Round-trip delay effect on iterative request-grant-accept scheduling algorithms for virtual output queue switches

Tobajas, F.; Esper-Chain, R.; Armas, V. de; Lopez, J.F.; Sarmiento, Roberto

doi:10.1109/glocom.2002.1188528

Cited by 9 publications

(4 citation statements)

References 9 publications

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“…One of the possible solutions to the problem of a propagation delay could be to increase the time slot. This would, however, lead to poor switch performance [10]. Another approach is to implement small buffers in the crosspoints along with VOQ input buffers, otherwise known as Combined Input and Crosspoint Queuing [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Impact of scheduling algorithms on performance of crosspoint-queued switch

Radonjić

Radusinović

2010

Ann. Telecommun.

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The performance analysis of the 32 × 32 crosspoint-queued switch is presented in this paper. Switches with small buffers in crosspoints have been evaluated in the late 1980s but mostly for uniform traffic. However, due to technological limitations of that time, it was impractical to implement large buffers together with switching fabric. The crosspoint-queued switch architecture has been recently brought back into focus since modern technology enables an easy implementation of large buffers in crosspoints. An advantage of this solution is the absence of control communication between linecards and schedulers. In this paper, the performances of four algorithms (longest queue first, round robin, exhaustive round robin, and frame-based round robin matching) are analyzed and compared. The results obtained for the crosspoint-queued switch are compared with the output queued switch. Throughput, average cell latency and instantaneous packet delay variance are evaluated under uniform and nonuniform traffic patterns. The results will show that the longest queue first algorithm has the highest throughput in many simulated cases but the highest average cell latency and delay variance among observed algorithms. It will also be shown that the choice of the scheduling algorithm does not play a role in the switch performance if the buffers are long enough. This will prove that some form of round-robinbased algorithms become a better choice for implementation due to their simplicity, small hardware requirements, and avoidance of the starvation problem, which is a major drawback of the longest queue first algorithm.

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Section: Introductionmentioning

confidence: 99%

Impact of scheduling algorithms on performance of crosspoint-queued switch

Radonjić

Radusinović

2010

Ann. Telecommun.

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“…In [9], it was shown that RTT delay significantly increases contention on output ports for VOQ IQ switches based on parallel and iterative scheduling algorithms. The problem with multi-cabinet implementation of VOQ IQ switch is that as many as RTT-fixed-size packets (or cells) units of switch matrix scheduler are required to maintain the work conservation of the switch.…”

Section: Introductionmentioning

confidence: 99%

Threshold-based Exhaustive Round-Robin for the CICQ Switch with Virtual Crosspoint Queues

Yoshigoe

2007

2007 IEEE International Conference on Communications

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A multi-cabinet implementation of a combined input and crosspoint queued (CICQ) switch introduces a large RTT latency between the line cards and switch fabric, requiring a large crosspoint (CP) buffer. A virtual crosspoint queues (VCQs), proposed in literature are shared among a set of virtual output queues (VOQs) and CP buffers for the same input port, reducing minimal memory size required inside the switch fabric. In this paper, a threshold-based exhaustive round-robin (T-ERR) arbitration is employed to improve the throughput of the CICQ switch with VCQs. The T-ERR at VCQ and CP arbiters serves packets residing in a longer queue more frequently than packet residing in a shorter queue. The T-ERR is simple yet drastically increases the throughput of the CICQ switch with small CP buffers. Simulation evaluations with unbalanced traffic show that the throughput of the CICQ switch with VCQs improves from 80% to 94% for CP buffer size of 4 cells and 73% to 83% for CP buffer size of 2 cells for RTT = 64 cell time. Furthermore, its throughput is independent of switch size and RTT. Thus, the proposed scheme makes the scalable implementation of a distributed CICQ switch practical.

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“…RTT delay significantly increases contention on output ports for VOQ IQ switches with parallel and iterative scheduling algorithms [17]. The problem with multi-cabinet implementation of VOQ IQ switch is that as many as RTTcell units of switch matrix scheduler are needed to maintain the work conservation of the switch.…”

Section: Introductionmentioning

confidence: 99%

The CICQ Switch with Virtual Crosspoint Queues for Large RTT

Yoshigoe

2006

2006 IEEE International Conference on Communications

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The memory size required for a combined input and crosspoint queued (CICQ) switch with an existing credit-based flow control is proportional to the flow control latency between the line cards and switch fabric. Recently, scalable packet switches were implemented with distributed units introducing a large RTT latency between the line cards and switch fabric, making the CP buffer requirement impractical. In this paper, a CICQ switch with virtual crosspoint queues (VCQs) is investigated. The VCQs unit resides inside the switch fabric and is dynamically shared among virtual output queues (VOQ) from the same source port and is operated at the line rate, making the implementation practical. The CICQ switch with VCQ can achieve high throughput for unbalanced traffic while reducing over 87% of the total buffer size requirement in the switch fabric, thus making the scalable implementation of a distributed CICQ switch practical.

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Round-trip delay effect on iterative request-grant-accept scheduling algorithms for virtual output queue switches

Cited by 9 publications

References 9 publications

Impact of scheduling algorithms on performance of crosspoint-queued switch

Impact of scheduling algorithms on performance of crosspoint-queued switch

Threshold-based Exhaustive Round-Robin for the CICQ Switch with Virtual Crosspoint Queues

The CICQ Switch with Virtual Crosspoint Queues for Large RTT

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