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      1 /*
      2  * libjingle
      3  * Copyright 2011, Google Inc.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions are met:
      7  *
      8  *  1. Redistributions of source code must retain the above copyright notice,
      9  *     this list of conditions and the following disclaimer.
     10  *  2. Redistributions in binary form must reproduce the above copyright notice,
     11  *     this list of conditions and the following disclaimer in the documentation
     12  *     and/or other materials provided with the distribution.
     13  *  3. The name of the author may not be used to endorse or promote products
     14  *     derived from this software without specific prior written permission.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
     17  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     18  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
     19  * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     20  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     21  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
     22  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     23  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
     24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
     25  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     26  */
     27 
     28 #ifndef TALK_BASE_BANDWIDTHSMOOTHER_H_
     29 #define TALK_BASE_BANDWIDTHSMOOTHER_H_
     30 
     31 #include "talk/base/rollingaccumulator.h"
     32 #include "talk/base/timeutils.h"
     33 
     34 namespace talk_base {
     35 
     36 // The purpose of BandwidthSmoother is to smooth out bandwidth
     37 // estimations so that 'trstate' messages can be triggered when we
     38 // are "sure" there is sufficient bandwidth.  To avoid frequent fluctuations,
     39 // we take a slightly pessimistic view of our bandwidth.  We only increase
     40 // our estimation when we have sampled bandwidth measurements of values
     41 // at least as large as the current estimation * percent_increase
     42 // for at least time_between_increase time.  If a sampled bandwidth
     43 // is less than our current estimation we immediately decrease our estimation
     44 // to that sampled value.
     45 // We retain the initial bandwidth guess as our current bandwidth estimation
     46 // until we have received (min_sample_count_percent * samples_count_to_average)
     47 // number of samples. Min_sample_count_percent must be in range [0, 1].
     48 class BandwidthSmoother {
     49  public:
     50   BandwidthSmoother(int initial_bandwidth_guess,
     51                     uint32 time_between_increase,
     52                     double percent_increase,
     53                     size_t samples_count_to_average,
     54                     double min_sample_count_percent);
     55 
     56   // Samples a new bandwidth measurement.
     57   // bandwidth is expected to be non-negative.
     58   // returns true if the bandwidth estimation changed
     59   bool Sample(uint32 sample_time, int bandwidth);
     60 
     61   int get_bandwidth_estimation() const {
     62     return bandwidth_estimation_;
     63   }
     64 
     65  private:
     66   uint32 time_between_increase_;
     67   double percent_increase_;
     68   uint32 time_at_last_change_;
     69   int bandwidth_estimation_;
     70   RollingAccumulator<int> accumulator_;
     71   double min_sample_count_percent_;
     72 };
     73 
     74 }  // namespace talk_base
     75 
     76 #endif  // TALK_BASE_BANDWIDTHSMOOTHER_H_
     77