On the Delays in Time-Varying Networks: Does Larger Service-Rate Variance Imply Larger Delays?
On the Delays in Time-Varying Networks: Does Larger Service-Rate Variance Imply Larger Delays?
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关于时变网络的延迟：较大的服务速率差异是否意味着较大的延迟？
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Patrick Thiran
中科院分区：
文献类型：
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作者：
Sébastien Henri;S. Shneer;Patrick Thiran
在所有网络中，链路或路由容量由于多种原因而波动，例如，无线信道上的衰落和多径效应、共享介质上的干扰和竞争用户、WAN路由器中的变化负载、电力线信道上的阻抗变化。这些波动严重影响分组延迟。本文研究了时变网络中的时滞。直观地说，我们预计，对于一个给定的平均服务速率，增加服务速率的可变性产生更大的延迟。我们发现情况并非总是如此。使用排队模型，包括随时间变化的服务率，我们表明，对于某些到达率，具有较大的服务率方差的队列提供较小的平均延迟比具有相同的平均服务率和较低的服务率方差的队列。我们还验证了无线测试平台上的这些发现。然后，我们研究的条件下，同时使用两个独立的路径有助于延迟，例如，在混合网络中，这两个路径使用不同的物理层技术。我们表明，使用两条路径并不总是更好，特别是对于低到达率。我们还表明，两条路径之间的最佳流量分配取决于到达率。
In all networks, link or route capacities fluctuate for multiple reasons, e.g., fading and multi-path effects on wireless channels, interference and contending users on a shared medium, varying loads in WAN routers, impedance changes on power-line channels. These fluctuations severely impact packet delays. In this paper, we study delays in time-varying networks. Intuitively, we expect that for a given average service rate, an increased service rate variability yields larger delays. We find that this is not always the case. Using a queuing model that includes time-varying service rates, we show that for certain arrival rates, a queue with larger service rate variance offers smaller average delays than a queue with the same average service rate and lower service rate variance. We also verify these findings on a wireless testbed. We then study the conditions under which using simultaneously two independent paths helps in terms of delays, for example, in hybrid networks where the two paths use different physical layer technologies. We show that using two paths is not always better, in particular for low arrival rates. We also show that the optimal traffic splitting between the two paths depends on the arrival rate.