In this paper we present a Quality of Service (QoS) management architecture for distributed multimedia applications in heterogeneous communication environments of wired and wireless networks. Gaps in network performance such as bandwidths and error rates between wired and wireless networks, as well as gaps in terminal performance in media handling between desktop computers and handheld computers, bring about heterogeneities. Furthermore, even performance gaps among various desktop computers cause heterogeneities. As a result of these heterogeneities in network and terminal performances and various user preferences, the QoS requirement from each receiver is different. Therefore, mechanisms that adjust and satisfy each QoS requirement are needed. We propose a proxy server called Communication Coordination Server (CCS), which intermediates a video server and a receiver and manages the QoS coordination. The CCS performs QoS admission, adjustment, and allocation mechanisms to satisfy the user's QoS requirement. Then transcoding is used to realize the allocated QoS, and it decodes the input video stream from the video server and encodes it within the CCS. A QoS mapping mechanism that translates application-level QoS into resource-level QoS is needed for the QoS admission. We also propose a new QoS mapping mechanism using spline functions that enables a continuous QoS translation. We have built a CCS prototype in our laboratory testbed, and have verified that the CCS can resolve the heterogeneities between the server and receiver by the QoS adjustment mechanism of the transcoding and the QoS admission.

We investigated performance of routing schemes in B-ISDN, for heterogeneous traffic flows under various bandwidths. In particular, we compared the simulated performance of these schemes by evaluating their blocking probabilities. To achieve high performance, these schemes use special kinds of routing algorithm, one which is pre-selection algorithm and one which is cyclic algorithm. We investigated the efficiency of the pre-selection algorithm and the robustness of the cyclic algorithm for nonuniform traffic and network resources. We found that these routing algorithm schemes can compensate for errors in resource design.

For distributed multimedia applications, the development of adaptive QoS (quality of service) management mechanisms is needed to guarantee various and changeable end-to-end QoS requirements. In this paper, we propose an adaptive QoS management framework based on multi-agent systems. In this framework, QoS management mechanisms are divided into two phases, the flow establishment and renegotiation phase and the media-transfer phase. An adaptation to system resource changes and various user requirements is accomplished by direct or indirect collaborations of the agents in each phase. In the flow establishment and renegotiation phase, application agents determine optimal resource allocation with QoS negotiations to maximize the total users' utility. In the media-transfer phase, stream agents collaborate to adjust each stream QoS reactively. In addition, personal agents help a novice user to specify stream QoS without any a priori knowledge of QoS. To make the interworking of agents tractable, a QoS mapping mechanism is needed to translate the QoS parameters from level to level, since the expression of QoS differs from level to level. As an example of multimedia application based on the proposed framework, a one-way video system is designed. The experimental results of computer simulation show the validity of the proposed framework.