Commit | Line | Data |
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4aed14e3 | 1 | /* tcp_timer.h 4.3 81/12/12 */ |
1c4a70b8 BJ |
2 | |
3 | /* | |
4 | * Definitions of the TCP timers. These timers are counted | |
5 | * down PR_SLOWHZ times a second. | |
6 | */ | |
7 | #define TCPT_NTIMERS 4 | |
8 | ||
9 | #define TCPT_REXMT 0 /* retransmit */ | |
405c9168 BJ |
10 | #define TCPT_PERSIST 1 /* retransmit persistance */ |
11 | #define TCPT_KEEP 2 /* keep alive */ | |
12 | #define TCPT_2MSL 3 /* 2*msl quiet time timer */ | |
13 | ||
14 | /* | |
15 | * The TCPT_REXMT timer is used to force retransmissions. | |
16 | * The TCP has the TCPT_REXMT timer set whenever segments | |
17 | * have been sent for which ACKs are expected but not yet | |
18 | * received. If an ACK is received which advances tp->snd_una, | |
19 | * then the retransmit timer is cleared (if there are no more | |
20 | * outstanding segments) or reset to the base value (if there | |
21 | * are more ACKs expected). Whenever the retransmit timer goes off, | |
22 | * we retransmit all unacknowledged segments, and do an exponential | |
23 | * backoff on the retransmit timer. | |
24 | * | |
25 | * The TCPT_PERSIST timer is used to keep window size information | |
26 | * flowing even if the window goes shut. If an output is attempted when there | |
27 | * is data ready to transmit, but nothing gets sent because the window | |
28 | * is shut, then we start the TCPT_PERSIST timer, and at intervals | |
29 | * send a single byte into the peers window to force him to update | |
30 | * our window information. We do this at most as often as TCPT_PERSMIN | |
31 | * time intervals, but no more frequently than the current estimate of | |
32 | * round-trip packet time. The TCPT_PERSIST timer is cleared whenever | |
33 | * we receive a window update from the peer. | |
34 | * | |
35 | * The TCPT_KEEP timer is used to keep connections alive. If an | |
36 | * connection is idle (no segments received) for TCPTV_KEEP amount of time, | |
37 | * but not yet established, then we drop the connection. If the connection | |
38 | * is established, then we force the peer to send us a segment by sending: | |
39 | * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> | |
40 | * This segment is (deliberately) outside the window, and should elicit | |
41 | * an ack segment in response from the peer. If, despite the TCPT_KEEP | |
42 | * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE | |
43 | * amount of time, then we drop the connection. | |
44 | */ | |
1c4a70b8 | 45 | |
4aed14e3 | 46 | #define TCP_TTL 15 /* time to live for TCP segs */ |
1c4a70b8 | 47 | /* |
405c9168 | 48 | * Time constants. |
1c4a70b8 | 49 | */ |
4aed14e3 | 50 | #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime */ |
405c9168 | 51 | #define TCPTV_SRTTBASE ( 1*PR_SLOWHZ) /* base roundtrip time */ |
4aed14e3 | 52 | #define TCPTV_KEEP ( 60*PR_SLOWHZ) /* keep alive - 1 min */ |
405c9168 | 53 | #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ |
1c4a70b8 | 54 | |
405c9168 BJ |
55 | #define TCPTV_MAXIDLE ( 4*TCPTV_KEEP) /* maximum allowable idle |
56 | time before drop conn */ | |
1c4a70b8 | 57 | |
405c9168 | 58 | #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ |
4aed14e3 | 59 | #define TCPTV_MAX (120*PR_SLOWHZ) /* maximum allowable value */ |
1c4a70b8 BJ |
60 | |
61 | #ifdef TCPTIMERS | |
62 | char *tcptimers[] = | |
405c9168 | 63 | { "REXMT", "KEEP", "PERSIST", "2MSL" }; |
1c4a70b8 | 64 | #endif |
405c9168 BJ |
65 | |
66 | /* | |
67 | * Retransmission smoothing constants. | |
68 | * Smoothed round trip time is updated by | |
69 | * tp->t_srtt = (tcp_alpha * tp->t_srtt) + ((1 - tcp_alpha) * tp->t_rtt) | |
70 | * each time a new value of tp->t_rtt is available. The initial | |
71 | * retransmit timeout is then based on | |
72 | * tp->t_timer[TCPT_REXMT] = tcp_beta * tp->t_srtt; | |
73 | * limited, however to be at least TCPTV_REXMTLO and at most TCPTV_REXMTHI. | |
74 | */ | |
75 | float tcp_alpha, tcp_beta; | |
76 | ||
77 | /* | |
78 | * Initial values of tcp_alpha and tcp_beta. | |
79 | * These are conservative: averaging over a long | |
80 | * period of time, and allowing for large individual deviations from | |
81 | * tp->t_srtt. | |
82 | */ | |
83 | #define TCP_ALPHA 0.9 | |
84 | #define TCP_BETA 2.0 | |
85 | ||
86 | /* | |
87 | * Force a time value to be in a certain range. | |
88 | */ | |
4aed14e3 | 89 | #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ |
405c9168 BJ |
90 | (tv) = (value); \ |
91 | if ((tv) < (tvmin)) \ | |
92 | (tv) = (tvmin); \ | |
93 | if ((tv) > (tvmax)) \ | |
4aed14e3 BJ |
94 | (tv) = (tvmax); \ |
95 | } |