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8ae0e4b4 KM |
1 | /* |
2 | * Copyright (c) 1982 Regents of the University of California. | |
3 | * All rights reserved. The Berkeley software License Agreement | |
4 | * specifies the terms and conditions for redistribution. | |
5 | * | |
6 | * @(#)tcp_timer.h 6.3 (Berkeley) %G% | |
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, | |
28 | * we retransmit all unacknowledged segments, and do an exponential | |
29 | * backoff on the retransmit timer. | |
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), | |
34 | * and the window is shut, then we start the TCPT_PERSIST timer, and at | |
35 | * intervals send a single byte into the peers window to force him to update | |
405c9168 BJ |
36 | * our window information. We do this at most as often as TCPT_PERSMIN |
37 | * time intervals, but no more frequently than the current estimate of | |
38 | * round-trip packet time. The TCPT_PERSIST timer is cleared whenever | |
39 | * we receive a window update from the peer. | |
40 | * | |
41 | * The TCPT_KEEP timer is used to keep connections alive. If an | |
42 | * connection is idle (no segments received) for TCPTV_KEEP amount of time, | |
43 | * but not yet established, then we drop the connection. If the connection | |
44 | * is established, then we force the peer to send us a segment by sending: | |
45 | * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> | |
46 | * This segment is (deliberately) outside the window, and should elicit | |
47 | * an ack segment in response from the peer. If, despite the TCPT_KEEP | |
48 | * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE | |
49 | * amount of time, then we drop the connection. | |
50 | */ | |
1c4a70b8 | 51 | |
4aed14e3 | 52 | #define TCP_TTL 15 /* time to live for TCP segs */ |
1c4a70b8 | 53 | /* |
405c9168 | 54 | * Time constants. |
1c4a70b8 | 55 | */ |
4aed14e3 | 56 | #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime */ |
7668259e MK |
57 | #define TCPTV_SRTTBASE 0 /* base roundtrip time; |
58 | if 0, no idea yet */ | |
bc8e4818 | 59 | #define TCPTV_KEEP ( 45*PR_SLOWHZ) /* keep alive - 45 secs */ |
405c9168 | 60 | #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ |
1c4a70b8 | 61 | |
bc8e4818 | 62 | #define TCPTV_MAXIDLE ( 8*TCPTV_KEEP) /* maximum allowable idle |
405c9168 | 63 | time before drop conn */ |
1c4a70b8 | 64 | |
405c9168 | 65 | #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ |
8e65fd66 BJ |
66 | #define TCPTV_MAX ( 30*PR_SLOWHZ) /* maximum allowable value */ |
67 | ||
68 | #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ | |
1c4a70b8 | 69 | |
fd5dc5f0 BJ |
70 | #define TCP_MAXRXTSHIFT 10 /* maximum retransmits */ |
71 | ||
1c4a70b8 BJ |
72 | #ifdef TCPTIMERS |
73 | char *tcptimers[] = | |
2f9fe2d6 | 74 | { "REXMT", "PERSIST", "KEEP", "2MSL" }; |
1c4a70b8 | 75 | #endif |
405c9168 BJ |
76 | |
77 | /* | |
78 | * Retransmission smoothing constants. | |
79 | * Smoothed round trip time is updated by | |
80 | * tp->t_srtt = (tcp_alpha * tp->t_srtt) + ((1 - tcp_alpha) * tp->t_rtt) | |
81 | * each time a new value of tp->t_rtt is available. The initial | |
82 | * retransmit timeout is then based on | |
83 | * tp->t_timer[TCPT_REXMT] = tcp_beta * tp->t_srtt; | |
84 | * limited, however to be at least TCPTV_REXMTLO and at most TCPTV_REXMTHI. | |
85 | */ | |
86 | float tcp_alpha, tcp_beta; | |
87 | ||
88 | /* | |
89 | * Initial values of tcp_alpha and tcp_beta. | |
90 | * These are conservative: averaging over a long | |
91 | * period of time, and allowing for large individual deviations from | |
92 | * tp->t_srtt. | |
93 | */ | |
94 | #define TCP_ALPHA 0.9 | |
95 | #define TCP_BETA 2.0 | |
96 | ||
97 | /* | |
98 | * Force a time value to be in a certain range. | |
99 | */ | |
4aed14e3 | 100 | #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ |
405c9168 BJ |
101 | (tv) = (value); \ |
102 | if ((tv) < (tvmin)) \ | |
103 | (tv) = (tvmin); \ | |
104 | if ((tv) > (tvmax)) \ | |
4aed14e3 BJ |
105 | (tv) = (tvmax); \ |
106 | } |