Estimation of Temporal Behavior in Distributed Systems

提出了一种适用于软实时分布式系统的网络体系结构。在该体系结构中，在网络的局域网部分采用固定数量的离散优先级等级的优先级调度。网络广域网段的分组调度和处理器调度采用EDF调度。提出了一种基于单跳局域网段时延约束的局域网段优先级分配算法，该算法由广域网段和处理机之间的时延分配和分组优先级分配决定。作为处理器调度，我们解析地推导了EDF调度中响应时间的估计方法。我们还提出了一种广域网段的分组调度算法ORC-GPS。该算法在控制时延的同时，能有效利用网络资源。ORC-GPS提供了比EDF和GPS更大的可调度区域。ORC-GPS是一种基于类的调度算法。调度参数是根据班级所需的最大延迟确定的。由于局域网段的优先级控制延时效果有限，不能改变一定的延迟值，所以广域网段的延时控制主要由广域网段控制，而局域网段的延时控制主要由优先级控制实现。ORC-GPS可以应用于该广域网段的时延控制。ORC-GPS参数是通过从总体允许的网络延迟中减去局域网部分的延迟而得到的剩余延迟来确定的。这样，就可以实现目标端到端的时延。

We proposed a network architecture for soft-real-time distributed systems. In the architecture, priority scheduling with fixed number of discrete priority levels available in VLAN header in Ethernet packets are used in LAN section of the network. Packet scheduling in WAN section of the network and processor scheduling adopt EDF scheduling. We proposed a priority assignment algorithm for LAN section based on delay constraint in one-hop LAN section which is determined from delay allocation to WAN section and processors, and on distribution of packet priority assignment in LAN section. As processor scheduling, we analytically derived estimation method for response time in EDF scheduling. We also proposed a packet scheduling algorithm called ORC-GPS for WAN section. The algorithm can utilize network efficiently while controlling delay. ORC-GPS provides larger schedulable region than both EDF and GPS. ORC-GPS is a class-based scheduling algorithm. Parameters for scheduling are determined on required maximum delays for classes. Since delay control by priority assignment in LAN section has only limited effect and we cannot vary delay from certain value, delay is mainly controlled in WAN section while delay control by priority classis performed in LAN section. ORC-GPS can be applied to this WAN section delay control. ORC-GPS parameters are determined from the residual delay derived by subtracting delay in LAN section from overall permissible network delay. In this way, the target end-to-end delay canbe realized.