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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 and use in source and binary forms are permitted
6: * provided that the above copyright notice and this paragraph are
7: * duplicated in all such forms and that any documentation,
8: * advertising materials, and other materials related to such
9: * distribution and use acknowledge that the software was developed
10: * by the University of California, Berkeley. The name of the
11: * University may not be used to endorse or promote products derived
12: * from this software without specific prior written permission.
13: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14: * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15: * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16: *
17: * @(#)tcp_timer.h 7.6 (Berkeley) 6/29/88
18: */
19:
20: /*
21: * Definitions of the TCP timers. These timers are counted
22: * down PR_SLOWHZ times a second.
23: */
24: #define TCPT_NTIMERS 4
25:
26: #define TCPT_REXMT 0 /* retransmit */
27: #define TCPT_PERSIST 1 /* retransmit persistance */
28: #define TCPT_KEEP 2 /* keep alive */
29: #define TCPT_2MSL 3 /* 2*msl quiet time timer */
30:
31: /*
32: * The TCPT_REXMT timer is used to force retransmissions.
33: * The TCP has the TCPT_REXMT timer set whenever segments
34: * have been sent for which ACKs are expected but not yet
35: * received. If an ACK is received which advances tp->snd_una,
36: * then the retransmit timer is cleared (if there are no more
37: * outstanding segments) or reset to the base value (if there
38: * are more ACKs expected). Whenever the retransmit timer goes off,
39: * we retransmit one unacknowledged segment, and do a backoff
40: * on the retransmit timer.
41: *
42: * The TCPT_PERSIST timer is used to keep window size information
43: * flowing even if the window goes shut. If all previous transmissions
44: * have been acknowledged (so that there are no retransmissions in progress),
45: * and the window is too small to bother sending anything, then we start
46: * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
47: * we go to transmit state. Otherwise, at intervals send a single byte
48: * into the peer's window to force him to update our window information.
49: * We do this at most as often as TCPT_PERSMIN time intervals,
50: * but no more frequently than the current estimate of round-trip
51: * packet time. The TCPT_PERSIST timer is cleared whenever we receive
52: * a window update from the peer.
53: *
54: * The TCPT_KEEP timer is used to keep connections alive. If an
55: * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
56: * but not yet established, then we drop the connection. Once the connection
57: * is established, if the connection is idle for TCPTV_KEEP_IDLE time
58: * (and keepalives have been enabled on the socket), we begin to probe
59: * the connection. We force the peer to send us a segment by sending:
60: * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
61: * This segment is (deliberately) outside the window, and should elicit
62: * an ack segment in response from the peer. If, despite the TCPT_KEEP
63: * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
64: * amount of time probing, then we drop the connection.
65: */
66:
67: #define TCP_TTL 30 /* default time to live for TCP segs */
68: /*
69: * Time constants.
70: */
71: #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */
72: #define TCPTV_SRTTBASE 0 /* base roundtrip time;
73: if 0, no idea yet */
74: #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */
75:
76: #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */
77: #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */
78:
79: #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */
80: #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */
81: #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */
82: #define TCPTV_KEEPCNT 8 /* max probes before drop */
83:
84: #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */
85: #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */
86:
87: #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
88:
89: #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
90:
91: #ifdef TCPTIMERS
92: char *tcptimers[] =
93: { "REXMT", "PERSIST", "KEEP", "2MSL" };
94: #endif
95:
96: /*
97: * Force a time value to be in a certain range.
98: */
99: #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \
100: (tv) = (value); \
101: if ((tv) < (tvmin)) \
102: (tv) = (tvmin); \
103: else if ((tv) > (tvmax)) \
104: (tv) = (tvmax); \
105: }
106:
107: #ifdef KERNEL
108: extern int tcp_keepidle; /* time before keepalive probes begin */
109: extern int tcp_keepintvl; /* time between keepalive probes */
110: extern int tcp_maxidle; /* time to drop after starting probes */
111: extern int tcp_ttl; /* time to live for TCP segs */
112: extern int tcp_backoff[];
113: #endif
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