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rtt.h revision 1.1.1.2 
      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