1 /* slcompress.h 7.3 90/01/20 */ 2 /* 3 * Definitions for tcp compression routines. 4 * 5 * $Header: slcompress.h,v 1.10 89/12/31 08:53:02 van Exp $ 6 * 7 * Copyright (c) 1989 Regents of the University of California. 8 * All rights reserved. 9 * 10 * Redistribution and use in source and binary forms are permitted 11 * provided that the above copyright notice and this paragraph are 12 * duplicated in all such forms and that any documentation, 13 * advertising materials, and other materials related to such 14 * distribution and use acknowledge that the software was developed 15 * by the University of California, Berkeley. The name of the 16 * University may not be used to endorse or promote products derived 17 * from this software without specific prior written permission. 18 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 19 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 20 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 21 * 22 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 23 * - Initial distribution. 24 */ 25 26 #define MAX_STATES 16 /* must be > 2 and < 256 */ 27 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ 28 29 /* 30 * Compressed packet format: 31 * 32 * The first octet contains the packet type (top 3 bits), TCP 33 * 'push' bit, and flags that indicate which of the 4 TCP sequence 34 * numbers have changed (bottom 5 bits). The next octet is a 35 * conversation number that associates a saved IP/TCP header with 36 * the compressed packet. The next two octets are the TCP checksum 37 * from the original datagram. The next 0 to 15 octets are 38 * sequence number changes, one change per bit set in the header 39 * (there may be no changes and there are two special cases where 40 * the receiver implicitly knows what changed -- see below). 41 * 42 * There are 5 numbers which can change (they are always inserted 43 * in the following order): TCP urgent pointer, window, 44 * acknowlegement, sequence number and IP ID. (The urgent pointer 45 * is different from the others in that its value is sent, not the 46 * change in value.) Since typical use of SLIP links is biased 47 * toward small packets (see comments on MTU/MSS below), changes 48 * use a variable length coding with one octet for numbers in the 49 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 50 * range 256 - 65535 or 0. (If the change in sequence number or 51 * ack is more than 65535, an uncompressed packet is sent.) 52 */ 53 54 /* 55 * Packet types (must not conflict with IP protocol version) 56 * 57 * The top nibble of the first octet is the packet type. There are 58 * three possible types: IP (not proto TCP or tcp with one of the 59 * control flags set); uncompressed TCP (a normal IP/TCP packet but 60 * with the 8-bit protocol field replaced by an 8-bit connection id -- 61 * this type of packet syncs the sender & receiver); and compressed 62 * TCP (described above). 63 * 64 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 65 * is logically part of the 4-bit "changes" field that follows. Top 66 * three bits are actual packet type. For backward compatibility 67 * and in the interest of conserving bits, numbers are chosen so the 68 * IP protocol version number (4) which normally appears in this nibble 69 * means "IP packet". 70 */ 71 72 /* packet types */ 73 #define TYPE_IP 0x40 74 #define TYPE_UNCOMPRESSED_TCP 0x70 75 #define TYPE_COMPRESSED_TCP 0x80 76 #define TYPE_ERROR 0x00 77 78 /* Bits in first octet of compressed packet */ 79 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 80 #define NEW_I 0x20 81 #define NEW_S 0x08 82 #define NEW_A 0x04 83 #define NEW_W 0x02 84 #define NEW_U 0x01 85 86 /* reserved, special-case values of above */ 87 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 88 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 89 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 90 91 #define TCP_PUSH_BIT 0x10 92 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 #define cs_ip slcs_u.csu_ip 111 #define cs_hdr slcs_u.csu_hdr 112 113 /* 114 * all the state data for one serial line (we need one of these 115 * per line). 116 */ 117 struct slcompress { 118 struct cstate *last_cs; /* most recently used tstate */ 119 u_char last_recv; /* last rcvd conn. id */ 120 u_char last_xmit; /* last sent conn. id */ 121 u_short flags; 122 #ifndef SL_NO_STATS 123 int sls_packets; /* outbound packets */ 124 int sls_compressed; /* outbound compressed packets */ 125 int sls_searches; /* searches for connection state */ 126 int sls_misses; /* times couldn't find conn. state */ 127 int sls_uncompressedin; /* inbound uncompressed packets */ 128 int sls_compressedin; /* inbound compressed packets */ 129 int sls_errorin; /* inbound unknown type packets */ 130 int sls_tossed; /* inbound packets tossed because of error */ 131 #endif 132 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 133 struct cstate rstate[MAX_STATES]; /* receive connection states */ 134 }; 135 /* flag values */ 136 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 137 138 extern void sl_compress_init(/* struct slcompress * */); 139 extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *, 140 struct slcompress *, int compress_cid_flag */); 141 extern int sl_uncompress_tcp(/* u_char **, int, u_char, struct slcompress * */); 142