Load-balanced flow scheduling for big data centers in clouds, in which a large amount of data needs to be transferred frequently among thousands of interconnected servers, is a key and challenging issue. The OpenFlow is a promising solution to balance data flows in data center networks through its programmatic traffic controller. Existing OpenFlow based scheduling schemes, however, statically set up routes only at the initialization stage of data transmissions, which suffers from dynamical flow distribution and changing network states in data centers and often results in poor system performance. In this paper, we propose a novel dynamical load-balanced scheduling (DLBS) approach for maximizing the network throughput while balancing workload dynamically. We first formulate the DLBS problem, and then develop a set of efficient heuristic scheduling algorithms for the two typical OpenFlow network models, which balance data flows time slot by time slot. Experimental results demonstrate that our DLBS approach significantly outperforms other representative load-balanced scheduling algorithms Round Robin and LOBUS; and the higher imbalance degree data flows in data centers exhibit, the more improvement our DLBS approach will bring to the data centers.

A Dynamical and Load-Balanced Flow Scheduling Approach for Big Data Centers in Clouds

An efficient iterative scheduling algorithm for input-queued switches, called round robin with longest queue first (RR/LQF), is proposed in this paper. RR/LQF consists of three phases: report, grant, and accept. In each phase, only a single-bit message per port is sent for reporting a packet arrival, granting an input for packet sending, or accepting a grant. In both the grant and accept phases, scheduling priority is given to the preferred input–output pairs first and the longest virtual output queuing (VOQ) next. The notion of the preferred input–output pair is to keep a global RR schedule among all the inputs and the outputs. By serving the preferred input–output pairs first, the match size tends to be maximized. By serving the longest VOQ next, the match weight is also boosted. When RR/LQF is executed for a single iteration (i.e., RR/LQF-1), we show by simulations that RR/LQF-1 outperforms all the existing single-bit-single-iteration scheduling algorithms. When RR/LQF is executed up to $N$ iterations (i.e., RR/LQF- $N$ ), we prove that under any admissible traffic pattern, RR/LQF- $N$ is stable with a speedup of $2-1/N$ , where $N$ is the switch size. To the best of our knowledge, this is the first work showing that an iterative scheduling algorithm is stable with a speedup less than 2. We then generalize RR/LQF to become a class of algorithms that have the same speedup bound of $2-1/N$ . Efforts are then made to further reduce the implementation complexity of RR/LQF. To this end, the pipelined RR/LQF and RR/RR, a simpler variant of RR/LQF, are proposed.

On Iterative Scheduling for Input-Queued Switches With a Speedup of $2-1/N$

Clos-network switches have attracted a lot of attention because of their modularity and scalability. However, out-of-sequence problems weigh heavily against the application of buffered Clos-network switches. A space-memory-memory (SMM) Clos-network switch is proposed in this study which is able to provide in-sequence service. There are two features in the proposed switch which are different from the previously proposed schemes. First, two-stage load-balanced Birkhoff-von Neumann (LB-BvN) switches are adopted for each second-stage module. Second, no inter-stage matching is needed. The key idea to provide in-order cell delivery in the proposed SMM Clos-network switch is that cells belonging to the same flow will experience the identical delay when passing through the LB-BvN switches at the second stage, and arrive at their destined third-stage module in order. Each switching module operates independently, which makes the proposed SMM Clos-network switch practical to implement in hardware. Simulations show that the proposed switch can achieve high performance under both Bernoulli and Bursty arrival traffic.

Space-memory-memory Clos-network switches with in-sequence service

Two-stage open queuing systems are used to model and evaluate interaction between two systems in computer and communication networks. Application areas include two-stage internetworking mechanisms, memory servers, and interaction of wireless communication systems. Realistic features, such as finite capacities, feedback from one stage to another, and failures of servers usually complicate analytic solutions. This study presents a new analytical model and solution approach for two-stage open queuing systems with feedback, blocking, and multiple servers, as well as failures at both stages. Unlike the existing studies, systems considered in both stages can be fault tolerant. Numerical results presented comparatively with simulation show that the new approach performs well, in terms of accuracy and computation time.

Fault-Tolerant Two-Stage Open Queuing Systems With Server Failures at Both Stages

A hybrid electro-optic router is attractive, where packet buffering and table lookup are carried out in electrical domain and switching is done optically. In this paper, we propose a load-balanced optical switch (LBOS) fabric for a hybrid router. LBOS comprises N linecards connected by an N-wavelength WDM fiber ring. Each linecard i is configured to receive on channel λi. To send a packet, it can select and transmit on an idle channel based on where the packet goes. The packet remains in the optical domain all the way from an input linecard/port to an output linecard/port. Meanwhile, the loading in the ring network is perfectly balanced by spreading the packets for different destinations to use different wavelengths, and packets for the same destination to use different time slots. With the pipelined operation of the LBOS, we show that LBOS is an optical counterpart of an efficient load-balanced electronic switch, and close-to-100% throughput can be obtained. To address the ring-fairness problem under the inadmissible traffic patterns, an efficient throughput-fair scheduler for LBOS is also devised.

Load-Balanced Optical Switch for High-Speed Router Design

A framework for designing feedback-based scheduling algorithms is proposed for elegantly solving the notorious packet missequencing problem of a load-balanced switch. Unlike existing approaches, we show that the efforts made in load balancing and keeping packets in order can complement each other. Specifically, at each middle-stage port between the two switch fabrics of a load-balanced switch, only a single-packet buffer for each virtual output queueing (VOQ) is required. Although packets belonging to the same flow pass through different middle-stage VOQs, the delays they experience at different middle-stage ports will be identical. This is made possible by properly selecting and coordinating the two sequences of switch configurations to form a joint sequence with both staggered symmetry property and in-order packet delivery property. Based on the staggered symmetry property, an efficient feedback mechanism is designed to allow the right middle-stage port occupancy vector to be delivered to the right input port at the right time. As a result, the performance of load balancing as well as the switch throughput is significantly improved. We further extend this feedback mechanism to support the multicabinet implementation of a load-balanced switch, where the propagation delay between switch linecards and switch fabrics is nonnegligible. As compared to the existing load-balanced switch architectures and scheduling algorithms, our solutions impose a modest requirement on switch hardware, but consistently yield better delay-throughput performance. Last but not least, some extensions and refinements are made to address the scalability, implementation, and fairness issues of our solutions.

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Bing Hu

Papers

Feedback-based scheduling for load-balanced two-stage switches