rtt.h revision 269257 
1/*
2 * util/rtt.h - UDP round trip time estimator for resend timeouts.
3 *
4 * Copyright (c) 2007, NLnet Labs. All rights reserved.
5 *
6 * This software is open source.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * Redistributions of source code must retain the above copyright notice,
13 * this list of conditions and the following disclaimer.
14 *
15 * Redistributions in binary form must reproduce the above copyright notice,
16 * this list of conditions and the following disclaimer in the documentation
17 * and/or other materials provided with the distribution.
18 *
19 * Neither the name of the NLNET LABS nor the names of its contributors may
20 * be used to endorse or promote products derived from this software without
21 * specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
26 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
27 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
29 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
30 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
31 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
32 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34 */
35
36/**
37 * \file
38 *
39 * This file contains a data type and functions to help estimate good
40 * round trip times for UDP resend timeout values.
41 */
42
43#ifndef UTIL_RTT_H
44#define UTIL_RTT_H
45
46/**
47 * RTT information. Keeps packet Round Trip Time.
48 */
49struct rtt_info {
50	/** smoothed rtt estimator, in milliseconds */
51	int srtt;
52	/** smoothed mean deviation, in milliseconds */
53	int rttvar;
54	/** current RTO in use, in milliseconds */
55	int rto;
56};
57
58/** min retransmit timeout value, in milliseconds */
59#define RTT_MIN_TIMEOUT	50
60/** max retransmit timeout value, in milliseconds */
61#define RTT_MAX_TIMEOUT 120000
62
63/**
64 * Initialize RTT estimators.
65 * @param rtt: The structure. Caller is responsible for allocation of it.
66 */
67void rtt_init(struct rtt_info* rtt);
68
69/**
70 * Get timeout to use for sending a UDP packet.
71 * @param rtt: round trip statistics structure.
72 * @return: timeout to use in milliseconds. Relative time value.
73 */
74int rtt_timeout(const struct rtt_info* rtt);
75
76/**
77 * Get unclamped timeout to use for server selection.
78 * Recent timeouts are reflected in the returned value.
79 * @param rtt: round trip statistics structure.
80 * @return: value to use in milliseconds.
81 */
82int rtt_unclamped(const struct rtt_info* rtt);
83
84/**
85 * RTT for valid responses. Without timeouts.
86 * @param rtt: round trip statistics structure.
87 * @return: value in msec.
88 */
89int rtt_notimeout(const struct rtt_info* rtt);
90
91/**
92 * Update the statistics with a new roundtrip estimate observation.
93 * @param rtt: round trip statistics structure.
94 * @param ms: estimate of roundtrip time in milliseconds.
95 */
96void rtt_update(struct rtt_info* rtt, int ms);
97
98/**
99 * Update the statistics with a new timout expired observation.
100 * @param rtt: round trip statistics structure.
101 * @param orig: original rtt time given for the query that timed out.
102 * 	Used to calculate the maximum responsible backed off time that
103 * 	can reasonably be applied.
104 */
105void rtt_lost(struct rtt_info* rtt, int orig);
106
107#endif /* UTIL_RTT_H */
108