1 /* 2 * Definitions for tcp compression routines. 3 * 4 * Copyright (c) 1988, 1989 by Van Jacobson, Lawrence Berkeley Laboratory 5 * All rights reserved. 6 * 7 * $Header: slcompress.h,v 1.6 89/06/05 08:29:13 van Exp $ 8 */ 9 10 #define MAX_STATES 16 /* must be > 2 and < 256 */ 11 #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ 12 13 /* 14 * Compressed packet format: 15 * 16 * The first octet contains the packet type (top 3 bits), TCP 17 * 'push' bit, and flags that indicate which of the 4 TCP sequence 18 * numbers have changed (bottom 5 bits). The next octet is a 19 * conversation number that associates a saved IP/TCP header with 20 * the compressed packet. The next two octets are the TCP checksum 21 * from the original datagram. The next 0 to 15 octets are 22 * sequence number changes, one change per bit set in the header 23 * (there may be no changes and there are two special cases where 24 * the receiver implicitly knows what changed -- see below). 25 * 26 * There are 5 numbers which can change (they are always inserted 27 * in the following order): TCP urgent pointer, window, 28 * acknowlegement, sequence number and IP ID. (The urgent pointer 29 * is different from the others in that its value is sent, not the 30 * change in value.) Since typical use of SLIP links is biased 31 * toward small packets (see comments on MTU/MSS below), changes 32 * use a variable length coding with one octet for numbers in the 33 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 34 * range 256 - 65535 or 0. (If the change in sequence number or 35 * ack is more than 65535, an uncompressed packet is sent.) 36 */ 37 38 /* 39 * Packet types (must not conflict with IP protocol version) 40 * 41 * The top nibble of the first octet is the packet type. There are 42 * three possible types: IP (not proto TCP or tcp with one of the 43 * control flags set); uncompressed TCP (a normal IP/TCP packet but 44 * with the 8-bit protocol field replaced by an 8-bit connection id -- 45 * this type of packet syncs the sender & receiver); and compressed 46 * TCP (described above). 47 * 48 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 49 * is logically part of the 4-bit "changes" field that follows. Top 50 * three bits are actual packet type. For backward compatibility 51 * and in the interest of conserving bits, numbers are chosen so the 52 * IP protocol version number (4) which normally appears in this nibble 53 * means "IP packet". 54 */ 55 56 /* packet types */ 57 #define TYPE_IP 0x40 58 #define TYPE_UNCOMPRESSED_TCP 0x70 59 #define TYPE_COMPRESSED_TCP 0x80 60 #define TYPE_ERROR 0x00 61 62 /* Bits in first octet of compressed packet */ 63 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 64 #define NEW_I 0x20 65 #define NEW_S 0x08 66 #define NEW_A 0x04 67 #define NEW_W 0x02 68 #define NEW_U 0x01 69 70 /* reserved, special-case values of above */ 71 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 72 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 73 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 74 75 #define TCP_PUSH_BIT 0x10 76 77 78 /* 79 * "state" data for each active tcp conversation on the wire. This is 80 * basically a copy of the entire IP/TCP header from the last packet 81 * we saw from the conversation together with a small identifier 82 * the transmit & receive ends of the line use to locate saved header. 83 */ 84 struct cstate { 85 struct cstate *cs_next; /* next most recently used cstate (xmit only) */ 86 u_short cs_hlen; /* size of hdr (receive only) */ 87 u_char cs_id; /* connection # associated with this state */ 88 u_char cs_filler; 89 union { 90 char hdr[MAX_HDR]; 91 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 92 } u; 93 }; 94 #define cs_ip u.csu_ip 95 96 /* 97 * all the state data for one serial line (we need one of these 98 * per line). 99 */ 100 struct slcompress { 101 struct cstate *last_cs; /* most recently used tstate */ 102 u_char last_recv; /* last rcvd conn. id */ 103 u_char last_xmit; /* last sent conn. id */ 104 u_short flags; 105 #ifndef NO_SL_STATS 106 int sls_packets; /* outbound packets */ 107 int sls_compressed; /* outbound compressed packets */ 108 int sls_searches; /* searches for connection state */ 109 int sls_misses; /* times couldn't find conn. state */ 110 int sls_uncompressedin; /* inbound uncompressed packets */ 111 int sls_compressedin; /* inbound compressed packets */ 112 int sls_errorin; /* inbound unknown type packets */ 113 int sls_tossed; /* inbound packets tossed because of error */ 114 #endif 115 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 116 struct cstate rstate[MAX_STATES]; /* receive connection states */ 117 }; 118 /* flag values */ 119 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 120 121 extern void sl_compress_init(/* struct slcompress * */); 122 extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *, struct slcompress * */); 123 extern int sl_uncompress_tcp(/* u_char **, int, u_char, struct slcompress * */); 124