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+/*
+ * util/rtt.h - 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.
+ */
+
+#ifndef UTIL_RTT_H
+#define UTIL_RTT_H
+
+/**
+ * RTT information. Keeps packet Round Trip Time.
+ */
+struct rtt_info {
+	/** smoothed rtt estimator, in milliseconds */
+	int srtt;
+	/** smoothed mean deviation, in milliseconds */
+	int rttvar;
+	/** current RTO in use, in milliseconds */
+	int rto;
+};
+
+/** min retransmit timeout value, in milliseconds */
+#define RTT_MIN_TIMEOUT	50
+/** max retransmit timeout value, in milliseconds */
+#define RTT_MAX_TIMEOUT 120000
+
+/**
+ * Initialize RTT estimators.
+ * @param rtt: The structure. Caller is responsible for allocation of it.
+ */
+void rtt_init(struct rtt_info* rtt);
+
+/** 
+ * Get timeout to use for sending a UDP packet.
+ * @param rtt: round trip statistics structure.
+ * @return: timeout to use in milliseconds. Relative time value.
+ */
+int rtt_timeout(const struct rtt_info* rtt);
+
+/** 
+ * Get unclamped timeout to use for server selection.
+ * Recent timeouts are reflected in the returned value.
+ * @param rtt: round trip statistics structure.
+ * @return: value to use in milliseconds. 
+ */
+int rtt_unclamped(const struct rtt_info* rtt);
+
+/**
+ * RTT for valid responses. Without timeouts.
+ * @param rtt: round trip statistics structure.
+ * @return: value in msec.
+ */
+int rtt_notimeout(const struct rtt_info* rtt);
+
+/**
+ * Update the statistics with a new roundtrip estimate observation.
+ * @param rtt: round trip statistics structure.
+ * @param ms: estimate of roundtrip time in milliseconds.
+ */
+void rtt_update(struct rtt_info* rtt, int ms);
+
+/**
+ * Update the statistics with a new timout expired observation.
+ * @param rtt: round trip statistics structure.
+ * @param orig: original rtt time given for the query that timed out.
+ * 	Used to calculate the maximum responsible backed off time that
+ * 	can reasonably be applied.
+ */
+void rtt_lost(struct rtt_info* rtt, int orig);
+
+#endif /* UTIL_RTT_H */