ultrix/slcompress.h

   1 /*
   2  * Definitions for tcp compression routines.
   3  *
   4  * $Id: slcompress.h,v 1.1 1996/09/26 06:19:39 paulus Exp $
   5  *
   6  * Copyright (c) 1989 Regents of the University of California.
   7  * 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@helios.ee.lbl.gov), Dec 31, 1989:
  22  *      - Initial distribution.
  23  */
  24
  25 #ifndef _SLCOMPRESS_H_
  26 #define _SLCOMPRESS_H_
  27
  28 #define MAX_STATES 16           /* must be > 2 and < 256 */
  29 #define MAX_HDR MLEN            /* XXX 4bsd-ism: should really be 128 */
  30
  31 /*
  32  * Compressed packet format:
  33  *
  34  * The first octet contains the packet type (top 3 bits), TCP
  35  * 'push' bit, and flags that indicate which of the 4 TCP sequence
  36  * numbers have changed (bottom 5 bits).  The next octet is a
  37  * conversation number that associates a saved IP/TCP header with
  38  * the compressed packet.  The next two octets are the TCP checksum
  39  * from the original datagram.  The next 0 to 15 octets are
  40  * sequence number changes, one change per bit set in the header
  41  * (there may be no changes and there are two special cases where
  42  * the receiver implicitly knows what changed -- see below).
  43  *
  44  * There are 5 numbers which can change (they are always inserted
  45  * in the following order): TCP urgent pointer, window,
  46  * acknowlegement, sequence number and IP ID.  (The urgent pointer
  47  * is different from the others in that its value is sent, not the
  48  * change in value.)  Since typical use of SLIP links is biased
  49  * toward small packets (see comments on MTU/MSS below), changes
  50  * use a variable length coding with one octet for numbers in the
  51  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
  52  * range 256 - 65535 or 0.  (If the change in sequence number or
  53  * ack is more than 65535, an uncompressed packet is sent.)
  54  */
  55
  56 /*
  57  * Packet types (must not conflict with IP protocol version)
  58  *
  59  * The top nibble of the first octet is the packet type.  There are
  60  * three possible types: IP (not proto TCP or tcp with one of the
  61  * control flags set); uncompressed TCP (a normal IP/TCP packet but
  62  * with the 8-bit protocol field replaced by an 8-bit connection id --
  63  * this type of packet syncs the sender & receiver); and compressed
  64  * TCP (described above).
  65  *
  66  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
  67  * is logically part of the 4-bit "changes" field that follows.  Top
  68  * three bits are actual packet type.  For backward compatibility
  69  * and in the interest of conserving bits, numbers are chosen so the
  70  * IP protocol version number (4) which normally appears in this nibble
  71  * means "IP packet".
  72  */
  73
  74 /* packet types */
  75 #define TYPE_IP 0x40
  76 #define TYPE_UNCOMPRESSED_TCP 0x70
  77 #define TYPE_COMPRESSED_TCP 0x80
  78 #define TYPE_ERROR 0x00
  79
  80 /* Bits in first octet of compressed packet */
  81 #define NEW_C   0x40    /* flag bits for what changed in a packet */
  82 #define NEW_I   0x20
  83 #define NEW_S   0x08
  84 #define NEW_A   0x04
  85 #define NEW_W   0x02
  86 #define NEW_U   0x01
  87
  88 /* reserved, special-case values of above */
  89 #define SPECIAL_I (NEW_S|NEW_W|NEW_U)           /* echoed interactive traffic */
  90 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)     /* unidirectional data */
  91 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  92
  93 #define TCP_PUSH_BIT 0x10
  94
  95
  96 /*
  97  * "state" data for each active tcp conversation on the wire.  This is
  98  * basically a copy of the entire IP/TCP header from the last packet
  99  * we saw from the conversation together with a small identifier
 100  * the transmit & receive ends of the line use to locate saved header.
 101  */
 102 struct cstate {
 103         struct cstate *cs_next; /* next most recently used cstate (xmit only) */
 104         u_short cs_hlen;        /* size of hdr (receive only) */
 105         u_char cs_id;           /* connection # associated with this state */
 106         u_char cs_filler;
 107         union {
 108                 char csu_hdr[MAX_HDR];
 109                 struct ip csu_ip;       /* ip/tcp hdr from most recent packet */
 110         } slcs_u;
 111 };
 112 #define cs_ip slcs_u.csu_ip
 113 #define cs_hdr slcs_u.csu_hdr
 114
 115 /*
 116  * all the state data for one serial line (we need one of these
 117  * per line).
 118  */
 119 struct slcompress {
 120         struct cstate *last_cs; /* most recently used tstate */
 121         u_char last_recv;       /* last rcvd conn. id */
 122         u_char last_xmit;       /* last sent conn. id */
 123         u_short flags;
 124 #ifndef SL_NO_STATS
 125         int sls_packets;        /* outbound packets */
 126         int sls_compressed;     /* outbound compressed packets */
 127         int sls_searches;       /* searches for connection state */
 128         int sls_misses;         /* times couldn't find conn. state */
 129         int sls_uncompressedin; /* inbound uncompressed packets */
 130         int sls_compressedin;   /* inbound compressed packets */
 131         int sls_errorin;        /* inbound unknown type packets */
 132         int sls_tossed;         /* inbound packets tossed because of error */
 133 #endif
 134         struct cstate tstate[MAX_STATES];       /* xmit connection states */
 135         struct cstate rstate[MAX_STATES];       /* receive connection states */
 136 };
 137 /* flag values */
 138 #define SLF_TOSS 1              /* tossing rcvd frames because of input err */
 139
 140 void    sl_compress_init(struct slcompress *);
 141 void    sl_compress_setup(struct slcompress *, int);
 142 u_int   sl_compress_tcp(struct mbuf *, struct ip *, struct slcompress *, int);
 143 int     sl_uncompress_tcp(u_char **, int, u_int, struct slcompress *);
 144 int     sl_uncompress_tcp_core(u_char *, int, int, u_int,
 145             struct slcompress *, u_char **, u_int *);
 146
 147 #endif /* _SLCOMPRESS_H_ */