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/*
* util/rtt.c - UDP round trip time estimator for resend timeouts.
*
* Copyright (c) 2007, NLnet Labs. All rights reserved.
*
* This software is open source.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* Neither the name of the NLNET LABS nor the names of its contributors may
* be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/**
* \file
*
* This file contains a data type and functions to help estimate good
* round trip times for UDP resend timeout values.
*/
#include "config.h"
#include "util/rtt.h"
/** calculate RTO from rtt information */
static int
calc_rto(const struct rtt_info* rtt)
{
/* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */
int rto = rtt->srtt + 4*rtt->rttvar;
if(rto < RTT_MIN_TIMEOUT)
rto = RTT_MIN_TIMEOUT;
if(rto > RTT_MAX_TIMEOUT)
rto = RTT_MAX_TIMEOUT;
return rto;
}
void
rtt_init(struct rtt_info* rtt)
{
rtt->srtt = 0;
rtt->rttvar = 94;
rtt->rto = calc_rto(rtt);
/* default value from the book is 0 + 4*0.75 = 3 seconds */
/* first RTO is 0 + 4*0.094 = 0.376 seconds */
}
int
rtt_timeout(const struct rtt_info* rtt)
{
return rtt->rto;
}
int
rtt_unclamped(const struct rtt_info* rtt)
{
if(calc_rto(rtt) != rtt->rto) {
/* timeout fallback has happened */
return rtt->rto;
}
/* return unclamped value */
return rtt->srtt + 4*rtt->rttvar;
}
void
rtt_update(struct rtt_info* rtt, int ms)
{
int delta = ms - rtt->srtt;
rtt->srtt += delta / 8; /* g = 1/8 */
if(delta < 0)
delta = -delta; /* |delta| */
rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
rtt->rto = calc_rto(rtt);
}
void
rtt_lost(struct rtt_info* rtt, int orig)
{
/* exponential backoff */
/* if a query succeeded and put down the rto meanwhile, ignore this */
if(rtt->rto < orig)
return;
/* the original rto is doubled, not the current one to make sure
* that the values in the cache are not increased by lots of
* queries simultaneously as they time out at the same time */
orig *= 2;
if(rtt->rto <= orig) {
rtt->rto = orig;
if(rtt->rto > RTT_MAX_TIMEOUT)
rtt->rto = RTT_MAX_TIMEOUT;
}
}
int rtt_notimeout(const struct rtt_info* rtt)
{
return calc_rto(rtt);
}
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