[Japanese | Thesis | Researches in Minoh Lab | Minoh Lab]
We propose a method for allocating bandwidth for the transmission of multiple video data streams and receiving them stably based on dynamic priority.
Recently, network links have being replaced with more broad ones because of progress of network technologies and lower pricing of broad links. Streaming technology was developed for such network environment to transmit real-time continuous audio/video data.
On the Internet of today, available bandwidth for each user to receive streaming data is much different and bandwidth even for a user can also be varied with time. It is not realistic, therefore, to transmit a high volume of video data to every receiver with unique transmission rate.
There is a method that adjust transmission rate to fit to each receiver's available bandwidth by sending unicast streams. However, this method increases load of sender and fill a network link with redundant data.
Multicast techniques are suitable to reduce the load and avoid congestion of network. The receivers which have the same available bandwidth can consist of a group. A sender adjusts transmission rates to each group's bandwidth and transmits encoded data to the group. However, this method can't reduce load of the sender to encode data for each transmission rate.
To solve this problem, there is another method on which a sender encodes the video signal, splits it into multiple layers of data, and transmits them for each multicast group. The video quality of the receiver will be improved as the amount of the receiving layers. The reciver can change receiving rate by adding and dropping layers. So, the receiver can adjust receiving transmission rate to the available bandwidth. This control method is called as Receiver-driven Layered Multicast (RLM). In this method, initially, a receiver receives only lowest layer. And the receiver adds layers in turn. When network congestion exceeds a threshold and packet loss occurs by adding a layer, the receiver drops the highest layer.
However, RLM is not effective for multiple video data streams transmission, because each receiver's control for video data streams is done independently. That is, if packet loss occurs by adding a layer for a receiver, other receivers may drop layers without finding why packet loss occurs.
In this paper, we propose a new method to control bandwidth of multiple video data streams sent for each receiver. This method is based on RLM and utilizes priority information on the video quality from the senders. This priority specifies which video data stream should be received with high quality, and a receiver uses RLM for the video data stream. And other video data streams should be received with the lowest quality by selecting the lowest layer only. Therefore, the video data streams of low priority have constant transmission rate, so they don't influence adjusting transmission rate of the video data stream of high priority.
When priority is changed, the receivers who are receiving high priority video data stream before the priority change can take next action by selecting from the following two actions: One, the receivers switch their receiving video data stream to follow high priority video data stream. Therefore, even the receivers who have few decoders can always receive high quality video. The other, the receivers continue to receive the same video data stream after the priority change.
We evaluated our method by comparing with RLM, on multiple video data streams transmission. With our method, the video data stream of high priority obtained broader bandwidth. In addition, the receivers achieved stable receiving layers. Besides, after the priority change, our method can allocate broader bandwidth for the video data stream of high priority.