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vj.h

00001 /*
00002  * Definitions for tcp compression routines.
00003  *
00004  * $Id: vj.h,v 1.7 2010/02/22 17:52:09 goldsimon Exp $
00005  *
00006  * Copyright (c) 1989 Regents of the University of California.
00007  * All rights reserved.
00008  *
00009  * Redistribution and use in source and binary forms are permitted
00010  * provided that the above copyright notice and this paragraph are
00011  * duplicated in all such forms and that any documentation,
00012  * advertising materials, and other materials related to such
00013  * distribution and use acknowledge that the software was developed
00014  * by the University of California, Berkeley.  The name of the
00015  * University may not be used to endorse or promote products derived
00016  * from this software without specific prior written permission.
00017  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
00018  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
00019  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
00020  *
00021  * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
00022  * - Initial distribution.
00023  */
00024 
00025 #ifndef VJ_H
00026 #define VJ_H
00027 
00028 #include "lwip/ip.h"
00029 #include "lwip/tcp_impl.h"
00030 
00031 #define MAX_SLOTS 16 /* must be > 2 and < 256 */
00032 #define MAX_HDR   128
00033 
00034 /*
00035  * Compressed packet format:
00036  *
00037  * The first octet contains the packet type (top 3 bits), TCP
00038  * 'push' bit, and flags that indicate which of the 4 TCP sequence
00039  * numbers have changed (bottom 5 bits).  The next octet is a
00040  * conversation number that associates a saved IP/TCP header with
00041  * the compressed packet.  The next two octets are the TCP checksum
00042  * from the original datagram.  The next 0 to 15 octets are
00043  * sequence number changes, one change per bit set in the header
00044  * (there may be no changes and there are two special cases where
00045  * the receiver implicitly knows what changed -- see below).
00046  * 
00047  * There are 5 numbers which can change (they are always inserted
00048  * in the following order): TCP urgent pointer, window,
00049  * acknowlegement, sequence number and IP ID.  (The urgent pointer
00050  * is different from the others in that its value is sent, not the
00051  * change in value.)  Since typical use of SLIP links is biased
00052  * toward small packets (see comments on MTU/MSS below), changes
00053  * use a variable length coding with one octet for numbers in the
00054  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
00055  * range 256 - 65535 or 0.  (If the change in sequence number or
00056  * ack is more than 65535, an uncompressed packet is sent.)
00057  */
00058 
00059 /*
00060  * Packet types (must not conflict with IP protocol version)
00061  *
00062  * The top nibble of the first octet is the packet type.  There are
00063  * three possible types: IP (not proto TCP or tcp with one of the
00064  * control flags set); uncompressed TCP (a normal IP/TCP packet but
00065  * with the 8-bit protocol field replaced by an 8-bit connection id --
00066  * this type of packet syncs the sender & receiver); and compressed
00067  * TCP (described above).
00068  *
00069  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
00070  * is logically part of the 4-bit "changes" field that follows.  Top
00071  * three bits are actual packet type.  For backward compatibility
00072  * and in the interest of conserving bits, numbers are chosen so the
00073  * IP protocol version number (4) which normally appears in this nibble
00074  * means "IP packet".
00075  */
00076 
00077 /* packet types */
00078 #define TYPE_IP               0x40
00079 #define TYPE_UNCOMPRESSED_TCP 0x70
00080 #define TYPE_COMPRESSED_TCP   0x80
00081 #define TYPE_ERROR            0x00
00082 
00083 /* Bits in first octet of compressed packet */
00084 #define NEW_C 0x40 /* flag bits for what changed in a packet */
00085 #define NEW_I 0x20
00086 #define NEW_S 0x08
00087 #define NEW_A 0x04
00088 #define NEW_W 0x02
00089 #define NEW_U 0x01
00090 
00091 /* reserved, special-case values of above */
00092 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
00093 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
00094 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
00095 
00096 #define TCP_PUSH_BIT 0x10
00097 
00098 
00099 /*
00100  * "state" data for each active tcp conversation on the wire.  This is
00101  * basically a copy of the entire IP/TCP header from the last packet
00102  * we saw from the conversation together with a small identifier
00103  * the transmit & receive ends of the line use to locate saved header.
00104  */
00105 struct cstate {
00106   struct cstate *cs_next; /* next most recently used state (xmit only) */
00107   u_short cs_hlen;        /* size of hdr (receive only) */
00108   u_char cs_id;           /* connection # associated with this state */
00109   u_char cs_filler;
00110   union {
00111     char csu_hdr[MAX_HDR];
00112     struct ip_hdr csu_ip;     /* ip/tcp hdr from most recent packet */
00113   } vjcs_u;
00114 };
00115 #define cs_ip vjcs_u.csu_ip
00116 #define cs_hdr vjcs_u.csu_hdr
00117 
00118 
00119 struct vjstat {
00120   unsigned long vjs_packets;        /* outbound packets */
00121   unsigned long vjs_compressed;     /* outbound compressed packets */
00122   unsigned long vjs_searches;       /* searches for connection state */
00123   unsigned long vjs_misses;         /* times couldn't find conn. state */
00124   unsigned long vjs_uncompressedin; /* inbound uncompressed packets */
00125   unsigned long vjs_compressedin;   /* inbound compressed packets */
00126   unsigned long vjs_errorin;        /* inbound unknown type packets */
00127   unsigned long vjs_tossed;         /* inbound packets tossed because of error */
00128 };
00129 
00130 /*
00131  * all the state data for one serial line (we need one of these per line).
00132  */
00133 struct vjcompress {
00134   struct cstate *last_cs;          /* most recently used tstate */
00135   u_char last_recv;                /* last rcvd conn. id */
00136   u_char last_xmit;                /* last sent conn. id */
00137   u_short flags;
00138   u_char maxSlotIndex;
00139   u_char compressSlot;             /* Flag indicating OK to compress slot ID. */
00140 #if LINK_STATS
00141   struct vjstat stats;
00142 #endif
00143   struct cstate tstate[MAX_SLOTS]; /* xmit connection states */
00144   struct cstate rstate[MAX_SLOTS]; /* receive connection states */
00145 };
00146 
00147 /* flag values */
00148 #define VJF_TOSS 1U /* tossing rcvd frames because of input err */
00149 
00150 extern void  vj_compress_init    (struct vjcompress *comp);
00151 extern u_int vj_compress_tcp     (struct vjcompress *comp, struct pbuf *pb);
00152 extern void  vj_uncompress_err   (struct vjcompress *comp);
00153 extern int   vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp);
00154 extern int   vj_uncompress_tcp   (struct pbuf **nb, struct vjcompress *comp);
00155 
00156 #endif /* VJ_H */