In current Data Center Networks (DCNs), Equal- Cost MultiPath (ECMP) is used as the de-facto routing protocol. However, ECMP does not differentiate between short and long flows, the two main categories of flows depending on their duration (lifetime). This issue causes hot-spots in the network, affecting negatively the Flow Completion Time (FCT) and the throughput, the two key performance metrics in data center networks. Previous work on load balancing proposed solutions such as splitting long flows into short flows, using per-packet forwarding approaches, and isolating the paths of short and long flows. We propose DiffFlow, a new load balancing solution which detects long flows and forwards packets using Random Packet Spraying (RPS) with help of SDN, whereas the flows with small duration are forwarded with ECMP by default. The use of ECMP for short flows is reasonable, as it does not create the out-of-order problem; at the same time, RPS for long flows can efficiently help to load balancing the entire network, given that long flows represent most of the traffic in DCNs. The results show that our DiffFlow solution outperforms both the individual usage of either RPS or ECMP, while the overall throughput achieved is maintained at the level comparable to RPS.
The general classification of different requirements and solutions for short and long flows in DCN has been discussed in @cite_3 . Here, we provide an overview of solutions related specifically to multipath forwarding schemes in DCNs.
@cite_3
2064941967 2037572363 1481933765 1990837243
In this paper, we survey different existing schemes for the transmission of flows in Data Center Networks (DCNs). The transport of flows in DCNs must cope with the bandwidth demands of the traffic that a large number of data center applications generates and achieve high utilization of the data center infrastructure to make the data center financially viable. Traffic in DCNs roughly comprises short flows, which are generated by the Partition Aggregate model adopted by several applications and have sizes of a few kilobytes, and long flows, which are data for the operation and maintenance of the data center and have sizes on the order of megabytes. Short flows must be transmitted (or completed) as soon as possible or within a deadline, and long flows must be serviced with a minimum acceptable throughput. The coexistence of short and long flows may jeopardize achieving both performance objectives simultaneously. This challenge has motivated growing research on schemes for managing the transmission of flows in DCNs. We describe several recent schemes aimed at reducing the flow completion time in DCNs. We also present a summary of existing solutions for the incast traffic phenomenon. We provide a comparison and classification of the surveyed schemes, describe their advantages and disadvantages, and show the different trends for scheme design. For completeness, we describe some DCN architectures, discuss the traffic patterns of DCNs, and discuss why some existing versions of transport protocols may not be usable in DCNs. At the end, we discuss some of the identified research challenges. Many existing data center network (DCN) flow scheduling schemes minimize flow completion times (FCT) based on prior knowledge of flows and custom switch designs, making them hard to use in practice. This paper introduces, Pias, a practical flow scheduling approach that minimizes FCT with no prior knowledge using commodity switches. At its heart, Pias leverages multiple priority queues available in commodity switches to implement a Multiple Level Feedback Queue (MLFQ), in which a PIAS flow gradually demotes from higher-priority queues to lower-priority queues based on the bytes it has sent. In this way, short flows are prioritized over long flows, which enables Pias to emulate Shortest Job First (SJF) scheduling without knowing the flow sizes beforehand. Our preliminary evaluation shows that Pias significantly outperforms all existing information-agnostic solutions. It improves average FCT for short flows by up to 50 and 40 over DCTCP [3] and L2DCT [16]. Compared to an ideal information-aware DCN transport, p-Fabric [5], it only shows 4.9 performance degradation for short flows in a production datacenter workload. Internet service provider faces a daunting challenge in provisioning network efficiently. We introduce a proactive multipath routing scheme that tries to route traffic according to its built-in properties. Based on mathematical analysis, our approach disperses incoming traffic flows onto multiple paths according to path qualities. Long-lived flows are detected and migrated to the shortest path if their QoS could be guaranteed there. Suggesting nondisjoint path set, four types of dispersion policies are analyzed, and flow classification policy which relates flow trigger with link state update period is investigated. Simulation experiments show that our approach outperforms traditional single path routing significantly. In this paper, we evaluate the performance of per-packet load balancing in data center networks (DCNs). Throughput and flow completion time are considered among the main metrics to evaluate the performance of the transport of flows over the presence of long flows in a DCN. Load balancing in a DCN may benefit those performance metrics but also it may generate out-of-order packet delivery. We investigate the impact of out-of-order packet delivery on the throughput and flow completion time of long and short flows, respectively, in a DCN. Our simulations confirm the presence of out-of-order packet delivery in a DCN using per-packet load balancing. Simulation results also reveal that per-packet load balancing may yield smaller average flow completion time for short flows and larger average throughput for long flows than the single-path transport model used by TCP despite the presence of out-of-order packet delivery. As the delay difference between alternative paths decreases, the occurrence of out-of-order packet delivery in per-packet load balancing also decreases. Therefore, under the studied scenarios, the benefits of the per-packet load balancing prevail.