release/src/router/ppp/include/net/vjcompress.h

   1 /*
   2  * Definitions for tcp compression routines.
   3  *
   4  * $Id: vjcompress.h,v 1.1.1.4 2003/10/14 08:09:53 sparq 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 _VJCOMPRESS_H_
  26 #define _VJCOMPRESS_H_
  27
  28 #define MAX_STATES 16           /* must be > 2 and < 256 */
  29 #define MAX_HDR    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 state (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     } vjcs_u;
 111 };
 112 #define cs_ip vjcs_u.csu_ip
 113 #define cs_hdr vjcs_u.csu_hdr
 114
 115 /*
 116  * all the state data for one serial line (we need one of these per line).
 117  */
 118 struct vjcompress {
 119     struct cstate *last_cs;     /* most recently used tstate */
 120     u_char last_recv;           /* last rcvd conn. id */
 121     u_char last_xmit;           /* last sent conn. id */
 122     u_short flags;
 123 #ifndef VJ_NO_STATS
 124     struct vjstat stats;
 125 #endif
 126     struct cstate tstate[MAX_STATES];   /* xmit connection states */
 127     struct cstate rstate[MAX_STATES];   /* receive connection states */
 128 };
 129
 130 /* flag values */
 131 #define VJF_TOSS 1              /* tossing rcvd frames because of input err */
 132
 133 extern void  vj_compress_init __P((struct vjcompress *comp, int max_state));
 134 extern u_int vj_compress_tcp __P((struct ip *ip, u_int mlen,
 135                                 struct vjcompress *comp, int compress_cid_flag,
 136                                 u_char **vjhdrp));
 137 extern void  vj_uncompress_err __P((struct vjcompress *comp));
 138 extern int   vj_uncompress_uncomp __P((u_char *buf, int buflen,
 139                                 struct vjcompress *comp));
 140 extern int   vj_uncompress_tcp __P((u_char *buf, int buflen, int total_len,
 141                                 struct vjcompress *comp, u_char **hdrp,
 142                                 u_int *hlenp));
 143
 144 #endif /* _VJCOMPRESS_H_ */