Large-scale online services and distributed execution engines (i.e., MapReduce and Dryad) generate large volumes of traffic in data center networks. As a consequence, significant congestion can occur in the data center network. To the best of our knowledge, most existing approaches either focus on local congestionaware mechanisms, which have only a poor ability to handle asymmetry or use explicit congestion notification packets, which are difficult to implement directly in switch hardware. These methods are insufficient to solve the congestion problem. In this paper, we focus on a congestion-free routing strategy, resorting to the global view of the data center network in a software-defined networking controller. Specifically, a timeslot allocation was first conducted for the coming packets, and then the corresponding routing paths were computed for each packet. In view of the efficiency, the timeslot allocation algorithm follows a heuristic pattern, and the path selection is modeled as a bin-packing problem. Simulation results showed that the congestion-free routing strategy proposed here performs well in throughput, queuing, and end-to-end round-trip time.To design a congestion-free routing strategy, a discrete time-slotted system where the timeslot length can range from hundreds of milliseconds to minutes is considered [10,11]. In each timeslot t , a number of flows generated by the applications arrive at the data center, and each packet of flows must be forwarded to the destination without causing any congestion in the data center. Hence, a congestionfree routing strategy is designed by taking advantage of an SDN controller to monitor the traffic and has a central network control [12,13]. Consequently, the key design is to assign timeslots and routing paths for each packet. As shown in Figure 1, the SDN controller contains three main functions: timeslot allocation, path selection, and SDN communication. Through communicating with switches, the SDN controller determined overall network situations as well as informed switches of the network modification. Once an endpoint (source) called for a transmission, the operating system sent this demand to the SDN controller. The source provided the controller with two pieces CONGESTION-FREE ROUTING STRATEGY 5737
Timeslot allocation designWe consider a discrete time-slotted system where time is slotted. In timeslot t , each endpoint can transmit or receive at most one Maximum Transmission Unit (MTU)-sized packet. Thus, when a large amount of flow arrives at the data center network, the first task is to allocate transfer time for them to avoid congestion. Here, timeslot allocation was conducted at the packet level.A congestion-free routing strategy design should ensure that traffic can only be routed in a congestion-free way and that it will satisfy both the input and output bandwidth constraints. Traditionally, today's data center networks are often organized into tiers, with tiers having various
