175115Sfenner/* 275115Sfenner * Definitions for tcp compression routines. 375115Sfenner * 4190207Srpaulo * @(#) $Header: /tcpdump/master/tcpdump/slcompress.h,v 1.2 2000-10-09 02:03:44 guy Exp $ (LBL) 575115Sfenner * 675115Sfenner * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of 775115Sfenner * California. All rights reserved. 875115Sfenner * 975115Sfenner * Redistribution and use in source and binary forms are permitted 1075115Sfenner * provided that the above copyright notice and this paragraph are 1175115Sfenner * duplicated in all such forms and that any documentation, 1275115Sfenner * advertising materials, and other materials related to such 1375115Sfenner * distribution and use acknowledge that the software was developed 1475115Sfenner * by the University of California, Berkeley. The name of the 1575115Sfenner * University may not be used to endorse or promote products derived 1675115Sfenner * from this software without specific prior written permission. 1775115Sfenner * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 1875115Sfenner * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 1975115Sfenner * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 2075115Sfenner * 2175115Sfenner * Van Jacobson (van@ee.lbl.gov), Dec 31, 1989: 2275115Sfenner * - Initial distribution. 2375115Sfenner */ 2475115Sfenner 2575115Sfenner/* 2675115Sfenner * Compressed packet format: 2775115Sfenner * 2875115Sfenner * The first octet contains the packet type (top 3 bits), TCP 2975115Sfenner * 'push' bit, and flags that indicate which of the 4 TCP sequence 3075115Sfenner * numbers have changed (bottom 5 bits). The next octet is a 3175115Sfenner * conversation number that associates a saved IP/TCP header with 3275115Sfenner * the compressed packet. The next two octets are the TCP checksum 3375115Sfenner * from the original datagram. The next 0 to 15 octets are 3475115Sfenner * sequence number changes, one change per bit set in the header 3575115Sfenner * (there may be no changes and there are two special cases where 3675115Sfenner * the receiver implicitly knows what changed -- see below). 3775115Sfenner * 3875115Sfenner * There are 5 numbers which can change (they are always inserted 3975115Sfenner * in the following order): TCP urgent pointer, window, 4075115Sfenner * acknowlegement, sequence number and IP ID. (The urgent pointer 4175115Sfenner * is different from the others in that its value is sent, not the 4275115Sfenner * change in value.) Since typical use of SLIP links is biased 4375115Sfenner * toward small packets (see comments on MTU/MSS below), changes 4475115Sfenner * use a variable length coding with one octet for numbers in the 4575115Sfenner * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 4675115Sfenner * range 256 - 65535 or 0. (If the change in sequence number or 4775115Sfenner * ack is more than 65535, an uncompressed packet is sent.) 4875115Sfenner */ 4975115Sfenner 5075115Sfenner/* 5175115Sfenner * Packet types (must not conflict with IP protocol version) 5275115Sfenner * 5375115Sfenner * The top nibble of the first octet is the packet type. There are 5475115Sfenner * three possible types: IP (not proto TCP or tcp with one of the 5575115Sfenner * control flags set); uncompressed TCP (a normal IP/TCP packet but 5675115Sfenner * with the 8-bit protocol field replaced by an 8-bit connection id -- 5775115Sfenner * this type of packet syncs the sender & receiver); and compressed 5875115Sfenner * TCP (described above). 5975115Sfenner * 6075115Sfenner * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 6175115Sfenner * is logically part of the 4-bit "changes" field that follows. Top 6275115Sfenner * three bits are actual packet type. For backward compatibility 6375115Sfenner * and in the interest of conserving bits, numbers are chosen so the 6475115Sfenner * IP protocol version number (4) which normally appears in this nibble 6575115Sfenner * means "IP packet". 6675115Sfenner */ 6775115Sfenner 6875115Sfenner/* packet types */ 6975115Sfenner#define TYPE_IP 0x40 7075115Sfenner#define TYPE_UNCOMPRESSED_TCP 0x70 7175115Sfenner#define TYPE_COMPRESSED_TCP 0x80 7275115Sfenner#define TYPE_ERROR 0x00 7375115Sfenner 7475115Sfenner/* Bits in first octet of compressed packet */ 7575115Sfenner#define NEW_C 0x40 /* flag bits for what changed in a packet */ 7675115Sfenner#define NEW_I 0x20 7775115Sfenner#define NEW_S 0x08 7875115Sfenner#define NEW_A 0x04 7975115Sfenner#define NEW_W 0x02 8075115Sfenner#define NEW_U 0x01 8175115Sfenner 8275115Sfenner/* reserved, special-case values of above */ 8375115Sfenner#define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 8475115Sfenner#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 8575115Sfenner#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 8675115Sfenner 8775115Sfenner#define TCP_PUSH_BIT 0x10 88