Packet-mode emulation of output-queued switches

Attiya, Hagit; Hay, David; Keslassy, Isaac

doi:10.1145/1148109.1148134

Cited by 8 publications

(1 citation statement)

References 25 publications

(33 reference statements)

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“…Packet mode scheduling has received a lot of research attention recently [4,35]. A packet is divided into a number of unit length cells and the scheduling policy is constrained to schedule all cells of a given packet contiguously.…”

Section: Introductionmentioning

confidence: 99%

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

2010

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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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Section: Introductionmentioning

confidence: 99%

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

2010

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On the Emulation of Finite-Buffered Output Queued Switches Using Combined Input-Output Queuing

Elhaddad

Melhem

2008

Lecture Notes in Computer Science

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Emulation of Output Queuing (OQ) switches using Combined Input-Output Queuing (CIOQ) switches has been studied extensively in the setting where the switch buffers have unlimited capacity. In this paper we study the general setting where the OQ switch and the CIOQ switch have finite buffer capacity B ≥ 1 packets at every output. We analyze the resource requirements of CIOQ policies in terms of the required fabric speedup and the additional buffer capacity needed at the CIOQ inputs: A CIOQ policy is said to be (s, b)-valid (for OQ emulation) if a CIOQ employing this policy can emulate an OQ switch using fabric speedup s ≥ 1, and without exceeding buffer occupancy b at any input port.For the family of work-conserving scheduling algorithms, we find that whereas every greedy CIOQ policy is valid at speedup B, no CIOQ policy is valid at speedup s < 3 √ B − 2 when preemption is allowed. We also find that CCF in particular is not valid at any speedup s < B. We then introduce a CIOQ policy, CEH, that is valid at speedup s ≥ p 2(B − 1). Under CEH, the buffer occupancy at any input never exceeds 1 + j B−1 s−1 k . Although the speedup required for the emulation of preemptive scheduling algorithms is not constant, it may be feasible in high-speed electronic or optical switches, which are expected to have limited buffering capacity.For non-preemptive scheduling algorithms, we characterize a trade-off between the CIOQ speedup and the input buffer occupancy. Specifically, we show that for any greedy policy that is valid at speedup s > 2, the input buffer occupancy cannot exceed 1 + l B−1 s−2 m . We also show that a greedy variant of the CCF policy is (2, B)-valid for the emulation of non-preemptive OQ algorithms with PIFO service disciplines.

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Modeling the interactions of congestion control and switch scheduling

Shpiner

Keslassy

2011

Computer Networks

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Abstract-In this paper, we study the interactions of user-based congestion control algorithms and router-based switch scheduling algorithms. We show that switch scheduling algorithms that were designed without taking into account these interactions can exhibit a completely different behavior when interacting with feedbackbased Internet traffic. Previous papers neglected or mitigated these interactions, and typically found that flow rates reach a fair equilibrium. On the contrary, we show that these interactions can lead to extreme unfairness with temporary flow starvation, as well as to large rate oscillations. For instance, we prove that this is the case for the MWM switch scheduling algorithm, even with a single router output and basic TCP flows. We also show that the iSLIP switch scheduling algorithm achieves fairness among ports, instead of fairness among flows. Finally, we fully characterize the network dynamics for both these switch scheduling algorithms.

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Packet-mode emulation of output-queued switches

Cited by 8 publications

References 25 publications

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

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

On the Emulation of Finite-Buffered Output Queued Switches Using Combined Input-Output Queuing

Modeling the interactions of congestion control and switch scheduling

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