86 lines
3.6 KiB
C
86 lines
3.6 KiB
C
/*
|
|
* Definitions for tcp compression routines.
|
|
*
|
|
* 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
|