1 /* 2 * Definitions for tcp compression routines. 3 * 4 * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of 5 * California. 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 * Van Jacobson (van@ee.lbl.gov), Dec 31, 1989: 20 * - Initial distribution. 21 */ 22 23 #define MAX_STATES 16 /* must be > 2 and < 256 */ 24 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ 25 26 /* 27 * Compressed packet format: 28 * 29 * The first octet contains the packet type (top 3 bits), TCP 30 * 'push' bit, and flags that indicate which of the 4 TCP sequence 31 * numbers have changed (bottom 5 bits). The next octet is a 32 * conversation number that associates a saved IP/TCP header with 33 * the compressed packet. The next two octets are the TCP checksum 34 * from the original datagram. The next 0 to 15 octets are 35 * sequence number changes, one change per bit set in the header 36 * (there may be no changes and there are two special cases where 37 * the receiver implicitly knows what changed -- see below). 38 * 39 * There are 5 numbers which can change (they are always inserted 40 * in the following order): TCP urgent pointer, window, 41 * acknowlegement, sequence number and IP ID. (The urgent pointer 42 * is different from the others in that its value is sent, not the 43 * change in value.) Since typical use of SLIP links is biased 44 * toward small packets (see comments on MTU/MSS below), changes 45 * use a variable length coding with one octet for numbers in the 46 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 47 * range 256 - 65535 or 0. (If the change in sequence number or 48 * ack is more than 65535, an uncompressed packet is sent.) 49 */ 50 51 /* 52 * Packet types (must not conflict with IP protocol version) 53 * 54 * The top nibble of the first octet is the packet type. There are 55 * three possible types: IP (not proto TCP or tcp with one of the 56 * control flags set); uncompressed TCP (a normal IP/TCP packet but 57 * with the 8-bit protocol field replaced by an 8-bit connection id -- 58 * this type of packet syncs the sender & receiver); and compressed 59 * TCP (described above). 60 * 61 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 62 * is logically part of the 4-bit "changes" field that follows. Top 63 * three bits are actual packet type. For backward compatibility 64 * and in the interest of conserving bits, numbers are chosen so the 65 * IP protocol version number (4) which normally appears in this nibble 66 * means "IP packet". 67 */ 68 69 /* packet types */ 70 #define TYPE_IP 0x40 71 #define TYPE_UNCOMPRESSED_TCP 0x70 72 #define TYPE_COMPRESSED_TCP 0x80 73 #define TYPE_ERROR 0x00 74 75 /* Bits in first octet of compressed packet */ 76 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 77 #define NEW_I 0x20 78 #define NEW_S 0x08 79 #define NEW_A 0x04 80 #define NEW_W 0x02 81 #define NEW_U 0x01 82 83 /* reserved, special-case values of above */ 84 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 85 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 86 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 87 88 #define TCP_PUSH_BIT 0x10 89 90 91 /* 92 * "state" data for each active tcp conversation on the wire. This is 93 * basically a copy of the entire IP/TCP header from the last packet 94 * we saw from the conversation together with a small identifier 95 * the transmit & receive ends of the line use to locate saved header. 96 */ 97 struct cstate { 98 struct cstate *cs_next; /* next most recently used cstate (xmit only) */ 99 u_short cs_hlen; /* size of hdr (receive only) */ 100 u_char cs_id; /* connection # associated with this state */ 101 u_char cs_filler; 102 union { 103 char csu_hdr[MAX_HDR]; 104 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 105 } slcs_u; 106 }; 107 #define cs_ip slcs_u.csu_ip 108 #define cs_hdr slcs_u.csu_hdr 109 110 /* 111 * all the state data for one serial line (we need one of these 112 * per line). 113 */ 114 struct slcompress { 115 struct cstate *last_cs; /* most recently used tstate */ 116 u_char last_recv; /* last rcvd conn. id */ 117 u_char last_xmit; /* last sent conn. id */ 118 u_short flags; 119 #ifndef SL_NO_STATS 120 u_int sls_packets; /* outbound packets */ 121 u_int sls_compressed; /* outbound compressed packets */ 122 u_int sls_searches; /* searches for connection state */ 123 u_int sls_misses; /* times couldn't find conn. state */ 124 u_int sls_uncompressedin;/* inbound uncompressed packets */ 125 u_int sls_compressedin; /* inbound compressed packets */ 126 u_int sls_errorin; /* inbound unknown type packets */ 127 u_int sls_tossed; /* inbound packets tossed because of error */ 128 #endif 129 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 130 struct cstate rstate[MAX_STATES]; /* receive connection states */ 131 }; 132 /* flag values */ 133 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 134 135 #ifdef KERNEL 136 #ifdef __STDC__ 137 extern void sl_compress_init(struct slcompress *); 138 extern u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *); 139 extern int sl_uncompress_tcp(struct mbuf *, int, u_int, struct slcompress *); 140 #else 141 extern void sl_compress_init(); 142 extern u_char sl_compress_tcp(); 143 extern int sl_uncompress_tcp(); 144 #endif 145 #endif 146 147