Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

Optical packet switching (OPS) is being considered as one of the switching technologies for a future optical internet. For contention resolution in an optical packet switching (OPS) system, the wavelength dimension is generally used in combination with a fibre delay line (FDL) buffer. In this study, the authors propose to reduce the number of tunable wavelength converters (TWCs) by sharing TWCs for cost-effective design of an asynchronous OPS system with a shared or an output FDL buffer. Asynchronous and variable-length packets are considered in the OPS system design. To investigate the number of TWCs needed for the OPS system, an algorithm is proposed, which searches for an available TWC and an unused internal wavelength, as well as an outgoing channel. This algorithm is applied to an OPS system with a shared or an output FDL buffer. Also, the number of internal wavelengths (i.e. the conversion range of the TWC) needed for an asynchronous OPS system is presented for cost reduction of the OPS system.

In an effort to reduce switch cost, we, for the first time, present the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths required for contention resolution of asynchronous and variable length packets, in the optical packet switch (OPS) with the shared fiber delay line (FDL) buffer. To optimize TWCs and internal wavelengths related to an OPS design cost, we proposed a scheduling algorithm for the limited TWCs and internal wavelengths. For three TWC alternatives (not shared, partially shared, and fully shared cases), the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of an OPS with full TWCs and internal wavelengths

In an effort to reduce switch cost, we present the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths required for contention resolution of asynchronous and variable length packets, in the optical packet switch (OPS) with the shared fiber delay line (FDL) buffer. To optimize TWCs and internal wavelengths related to OPS design cost, we proposed a scheduling algorithm for the limited TWCs and internal wavelengths. For three TWC alternatives (not shared, partially shared, and fully shared cases), the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of an OPS with full TWCs and internal wavelengths.

At a switching node in an optical packet switching (OPS) network, packet contention occurs whenever two or more packets try to reach the same output port of the node at the same wavelength, consequently it degrades network performance. Previous works on optical packet switching flourishingly adopted optical buffering with optical fibre delay line (FDL), wavelength conversion, or deflection routing to resolve packet contention. In this paper, we focus on the optical fibre delay line approach, especially the selection of proper length of FDL under asynchronous variable length packet traffic. As the length of fibre coils equipped in a FDL optical buffering system is impossible to be reconfigured frequently, a proper length of FDL should be determined during manufacture. The motivation is to observe the impact factors on FDL optical system performance in a WDM network scenario, and provide the empirical data as supports to select the proper length of FDL in an OPS node system.

In the optical packet switch (OPS) with the hybrid buffer for contention resolution of asynchronous and variable length packets, the optimum numbers of tunable wavelength converters (TWCs) and internal wavelengths is, for the first time, presented for reducing switch cost. The hybrid buffer was addressed, to reduce packet loss further as one of the alternative buffer structures for contention resolution of asynchronous and variable length packets, which consists of the FDL buffer and the electronic buffer. To optimize TWCs and internal wavelengths related to design cost of the OPS with the hybrid buffer, we proposed a scheduling algorithm for the hybrid buffer with the limited TWCs and internal wavelengths. For the fully shared TWC structure, the optimum numbers of TWCs and internal wavelengths to guarantee minimum packet loss are evaluated to prevent resource waste under the hybrid buffer. Under a given load, TWCs and internal wavelengths could be significantly reduced, guaranteeing the same packet loss as the performance of the hybrid buffer structured OPS with more number of TWCs and internal wavelengths.

The virtual output queue (VOQ) has been used in input queued and input-output queued packet switches which require switch plane scheduling algorithms to achieve high throughput. However, existing scheduling algorithms such as iSLIP are designed for scheduling fixed size cell units and introduce unfairness in packet latency among VOQs if used for scheduling variable sized packet units. A self-optimized latency (SOL) scheduling algorithm is proposed to deal with scheduling variable-length packets. The SOL is a credit-based scheduling algorithm which assigns a credit flow for each VOQ. During operation, the SOL examines credit flows to grant access to VOQs through the switch plane. Moreover, the SOL also works in conjunction with an average packet length scheduling concept to modify credit flows based on size of packets transferred through the switch plane in order to increase fairness among VOQs. Simulation results show that the SOL scheduling algorithm in a switch plane significantly reduces the packet latency compared to iSLIP scheduling algorithm.

Optical Packet Switching (OPS) has emerged as a promising candidate for the future all-optical core network. A crucial issue in such networks is how the packet length distribution (PLD) influences the performance under different traffic scenarios. In this paper we investigate how a deterministic, empirical and exponential PLD influences the Packet Loss Rate (PLR) in an optical packet switch in the case of a Poisson arrival process and a bursty Hyperexponential arrival process. We consider optical packet switches with and without Fibre Delay Line (FDL) contention buffers. Our results show that in the case of OPS without FDL buffering and with a Hyperexponential arrival process, the empirical PLD yields the lowest PLR. However, in the case of OPS with FDL buffering, the deterministic PLD yields the lowest PLR.

