The Research On Threshold Constrained And TCP-Friendly Congestion Control Mechanisms For Multimedia Streaming Applications

Multimedia streaming (MS) applications have been rapidly increased in recent years over Internet. Current MS applications still lack efficient congestion control mechanisms, then they compete unfairly bandwidth with TCP flows. So, the research on "TCP-friendly" congestion control mechanisms for MS applications is a hotspot of research in the present computer network area.Many proposed TCP-friendly congestion control mechanisms are normally short of consideration about the threshold-constrained characteristic of MS, so that they are not preferably fit for the MS application. In this paper, on the basis of theory of model-based TCP-friendly congesion control, we increase the consideration of threshold-constrained characteristic of MS, and pay much attention on the research of trade of between TCP-friendliness and such characteristic.We compare the current typical TCP-friendly congestion control mechanisms, and put much emphasis on the TFRC mechanism which is not consider about the the MS's threshold constrained characteristic, and propose a threshold constrained rate control mechanisms for MS, called TCRC. This mechanism introduce the minimun rate constrained technology and transient state timer, the result show that, TCRC will be free of the disturb of temporary congestion, guarantee the effeciency of MS applications; at the same time, TCRC prevent data stream from aggravating the persistent congestion; and TCRC can get similar TCP-friendliness to TFRC in stable state.We also proposed a improved TCRC edition under the multiplexing circumstance, called MTCRC (Multiplexing-TCRC). We introduce the technology of the probabilistic based random experiment, so that the aggregation of multiple MTCRC flows behaves in a TCP-friendly manner. Results show that: in the low loss rate circumstances, MTCRC have the same good TCP-friendliness with TFRC; while in high loss rate circumstances, MTCRC are better than TFRC is the TCP-friendly aspect; and MTCRC can assure that the sending rate is above the minimun rate in the running time, so the MS application can be available.In a word, TCRC and MTCRC resolve soundly the tradeoff between the minimum rate threshold and the TCP-friendliness. The simulation results in ns-2 simulator show that these two protocols have similar TCP-friendliness with TFRC,while they enhance functions for the threshold-constrained characteristic of MS. So they are more suitable for MS than TFRC.