#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. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. * * Van Jacobson ([email protected]), Dec 31, 1989: * - Initial distribution. * * * modified for KA9Q Internet Software Package by * Katie Stevens ([email protected]) * University of California, Davis * Computing Services * - 01-31-90 initial adaptation * * - Feb 1991 [email protected] * 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 … #define SL_TYPE_UNCOMPRESSED_TCP … #define SL_TYPE_COMPRESSED_TCP … #define SL_TYPE_ERROR … /* Bits in first octet of compressed packet */ #define NEW_C … #define NEW_I … #define NEW_S … #define NEW_A … #define NEW_W … #define NEW_U … /* reserved, special-case values of above */ #define SPECIAL_I … #define SPECIAL_D … #define SPECIALS_MASK … #define TCP_PUSH_BIT … /* * 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 */ byte_t; 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 { … }; #define NULLSLSTATE … /* * all the state data for one serial line (we need one of these per line). */ struct slcompress { … }; #define NULLSLCOMPR … /* 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 */
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