We develop an integrated optical packet and circuit switching node in which signaling via optical packet switching is implemented. We demonstrate 80 (8λ × 10) Gbit/s optical packet switching with <;1E-4 packet-loss-rate, 8-lightpaths establishment, and dynamic wavelength-resources control.

We present a performance model for fiber delay line (FDL) buffers having access to multiple wavelengths on an output fiber. In optical burst switching and optical packet switching, contending bursts (or packets) need to be dealt with in an effective way, and both wavelength conversion and optical buffering are viable solutions. The buffer studied here includes both solutions, with full wavelength conversion. It is situated at the output, and handles independent arrivals. We apply an analytic discrete-time queueing model to evaluate performance in terms of loss. We mainly consider the impact of burst size (fixed or varying), scheduling policy, and buffer size. Several numerical examples assess the accuracy of our approximation, and show that our approach is applicable when burst sizes are fixed, and, when a round-robin scheduling policy is adopted, also when burst sizes vary.

We discuss the introduction/implementation of optical IP routers, then we introduce a novel scheduling algorithm incorporating void filling and aimed at optical routing of asynchronous, variable packet length packets. We describe its structure and discuss the complexity issues. Albeit introduced with the purpose of cancelling expensive optical synchronization, we argue that this approach represents the most viable all-optical approach for implementing packets-over-SONET (IP-centric scenario). We also present simulations under self-similar traffic conditions which point to the inefficiency of optical buffering to combat the effects of self-similarity, and we outline alternative strategies for proper buffer dimensioning.

In this paper, we propose a novel optical packet switching mechanism incorporating void filling that makes some packets switch in optical domain, others in electronic domain. The optical packet switching is solved in time, space, wavelength and electronic domain. We also present numerical simulations under Poisson traffic and variable IP packet length condition. Simulation results have shown improvement in packet loss probability by using our switching mechanism.

Packet contention is a major issue in optical packet switching network. To resolve contention, optical buffering approach is used using Fiber Delay Lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output-port and free FDLs. This paper proposes a selective minimum delay value algorithm (SMDV) to resolve contention for shared FDL buffering architecture in order to ensure the availability of output-port for the contended packet after coming out from FDL. Simulation result shows that proposed scheme can achieve a packet loss rate of ~ even at heavy traffic load 0.9 for 32×32 switch using 32 variable length FDL.

Internet data is transmitted in variable-size packets to provide flexibility for different applications. There has been a growing interest in developing the design of Internet routers based variable-length packets to improve performance and reduce the amount of re-assembly memory. However, most of variable-length designs follow a time-slotted approach, which make them similar to routers that switch fixed-length packets. The use of slotted timing makes padding necessary when packet sizes are not proportional to the time-slot length. In this paper, we investigate the impact of concatenating packets to reduce the amount of padding in variable-length packet switches. This approach increases the utilization of interconnection bandwidth and overall throughput performance. Performance evaluation in an input-queued packet switch using packet concatenation is presented.

In this paper, a buffer control strategy called limited greedy mode (LGM) is presented to handle fibre delay line (FDL) contentions which often occur in optical packet switch with shared FDL‐buffer. In order to make full use of the FDL‐buffer, three scheduling algorithms based on the LGM, i.e. Shortest Queue Based on Limited Greedy Mode (SQLGM), Increasing Queue Based on Limited Greedy Mode (IQLGM) and Shortest Queue Considering Output Void (SQCOV) are proposed. Performances of these three algorithms are evaluated by simulation experiments. Simulation results show that the SQCOV achieves the best performance. In addition, the buffering performance of shared FDL‐buffer also depends on the greedy degree of LGM and the granularity of FDL. Copyright © 2009 John Wiley &amp; Sons, Ltd.

This paper considers an optical packet-switched node with limited buffer capabilities and subject to asynchronous, variable-length packets and connection-oriented operation. In such a scenario, we address the problem of providing QoS. While existing solutions focus on applying some form of resources reservation on top of the contention resolution algorithm, here we propose a novel method: given a set of K categories of service to be provided in the network, K different contention resolution algorithms are implemented to cope with the requirements of such service categories. In this paper, we define three different OPS service categories based on three different contention resolution algorithms, we design an ad-hoc pool of fiber delay lines for such a scheme, and evaluate its performance by simulation. The obtained results indicate the merits of our method which opens up future interesting developments for a whole network scenario studies.