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Diffstat (limited to 'include/net/vjcompress.h')
| -rw-r--r-- | include/net/vjcompress.h | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/include/net/vjcompress.h b/include/net/vjcompress.h new file mode 100644 index 000000000..83785b277 --- /dev/null +++ b/include/net/vjcompress.h @@ -0,0 +1,144 @@ +/* + * Definitions for tcp compression routines. + * + * $Id: vjcompress.h,v 1.1 2001/01/16 10:03:48 andersen 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 MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. + * + * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: + * - Initial distribution. + */ + +#ifndef _VJCOMPRESS_H_ +#define _VJCOMPRESS_H_ + +#define MAX_STATES 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_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 + + +/* + * "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 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 + +/* + * 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; +#ifndef VJ_NO_STATS + struct vjstat stats; +#endif + struct cstate tstate[MAX_STATES]; /* xmit connection states */ + struct cstate rstate[MAX_STATES]; /* receive connection states */ +}; + +/* flag values */ +#define VJF_TOSS 1 /* tossing rcvd frames because of input err */ + +extern void vj_compress_init __P((struct vjcompress *comp, int max_state)); +extern u_int vj_compress_tcp __P((struct ip *ip, u_int mlen, + struct vjcompress *comp, int compress_cid_flag, + u_char **vjhdrp)); +extern void vj_uncompress_err __P((struct vjcompress *comp)); +extern int vj_uncompress_uncomp __P((u_char *buf, int buflen, + struct vjcompress *comp)); +extern int vj_uncompress_tcp __P((u_char *buf, int buflen, int total_len, + struct vjcompress *comp, u_char **hdrp, + u_int *hlenp)); + +#endif /* _VJCOMPRESS_H_ */ |