2 * Copyright (c) 1982, 1986, 1993, 1994, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * @(#)tcp_var.h 8.4 (Berkeley) 5/24/95
34 * $FreeBSD: src/sys/netinet/tcp_var.h,v 1.56.2.13 2003/02/03 02:34:07 hsu Exp $
35 * $DragonFly: src/sys/netinet/tcp_var.h,v 1.4 2003/07/24 01:31:07 dillon Exp $
38 #ifndef _NETINET_TCP_VAR_H_
39 #define _NETINET_TCP_VAR_H_
41 #include <netinet/in_pcb.h> /* needed for in_conninfo, inp_gen_t */
44 * Kernel variables for tcp.
46 extern int tcp_do_rfc1323;
47 extern int tcp_do_rfc1644;
49 /* TCP segment queue entry */
51 LIST_ENTRY(tseg_qent) tqe_q;
52 int tqe_len; /* TCP segment data length */
53 struct tcphdr *tqe_th; /* a pointer to tcp header */
54 struct mbuf *tqe_m; /* mbuf contains packet */
56 LIST_HEAD(tsegqe_head, tseg_qent);
58 MALLOC_DECLARE(M_TSEGQ);
62 u_char tt_ipgen[40]; /* the size must be of max ip header, now IPv6 */
66 #define tcp6cb tcpcb /* for KAME src sync over BSD*'s */
69 * Tcp control block, one per tcp; fields:
70 * Organized for 16 byte cacheline efficiency.
73 struct tsegqe_head t_segq;
74 int t_dupacks; /* consecutive dup acks recd */
75 struct tcptemp *unused; /* unused */
77 struct callout *tt_rexmt; /* retransmit timer */
78 struct callout *tt_persist; /* retransmit persistence */
79 struct callout *tt_keep; /* keepalive */
80 struct callout *tt_2msl; /* 2*msl TIME_WAIT timer */
81 struct callout *tt_delack; /* delayed ACK timer */
83 struct inpcb *t_inpcb; /* back pointer to internet pcb */
84 int t_state; /* state of this connection */
86 #define TF_ACKNOW 0x000001 /* ack peer immediately */
87 #define TF_DELACK 0x000002 /* ack, but try to delay it */
88 #define TF_NODELAY 0x000004 /* don't delay packets to coalesce */
89 #define TF_NOOPT 0x000008 /* don't use tcp options */
90 #define TF_SENTFIN 0x000010 /* have sent FIN */
91 #define TF_REQ_SCALE 0x000020 /* have/will request window scaling */
92 #define TF_RCVD_SCALE 0x000040 /* other side has requested scaling */
93 #define TF_REQ_TSTMP 0x000080 /* have/will request timestamps */
94 #define TF_RCVD_TSTMP 0x000100 /* a timestamp was received in SYN */
95 #define TF_SACK_PERMIT 0x000200 /* other side said I could SACK */
96 #define TF_NEEDSYN 0x000400 /* send SYN (implicit state) */
97 #define TF_NEEDFIN 0x000800 /* send FIN (implicit state) */
98 #define TF_NOPUSH 0x001000 /* don't push */
99 #define TF_REQ_CC 0x002000 /* have/will request CC */
100 #define TF_RCVD_CC 0x004000 /* a CC was received in SYN */
101 #define TF_SENDCCNEW 0x008000 /* send CCnew instead of CC in SYN */
102 #define TF_MORETOCOME 0x010000 /* More data to be appended to sock */
103 #define TF_LQ_OVERFLOW 0x020000 /* listen queue overflow */
104 #define TF_LASTIDLE 0x040000 /* connection was previously idle */
105 #define TF_RXWIN0SENT 0x080000 /* sent a receiver win 0 in response */
106 #define TF_FASTRECOVERY 0x100000 /* in NewReno Fast Recovery */
107 #define TF_WASFRECOVERY 0x200000 /* was in NewReno Fast Recovery */
108 int t_force; /* 1 if forcing out a byte */
110 tcp_seq snd_una; /* send unacknowledged */
111 tcp_seq snd_max; /* highest sequence number sent;
112 * used to recognize retransmits
114 tcp_seq snd_nxt; /* send next */
115 tcp_seq snd_up; /* send urgent pointer */
117 tcp_seq snd_wl1; /* window update seg seq number */
118 tcp_seq snd_wl2; /* window update seg ack number */
119 tcp_seq iss; /* initial send sequence number */
120 tcp_seq irs; /* initial receive sequence number */
122 tcp_seq rcv_nxt; /* receive next */
123 tcp_seq rcv_adv; /* advertised window */
124 u_long rcv_wnd; /* receive window */
125 tcp_seq rcv_up; /* receive urgent pointer */
127 u_long snd_wnd; /* send window */
128 u_long snd_cwnd; /* congestion-controlled window */
129 u_long snd_bwnd; /* bandwidth-controlled window */
130 u_long snd_ssthresh; /* snd_cwnd size threshold for
131 * for slow start exponential to
134 u_long snd_bandwidth; /* calculated bandwidth or 0 */
135 tcp_seq snd_recover; /* for use in NewReno fast recovery */
137 u_int t_maxopd; /* mss plus options */
139 u_long t_rcvtime; /* inactivity time */
140 u_long t_starttime; /* time connection was established */
141 int t_rtttime; /* round trip time */
142 tcp_seq t_rtseq; /* sequence number being timed */
144 int t_bw_rtttime; /* used for bandwidth calculation */
145 tcp_seq t_bw_rtseq; /* used for bandwidth calculation */
147 int t_rxtcur; /* current retransmit value (ticks) */
148 u_int t_maxseg; /* maximum segment size */
149 int t_srtt; /* smoothed round-trip time */
150 int t_rttvar; /* variance in round-trip time */
152 int t_rxtshift; /* log(2) of rexmt exp. backoff */
153 u_int t_rttmin; /* minimum rtt allowed */
154 u_int t_rttbest; /* best rtt we've seen */
155 u_long t_rttupdated; /* number of times rtt sampled */
156 u_long max_sndwnd; /* largest window peer has offered */
158 int t_softerror; /* possible error not yet reported */
159 /* out-of-band data */
160 char t_oobflags; /* have some */
161 char t_iobc; /* input character */
162 #define TCPOOB_HAVEDATA 0x01
163 #define TCPOOB_HADDATA 0x02
164 /* RFC 1323 variables */
165 u_char snd_scale; /* window scaling for send window */
166 u_char rcv_scale; /* window scaling for recv window */
167 u_char request_r_scale; /* pending window scaling */
168 u_char requested_s_scale;
169 u_long ts_recent; /* timestamp echo data */
171 u_long ts_recent_age; /* when last updated */
172 tcp_seq last_ack_sent;
173 /* RFC 1644 variables */
174 tcp_cc cc_send; /* send connection count */
175 tcp_cc cc_recv; /* receive connection count */
177 u_long snd_cwnd_prev; /* cwnd prior to retransmit */
178 u_long snd_ssthresh_prev; /* ssthresh prior to retransmit */
179 tcp_seq snd_recover_prev; /* snd_recover prior to retransmit */
180 u_long t_badrxtwin; /* window for retransmit recovery */
181 u_char snd_limited; /* segments limited transmitted */
184 #define IN_FASTRECOVERY(tp) (tp->t_flags & TF_FASTRECOVERY)
185 #define ENTER_FASTRECOVERY(tp) tp->t_flags |= TF_FASTRECOVERY
186 #define EXIT_FASTRECOVERY(tp) tp->t_flags &= ~TF_FASTRECOVERY
189 * Structure to hold TCP options that are only used during segment
190 * processing (in tcp_input), but not held in the tcpcb.
