1 /* 2 * Definitions for tcp compression routines. 3 * 4 * $Id: slcompress.h,v 1.4 1994/09/21 06:50:08 paulus Exp $ 5 * 6 * Copyright (c) 1989 Regents of the University of California. 7 * All rights reserved. 8 * 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. 20 * 21 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 22 * - Initial distribution. 23 */ 24 25 #ifndef _SLCOMPRESS_H_ 26 #define _SLCOMPRESS_H_ 27 28 #define MAX_STATES 16 /* must be > 2 and < 256 */ 29 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ 30 31 /* 32 * Compressed packet format: 33 * 34 * The first octet contains the packet type (top 3 bits), TCP 35 * 'push' bit, and flags that indicate which of the 4 TCP sequence 36 * numbers have changed (bottom 5 bits). The next octet is a 37 * conversation number that associates a saved IP/TCP header with 38 * the compressed packet. The next two octets are the TCP checksum 39 * from the original datagram. The next 0 to 15 octets are 40 * sequence number changes, one change per bit set in the header 41 * (there may be no changes and there are two special cases where 42 * the receiver implicitly knows what changed -- see below). 43 * 44 * There are 5 numbers which can change (they are always inserted 45 * in the following order): TCP urgent pointer, window, 46 * acknowlegement, sequence number and IP ID. (The urgent pointer 47 * is different from the others in that its value is sent, not the 48 * change in value.) Since typical use of SLIP links is biased 49 * toward small packets (see comments on MTU/MSS below), changes 50 * use a variable length coding with one octet for numbers in the 51 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 52 * range 256 - 65535 or 0. (If the change in sequence number or 53 * ack is more than 65535, an uncompressed packet is sent.) 54 */ 55 56 /* 57 * Packet types (must not conflict with IP protocol version) 58 * 59 * The top nibble of the first octet is the packet type. There are 60 * three possible types: IP (not proto TCP or tcp with one of the 61 * control flags set); uncompressed TCP (a normal IP/TCP packet but 62 * with the 8-bit protocol field replaced by an 8-bit connection id -- 63 * this type of packet syncs the sender & receiver); and compressed 64 * TCP (described above). 65 * 66 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 67 * is logically part of the 4-bit "changes" field that follows. Top 68 * three bits are actual packet type. For backward compatibility 69 * and in the interest of conserving bits, numbers are chosen so the 70 * IP protocol version number (4) which normally appears in this nibble 71 * means "IP packet". 72 */ 73 74 /* packet types */ 75 #define TYPE_IP 0x40 76 #define TYPE_UNCOMPRESSED_TCP 0x70 77 #define TYPE_COMPRESSED_TCP 0x80 78 #define TYPE_ERROR 0x00 79 80 /* Bits in first octet of compressed packet */ 81 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 82 #define NEW_I 0x20 83 #define NEW_S 0x08 84 #define NEW_A 0x04 85 #define NEW_W 0x02 86 #define NEW_U 0x01 87 88 /* reserved, special-case values of above */ 89 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 90 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 91 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 92 93 #define TCP_PUSH_BIT 0x10 94 95 96 /* 97 * "state" data for each active tcp conversation on the wire. This is 98 * basically a copy of the entire IP/TCP header from the last packet 99 * we saw from the conversation together with a small identifier 100 * the transmit & receive ends of the line use to locate saved header. 101 */ 102 struct cstate { 103 struct cstate *cs_next; /* next most recently used cstate (xmit only) */ 104 u_short cs_hlen; /* size of hdr (receive only) */ 105 u_char cs_id; /* connection # associated with this state */ 106 u_char cs_filler; 107 union { 108 char csu_hdr[MAX_HDR]; 109 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 110 } slcs_u; 111 }; 112 #define cs_ip slcs_u.csu_ip 113 #define cs_hdr slcs_u.csu_hdr 114 115 /* 116 * all the state data for one serial line (we need one of these 117 * per line). 118 */ 119 struct slcompress { 120 struct cstate *last_cs; /* most recently used tstate */ 121 u_char last_recv; /* last rcvd conn. id */ 122 u_char last_xmit; /* last sent conn. id */ 123 u_short flags; 124 #ifndef SL_NO_STATS 125 int sls_packets; /* outbound packets */ 126 int sls_compressed; /* outbound compressed packets */ 127 int sls_searches; /* searches for connection state */ 128 int sls_misses; /* times couldn't find conn. state */ 129 int sls_uncompressedin; /* inbound uncompressed packets */ 130 int sls_compressedin; /* inbound compressed packets */ 131 int sls_errorin; /* inbound unknown type packets */ 132 int sls_tossed; /* inbound packets tossed because of error */ 133 #endif 134 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 135 struct cstate rstate[MAX_STATES]; /* receive connection states */ 136 }; 137 /* flag values */ 138 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 139 140 void sl_compress_init __P((struct slcompress *)); 141 void sl_compress_setup __P((struct slcompress *, int)); 142 u_int sl_compress_tcp __P((struct mbuf *, 143 struct ip *, struct slcompress *, int)); 144 int sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *)); 145 int sl_uncompress_tcp_core __P((u_char *, int, int, u_int, 146 struct slcompress *, u_char **, u_int *)); 147 148 #endif /* _SLCOMPRESS_H_ */ 149