tailieunhanh - Lịch khai giảng trong các hệ thống thời gian thực P7

Packet Scheduling in Networks The networks under consideration in this chapter have a point-to-point interconnection structure; they are also called multi-hop networks and they use packet-switching techniques. In this case, guaranteeing time constraints is more complicated than for multiple access LANs, seen in the previous chapter, because we have to consider message delivery time constraints across multiple stages (or hops) in the network. In this type of network, there is only one source node for any network link, so the issue to be addressed is not only that of access to the medium but also that of packet scheduling. . | Scheduling in Real-Time Systems. Francis Cottet Joëlle Delacroix Claude Kaiser and Zoubir Mammeri Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84766-2 7 Packet Scheduling in Networks The networks under consideration in this chapter have a point-to-point interconnection structure they are also called multi-hop networks and they use packet-switching techniques. In this case guaranteeing time constraints is more complicated than for multiple access LANs seen in the previous chapter because we have to consider message delivery time constraints across multiple stages or hops in the network. In this type of network there is only one source node for any network link so the issue to be addressed is not only that of access to the medium but also that of packet scheduling. Introduction The advent of high-speed networks has introduced opportunities for new distributed applications such as video conferencing medical imaging remote command and control systems telephony distributed interactive simulation audio and video broadcasts games and so on. These applications have stringent performance requirements in terms of throughput delay jitter and loss rate Aras et al. 1994 . Whereas the guaranteed bandwidth must be large enough to accommodate motion video and audio streams at acceptable resolution the end-to-end delay must be small enough for interactive communication. In order to avoid breaks in continuity of audio and video playback delay jitter and loss must be sufficiently small. Current packet-switching networks such as the Internet offer only a best effort service where the performance of each user can degrade significantly when the network is overloaded. Thus there is a need to provide network services with performance guarantees and develop scheduling algorithms supporting these services. In this chapter we will be concentrating on issues related to packet scheduling to guarantee time constraints of messages particularly end-to-end deadlines and jitter constraints in