Weighted round robin scheduling in input-queued packet switches subject to deadline constraints

Ankara : Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent Univ., 2000.Thesis (Master's) -- Bilkent University, 2000.Includes bibliographical references leaves 59-63In this thesis work, the problem of scheduling deadline constrained traffic is studied. The problem is explored in terms of Weighted Round Robin (WRR) service discipline in input queued packet switches. Application of the problem may arise in packet switching networks and Satellite-Switched Time Division Multiple Access (SS/TDMA) systems. A new formulation of the problem is presented. The main contribution of the thesis is a ’’backward extraction” technique to schedule packet forwarding through the switch fabric. A number of heuristic algorithms, each based on backward extraction, are proposed, and their performances are studied via simulation. Numerical results show that the algorithms perform significantly better than earlier proposed algorithms. The experimental results strongly assert Philp and Liu conjecture.Rai, Idris AM.S

Fastpass: A Centralized “Zero-Queue” Datacenter Network

An ideal datacenter network should provide several properties, including low median and tail latency, high utilization (throughput), fair allocation of network resources between users or applications, deadline-aware scheduling, and congestion (loss) avoidance. Current datacenter networks inherit the principles that went into the design of the Internet, where packet transmission and path selection decisions are distributed among the endpoints and routers. Instead, we propose that each sender should delegate control—to a centralized arbiter—of when each packet should be transmitted and what path it should follow. This paper describes Fastpass, a datacenter network architecture built using this principle. Fastpass incorporates two fast algorithms: the first determines the time at which each packet should be transmitted, while the second determines the path to use for that packet. In addition, Fastpass uses an efficient protocol between the endpoints and the arbiter and an arbiter replication strategy for fault-tolerant failover. We deployed and evaluated Fastpass in a portion of Facebook’s datacenter network. Our results show that Fastpass achieves high throughput comparable to current networks at a 240 reduction is queue lengths (4.35 Mbytes reducing to 18 Kbytes), achieves much fairer and consistent flow throughputs than the baseline TCP (5200 reduction in the standard deviation of per-flow throughput with five concurrent connections), scalability from 1 to 8 cores in the arbiter implementation with the ability to schedule 2.21 Terabits/s of traffic in software on eight cores, and a 2.5 reduction in the number of TCP retransmissions in a latency-sensitive service at Facebook.National Science Foundation (U.S.) (grant IIS-1065219)Irwin Mark Jacobs and Joan Klein Jacobs Presidential FellowshipHertz Foundation (Fellowship

Performance Management in ATM Networks

ATM is representative of the connection-oriented resource provisioning classof protocols. The ATM network is expected to provide end-to-end QoS guaranteesto connections in the form of bounds on delays, errors and/or losses. Performancemanagement involves measurement of QoS parameters, and application of controlmeasures (if required) to improve the QoS provided to connections, or to improvethe resource utilization at switches. QoS provisioning is very important for realtimeconnections in which losses are irrecoverable and delays cause interruptionsin service. QoS of connections on a node is a direct function of the queueing andscheduling on the switch. Most scheduling architectures provide static allocationof resources (scheduling priority, maximum buffer) at connection setup time. Endto-end bounds are obtainable for some schedulers, however these are precluded forheterogeneously composed networks. The resource allocation does not adapt to theQoS provided on connections in real time. In addition, mechanisms to measurethe QoS of a connection in real-time are scarce.In this thesis, a novel framework for performance management is proposed. Itprovides QoS guarantees to real time connections. It comprises of in-service QoSmonitoring mechanisms, a hierarchical scheduling algorithm based on dynamicpriorities that are adaptive to measurements, and methods to tune the schedulers atindividual nodes based on the end-to-end measurements. Also, a novel scheduler isintroduced for scheduling maximum delay sensitive traffic. The worst case analysisfor the leaky bucket constrained traffic arrivals is presented for this scheduler. Thisscheduler is also implemented on a switch and its practical aspects are analyzed.In order to understand the implementability of complex scheduling mechanisms,a comprehensive survey of the state-of-the-art technology used in the industry isperformed. The thesis also introduces a method of measuring the one-way delayand jitter in a connection using in-service monitoring by special cells

