1 /* slcompress.h 7.5 93/06/04 */ 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 * %sccs.include.redist.c% 11 * 12 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 13 * - Initial distribution. 14 */ 15 16 #define MAX_STATES 16 /* must be > 2 and < 256 */ 17 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ 18 19 /* 20 * Compressed packet format: 21 * 22 * The first octet contains the packet type (top 3 bits), TCP 23 * 'push' bit, and flags that indicate which of the 4 TCP sequence 24 * numbers have changed (bottom 5 bits). The next octet is a 25 * conversation number that associates a saved IP/TCP header with 26 * the compressed packet. The next two octets are the TCP checksum 27 * from the original datagram. The next 0 to 15 octets are 28 * sequence number changes, one change per bit set in the header 29 * (there may be no changes and there are two special cases where 30 * the receiver implicitly knows what changed -- see below). 31 * 32 * There are 5 numbers which can change (they are always inserted 33 * in the following order): TCP urgent pointer, window, 34 * acknowlegement, sequence number and IP ID. (The urgent pointer 35 * is different from the others in that its value is sent, not the 36 * change in value.) Since typical use of SLIP links is biased 37 * toward small packets (see comments on MTU/MSS below), changes 38 * use a variable length coding with one octet for numbers in the 39 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 40 * range 256 - 65535 or 0. (If the change in sequence number or 41 * ack is more than 65535, an uncompressed packet is sent.) 42 */ 43 44 /* 45 * Packet types (must not conflict with IP protocol version) 46 * 47 * The top nibble of the first octet is the packet type. There are 48 * three possible types: IP (not proto TCP or tcp with one of the 49 * control flags set); uncompressed TCP (a normal IP/TCP packet but 50 * with the 8-bit protocol field replaced by an 8-bit connection id -- 51 * this type of packet syncs the sender & receiver); and compressed 52 * TCP (described above). 53 * 54 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 55 * is logically part of the 4-bit "changes" field that follows. Top 56 * three bits are actual packet type. For backward compatibility 57 * and in the interest of conserving bits, numbers are chosen so the 58 * IP protocol version number (4) which normally appears in this nibble 59 * means "IP packet". 60 */ 61 62 /* packet types */ 63 #define TYPE_IP 0x40 64 #define TYPE_UNCOMPRESSED_TCP 0x70 65 #define TYPE_COMPRESSED_TCP 0x80 66 #define TYPE_ERROR 0x00 67 68 /* Bits in first octet of compressed packet */ 69 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 70 #define NEW_I 0x20 71 #define NEW_S 0x08 72 #define NEW_A 0x04 73 #define NEW_W 0x02 74 #define NEW_U 0x01 75 76 /* reserved, special-case values of above */ 77 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 78 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 79 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 80 81 #define TCP_PUSH_BIT 0x10 82 83 84 /* 85 * "state" data for each active tcp conversation on the wire. This is 86 * basically a copy of the entire IP/TCP header from the last packet 87 * we saw from the conversation together with a small identifier 88 * the transmit & receive ends of the line use to locate saved header. 89 */ 90 struct cstate { 91 struct cstate *cs_next; /* next most recently used cstate (xmit only) */ 92 u_short cs_hlen; /* size of hdr (receive only) */ 93 u_char cs_id; /* connection # associated with this state */ 94 u_char cs_filler; 95 union { 96 char csu_hdr[MAX_HDR]; 97 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 98 } slcs_u; 99 }; 100 #define cs_ip slcs_u.csu_ip 101 #define cs_hdr slcs_u.csu_hdr 102 103 /* 104 * all the state data for one serial line (we need one of these 105 * per line). 106 */ 107 struct slcompress { 108 struct cstate *last_cs; /* most recently used tstate */ 109 u_char last_recv; /* last rcvd conn. id */ 110 u_char last_xmit; /* last sent conn. id */ 111 u_short flags; 112 #ifndef SL_NO_STATS 113 int sls_packets; /* outbound packets */ 114 int sls_compressed; /* outbound compressed packets */ 115 int sls_searches; /* searches for connection state */ 116 int sls_misses; /* times couldn't find conn. state */ 117 int sls_uncompressedin; /* inbound uncompressed packets */ 118 int sls_compressedin; /* inbound compressed packets */ 119 int sls_errorin; /* inbound unknown type packets */ 120 int sls_tossed; /* inbound packets tossed because of error */ 121 #endif 122 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 123 struct cstate rstate[MAX_STATES]; /* receive connection states */ 124 }; 125 /* flag values */ 126 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 127 128 void sl_compress_init __P((struct slcompress *)); 129 u_int sl_compress_tcp __P((struct mbuf *, 130 struct ip *, struct slcompress *, int)); 131 int sl_uncompress_tcp __P((u_char **, int, u_int, struct slcompress *)); 132