Shuji Tasaka

A synchronization mechanism for continuous media in multimedia communications

This paper proposes a media synchronization mechanism which adjusts the output timing among stored continuous media streams in multimedia communications. The proposed method consists of intra-stream and inter-stream synchronization mechanisms. The inter-stream synchronization control is performed after the intra-stream synchronization control. Then, whether the intra-stream synchronization is still maintained or not is checked. The mechanism con be used in networks which have unknown delay bounds, and it does not suppose periodical generation of media units such as video frames. It also deals with two types of media streams depending on how strictly to synchronize media streams: tightly-coupled media streams and loosely-coupled media streams. Furthermore, we enhance the mechanism to support real-time-inputted media streams as in TV conferencing.

A group synchronization mechanism for stored media in multicast communications

This paper proposes a group synchronization mechanism, which synchronizes slave destinations with the master destination, for stored media in multicast communications. At the master and slave destinations, intra-stream and inter-stream synchronization mechanisms which were proposed by the authors are employed to output the master media stream and slave media streams synchronously. We achieve group synchronization by adjusting the output timing of the master media stream at each slave destination to that at the master destination. We also deal with traffic control by media scaling and control of joining an in-progress multicast group. Furthermore, the paper presents experimental results using an ATM network. It shows the validity of the mechanism and illustrates the influence of parameters on the system performance.

Integrated video and data transmission in the TDD ALOHA-reservation wireless LAN

The proliferation of personal communication networks and an increasing demand for multimedia communications stimulate the development of wireless multimedia networking. This paper considers integrated variable bit-rate video and data transmission over a wireless LAN which consists of a single base station and many terminals. The performance of a LAN with the TDD ALOHA-reservation MAC protocol is evaluated through simulation in the presence of transmission errors. Selective-repeat ARQ control is carried out over both video and data. Regarding video traffic, we also examine the applicability of a packet discard technique, which discards packets with elapsed time of more than a threshold value. The simulation results show that the ARQ is indispensable to video as well as data, while the packet discard technique is effective just for high bit-error rates at which only poor performance is achieved.

Measured performance of a live media synchronization mechanism in an ATM network

This paper proposes a media synchronization mechanism for live media streams. The mechanism can also handle stored media streams by changing the parameter values. The authors have implemented the mechanism on a lip-synch experimental system using an ATM network. Live video of a speaker and his voice realtime-inputted at a source workstation are transferred separately on two distinct TCP connections, and then they are synchronized and outputted at a destination workstation. This paper also evaluates the system performance such as the mean square error of synchronization, average output rate, and the average delay time.

Performance measurement of a stored media synchronization mechanism: quick recovery scheme

This paper presents measured performance of a media synchronization mechanism which was proposed by the authors, focusing on the quick recovery scheme. The mechanism has been implemented for lip-synch on an experimental system, which consists of a source-destination workstation pair connected via an FDDI network. Video of a speaker and her voice stored in the source workstation are transferred to the destination workstation, and then they are synchronized and outputted at the destination. Using the system, we have confirmed the validity of the mechanism. We clarify how to set the threshold and parameter values defined in the mechanism by evaluating its performance. We also demonstrate that the intra-stream synchronization control for each stream in addition to the inter-stream control necessary for high quality synchronization.

Stored media synchronization in wireless LANs

This paper proposes two schemes for synchronization of stored voice and video media units (MUs) in wireless LANs. The schemes, called nondistinctive and distinctive, are based on interleaving of the two kinds of MU. The former does not distinguish between voice and video MUs in the interleaved stream, while the latter does. To evaluate their performance and confirm the effectiveness in comparison with the scheme of no-control, we developed an experimental system using the ALTAIR wireless LAN. The mean square error of synchronization, total pause time, throughput and total output time of the three schemes were measured. As a result, we see that the control of intrastream synchronization is indispensable for heavy traffic and that the interleaving serves as an effective mechanism for inter-stream synchronization. Then, it is shown that the nondistinctive scheme with an appropriate size of the voice MU should be employed.

Single-stream versus multi-stream for live media synchronization

This paper presents a performance comparison between the single-stream and the multi-stream approaches for lip synchronization of live media (voice and video). The former transmits a single transport stream of interleaved voice and video, while the latter treats the two media as separate transport streams. Each approach has an option not to exert the synchronization control at the destination, which leads to four basic schemes. On an interconnected ATM-wireless LAN, we implemented the four basic schemes with RTP/RTCP on top of UDP and two variants which exercise dynamic resolution control of JPEG video. By the performance measurement of the six schemes, we compare them to identify and evaluate the advantages and disadvantages of each approach.

Congestion control for integrated video and data transmission in a wireless LAN

This paper studies two congestion control schemes for integrated variable bit-rate video and data transmission in a centrally controlled wireless LAN. One is a dynamic resolution control scheme which switches the spatial or temporal resolution of video according to the network loads; the other is a packet discard scheme which discards video packets with elapsed time of more than a threshold value. In addition to selective repeat ARQ control over both video and data, we apply the two schemes to video transmission separately or jointly. To examine the efficiency of the schemes, we carry out simulations using a sequence of real video frames obtained from a JPEG encoded movie. We also evaluate the video quality of the simulation output by subjective assessment. As a result, we find that the dynamic resolution control scheme is effective under high-load conditions and achieves better performance than the packet discard scheme. A combination of the two schemes provides no substantial improvement.

Performance evaluation of a dynamic video resolution control scheme in media-synchronized video and audio communications

This paper studies a congestion control scheme in integrated variable bit-rate (VBR) video, audio and data (e.g., image or text) communications, where each video stream is synchronized with the corresponding audio stream. When the audio and-video streams are output, media-synchronization control is performed. To avoid congestion, we employ a dynamic video resolution control scheme which dynamically changes the video encoding rate according to the network loads. By simulation, the paper evaluates the performance of the scheme in terms of throughput, loss rate, average delay, and mean square error of synchronization. Numerical results show the effectiveness of the scheme.