  In this paper, we propose a quality-centric congestion control for multimedia
streaming over IP networks, which we refer to as media-TCP. Unlike existing
congestion control schemes that adapt a user's sending rate merely to the
network condition, our solution adapts the sending rate to both the network
condition and the application characteristics by explicitly considering the
distortion impacts, delay deadlines, and interdependencies of different video
packet classes. Hence, our media-aware solution is able to provide differential
services for transmitting various packet classes and thereby, further improves
the multimedia streaming quality. We model this problem using a Finite-Horizon
Markov Decision Process (FHMDP) and determine the optimal congestion control
policy that maximizes the long-term multimedia quality, while adhering to the
horizon- TCP-friendliness constraint, which ensures long-term fairness with
existing TCP applications. We show that the FHMDP problem can be decomposed
into multiple optimal stopping problems, which admit a low-complexity
threshold-based solution. Moreover, unlike existing congestion control
approaches, which focus on maintaining throughput-based fairness among users,
the proposed media-TCP aims to achieve quality-based fairness among multimedia
users. We also derive sufficient conditions for multiple multimedia users to
achieve quality-based fairness using media-TCP congestion control. Our
simulation results show that the proposed media-TCP achieves more than 3dB
improvement in terms of PSNR over the conventional TCP congestion control
approaches, with the largest improvements observed for real-time streaming
applications requiring stringent playback delays.