191 * It's basically used to reduce the number of parameters
195 u_long to_flags; /* which options are present */
196 #define TOF_TS 0x0001 /* timestamp */
197 #define TOF_CC 0x0002 /* CC and CCnew are exclusive */
198 #define TOF_CCNEW 0x0004
199 #define TOF_CCECHO 0x0008
200 #define TOF_MSS 0x0010
201 #define TOF_SCALE 0x0020
204 tcp_cc to_cc; /* holds CC or CCnew */
207 u_int8_t to_requested_s_scale;
212 inp_gen_t sc_inp_gencnt; /* pointer check */
213 struct tcpcb *sc_tp; /* tcb for listening socket */
214 struct mbuf *sc_ipopts; /* source route */
215 struct in_conninfo sc_inc; /* addresses */
216 #define sc_route sc_inc.inc_route
217 #define sc_route6 sc_inc.inc6_route
218 u_int32_t sc_tsrecent;
219 tcp_cc sc_cc_send; /* holds CC or CCnew */
221 tcp_seq sc_irs; /* seq from peer */
222 tcp_seq sc_iss; /* our ISS */
223 u_long sc_rxttime; /* retransmit time */
224 u_int16_t sc_rxtslot; /* retransmit counter */
225 u_int16_t sc_peer_mss; /* peer's MSS */
226 u_int16_t sc_wnd; /* advertised window */
227 u_int8_t sc_requested_s_scale:4,
228 sc_request_r_scale:4;
230 #define SCF_NOOPT 0x01 /* no TCP options */
231 #define SCF_WINSCALE 0x02 /* negotiated window scaling */
232 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */
233 #define SCF_CC 0x08 /* negotiated CC */
234 #define SCF_UNREACH 0x10 /* icmp unreachable received */
235 #define SCF_KEEPROUTE 0x20 /* keep cloned route */
236 TAILQ_ENTRY(syncache) sc_hash;
237 TAILQ_ENTRY(syncache) sc_timerq;
240 struct syncache_head {
241 TAILQ_HEAD(, syncache) sch_bucket;
246 * The TAO cache entry which is stored in the protocol family specific
247 * portion of the route metrics.
250 tcp_cc tao_cc; /* latest CC in valid SYN */
251 tcp_cc tao_ccsent; /* latest CC sent to peer */
252 u_short tao_mssopt; /* peer's cached MSS */
254 u_short tao_flags; /* cache status flags */
255 #define TAOF_DONT 0x0001 /* peer doesn't understand rfc1644 */
256 #define TAOF_OK 0x0002 /* peer does understand rfc1644 */
257 #define TAOF_UNDEF 0 /* we don't know yet */
260 #define rmx_taop(r) ((struct rmxp_tao *)(r).rmx_filler)
262 #define intotcpcb(ip) ((struct tcpcb *)(ip)->inp_ppcb)
263 #define sototcpcb(so) (intotcpcb(sotoinpcb(so)))
266 * The smoothed round-trip time and estimated variance
267 * are stored as fixed point numbers scaled by the values below.
268 * For convenience, these scales are also used in smoothing the average
269 * (smoothed = (1/scale)sample + ((scale-1)/scale)smoothed).
270 * With these scales, srtt has 3 bits to the right of the binary point,
271 * and thus an "ALPHA" of 0.875. rttvar has 2 bits to the right of the
272 * binary point, and is smoothed with an ALPHA of 0.75.
274 #define TCP_RTT_SCALE 32 /* multiplier for srtt; 3 bits frac. */
275 #define TCP_RTT_SHIFT 5 /* shift for srtt; 3 bits frac. */
276 #define TCP_RTTVAR_SCALE 16 /* multiplier for rttvar; 2 bits */
277 #define TCP_RTTVAR_SHIFT 4 /* shift for rttvar; 2 bits */
278 #define TCP_DELTA_SHIFT 2 /* see tcp_input.c */
281 * The initial retransmission should happen at rtt + 4 * rttvar.
