1 | /* |
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2 | * Definitions for tcp compression routines. |
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3 | * |
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4 | * @(#) $Header: /tcpdump/master/tcpdump/slcompress.h,v 1.2 2000-10-09 02:03:44 guy Exp $ (LBL) |
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5 | * |
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6 | * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of |
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7 | * California. All rights reserved. |
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8 | * |
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9 | * Redistribution and use in source and binary forms are permitted |
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10 | * provided that the above copyright notice and this paragraph are |
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11 | * duplicated in all such forms and that any documentation, |
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12 | * advertising materials, and other materials related to such |
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13 | * distribution and use acknowledge that the software was developed |
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14 | * by the University of California, Berkeley. The name of the |
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15 | * University may not be used to endorse or promote products derived |
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16 | * from this software without specific prior written permission. |
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17 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR |
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18 | * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
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19 | * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
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20 | * |
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21 | * Van Jacobson (van@ee.lbl.gov), Dec 31, 1989: |
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22 | * - Initial distribution. |
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23 | */ |
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24 | |
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25 | /* |
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26 | * Compressed packet format: |
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27 | * |
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28 | * The first octet contains the packet type (top 3 bits), TCP |
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29 | * 'push' bit, and flags that indicate which of the 4 TCP sequence |
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30 | * numbers have changed (bottom 5 bits). The next octet is a |
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31 | * conversation number that associates a saved IP/TCP header with |
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32 | * the compressed packet. The next two octets are the TCP checksum |
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33 | * from the original datagram. The next 0 to 15 octets are |
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34 | * sequence number changes, one change per bit set in the header |
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35 | * (there may be no changes and there are two special cases where |
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36 | * the receiver implicitly knows what changed -- see below). |
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37 | * |
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38 | * There are 5 numbers which can change (they are always inserted |
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39 | * in the following order): TCP urgent pointer, window, |
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40 | * acknowlegement, sequence number and IP ID. (The urgent pointer |
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41 | * is different from the others in that its value is sent, not the |
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42 | * change in value.) Since typical use of SLIP links is biased |
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43 | * toward small packets (see comments on MTU/MSS below), changes |
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44 | * use a variable length coding with one octet for numbers in the |
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45 | * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the |
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46 | * range 256 - 65535 or 0. (If the change in sequence number or |
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47 | * ack is more than 65535, an uncompressed packet is sent.) |
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48 | */ |
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49 | |
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50 | /* |
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51 | * Packet types (must not conflict with IP protocol version) |
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52 | * |
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53 | * The top nibble of the first octet is the packet type. There are |
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54 | * three possible types: IP (not proto TCP or tcp with one of the |
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55 | * control flags set); uncompressed TCP (a normal IP/TCP packet but |
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56 | * with the 8-bit protocol field replaced by an 8-bit connection id -- |
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57 | * this type of packet syncs the sender & receiver); and compressed |
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58 | * TCP (described above). |
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59 | * |
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60 | * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and |
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61 | * is logically part of the 4-bit "changes" field that follows. Top |
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62 | * three bits are actual packet type. For backward compatibility |
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63 | * and in the interest of conserving bits, numbers are chosen so the |
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64 | * IP protocol version number (4) which normally appears in this nibble |
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65 | * means "IP packet". |
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66 | */ |
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67 | |
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68 | /* packet types */ |
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69 | #define TYPE_IP 0x40 |
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70 | #define TYPE_UNCOMPRESSED_TCP 0x70 |
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71 | #define TYPE_COMPRESSED_TCP 0x80 |
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72 | #define TYPE_ERROR 0x00 |
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73 | |
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74 | /* Bits in first octet of compressed packet */ |
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75 | #define NEW_C 0x40 /* flag bits for what changed in a packet */ |
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76 | #define NEW_I 0x20 |
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77 | #define NEW_S 0x08 |
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78 | #define NEW_A 0x04 |
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79 | #define NEW_W 0x02 |
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80 | #define NEW_U 0x01 |
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81 | |
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82 | /* reserved, special-case values of above */ |
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83 | #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ |
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84 | #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ |
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85 | #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) |
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86 | |
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87 | #define TCP_PUSH_BIT 0x10 |
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