References 5. Conclusion

نویسندگان

  • G. v. Bochmann
  • A. Hafid
  • B. Kerherve
  • J. Gecsei
چکیده

27 the communication subsystem ; (2) they react only after the occurrence of end-to-end QoS violation ; and (3) they react to QoS violation by renegotiating a degraded QoS and thus they are restricted to applications that can accept a varying QoS. In this paper we presented an approach which allows to recover automatically from QoS violations, and only require user/application intervention (existing approaches) when the system has not enough resources to support the current load. The proposed approach consists of high level interactions between management entities and thus may be applied to an arbitrary system (several domains) with different adaptation and reservation schemes. A number of instantiations of the proposed schemes may be developed based on the characteristics of the environment (systems et applications). We have presented three schemes for QoS adaptation: the component resource reconfiguration (CRS), the resource reconfiguration scheme (RRS), and the delay recovery scheme (DRS). CRS allows to recover from any QoS violation by selecting one or more alternate components and by performing a user-transparent transition from the primary components to the alternative ones. RRS allows to recover from QoS violations, specifically delay, jitter, and loss rate violations, by changing the distribution of QoS levels that each component will support. It integrates, in a suitable way, the two possible approaches that can be used to deal with QoS violation: to maintain, if possible, the initially agreed QoS, and otherwise to initiate a renegotiation with the user/applica-tion. DRS allows to recover from delay violations of specific components for each individual data unit which is transmitted. The role of DRS is to avoid, if possible, end-to-end delay violation, but it introduces an important overhead. The proposed schemes, especially CRS, are able to support a graceful degradation. Indeed, when the QoS manager fails to find an alternate configuration which supports the initially agreed QoS, it may select a configuration which supports a lower QoS in a graceful way, e.g., continue playing black&white video instead of the initial color video. A scheme which supports the characteristics of RDS, RRS and CRS, may be more efficient. As an example, for the delay parameter, the following scenario may be used: (1) DRS is used to maintain end-to-end delay of each data unit. (2) If a component is in difficulty to supports its delay requirements, RRS is used to reconfig-ure the resource distribution of the components in a way to satisfy end-to-end delay …

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تاریخ انتشار 1997