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1.1 root 1: /*
2: * Copyright (c) 1982, 1986 Regents of the University of California.
3: * All rights reserved.
4: *
5: * Redistribution is only permitted until one year after the first shipment
6: * of 4.4BSD by the Regents. Otherwise, redistribution and use in source and
7: * binary forms are permitted provided that: (1) source distributions retain
8: * this entire copyright notice and comment, and (2) distributions including
9: * binaries display the following acknowledgement: This product includes
10: * software developed by the University of California, Berkeley and its
11: * contributors'' in the documentation or other materials provided with the
12: * distribution and in all advertising materials mentioning features or use
13: * of this software. Neither the name of the University nor the names of
14: * its contributors may be used to endorse or promote products derived from
15: * this software without specific prior written permission.
16: * THIS SOFTWARE IS PROVIDED AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
17: * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
18: * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
19: *
20: * @(#)tcp_timer.h 7.8 (Berkeley) 6/28/90
21: */
22:
23: /*
24: * Definitions of the TCP timers. These timers are counted
25: * down PR_SLOWHZ times a second.
26: */
27: #define TCPT_NTIMERS 4
28:
29: #define TCPT_REXMT 0 /* retransmit */
30: #define TCPT_PERSIST 1 /* retransmit persistance */
31: #define TCPT_KEEP 2 /* keep alive */
32: #define TCPT_2MSL 3 /* 2*msl quiet time timer */
33:
34: /*
35: * The TCPT_REXMT timer is used to force retransmissions.
36: * The TCP has the TCPT_REXMT timer set whenever segments
37: * have been sent for which ACKs are expected but not yet
38: * received. If an ACK is received which advances tp->snd_una,
39: * then the retransmit timer is cleared (if there are no more
40: * outstanding segments) or reset to the base value (if there
41: * are more ACKs expected). Whenever the retransmit timer goes off,
42: * we retransmit one unacknowledged segment, and do a backoff
43: * on the retransmit timer.
44: *
45: * The TCPT_PERSIST timer is used to keep window size information
46: * flowing even if the window goes shut. If all previous transmissions
47: * have been acknowledged (so that there are no retransmissions in progress),
48: * and the window is too small to bother sending anything, then we start
49: * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
50: * we go to transmit state. Otherwise, at intervals send a single byte
51: * into the peer's window to force him to update our window information.
52: * We do this at most as often as TCPT_PERSMIN time intervals,
53: * but no more frequently than the current estimate of round-trip
54: * packet time. The TCPT_PERSIST timer is cleared whenever we receive
55: * a window update from the peer.
56: *
57: * The TCPT_KEEP timer is used to keep connections alive. If an
58: * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
59: * but not yet established, then we drop the connection. Once the connection
60: * is established, if the connection is idle for TCPTV_KEEP_IDLE time
61: * (and keepalives have been enabled on the socket), we begin to probe
62: * the connection. We force the peer to send us a segment by sending:
63: * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
64: * This segment is (deliberately) outside the window, and should elicit
65: * an ack segment in response from the peer. If, despite the TCPT_KEEP
66: * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
67: * amount of time probing, then we drop the connection.
68: */
69:
70: #define TCP_TTL 60 /* default time to live for TCP segs */
71: /*
72: * Time constants.
73: */
74: #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */
75: #define TCPTV_SRTTBASE 0 /* base roundtrip time;
76: if 0, no idea yet */
77: #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
78:
79: #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */
80: #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */
81:
82: #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */
83: #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */
84: #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */
85: #define TCPTV_KEEPCNT 8 /* max probes before drop */
86:
87: #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */
88: #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */
89:
90: #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
91:
92: #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
93:
94: #ifdef TCPTIMERS
95: char *tcptimers[] =
96: { "REXMT", "PERSIST", "KEEP", "2MSL" };
97: #endif
98:
99: /*
100: * Force a time value to be in a certain range.
101: */
102: #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
103: (tv) = (value); \
104: if ((tv) < (tvmin)) \
105: (tv) = (tvmin); \
106: else if ((tv) > (tvmax)) \
107: (tv) = (tvmax); \
108: }
109:
110: #ifdef KERNEL
111: extern int tcp_keepidle; /* time before keepalive probes begin */
112: extern int tcp_keepintvl; /* time between keepalive probes */
113: extern int tcp_maxidle; /* time to drop after starting probes */
114: extern int tcp_ttl; /* time to live for TCP segs */
115: extern int tcp_backoff[];
116: #endif
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