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   1 /*
   2  * Definitions for tcp compression routines.
   3  *
   4  * @(#) $Header: /tcpdump/master/tcpdump/linux-include/net/Attic/slcompress.h,v 1.15 1999-10-07 23:47:14 mcr Exp $ (LBL)
   5  *
   6  * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of
   7  * California. All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms are permitted
  10  * provided that the above copyright notice and this paragraph are
  11  * duplicated in all such forms and that any documentation,
  12  * advertising materials, and other materials related to such
  13  * distribution and use acknowledge that the software was developed
  14  * by the University of California, Berkeley.  The name of the
  15  * University may not be used to endorse or promote products derived
  16  * from this software without specific prior written permission.
  17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  18  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  19  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20  *
  21  *      Van Jacobson (van@ee.lbl.gov), Dec 31, 1989:
  22  *      - Initial distribution.
  23  */
  24
  25 #define MAX_STATES 16           /* must be > 2 and < 256 */
  26 #define MAX_HDR MLEN            /* XXX 4bsd-ism: should really be 128 */
  27
  28 /*
  29  * Compressed packet format:
  30  *
  31  * The first octet contains the packet type (top 3 bits), TCP
  32  * 'push' bit, and flags that indicate which of the 4 TCP sequence
  33  * numbers have changed (bottom 5 bits).  The next octet is a
  34  * conversation number that associates a saved IP/TCP header with
  35  * the compressed packet.  The next two octets are the TCP checksum
  36  * from the original datagram.  The next 0 to 15 octets are
  37  * sequence number changes, one change per bit set in the header
  38  * (there may be no changes and there are two special cases where
  39  * the receiver implicitly knows what changed -- see below).
  40  *
  41  * There are 5 numbers which can change (they are always inserted
  42  * in the following order): TCP urgent pointer, window,
  43  * acknowlegement, sequence number and IP ID.  (The urgent pointer
  44  * is different from the others in that its value is sent, not the
  45  * change in value.)  Since typical use of SLIP links is biased
  46  * toward small packets (see comments on MTU/MSS below), changes
  47  * use a variable length coding with one octet for numbers in the
  48  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
  49  * range 256 - 65535 or 0.  (If the change in sequence number or
  50  * ack is more than 65535, an uncompressed packet is sent.)
  51  */
  52
  53 /*
  54  * Packet types (must not conflict with IP protocol version)
  55  *
  56  * The top nibble of the first octet is the packet type.  There are
  57  * three possible types: IP (not proto TCP or tcp with one of the
  58  * control flags set); uncompressed TCP (a normal IP/TCP packet but
  59  * with the 8-bit protocol field replaced by an 8-bit connection id --
  60  * this type of packet syncs the sender & receiver); and compressed
  61  * TCP (described above).
  62  *
  63  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
  64  * is logically part of the 4-bit "changes" field that follows.  Top
  65  * three bits are actual packet type.  For backward compatibility
  66  * and in the interest of conserving bits, numbers are chosen so the
  67  * IP protocol version number (4) which normally appears in this nibble
  68  * means "IP packet".
  69  */
  70
  71 /* packet types */
  72 #define TYPE_IP 0x40
  73 #define TYPE_UNCOMPRESSED_TCP 0x70
  74 #define TYPE_COMPRESSED_TCP 0x80
  75 #define TYPE_ERROR 0x00
  76
  77 /* Bits in first octet of compressed packet */
  78 #define NEW_C   0x40    /* flag bits for what changed in a packet */
  79 #define NEW_I   0x20
  80 #define NEW_S   0x08
  81 #define NEW_A   0x04
  82 #define NEW_W   0x02
  83 #define NEW_U   0x01
  84
  85 /* reserved, special-case values of above */
  86 #define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
  87 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
  88 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  89
  90 #define TCP_PUSH_BIT 0x10
  91
  92
  93 /*
  94  * "state" data for each active tcp conversation on the wire.  This is
  95  * basically a copy of the entire IP/TCP header from the last packet
  96  * we saw from the conversation together with a small identifier
  97  * the transmit & receive ends of the line use to locate saved header.
  98  */
  99 struct cstate {
 100         struct cstate *cs_next; /* next most recently used cstate (xmit only) */
 101         u_short cs_hlen;        /* size of hdr (receive only) */
 102         u_char cs_id;           /* connection # associated with this state */
 103         u_char cs_filler;
 104         union {
 105                 char csu_hdr[MAX_HDR];
 106                 struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
 107         } slcs_u;
 108 };
 109 #define cs_ip slcs_u.csu_ip
 110 #define cs_hdr slcs_u.csu_hdr
 111
 112 /*
 113  * all the state data for one serial line (we need one of these
 114  * per line).
 115  */
 116 struct slcompress {
 117         struct cstate *last_cs; /* most recently used tstate */
 118         u_char last_recv;       /* last rcvd conn. id */
 119         u_char last_xmit;       /* last sent conn. id */
 120         u_short flags;
 121 #ifndef SL_NO_STATS
 122         u_int sls_packets;      /* outbound packets */
 123         u_int sls_compressed;   /* outbound compressed packets */
 124         u_int sls_searches;     /* searches for connection state */
 125         u_int sls_misses;       /* times couldn't find conn. state */
 126         u_int sls_uncompressedin;/* inbound uncompressed packets */
 127         u_int sls_compressedin; /* inbound compressed packets */
 128         u_int sls_errorin;      /* inbound unknown type packets */
 129         u_int sls_tossed;       /* inbound packets tossed because of error */
 130 #endif
 131         struct cstate tstate[MAX_STATES];       /* xmit connection states */
 132         struct cstate rstate[MAX_STATES];       /* receive connection states */
 133 };
 134 /* flag values */
 135 #define SLF_TOSS 1              /* tossing rcvd frames because of input err */
 136
 137 #ifdef KERNEL
 138 #ifdef __STDC__
 139 extern  void sl_compress_init(struct slcompress *);
 140 extern  u_char sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *);
 141 extern  int sl_uncompress_tcp(struct mbuf *, int, u_int, struct slcompress *);
 142 #else
 143 extern  void sl_compress_init();
 144 extern  u_char sl_compress_tcp();
 145 extern  int sl_uncompress_tcp();
 146 #endif
 147 #endif
 148