282 * Because of the way we do the smoothing, srtt and rttvar
283 * will each average +1/2 tick of bias. When we compute
284 * the retransmit timer, we want 1/2 tick of rounding and
285 * 1 extra tick because of +-1/2 tick uncertainty in the
286 * firing of the timer. The bias will give us exactly the
287 * 1.5 tick we need. But, because the bias is
288 * statistical, we have to test that we don't drop below
289 * the minimum feasible timer (which is 2 ticks).
290 * This version of the macro adapted from a paper by Lawrence
291 * Brakmo and Larry Peterson which outlines a problem caused
292 * by insufficient precision in the original implementation,
293 * which results in inappropriately large RTO values for very
296 #define TCP_REXMTVAL(tp) \
297 max((tp)->t_rttmin, (((tp)->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT)) \
298 + (tp)->t_rttvar) >> TCP_DELTA_SHIFT)
302 * Many of these should be kept per connection,
303 * but that's inconvenient at the moment.
306 u_long tcps_connattempt; /* connections initiated */
307 u_long tcps_accepts; /* connections accepted */
308 u_long tcps_connects; /* connections established */
309 u_long tcps_drops; /* connections dropped */
310 u_long tcps_conndrops; /* embryonic connections dropped */
311 u_long tcps_closed; /* conn. closed (includes drops) */
312 u_long tcps_segstimed; /* segs where we tried to get rtt */
313 u_long tcps_rttupdated; /* times we succeeded */
314 u_long tcps_delack; /* delayed acks sent */
315 u_long tcps_timeoutdrop; /* conn. dropped in rxmt timeout */
316 u_long tcps_rexmttimeo; /* retransmit timeouts */
317 u_long tcps_persisttimeo; /* persist timeouts */
318 u_long tcps_keeptimeo; /* keepalive timeouts */
319 u_long tcps_keepprobe; /* keepalive probes sent */
320 u_long tcps_keepdrops; /* connections dropped in keepalive */
322 u_long tcps_sndtotal; /* total packets sent */
323 u_long tcps_sndpack; /* data packets sent */
324 u_long tcps_sndbyte; /* data bytes sent */
325 u_long tcps_sndrexmitpack; /* data packets retransmitted */
326 u_long tcps_sndrexmitbyte; /* data bytes retransmitted */
327 u_long tcps_sndacks; /* ack-only packets sent */
328 u_long tcps_sndprobe; /* window probes sent */
329 u_long tcps_sndurg; /* packets sent with URG only */
330 u_long tcps_sndwinup; /* window update-only packets sent */
331 u_long tcps_sndctrl; /* control (SYN|FIN|RST) packets sent */
333 u_long tcps_rcvtotal; /* total packets received */
334 u_long tcps_rcvpack; /* packets received in sequence */
335 u_long tcps_rcvbyte; /* bytes received in sequence */
336 u_long tcps_rcvbadsum; /* packets received with ccksum errs */
337 u_long tcps_rcvbadoff; /* packets received with bad offset */
338 u_long tcps_rcvmemdrop; /* packets dropped for lack of memory */
339 u_long tcps_rcvshort; /* packets received too short */
340 u_long tcps_rcvduppack; /* duplicate-only packets received */
341 u_long tcps_rcvdupbyte; /* duplicate-only bytes received */
342 u_long tcps_rcvpartduppack; /* packets with some duplicate data */
343 u_long tcps_rcvpartdupbyte; /* dup. bytes in part-dup. packets */
344 u_long tcps_rcvoopack; /* out-of-order packets received */
