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Annotation of Net2/net/slcompress.h, revision 1.1

1.1     ! root        1: /*     slcompress.h    7.4     90/06/28        */
        !             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, with or without
        !            11:  * modification, are permitted provided that the following conditions
        !            12:  * are met:
        !            13:  * 1. Redistributions of source code must retain the above copyright
        !            14:  *    notice, this list of conditions and the following disclaimer.
        !            15:  * 2. Redistributions in binary form must reproduce the above copyright
        !            16:  *    notice, this list of conditions and the following disclaimer in the
        !            17:  *    documentation and/or other materials provided with the distribution.
        !            18:  * 3. All advertising materials mentioning features or use of this software
        !            19:  *    must display the following acknowledgement:
        !            20:  *     This product includes software developed by the University of
        !            21:  *     California, Berkeley and its contributors.
        !            22:  * 4. Neither the name of the University nor the names of its contributors
        !            23:  *    may be used to endorse or promote products derived from this software
        !            24:  *    without specific prior written permission.
        !            25:  *
        !            26:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            27:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            28:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            29:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            30:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            31:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            32:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            33:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            34:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            35:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            36:  * SUCH DAMAGE.
        !            37:  *
        !            38:  *     Van Jacobson ([email protected]), Dec 31, 1989:
        !            39:  *     - Initial distribution.
        !            40:  */
        !            41: 
        !            42: #define MAX_STATES 16          /* must be > 2 and < 256 */
        !            43: #define MAX_HDR MLEN           /* XXX 4bsd-ism: should really be 128 */
        !            44: 
        !            45: /*
        !            46:  * Compressed packet format:
        !            47:  *
        !            48:  * The first octet contains the packet type (top 3 bits), TCP
        !            49:  * 'push' bit, and flags that indicate which of the 4 TCP sequence
        !            50:  * numbers have changed (bottom 5 bits).  The next octet is a
        !            51:  * conversation number that associates a saved IP/TCP header with
        !            52:  * the compressed packet.  The next two octets are the TCP checksum
        !            53:  * from the original datagram.  The next 0 to 15 octets are
        !            54:  * sequence number changes, one change per bit set in the header
        !            55:  * (there may be no changes and there are two special cases where
        !            56:  * the receiver implicitly knows what changed -- see below).
        !            57:  * 
        !            58:  * There are 5 numbers which can change (they are always inserted
        !            59:  * in the following order): TCP urgent pointer, window,
        !            60:  * acknowlegement, sequence number and IP ID.  (The urgent pointer
        !            61:  * is different from the others in that its value is sent, not the
        !            62:  * change in value.)  Since typical use of SLIP links is biased
        !            63:  * toward small packets (see comments on MTU/MSS below), changes
        !            64:  * use a variable length coding with one octet for numbers in the
        !            65:  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
        !            66:  * range 256 - 65535 or 0.  (If the change in sequence number or
        !            67:  * ack is more than 65535, an uncompressed packet is sent.)
        !            68:  */
        !            69: 
        !            70: /*
        !            71:  * Packet types (must not conflict with IP protocol version)
        !            72:  *
        !            73:  * The top nibble of the first octet is the packet type.  There are
        !            74:  * three possible types: IP (not proto TCP or tcp with one of the
        !            75:  * control flags set); uncompressed TCP (a normal IP/TCP packet but
        !            76:  * with the 8-bit protocol field replaced by an 8-bit connection id --
        !            77:  * this type of packet syncs the sender & receiver); and compressed
        !            78:  * TCP (described above).
        !            79:  *
        !            80:  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
        !            81:  * is logically part of the 4-bit "changes" field that follows.  Top
        !            82:  * three bits are actual packet type.  For backward compatibility
        !            83:  * and in the interest of conserving bits, numbers are chosen so the
        !            84:  * IP protocol version number (4) which normally appears in this nibble
        !            85:  * means "IP packet".
        !            86:  */
        !            87: 
        !            88: /* packet types */
        !            89: #define TYPE_IP 0x40
        !            90: #define TYPE_UNCOMPRESSED_TCP 0x70
        !            91: #define TYPE_COMPRESSED_TCP 0x80
        !            92: #define TYPE_ERROR 0x00
        !            93: 
        !            94: /* Bits in first octet of compressed packet */
        !            95: #define NEW_C  0x40    /* flag bits for what changed in a packet */
        !            96: #define NEW_I  0x20
        !            97: #define NEW_S  0x08
        !            98: #define NEW_A  0x04
        !            99: #define NEW_W  0x02
        !           100: #define NEW_U  0x01
        !           101: 
        !           102: /* reserved, special-case values of above */
        !           103: #define SPECIAL_I (NEW_S|NEW_W|NEW_U)          /* echoed interactive traffic */
        !           104: #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)    /* unidirectional data */
        !           105: #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
        !           106: 
        !           107: #define TCP_PUSH_BIT 0x10
        !           108: 
        !           109: 
        !           110: /*
        !           111:  * "state" data for each active tcp conversation on the wire.  This is
        !           112:  * basically a copy of the entire IP/TCP header from the last packet
        !           113:  * we saw from the conversation together with a small identifier
        !           114:  * the transmit & receive ends of the line use to locate saved header.
        !           115:  */
        !           116: struct cstate {
        !           117:        struct cstate *cs_next; /* next most recently used cstate (xmit only) */
        !           118:        u_short cs_hlen;        /* size of hdr (receive only) */
        !           119:        u_char cs_id;           /* connection # associated with this state */
        !           120:        u_char cs_filler;
        !           121:        union {
        !           122:                char csu_hdr[MAX_HDR];
        !           123:                struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
        !           124:        } slcs_u;
        !           125: };
        !           126: #define cs_ip slcs_u.csu_ip
        !           127: #define cs_hdr slcs_u.csu_hdr
        !           128: 
        !           129: /*
        !           130:  * all the state data for one serial line (we need one of these
        !           131:  * per line).
        !           132:  */
        !           133: struct slcompress {
        !           134:        struct cstate *last_cs; /* most recently used tstate */
        !           135:        u_char last_recv;       /* last rcvd conn. id */
        !           136:        u_char last_xmit;       /* last sent conn. id */
        !           137:        u_short flags;
        !           138: #ifndef SL_NO_STATS
        !           139:        int sls_packets;        /* outbound packets */
        !           140:        int sls_compressed;     /* outbound compressed packets */
        !           141:        int sls_searches;       /* searches for connection state */
        !           142:        int sls_misses;         /* times couldn't find conn. state */
        !           143:        int sls_uncompressedin; /* inbound uncompressed packets */
        !           144:        int sls_compressedin;   /* inbound compressed packets */
        !           145:        int sls_errorin;        /* inbound unknown type packets */
        !           146:        int sls_tossed;         /* inbound packets tossed because of error */
        !           147: #endif
        !           148:        struct cstate tstate[MAX_STATES];       /* xmit connection states */
        !           149:        struct cstate rstate[MAX_STATES];       /* receive connection states */
        !           150: };
        !           151: /* flag values */
        !           152: #define SLF_TOSS 1             /* tossing rcvd frames because of input err */
        !           153: 
        !           154: extern void sl_compress_init(/* struct slcompress * */);
        !           155: extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *,
        !           156:                                struct slcompress *, int compress_cid_flag */);
        !           157: extern int sl_uncompress_tcp(/* u_char **, int,  u_char, struct slcompress * */);

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