Packet-mode policies for input-queued switches

Guez, Dan; Kesselman, Alex; Rosen, Alon

doi:10.1145/1007912.1007927

Cited by 8 publications

(6 citation statements)

References 22 publications

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“…In a related setting, Guez et al [6] studies the problem of maximizing the throughput of packets on inputqueued switches. Packets are queued at input ports, and are forwarded to output ports through a cross switch fabric.…”

Section: Related Workmentioning

confidence: 99%

“…Such flow scheduling instances arise in diverse scenarios in networks and distributed systems, where requests for communication or data transfer need to be satisfied, while meeting constraints at the source and destination ports of the requests. For instance, allocating resources for packet flows in a crossbar switch is a classic example of this flow scheduling problem [4,5,6,16]. More recently, variants of ecfs have been used to model the scheduling of dynamically reconfigurable topologies [10,2].…”

Section: Introductionmentioning

confidence: 99%

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Improved Bounds for Scheduling Flows under Endpoint Capacity Constraints

Pa¹,

Rajaraman²,

Stalfa³

2021

Preprint

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We consider the problem of scheduling flows subject to endpoint capacity constraints. We are given a set of capacitated nodes and an online sequence of requests where each request has a release time and a demand that needs to be routed between two nodes. A schedule specifies, for each time step, the requests that are routed in that step under the constraint that the total demand routed on a node in any step is at most its capacity. A key performance metric in such a scheduling scenario is the response time (or flow time) of a request, which is the difference between the time the request is completed and its release time. Previous work has shown that it is impossible to achieve bounded competitive ratio for average response time without resource augmentation, and that a constant factor competitive ratio is achievable with augmentation exceeding two (Dinitz-Moseley Infocom 2020). For the maximum response time objective, the best known result is a 2-competitive algorithm with a resource augmentation at least 4 (Jahanjou et al SPAA 2020).In this paper, we present improved bounds for the above flow scheduling problem under various response time objectives. Our first result is a lower bound showing that, without resource augmentation, the best competitive ratio for the maximum response time objective is Ω(n), where n is the number of nodes. The remaining results present simple, resource-augmented algorithms that are competitive for the maximum response time objective in their respective settings. Our first algorithm, Proportional Allocation, uses (1 + ε) resource augmentation to achieve a (1/ε)-competitive ratio for maximum response time in the setting with general demands, general capacities, and splittable jobs, for any ε > 0. Our second algorithm, Batch Decomposition, is 2-competitive (resp., matches optimum) for maximum response time using resource augmentation 2 (resp., 4) in the setting with unit demands, unit capacities, and unsplittable jobs. We also derive bounds for the simultaneous approximation of average and maximum response time metrics.

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Section: Related Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improved Bounds for Scheduling Flows under Endpoint Capacity Constraints

Pa¹,

Rajaraman²,

Stalfa³

2021

Preprint

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“…Kesselman et al [22] also propose a 18-competitive policy for the case of variable value packets with Priority Queuing (PQ) buffers, where packets of the highest value are sent first. Guez et al [15] consider packet-mode scheduling for CIOQ switches.…”

Section: Related Workmentioning

confidence: 99%

Packet mode and QoS algorithms for buffered crossbar switches with FIFO queuing

2010

Self Cite

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The buffered crossbar switch architecture has recently gained considerable research attention. In such a switch, besides normal input and output queues, a small buffer is associated with each crosspoint. Due to the introduction of crossbar buffers, output and input dependency is eliminated, and the scheduling process is greatly simplified. We analyze the performance of switch policies by means of competitive analysis, where a uniform guarantee is provided for all traffic patterns. We assume that each packet has an intrinsic value designating its priority and the goal of the switch policy is to maximize the weighted throughput of the switch. We consider FIFO queueing buffering policies, which are deployed by the majority of today's Internet routers. In packet-mode scheduling, a packet is divided into a number of unit length cells and the scheduling policy is constrained to schedule all the cells contiguously, which removes reassembly overhead and improves Quality-of-Service. For the case of variable length packets with uniform value density (Best Effort model), where the packet value is proportional to its size, we present a packet-mode greedy switch policy that is 7-competitive. For the case of unit size packets with variable values (Differentiated Services model), we propose a A preliminary version of this paper appeared in [23].β-preemptive (β is a preemption factor) greedy switch policy that achieves a competitive ratio of 6 + 4β + β 2 + 3/(β − 1). In particular, its competitive ratio is at most 19.95 for the preemption factor of β = 1.67. As far as we know, this is the first constant-competitive FIFO policy for this architecture in the case of variable value packets. In addition, we evaluate performance of β-preemptive greedy switch policy by simulations and show that it outperforms other natural switch policies. The presented policies are simple and thus can be efficiently implemented at high speeds. Moreover, our results hold for any value of the internal switch fabric speedup.

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“…Marsan et al [21] also show that under low load and small packet size variance, packet-mode schedulers may achieve better average packet delay than cellbased schedulers. A different line of research used competitive analysis to evaluate packet-mode scheduling, when each packet has a weight representing its importance and a deadline until which it should be delivered from the switch [12].…”

Section: Related Workmentioning

confidence: 99%

Packet-mode emulation of output-queued switches

Attiya

Hay

Keslassy

2006

Proceedings of the Eighteenth Annual ACM Symposium on Parallelism in Algorithms and Architectures

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Most common network protocols (e.g., the Internet Protocol) work with variable size packets, whereas contemporary switches still operate with fixed size cells, which are easier to transmit and buffer. This necessitates packet segmentation and reassembly modules, resulting in significant computation and communication overhead that might be too costly as switches become faster and bigger. It is therefore imperative to investigate an alternative mode of scheduling, in which packets are scheduled contiguously over the switch fabric.This paper investigates the cost of packet-mode scheduling for the combined input output queued (CIOQ) switch architecture.We devise frame-based schedulers that allow a packetmode CIOQ switch with small speedup to mimic an ideal output-queued switch with bounded relative queuing delay. The schedulers are pipelined and are based on matrix decomposition.Our schedulers demonstrate a trade-off between the switch speedup and the relative queuing delay incurred while mimicking an output-queued switch. When the switch is allowed to incur high relative queuing delay, a speedup arbitrarily close to 2 suffices to mimic an ideal output-queued switch. This implies that packet-mode scheduling does not require higher speedup than a cell-based scheduler. The relative queuing delay can be significantly reduced with just a doubling of the speedup. We further show that it is impossible to achieve zero relative queuing delay (that is, a perfect emulation), regardless of the switch speedup.Finally, we show that a speedup arbitrarily close to 1 suffices to mimic an output-queued switch with a bounded buffer size.

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Packet-mode policies for input-queued switches

Cited by 8 publications

References 22 publications

Improved Bounds for Scheduling Flows under Endpoint Capacity Constraints

Improved Bounds for Scheduling Flows under Endpoint Capacity Constraints

Packet mode and QoS algorithms for buffered crossbar switches with FIFO queuing

Packet-mode emulation of output-queued switches

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