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 */ 49 struct 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 extern int RTT_MIN_TIMEOUT; 60 /** max retransmit timeout value, in milliseconds */ 61 extern int RTT_MAX_TIMEOUT; 62 63 /** 64 * Initialize RTT estimators. 65 * @param rtt: The structure. Caller is responsible for allocation of it. 66 */ 67 void 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 */ 74 int 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 */ 82 int 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 */ 89 int 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 */ 96 void rtt_update(struct rtt_info* rtt, int ms); 97 98 /** 99 * Update the statistics with a new timeout 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 */ 105 void rtt_lost(struct rtt_info* rtt, int orig); 106 107 #endif /* UTIL_RTT_H */ 108