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8ae0e4b4 | 1 | /* |
0880b18e | 2 | * Copyright (c) 1982, 1986 Regents of the University of California. |
8ae0e4b4 KM |
3 | * All rights reserved. The Berkeley software License Agreement |
4 | * specifies the terms and conditions for redistribution. | |
5 | * | |
0880b18e | 6 | * @(#)tcp_timer.h 7.1 (Berkeley) %G% |
8ae0e4b4 | 7 | */ |
1c4a70b8 BJ |
8 | |
9 | /* | |
10 | * Definitions of the TCP timers. These timers are counted | |
11 | * down PR_SLOWHZ times a second. | |
12 | */ | |
2f9fe2d6 | 13 | #define TCPT_NTIMERS 4 |
1c4a70b8 BJ |
14 | |
15 | #define TCPT_REXMT 0 /* retransmit */ | |
405c9168 BJ |
16 | #define TCPT_PERSIST 1 /* retransmit persistance */ |
17 | #define TCPT_KEEP 2 /* keep alive */ | |
18 | #define TCPT_2MSL 3 /* 2*msl quiet time timer */ | |
19 | ||
20 | /* | |
21 | * The TCPT_REXMT timer is used to force retransmissions. | |
22 | * The TCP has the TCPT_REXMT timer set whenever segments | |
23 | * have been sent for which ACKs are expected but not yet | |
24 | * received. If an ACK is received which advances tp->snd_una, | |
25 | * then the retransmit timer is cleared (if there are no more | |
26 | * outstanding segments) or reset to the base value (if there | |
27 | * are more ACKs expected). Whenever the retransmit timer goes off, | |
6209c5c4 MK |
28 | * we retransmit one unacknowledged segment, and do a backoff |
29 | * on the retransmit timer. | |
405c9168 BJ |
30 | * |
31 | * The TCPT_PERSIST timer is used to keep window size information | |
bc8e4818 BJ |
32 | * flowing even if the window goes shut. If all previous transmissions |
33 | * have been acknowledged (so that there are no retransmissions in progress), | |
6209c5c4 MK |
34 | * and the window is too small to bother sending anything, then we start |
35 | * the TCPT_PERSIST timer. When it expires, if the window is nonzero, | |
36 | * we go to transmit state. Otherwise, at intervals send a single byte | |
37 | * into the peer's window to force him to update our window information. | |
38 | * We do this at most as often as TCPT_PERSMIN time intervals, | |
39 | * but no more frequently than the current estimate of round-trip | |
40 | * packet time. The TCPT_PERSIST timer is cleared whenever we receive | |
41 | * a window update from the peer. | |
405c9168 BJ |
42 | * |
43 | * The TCPT_KEEP timer is used to keep connections alive. If an | |
44 | * connection is idle (no segments received) for TCPTV_KEEP amount of time, | |
45 | * but not yet established, then we drop the connection. If the connection | |
46 | * is established, then we force the peer to send us a segment by sending: | |
47 | * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> | |
48 | * This segment is (deliberately) outside the window, and should elicit | |
49 | * an ack segment in response from the peer. If, despite the TCPT_KEEP | |
50 | * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE | |
51 | * amount of time, then we drop the connection. | |
52 | */ | |
1c4a70b8 | 53 | |
99d13dad | 54 | #define TCP_TTL 30 /* time to live for TCP segs */ |
1c4a70b8 | 55 | /* |
405c9168 | 56 | * Time constants. |
1c4a70b8 | 57 | */ |
6209c5c4 | 58 | #define TCPTV_MSL ( 15*PR_SLOWHZ) /* max seg lifetime */ |
7668259e MK |
59 | #define TCPTV_SRTTBASE 0 /* base roundtrip time; |
60 | if 0, no idea yet */ | |
6a4fd140 | 61 | #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */ |
e8355345 | 62 | |
bc8e4818 | 63 | #define TCPTV_KEEP ( 45*PR_SLOWHZ) /* keep alive - 45 secs */ |
405c9168 | 64 | #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ |
1c4a70b8 | 65 | |
bc8e4818 | 66 | #define TCPTV_MAXIDLE ( 8*TCPTV_KEEP) /* maximum allowable idle |
405c9168 | 67 | time before drop conn */ |
1c4a70b8 | 68 | |
405c9168 | 69 | #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ |
8e65fd66 BJ |
70 | #define TCPTV_MAX ( 30*PR_SLOWHZ) /* maximum allowable value */ |
71 | ||
72 | #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ | |
1c4a70b8 | 73 | |
6209c5c4 | 74 | #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ |
fd5dc5f0 | 75 | |
1c4a70b8 BJ |
76 | #ifdef TCPTIMERS |
77 | char *tcptimers[] = | |
2f9fe2d6 | 78 | { "REXMT", "PERSIST", "KEEP", "2MSL" }; |
1c4a70b8 | 79 | #endif |
405c9168 BJ |
80 | |
81 | /* | |
82 | * Retransmission smoothing constants. | |
83 | * Smoothed round trip time is updated by | |
84 | * tp->t_srtt = (tcp_alpha * tp->t_srtt) + ((1 - tcp_alpha) * tp->t_rtt) | |
85 | * each time a new value of tp->t_rtt is available. The initial | |
86 | * retransmit timeout is then based on | |
87 | * tp->t_timer[TCPT_REXMT] = tcp_beta * tp->t_srtt; | |
e8355345 | 88 | * limited, however to be at least TCPTV_MIN and at most TCPTV_MAX. |
405c9168 BJ |
89 | */ |
90 | float tcp_alpha, tcp_beta; | |
91 | ||
92 | /* | |
93 | * Initial values of tcp_alpha and tcp_beta. | |
94 | * These are conservative: averaging over a long | |
95 | * period of time, and allowing for large individual deviations from | |
96 | * tp->t_srtt. | |
97 | */ | |
98 | #define TCP_ALPHA 0.9 | |
99 | #define TCP_BETA 2.0 | |
100 | ||
101 | /* | |
102 | * Force a time value to be in a certain range. | |
103 | */ | |
4aed14e3 | 104 | #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ |
405c9168 BJ |
105 | (tv) = (value); \ |
106 | if ((tv) < (tvmin)) \ | |
107 | (tv) = (tvmin); \ | |
108 | if ((tv) > (tvmax)) \ | |
4aed14e3 BJ |
109 | (tv) = (tvmax); \ |
110 | } |