int bytesTotal = 0;
int bytesPerSecond = 0;
DateTime startTime = DateTime.Now;
	
do {
  bytesRead = receiveStream.Read( ... );
  bytesTotal += bytesRead;
  bytesPerSecond = bytesTotal / (DateTime.Now - startTime).TotalSeconds;
	
  ...
} while(bytesRead > 0);

public class RunningAverage {
  public RunningAverage(int samplesCount) {
    samples = new Sample[samplesCount];
    for (int i = 0; i < samplesCount; i++)
      samples[i] = new Sample( );
    currentSample = 0;
  }
	
  class Sample {
    public Sample( ) { }
	
    public Sample(double weighting, double measuredValue) {
      Set(weighting, measuredValue);
    }
	
    public void Set(double weighting, double measuredValue) {
      this.weighting = weighting;
      this.measuredValue = measuredValue;
      isValid = true;
    }
	
    private double weighting;
    public double Weighting { get { return weighting; } }
	
    private double measuredValue;
    public double MeasuredValue { get { return measuredValue; } }
	
    private bool isValid;
    public bool IsValid { get { return isValid; } }
  }
	
  Sample[] samples;
  int currentSample;
	
  public void AddSample(double weighting, double measuredValue) {
    samples[currentSample++].Set(weighting, measuredValue);
    if (currentSample >= samples.Length)
      currentSample = 0;
  }
	
  public double GetCurrentAverage( ) {
    double totalValue = 0;
    double totalWeighting = 0;
    foreach (Sample sample in samples)
      if (sample.IsValid) {
        totalValue += sample.MeasuredValue;
        totalWeighting += sample.Weighting;
      }
    return totalValue / totalWeighting;
  }
}

RunningAverage average = new RunningAverage(100);
DateTime timeStamp = DateTime.Now;
	
do {
  bytesRead = receiveStream.Read( ... );
  DateTime newTimeStamp = DateTime.Now;
  average.AddSample(newTimeStamp.TotalSeconds - timeStamp.TotalSeconds, bytesRead);
  timeStamp = newTimeStamp;
  // access average.GetCurrentAverage() if needed
	
  ...
} while(bytesRead > 0);