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1 | /* |
2 | * Definitions for tcp compression routines. | |
3 | * | |
4 | * Copyright (c) 1988, 1989 by Van Jacobson, Lawrence Berkeley Laboratory | |
5 | * All rights reserved. | |
6 | * | |
270f7144 | 7 | * $Header: slcompress.h,v 1.6 89/06/05 08:29:13 van Exp $ |
5ca196bd MK |
8 | */ |
9 | ||
10 | #define MAX_STATES 16 /* must be > 2 and < 256 */ | |
11 | #define MAX_HDR MLEN /* XXX 4bsd-ism: should really be 128 */ | |
12 | ||
13 | /* | |
14 | * Compressed packet format: | |
15 | * | |
16 | * The first octet contains the packet type (top 3 bits), TCP | |
17 | * 'push' bit, and flags that indicate which of the 4 TCP sequence | |
18 | * numbers have changed (bottom 5 bits). The next octet is a | |
19 | * conversation number that associates a saved IP/TCP header with | |
20 | * the compressed packet. The next two octets are the TCP checksum | |
21 | * from the original datagram. The next 0 to 15 octets are | |
22 | * sequence number changes, one change per bit set in the header | |
23 | * (there may be no changes and there are two special cases where | |
24 | * the receiver implicitly knows what changed -- see below). | |
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25 | * |
26 | * There are 5 numbers which can change (they are always inserted | |
27 | * in the following order): TCP urgent pointer, window, | |
28 | * acknowlegement, sequence number and IP ID. (The urgent pointer | |
29 | * is different from the others in that its value is sent, not the | |
30 | * change in value.) Since typical use of SLIP links is biased | |
31 | * toward small packets (see comments on MTU/MSS below), changes | |
32 | * use a variable length coding with one octet for numbers in the | |
33 | * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the | |
34 | * range 256 - 65535 or 0. (If the change in sequence number or | |
35 | * ack is more than 65535, an uncompressed packet is sent.) | |
36 | */ | |
37 | ||
38 | /* | |
39 | * Packet types (must not conflict with IP protocol version) | |
40 | * | |
41 | * The top nibble of the first octet is the packet type. There are | |
42 | * three possible types: IP (not proto TCP or tcp with one of the | |
43 | * control flags set); uncompressed TCP (a normal IP/TCP packet but | |
44 | * with the 8-bit protocol field replaced by an 8-bit connection id -- | |
45 | * this type of packet syncs the sender & receiver); and compressed | |
46 | * TCP (described above). | |
47 | * | |
48 | * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and | |
49 | * is logically part of the 4-bit "changes" field that follows. Top | |
50 | * three bits are actual packet type. For backward compatibility | |
51 | * and in the interest of conserving bits, numbers are chosen so the | |
52 | * IP protocol version number (4) which normally appears in this nibble | |
53 | * means "IP packet". | |
54 | */ | |
55 | ||
56 | /* packet types */ | |
57 | #define TYPE_IP 0x40 | |
270f7144 | 58 | #define TYPE_UNCOMPRESSED_TCP 0x70 |
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59 | #define TYPE_COMPRESSED_TCP 0x80 |
60 | #define TYPE_ERROR 0x00 | |
61 | ||
62 | /* Bits in first octet of compressed packet */ | |
63 | #define NEW_C 0x40 /* flag bits for what changed in a packet */ | |
64 | #define NEW_I 0x20 | |
65 | #define NEW_S 0x08 | |
66 | #define NEW_A 0x04 | |
67 | #define NEW_W 0x02 | |
68 | #define NEW_U 0x01 | |
69 | ||
70 | /* reserved, special-case values of above */ | |
71 | #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ | |
72 | #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ | |
73 | #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) | |
74 | ||
75 | #define TCP_PUSH_BIT 0x10 | |
76 | ||
77 | ||
78 | /* | |
79 | * "state" data for each active tcp conversation on the wire. This is | |
80 | * basically a copy of the entire IP/TCP header from the last packet | |
81 | * we saw from the conversation together with a small identifier | |
82 | * the transmit & receive ends of the line use to locate saved header. | |
83 | */ | |
84 | struct cstate { | |
85 | struct cstate *cs_next; /* next most recently used cstate (xmit only) */ | |
86 | u_short cs_hlen; /* size of hdr (receive only) */ | |
87 | u_char cs_id; /* connection # associated with this state */ | |
88 | u_char cs_filler; | |
89 | union { | |
90 | char hdr[MAX_HDR]; | |
91 | struct ip csu_ip; /* ip/tcp hdr from most recent packet */ | |
92 | } u; | |
93 | }; | |
94 | #define cs_ip u.csu_ip | |
95 | ||
96 | /* | |
97 | * all the state data for one serial line (we need one of these | |
98 | * per line). | |
99 | */ | |
100 | struct slcompress { | |
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101 | struct cstate *last_cs; /* most recently used tstate */ |
102 | u_char last_recv; /* last rcvd conn. id */ | |
103 | u_char last_xmit; /* last sent conn. id */ | |
5ca196bd | 104 | u_short flags; |
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105 | #ifndef NO_SL_STATS |
106 | int sls_packets; /* outbound packets */ | |
107 | int sls_compressed; /* outbound compressed packets */ | |
108 | int sls_searches; /* searches for connection state */ | |
109 | int sls_misses; /* times couldn't find conn. state */ | |
110 | int sls_uncompressedin; /* inbound uncompressed packets */ | |
111 | int sls_compressedin; /* inbound compressed packets */ | |
112 | int sls_errorin; /* inbound unknown type packets */ | |
113 | int sls_tossed; /* inbound packets tossed because of error */ | |
114 | #endif | |
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115 | struct cstate tstate[MAX_STATES]; /* xmit connection states */ |
116 | struct cstate rstate[MAX_STATES]; /* receive connection states */ | |
117 | }; | |
118 | /* flag values */ | |
119 | #define SLF_TOSS 1 /* tossing rcvd frames because of input err */ | |
120 | ||
121 | extern void sl_compress_init(/* struct slcompress * */); | |
122 | extern u_char sl_compress_tcp(/* struct mbuf *, struct ip *, struct slcompress * */); | |
270f7144 | 123 | extern int sl_uncompress_tcp(/* u_char **, int, u_char, struct slcompress * */); |