345 u_long tcps_rcvoobyte; /* out-of-order bytes received */
346 u_long tcps_rcvpackafterwin; /* packets with data after window */
347 u_long tcps_rcvbyteafterwin; /* bytes rcvd after window */
348 u_long tcps_rcvafterclose; /* packets rcvd after "close" */
349 u_long tcps_rcvwinprobe; /* rcvd window probe packets */
350 u_long tcps_rcvdupack; /* rcvd duplicate acks */
351 u_long tcps_rcvacktoomuch; /* rcvd acks for unsent data */
352 u_long tcps_rcvackpack; /* rcvd ack packets */
353 u_long tcps_rcvackbyte; /* bytes acked by rcvd acks */
354 u_long tcps_rcvwinupd; /* rcvd window update packets */
355 u_long tcps_pawsdrop; /* segments dropped due to PAWS */
356 u_long tcps_predack; /* times hdr predict ok for acks */
357 u_long tcps_preddat; /* times hdr predict ok for data pkts */
358 u_long tcps_pcbcachemiss;
359 u_long tcps_cachedrtt; /* times cached RTT in route updated */
360 u_long tcps_cachedrttvar; /* times cached rttvar updated */
361 u_long tcps_cachedssthresh; /* times cached ssthresh updated */
362 u_long tcps_usedrtt; /* times RTT initialized from route */
363 u_long tcps_usedrttvar; /* times RTTVAR initialized from rt */
364 u_long tcps_usedssthresh; /* times ssthresh initialized from rt*/
365 u_long tcps_persistdrop; /* timeout in persist state */
366 u_long tcps_badsyn; /* bogus SYN, e.g. premature ACK */
367 u_long tcps_mturesent; /* resends due to MTU discovery */
368 u_long tcps_listendrop; /* listen queue overflows */
370 u_long tcps_sc_added; /* entry added to syncache */
371 u_long tcps_sc_retransmitted; /* syncache entry was retransmitted */
372 u_long tcps_sc_dupsyn; /* duplicate SYN packet */
373 u_long tcps_sc_dropped; /* could not reply to packet */
374 u_long tcps_sc_completed; /* successful extraction of entry */
375 u_long tcps_sc_bucketoverflow; /* syncache per-bucket limit hit */
376 u_long tcps_sc_cacheoverflow; /* syncache cache limit hit */
377 u_long tcps_sc_reset; /* RST removed entry from syncache */
378 u_long tcps_sc_stale; /* timed out or listen socket gone */
379 u_long tcps_sc_aborted; /* syncache entry aborted */
380 u_long tcps_sc_badack; /* removed due to bad ACK */
381 u_long tcps_sc_unreach; /* ICMP unreachable received */
382 u_long tcps_sc_zonefail; /* zalloc() failed */
383 u_long tcps_sc_sendcookie; /* SYN cookie sent */
384 u_long tcps_sc_recvcookie; /* SYN cookie received */
388 * TCB structure exported to user-land via sysctl(3).
389 * Evil hack: declare only if in_pcb.h and sys/socketvar.h have been
390 * included. Not all of our clients do.
392 #if defined(_NETINET_IN_PCB_H_) && defined(_SYS_SOCKETVAR_H_)
397 struct xsocket xt_socket;
398 u_quad_t xt_alignment_hack;
403 * Names for TCP sysctl objects
405 #define TCPCTL_DO_RFC1323 1 /* use RFC-1323 extensions */
406 #define TCPCTL_DO_RFC1644 2 /* use RFC-1644 extensions */
407 #define TCPCTL_MSSDFLT 3 /* MSS default */
408 #define TCPCTL_STATS 4 /* statistics (read-only) */
409 #define TCPCTL_RTTDFLT 5 /* default RTT estimate */
410 #define TCPCTL_KEEPIDLE 6 /* keepalive idle timer */
411 #define TCPCTL_KEEPINTVL 7 /* interval to send keepalives */
412 #define TCPCTL_SENDSPACE 8 /* send buffer space */
