unbound/util/rtt.h

   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 #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  */
  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 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  */
 105 void rtt_lost(struct rtt_info* rtt, int orig);
 106
 107 #endif /* UTIL_RTT_H */