1 /* 2 * THIS CODE IS NOT FOR DISTRIBUTION! 3 * KEEP YOUR GRUBBY HANDS OFF UNLESS AUTHORIZED BY VAN JACOBSON TO COPY! 4 * ASK SAM, MIKE, OR BILL ABOUT IT. 5 */ 6 7 /* 8 * Definitions for tcp compression routines. 9 * 10 * Copyright (c) 1988, 1989 by Van Jacobson, Lawrence Berkeley Laboratory 11 * All rights reserved. 12 * 13 * $Header: slcompress.h,v 1.3 89/03/19 18:10:38 van Locked $ 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 * { Note that the ip version number field this overlays is 4 bits 33 * wide, and that we use type 4 to pass thru unaltered packets, 34 * type 5 to pass thru uncompressed packets that will be state 35 * information indexed by conversation. If msb (e.g type 8) is 36 * set, the other type bits are stolen to encode the difference 37 * information of a compressed TCP packet. -wfj } 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 0x50 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 hdr[MAX_HDR]; 104 struct ip csu_ip; /* ip/tcp hdr from most recent packet */ 105 } u; 106 }; 107 #define cs_ip u.csu_ip 108 109 /* 110 * all the state data for one serial line (we need one of these 111 * per line). 112 */ 113 struct slcompress { 114 struct cstate *last_cs; /* most recently used tstate */ 115 u_char last_recv; /* last rcvd conn. id */ 116 u_char last_xmit; /* last sent conn. id */ 117 u_short flags; 118 struct cstate tstate[MAX_STATES]; /* xmit connection states */ 119 struct cstate rstate[MAX_STATES]; /* receive connection states */ 120 }; 121 /* flag values */ 122 #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ 123 124 extern void sl_compress_init(/* struct slcompress * */); 125 extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *, struct slcompress * */); 126 extern struct mbuf *sl_uncompress_tcp(/* struct mbuf *, u_char, struct slcompress * */); 127