413 #define TCPCTL_RECVSPACE 9 /* receive buffer space */
414 #define TCPCTL_KEEPINIT 10 /* timeout for establishing syn */
415 #define TCPCTL_PCBLIST 11 /* list of all outstanding PCBs */
416 #define TCPCTL_DELACKTIME 12 /* time before sending delayed ACK */
417 #define TCPCTL_V6MSSDFLT 13 /* MSS default for IPv6 */
418 #define TCPCTL_MAXID 14
420 #define TCPCTL_NAMES { \
422 { "rfc1323", CTLTYPE_INT }, \
423 { "rfc1644", CTLTYPE_INT }, \
424 { "mssdflt", CTLTYPE_INT }, \
425 { "stats", CTLTYPE_STRUCT }, \
426 { "rttdflt", CTLTYPE_INT }, \
427 { "keepidle", CTLTYPE_INT }, \
428 { "keepintvl", CTLTYPE_INT }, \
429 { "sendspace", CTLTYPE_INT }, \
430 { "recvspace", CTLTYPE_INT }, \
431 { "keepinit", CTLTYPE_INT }, \
432 { "pcblist", CTLTYPE_STRUCT }, \
433 { "delacktime", CTLTYPE_INT }, \
434 { "v6mssdflt", CTLTYPE_INT }, \
440 SYSCTL_DECL(_net_inet_tcp);
443 extern struct inpcbhead tcb; /* head of queue of active tcpcb's */
444 extern struct inpcbinfo tcbinfo;
445 extern struct tcpstat tcpstat; /* tcp statistics */
446 extern int tcp_mssdflt; /* XXX */
447 extern int tcp_delack_enabled;
448 extern int tcp_do_newreno;
449 extern int path_mtu_discovery;
451 extern int ss_fltsz_local;
453 void tcp_canceltimers __P((struct tcpcb *));
455 tcp_close __P((struct tcpcb *));
456 void tcp_ctlinput __P((int, struct sockaddr *, void *));
457 int tcp_ctloutput __P((struct socket *, struct sockopt *));
459 tcp_drop __P((struct tcpcb *, int));
460 void tcp_drain __P((void));
461 void tcp_fasttimo __P((void));
463 tcp_gettaocache __P((struct in_conninfo *));
464 void tcp_init __P((void));
465 void tcp_input __P((struct mbuf *, int, int));
466 void tcp_mss __P((struct tcpcb *, int));
467 int tcp_mssopt __P((struct tcpcb *));
468 void tcp_drop_syn_sent __P((struct inpcb *, int));
469 void tcp_mtudisc __P((struct inpcb *, int));
471 tcp_newtcpcb __P((struct inpcb *));
472 int tcp_output __P((struct tcpcb *));
473 void tcp_quench __P((struct inpcb *, int));
474 void tcp_respond __P((struct tcpcb *, void *,
475 struct tcphdr *, struct mbuf *, tcp_seq, tcp_seq, int));
477 tcp_rtlookup __P((struct in_conninfo *));
478 void tcp_setpersist __P((struct tcpcb *));
479 void tcp_slowtimo __P((void));
481 tcp_maketemplate __P((struct tcpcb *));
482 void tcp_fillheaders __P((struct tcpcb *, void *, void *));
484 tcp_timers __P((struct tcpcb *, int));
485 void tcp_trace __P((int, int, struct tcpcb *, void *, struct tcphdr *,
487 void tcp_xmit_bandwidth_limit(struct tcpcb *tp, tcp_seq ack_seq);
488 void syncache_init(void);
489 void syncache_unreach(struct in_conninfo *, struct tcphdr *);
490 int syncache_expand(struct in_conninfo *, struct tcphdr *,
491 struct socket **, struct mbuf *);
492 int syncache_add(struct in_conninfo *, struct tcpopt *,
493 struct tcphdr *, struct socket **, struct mbuf *);
494 void syncache_chkrst(struct in_conninfo *, struct tcphdr *);
495 void syncache_badack(struct in_conninfo *);
497 extern struct pr_usrreqs tcp_usrreqs;
498 extern u_long tcp_sendspace;
499 extern u_long tcp_recvspace;
500 tcp_seq tcp_new_isn __P((struct tcpcb *));
504 #endif /* _NETINET_TCP_VAR_H_ */