1 /* 2 * Definitions for tcp compression routines. 3 * 4 * @(#) $Header: /tcpdump/master/tcpdump/slcompress.h,v 1.2 2000/10/09 02:03:44 guy Exp $ (LBL) 5 * 6 * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of 7 * California. 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 (at) ee.lbl.gov), Dec 31, 1989: 22 * - Initial distribution. 23 */ 24 25 /* 26 * Compressed packet format: 27 * 28 * The first octet contains the packet type (top 3 bits), TCP 29 * 'push' bit, and flags that indicate which of the 4 TCP sequence 30 * numbers have changed (bottom 5 bits). The next octet is a 31 * conversation number that associates a saved IP/TCP header with 32 * the compressed packet. The next two octets are the TCP checksum 33 * from the original datagram. The next 0 to 15 octets are 34 * sequence number changes, one change per bit set in the header 35 * (there may be no changes and there are two special cases where 36 * the receiver implicitly knows what changed -- see below). 37 * 38 * There are 5 numbers which can change (they are always inserted 39 * in the following order): TCP urgent pointer, window, 40 * acknowlegement, sequence number and IP ID. (The urgent pointer 41 * is different from the others in that its value is sent, not the 42 * change in value.) Since typical use of SLIP links is biased 43 * toward small packets (see comments on MTU/MSS below), changes 44 * use a variable length coding with one octet for numbers in the 45 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 46 * range 256 - 65535 or 0. (If the change in sequence number or 47 * ack is more than 65535, an uncompressed packet is sent.) 48 */ 49 50 /* 51 * Packet types (must not conflict with IP protocol version) 52 * 53 * The top nibble of the first octet is the packet type. There are 54 * three possible types: IP (not proto TCP or tcp with one of the 55 * control flags set); uncompressed TCP (a normal IP/TCP packet but 56 * with the 8-bit protocol field replaced by an 8-bit connection id -- 57 * this type of packet syncs the sender & receiver); and compressed 58 * TCP (described above). 59 * 60 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 61 * is logically part of the 4-bit "changes" field that follows. Top 62 * three bits are actual packet type. For backward compatibility 63 * and in the interest of conserving bits, numbers are chosen so the 64 * IP protocol version number (4) which normally appears in this nibble 65 * means "IP packet". 66 */ 67 68 /* packet types */ 69 #define TYPE_IP 0x40 70 #define TYPE_UNCOMPRESSED_TCP 0x70 71 #define TYPE_COMPRESSED_TCP 0x80 72 #define TYPE_ERROR 0x00 73 74 /* Bits in first octet of compressed packet */ 75 #define NEW_C 0x40 /* flag bits for what changed in a packet */ 76 #define NEW_I 0x20 77 #define NEW_S 0x08 78 #define NEW_A 0x04 79 #define NEW_W 0x02 80 #define NEW_U 0x01 81 82 /* reserved, special-case values of above */ 83 #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 84 #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 85 #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 86 87 #define TCP_PUSH_BIT 0x10 88
