| /* |
| * Definitions for tcp compression routines. |
| * |
| * @(#) $Header: /tcpdump/master/tcpdump/slcompress.h,v 1.2 2000/10/09 02:03:44 guy Exp $ (LBL) |
| * |
| * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of |
| * California. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms are permitted |
| * provided that the above copyright notice and this paragraph are |
| * duplicated in all such forms and that any documentation, |
| * advertising materials, and other materials related to such |
| * distribution and use acknowledge that the software was developed |
| * by the University of California, Berkeley. The name of the |
| * University may not be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR |
| * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
| * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
| * |
| * Van Jacobson (van@ee.lbl.gov), Dec 31, 1989: |
| * - Initial distribution. |
| */ |
| |
| /* |
| * Compressed packet format: |
| * |
| * The first octet contains the packet type (top 3 bits), TCP |
| * 'push' bit, and flags that indicate which of the 4 TCP sequence |
| * numbers have changed (bottom 5 bits). The next octet is a |
| * conversation number that associates a saved IP/TCP header with |
| * the compressed packet. The next two octets are the TCP checksum |
| * from the original datagram. The next 0 to 15 octets are |
| * sequence number changes, one change per bit set in the header |
| * (there may be no changes and there are two special cases where |
| * the receiver implicitly knows what changed -- see below). |
| * |
| * There are 5 numbers which can change (they are always inserted |
| * in the following order): TCP urgent pointer, window, |
| * acknowlegement, sequence number and IP ID. (The urgent pointer |
| * is different from the others in that its value is sent, not the |
| * change in value.) Since typical use of SLIP links is biased |
| * toward small packets (see comments on MTU/MSS below), changes |
| * use a variable length coding with one octet for numbers in the |
| * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the |
| * range 256 - 65535 or 0. (If the change in sequence number or |
| * ack is more than 65535, an uncompressed packet is sent.) |
| */ |
| |
| /* |
| * Packet types (must not conflict with IP protocol version) |
| * |
| * The top nibble of the first octet is the packet type. There are |
| * three possible types: IP (not proto TCP or tcp with one of the |
| * control flags set); uncompressed TCP (a normal IP/TCP packet but |
| * with the 8-bit protocol field replaced by an 8-bit connection id -- |
| * this type of packet syncs the sender & receiver); and compressed |
| * TCP (described above). |
| * |
| * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and |
| * is logically part of the 4-bit "changes" field that follows. Top |
| * three bits are actual packet type. For backward compatibility |
| * and in the interest of conserving bits, numbers are chosen so the |
| * IP protocol version number (4) which normally appears in this nibble |
| * means "IP packet". |
| */ |
| |
| /* packet types */ |
| #define TYPE_IP 0x40 |
| #define TYPE_UNCOMPRESSED_TCP 0x70 |
| #define TYPE_COMPRESSED_TCP 0x80 |
| #define TYPE_ERROR 0x00 |
| |
| /* Bits in first octet of compressed packet */ |
| #define NEW_C 0x40 /* flag bits for what changed in a packet */ |
| #define NEW_I 0x20 |
| #define NEW_S 0x08 |
| #define NEW_A 0x04 |
| #define NEW_W 0x02 |
| #define NEW_U 0x01 |
| |
| /* reserved, special-case values of above */ |
| #define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ |
| #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ |
| #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) |
| |
| #define TCP_PUSH_BIT 0x10 |
