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#ifndef _SLHC_H
#define _SLHC_H
* Definitions for tcp compression routines.
* $Header: slcompress.h,v 1.10 89/12/31 08:53:02 van 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.
* modified for KA9Q Internet Software Package by
* Katie Stevens (
* University of California, Davis
* Computing Services
* - 01-31-90 initial adaptation
* - Feb 1991
* variable number of conversation slots
* allow zero or one slots
* separate routines
* status display
* 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,
* acknowledgment, 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".
#include <linux/ip.h>
#include <linux/tcp.h>
/* SLIP compression masks for len/vers byte */
#define SL_TYPE_IP 0x40
#define SL_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
* data type and sizes conversion assumptions:
* VJ code KA9Q style generic
* u_char byte_t unsigned char 8 bits
* u_short int16 unsigned short 16 bits
* u_int int16 unsigned short 16 bits
* u_long unsigned long unsigned long 32 bits
* int int32 long 32 bits
typedef __u8 byte_t;
typedef __u32 int32;
* "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 {
byte_t cs_this; /* connection id number (xmit) */
struct cstate *next; /* next in ring (xmit) */
struct iphdr cs_ip; /* ip/tcp hdr from most recent packet */
struct tcphdr cs_tcp;
unsigned char cs_ipopt[64];
unsigned char cs_tcpopt[64];
int cs_hsize;
#define NULLSLSTATE (struct cstate *)0
* all the state data for one serial line (we need one of these per line).
struct slcompress {
struct cstate *tstate; /* transmit connection states (array)*/
struct cstate *rstate; /* receive connection states (array)*/
byte_t tslot_limit; /* highest transmit slot id (0-l)*/
byte_t rslot_limit; /* highest receive slot id (0-l)*/
byte_t xmit_oldest; /* oldest xmit in ring */
byte_t xmit_current; /* most recent xmit id */
byte_t recv_current; /* most recent rcvd id */
byte_t flags;
#define SLF_TOSS 0x01 /* tossing rcvd frames until id received */
int32 sls_o_nontcp; /* outbound non-TCP packets */
int32 sls_o_tcp; /* outbound TCP packets */
int32 sls_o_uncompressed; /* outbound uncompressed packets */
int32 sls_o_compressed; /* outbound compressed packets */
int32 sls_o_searches; /* searches for connection state */
int32 sls_o_misses; /* times couldn't find conn. state */
int32 sls_i_uncompressed; /* inbound uncompressed packets */
int32 sls_i_compressed; /* inbound compressed packets */
int32 sls_i_error; /* inbound error packets */
int32 sls_i_tossed; /* inbound packets tossed because of error */
int32 sls_i_runt;
int32 sls_i_badcheck;
#define NULLSLCOMPR (struct slcompress *)0
/* In slhc.c: */
struct slcompress *slhc_init(int rslots, int tslots);
void slhc_free(struct slcompress *comp);
int slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
unsigned char *ocp, unsigned char **cpp, int compress_cid);
int slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize);
int slhc_remember(struct slcompress *comp, unsigned char *icp, int isize);
int slhc_toss(struct slcompress *comp);
#endif /* _SLHC_H */