TFRC USED FOR VIDEO TRANSMISSION

A very important issue on video transmission is high fluctuations and oscillations which may damage the video transmission, which demands smooth transmission rates. Most video algorithms such as MPEG2 utilize the three major frame types (I-frames, P-frames, B-frames). The video bit rate tends to vary according to the complexity of the frame data, for example an I-frame would be more complex compared to a P-frame as it results in more bits after compression. The same also applies to scene changes and high motion scenes in a video sequence as they tend to incur a higher prediction error which results in a lower compression efficiency. Thus a typical video bit rate will have occasional “pulses”. A smoothed transmission rate will reduce these “pulses” and ends up affecting the video quality. To prevent oscillatory behavior in environments with a low degree of statistical multiplexing it is useful to modify sender’s transmit rate to provide congestion avoidance behavior by reducing the transmit rate as the queuing delay (and hence RTT) increases. To do this the sender maintains an estimate of the long-term RTT and modifies its sending rate depending on how the most recent sample of the RTT differs from this value. The long-term sample is R_sqmean, and is set as follows: