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* Definitions for tcp compression routines.
* $Id: vj.h,v 1.7 2010/02/22 17:52:09 goldsimon Exp $
* Copyright (c) 1989 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.
* Van Jacobson (, Dec 31, 1989:
* - Initial distribution.
#ifndef VJ_H
#define VJ_H
#include "lwip/ip.h"
#include "lwip/tcp_impl.h"
#define MAX_SLOTS 16 /* must be > 2 and < 256 */
#define MAX_HDR 128
* 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_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 TCP_PUSH_BIT 0x10
* "state" data for each active tcp conversation on the wire. This is
* basically a copy of the entire IP/TCP header from the last packet
* we saw from the conversation together with a small identifier
* the transmit & receive ends of the line use to locate saved header.
struct cstate {
struct cstate *cs_next; /* next most recently used state (xmit only) */
u_short cs_hlen; /* size of hdr (receive only) */
u_char cs_id; /* connection # associated with this state */
u_char cs_filler;
union {
char csu_hdr[MAX_HDR];
struct ip_hdr csu_ip; /* ip/tcp hdr from most recent packet */
} vjcs_u;
#define cs_ip vjcs_u.csu_ip
#define cs_hdr vjcs_u.csu_hdr
struct vjstat {
unsigned long vjs_packets; /* outbound packets */
unsigned long vjs_compressed; /* outbound compressed packets */
unsigned long vjs_searches; /* searches for connection state */
unsigned long vjs_misses; /* times couldn't find conn. state */
unsigned long vjs_uncompressedin; /* inbound uncompressed packets */
unsigned long vjs_compressedin; /* inbound compressed packets */
unsigned long vjs_errorin; /* inbound unknown type packets */
unsigned long vjs_tossed; /* inbound packets tossed because of error */
* all the state data for one serial line (we need one of these per line).
struct vjcompress {
struct cstate *last_cs; /* most recently used tstate */
u_char last_recv; /* last rcvd conn. id */
u_char last_xmit; /* last sent conn. id */
u_short flags;
u_char maxSlotIndex;
u_char compressSlot; /* Flag indicating OK to compress slot ID. */
struct vjstat stats;
struct cstate tstate[MAX_SLOTS]; /* xmit connection states */
struct cstate rstate[MAX_SLOTS]; /* receive connection states */
/* flag values */
#define VJF_TOSS 1U /* tossing rcvd frames because of input err */
extern void vj_compress_init (struct vjcompress *comp);
extern u_int vj_compress_tcp (struct vjcompress *comp, struct pbuf *pb);
extern void vj_uncompress_err (struct vjcompress *comp);
extern int vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp);
extern int vj_uncompress_tcp (struct pbuf **nb, struct vjcompress *comp);
#endif /* VJ_H */