NUMFabric: Fast and Flexible Bandwidth Allocation in Datacenters

We present xFabric, a novel datacenter transport design that provides flexible and fast bandwidth allocation control. xFabric is flexible: it enables operators to specify how bandwidth is allocated amongst contending flows to optimize for different service-level objectives such as minimizing flow completion times, weighted allocations, different notions of fairness, etc. xFabric is also very fast, it converges to the specified allocation one-to-two order of magnitudes faster than prior schemes. Underlying xFabric, is a novel distributed algorithm that uses in-network packet scheduling to rapidly solve general network utility maximization problems for bandwidth allocation. We evaluate xFabric using realistic datacenter topologies and highly dynamic workloads and show that it is able to provide flexibility and fast convergence in such stressful environments.Google Faculty Research Awar

An Optimal Lower Bound for Buffer Management in Multi-Queue Switches

In the online packet buffering problem (also known as the unweighted FIFO variant of buffer management), we focus on a single network packet switching device with several input ports and one output port. This device forwards unit-size, unit-value packets from input ports to the output port. Buffers attached to input ports may accumulate incoming packets for later transmission; if they cannot accommodate all incoming packets, their excess is lost. A packet buffering algorithm has to choose from which buffers to transmit packets in order to minimize the number of lost packets and thus maximize the throughput. We present a tight lower bound of e/(e-1) ~ 1.582 on the competitive ratio of the throughput maximization, which holds even for fractional or randomized algorithms. This improves the previously best known lower bound of 1.4659 and matches the performance of the algorithm Random Schedule. Our result contradicts the claimed performance of the algorithm Random Permutation; we point out a flaw in its original analysis

On delay stable communications in asynchronous networks

This dissertation defines a frame forwarding technique offering a fixed delay to a subclass of traffic in closed industrial control networks. In these networks bandwidth is dedicated to periodic traffic supporting tight inter-process control and control loop communication. Ideally periodic traffic arrival will have minimal delay-jitter with constant realized delays. This simplifies the implementation of connected control devices. Furthermore networks are simplified with asynchronous node and switch operation. Switch designs are simplified as there is no dependence on adjacent switch clock operation. Correct network function only relies on switches directly traversed by each flow and is not dependent on complex clock synchronization mechanisms. Existing packet scheduling schemes that attempt to minimize delay-jitter, suffer from either requiring inter-switch clock coordination (i.e. RCSP-DJ), or maintain a fixed priority so that the highest priority flows must contend without regard to past frame arrival treatment (i.e. RCSP-RJ). In this dissertation the FlexTDMA protocol is defined which supports closed network communication. FlexTDMA will be enhanced to accommodate real-world networking conditions (FlexTDMA+) and will be enhanced to support simultaneous multicast (FlexTDMA++). The FlexTDMA scheduling algorithm delivers frame data on each flow nearly at the maximal delay bound with minimal delay-jitter in an asynchronous network. Industrial control switching network systems will benefit from FlexTDMA when the complexity of system level synchronization is unacceptable, but the component switches must operate independently. FlexTDMA does not require synchronous network clock coordination and preserves the data content of frames. FlexTDMA+ includes three improvements: baseline preemption, partial baselining and baseline deadline density control, which are used to support real-world conditions of node periodic on-off transmission, clock drift, frame loss and bandwidth load. FlexTDMA++ supports simultaneous multicast under real-world conditions of switch failures, node periodic on-off transmission, clock drift, frame loss and bandwidth load

Efficient Q. S support for higt-performance interconnects

Las redes de interconexión son un componente clave en un gran número de sistemas. Los mecanismos de calidad de servicio (qos) son responsables de asegurar que se alcanza un cierto rendimiento en la red. Las soluciones tradicionales para ofrecer qos en redes de interconexión de altas prestaciones normalmente se basan en arquitecturas complejas. El principal objetivo de esta tesis es investigar si podemos ofrecer mecanismos eficientes de qos. Nuestro propósito es alcanzar un soporte completo de qos con el mínimo de recursos. Para ello, se identifican redundancias en los mecanismos propuestos de qos y son eliminados sin afectar al rendimiento. Esta tesis consta de tres partes. En la primera comenzamos con las propuestas tradicionales de qos a nivel de clase de tráfico. En la segunda parte, proponemos como adaptar los mecanismos de qos basados en deadlines para redes de interconexión de altas prestaciones. Por último, también investigamos la interacción de los mecanismos de qos con el control de congestión