_char last_xmit; /* last sent conn. id */ 122 u_short flags; 123 struct cstate tstate[MAX_VJ_STATES]; /* xmit connection states */ 124 struct cstate rstate[MAX_VJ_STATES]; /* receive connection states */ 125 }; 126 127 struct slstat { 128 int sls_packets; /* outbound packets */ 129 int sls_compressed; /* outbound compressed packets */ 130 int sls_searches; /* searches for connection state */ 131 int sls_misses; /* times couldn't find conn. state */ 132 int sls_uncompressedin; /* inbound uncompressed packets */ 133 int sls_compressedin; /* inbound compressed packets */ 134 int sls_errorin; /* inbound unknown type packets */ 135 int sls_tossed; /* inbound packets tossed because of error */ 136 }; 137 138 /* flag values */ 139 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 140 141 struct mbuf; 142 struct cmdargs; 143 144 extern void sl_compress_init(struct slcompress *, int); 145 extern u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *, 146 struct slstat *, int); 147 extern int sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *, 148 struct slstat *, int); 149 extern int sl_Show(struct cmdargs const *); 150