156893Sfenner/* 256893Sfenner * Definitions for tcp compression routines. 356893Sfenner * 456893Sfenner * Copyright (c) 1989, 1990, 1992, 1993 Regents of the University of 5127668Sbms * California. All rights reserved. 656893Sfenner * 756893Sfenner * Redistribution and use in source and binary forms are permitted 856893Sfenner * provided that the above copyright notice and this paragraph are 9127668Sbms * duplicated in all such forms and that any documentation, 1056893Sfenner * advertising materials, and other materials related to such 1156893Sfenner * distribution and use acknowledge that the software was developed 12127668Sbms * by the University of California, Berkeley. The name of the 1356893Sfenner * University may not be used to endorse or promote products derived 1456893Sfenner * from this software without specific prior written permission. 1556893Sfenner * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 16127668Sbms * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 1756893Sfenner * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 1856893Sfenner * 1956893Sfenner * Van Jacobson (van@ee.lbl.gov), Dec 31, 1989: 2056893Sfenner * - Initial distribution. 21127668Sbms */ 2256893Sfenner 2356893Sfenner/* 2456893Sfenner * Compressed packet format: 25127668Sbms * 2656893Sfenner * The first octet contains the packet type (top 3 bits), TCP 2756893Sfenner * 'push' bit, and flags that indicate which of the 4 TCP sequence 2856893Sfenner * numbers have changed (bottom 5 bits). The next octet is a 2956893Sfenner * conversation number that associates a saved IP/TCP header with 3056893Sfenner * the compressed packet. The next two octets are the TCP checksum 3156893Sfenner * from the original datagram. The next 0 to 15 octets are 3256893Sfenner * sequence number changes, one change per bit set in the header 3356893Sfenner * (there may be no changes and there are two special cases where 3456893Sfenner * the receiver implicitly knows what changed -- see below). 3556893Sfenner * 3656893Sfenner * There are 5 numbers which can change (they are always inserted 3756893Sfenner * in the following order): TCP urgent pointer, window, 3856893Sfenner * acknowledgement, sequence number and IP ID. (The urgent pointer 39127668Sbms * is different from the others in that its value is sent, not the 4056893Sfenner * change in value.) Since typical use of SLIP links is biased 4156893Sfenner * toward small packets (see comments on MTU/MSS below), changes 42127668Sbms * use a variable length coding with one octet for numbers in the 43127668Sbms * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the 4456893Sfenner * range 256 - 65535 or 0. (If the change in sequence number or 4556893Sfenner * ack is more than 65535, an uncompressed packet is sent.) 46127668Sbms */ 4756893Sfenner 4856893Sfenner/* 4956893Sfenner * Packet types (must not conflict with IP protocol version) 5056893Sfenner * 5156893Sfenner * The top nibble of the first octet is the packet type. There are 5256893Sfenner * three possible types: IP (not proto TCP or tcp with one of the 5356893Sfenner * control flags set); uncompressed TCP (a normal IP/TCP packet but 5456893Sfenner * with the 8-bit protocol field replaced by an 8-bit connection id -- 5556893Sfenner * this type of packet syncs the sender & receiver); and compressed 5656893Sfenner * TCP (described above). 5756893Sfenner * 5856893Sfenner * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and 5956893Sfenner * is logically part of the 4-bit "changes" field that follows. Top 6056893Sfenner * three bits are actual packet type. For backward compatibility 61 * and in the interest of conserving bits, numbers are chosen so the 62 * IP protocol version number (4) which normally appears in this nibble 63 * means "IP packet". 64 */ 65 66/* packet types */ 67#define TYPE_IP 0x40 68#define TYPE_UNCOMPRESSED_TCP 0x70 69#define TYPE_COMPRESSED_TCP 0x80 70#define TYPE_ERROR 0x00 71 72/* Bits in first octet of compressed packet */ 73#define NEW_C 0x40 /* flag bits for what changed in a packet */ 74#define NEW_I 0x20 75#define NEW_S 0x08 76#define NEW_A 0x04 77#define NEW_W 0x02 78#define NEW_U 0x01 79 80/* reserved, special-case values of above */ 81#define SPECIAL_I (NEW_S|NEW_W|NEW_U) /* echoed interactive traffic */ 82#define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */ 83#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U) 84 85#define TCP_PUSH_BIT 0x10 86