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vj.h
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1 /*
2  * Definitions for tcp compression routines.
3  *
4  * $Id: vj.h,v 1.7 2010/02/22 17:52:09 goldsimon 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 VJ_H
26 #define VJ_H
27 
28 #include "lwip/ip.h"
29 #include "lwip/tcp_impl.h"
30 
31 #define MAX_SLOTS 16 /* must be > 2 and < 256 */
32 #define MAX_HDR 128
33 
34 /*
35  * Compressed packet format:
36  *
37  * The first octet contains the packet type (top 3 bits), TCP
38  * 'push' bit, and flags that indicate which of the 4 TCP sequence
39  * numbers have changed (bottom 5 bits). The next octet is a
40  * conversation number that associates a saved IP/TCP header with
41  * the compressed packet. The next two octets are the TCP checksum
42  * from the original datagram. The next 0 to 15 octets are
43  * sequence number changes, one change per bit set in the header
44  * (there may be no changes and there are two special cases where
45  * the receiver implicitly knows what changed -- see below).
46  *
47  * There are 5 numbers which can change (they are always inserted
48  * in the following order): TCP urgent pointer, window,
49  * acknowlegement, sequence number and IP ID. (The urgent pointer
50  * is different from the others in that its value is sent, not the
51  * change in value.) Since typical use of SLIP links is biased
52  * toward small packets (see comments on MTU/MSS below), changes
53  * use a variable length coding with one octet for numbers in the
54  * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
55  * range 256 - 65535 or 0. (If the change in sequence number or
56  * ack is more than 65535, an uncompressed packet is sent.)
57  */
58 
59 /*
60  * Packet types (must not conflict with IP protocol version)
61  *
62  * The top nibble of the first octet is the packet type. There are
63  * three possible types: IP (not proto TCP or tcp with one of the
64  * control flags set); uncompressed TCP (a normal IP/TCP packet but
65  * with the 8-bit protocol field replaced by an 8-bit connection id --
66  * this type of packet syncs the sender & receiver); and compressed
67  * TCP (described above).
68  *
69  * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
70  * is logically part of the 4-bit "changes" field that follows. Top
71  * three bits are actual packet type. For backward compatibility
72  * and in the interest of conserving bits, numbers are chosen so the
73  * IP protocol version number (4) which normally appears in this nibble
74  * means "IP packet".
75  */
76 
77 /* packet types */
78 #define TYPE_IP 0x40
79 #define TYPE_UNCOMPRESSED_TCP 0x70
80 #define TYPE_COMPRESSED_TCP 0x80
81 #define TYPE_ERROR 0x00
82 
83 /* Bits in first octet of compressed packet */
84 #define NEW_C 0x40 /* flag bits for what changed in a packet */
85 #define NEW_I 0x20
86 #define NEW_S 0x08
87 #define NEW_A 0x04
88 #define NEW_W 0x02
89 #define NEW_U 0x01
90 
91 /* reserved, special-case values of above */
92 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */
93 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
94 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
95 
96 #define TCP_PUSH_BIT 0x10
97 
98 
99 /*
100  * "state" data for each active tcp conversation on the wire. This is
101  * basically a copy of the entire IP/TCP header from the last packet
102  * we saw from the conversation together with a small identifier
103  * the transmit & receive ends of the line use to locate saved header.
104  */
105 struct cstate {
106  struct cstate *cs_next; /* next most recently used state (xmit only) */
107  u_short cs_hlen; /* size of hdr (receive only) */
108  u_char cs_id; /* connection # associated with this state */
109  u_char cs_filler;
110  union {
111  char csu_hdr[MAX_HDR];
112  struct ip_hdr csu_ip; /* ip/tcp hdr from most recent packet */
113  } vjcs_u;
114 };
115 #define cs_ip vjcs_u.csu_ip
116 #define cs_hdr vjcs_u.csu_hdr
117 
118 
119 struct vjstat {
120  unsigned long vjs_packets; /* outbound packets */
121  unsigned long vjs_compressed; /* outbound compressed packets */
122  unsigned long vjs_searches; /* searches for connection state */
123  unsigned long vjs_misses; /* times couldn't find conn. state */
124  unsigned long vjs_uncompressedin; /* inbound uncompressed packets */
125  unsigned long vjs_compressedin; /* inbound compressed packets */
126  unsigned long vjs_errorin; /* inbound unknown type packets */
127  unsigned long vjs_tossed; /* inbound packets tossed because of error */
128 };
129 
130 /*
131  * all the state data for one serial line (we need one of these per line).
132  */
133 struct vjcompress {
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  u_char maxSlotIndex;
139  u_char compressSlot; /* Flag indicating OK to compress slot ID. */
140 #if LINK_STATS
141  struct vjstat stats;
142 #endif
143  struct cstate tstate[MAX_SLOTS]; /* xmit connection states */
144  struct cstate rstate[MAX_SLOTS]; /* receive connection states */
145 };
146 
147 /* flag values */
148 #define VJF_TOSS 1U /* tossing rcvd frames because of input err */
149 
150 extern void vj_compress_init (struct vjcompress *comp);
151 extern u_int vj_compress_tcp (struct vjcompress *comp, struct pbuf *pb);
152 extern void vj_uncompress_err (struct vjcompress *comp);
153 extern int vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp);
154 extern int vj_uncompress_tcp (struct pbuf **nb, struct vjcompress *comp);
155 
156 #endif /* VJ_H */