Analytical MMAP-Based Bounds for Packet Loss in Optical Packet Switching with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. A crucial issue in packet switched networks is the avoidance of packet losses stemming from contention. In OPS, contention can be solved using a combination of exploitation of the wavelength domain (through wavelength conversion) and buffering. To provide optical buffering, fiber delay lines (FDLs) are used. In this paper, we focus on an optical packet switch with recirculating FDL buffers and wavelength converters. We introduce the Markovian arrival process with marked transitions (MMAP), which has very desirable properties as a traffic model for OPS performance assessment. Using this model, we determine lower and upper bounds for the packet loss rate (PLR) achieved by the aforementioned switch. The calculation of the PLR bounds through matrix analytical methods is repeated for a wide range of traffic conditions, including highly non-uniform traffic, both in space (i.e., packet destinations) and time (bursty traffic). The quality of these bounds is verified through comparison with simulation results.     

混合缓存型异步光分组交换的一种改进FF-VF算法

光纤延迟线（FDL）是异步光分组交换（OPS）采用的时域冲突解决方案,通过计算其分组丢失率（PLR）发现,在业务负载高,特别是业务负载大于0．7时,PLR性能较差。研究以FDL作为主要的常规缓存、以电存储器作为辅助缓存的光电混合缓存结构,并用改进的首选即中的填空（IFF-VF）算法调度冲突的分组,达到改善可变长OPS的PLR目的。分析和仿真结果表明,光电混合缓存和IFF-VF算法能改善可变长OPS在负载较高时的PLR性能,并减少FDL的数目。     

High-Performance Hybrid-Switching Optical Router for IP over WDM Integration

Because pure electrical routers with their bandwidth limitations can hardly keep up with the tremendous traffic growth in the Internet, optical routers based on various optical switching techniques including optical wavelength switching (OWS), optical burst switching (OBS), and optical packet switching (OPS) have been suggested to cope with this problem. However, because OBS and OPS are both in their early experimental phase and OWS only provides coarse granularity switching, a hybrid-switching optical router with combined OWS and electrical packet switching is a necessity in order to accommodate the entire multi-granularity traffic with multi-service requirements in a cost-effective manner. Its coordination capability of optical circuit switching and electrical packet switching enables efficient/intelligent usage of network resources. In this paper, we first review research and developments of such IP routers employing optical switching/interconnection techniques and examine how these techniques can be used inside routers to scale node capacity and to improve optical Internet performance. We also present and study the performance of a terabit optical router with an optical-electrical hybrid-switching fabric. The node architecture is based on the idea of IP over WDM integration with Generalized Multi-Protocol Label Switching (GMPLS). The network-level performance evaluations show that the proposed hybrid-switching optical router is a cost-effective solution for building the next generation GMPLS-based multi-granularity optical Internet.     

Node pacing for small optical RAM-buffered packet-switching networks

One of the difficulties with optical packet switched (OPS) networks is buffering optical packets in the network. The only available solution that can currently be used for buffering in the optical domain is using long fiber lines called fiber delay lines (FDLs), which have severe limitations. Moreover, the research on optical RAM presently being done is not expected to achieve a large capacity soon. However, the burstiness of Internet traffic causes high packet drop rates and low utilization in very small buffered OPS networks. We therefore propose a new node-based pacing algorithm for decreasing burstiness. We show that by applying some simple pacing at the edge or core backbone nodes, the performance of very small optical RAM buffered core OPS networks with variable-length packets can be notably increased.     

Buffering management schemes for optical variable length packets under limited packet sorting

This paper studies several buffering strategies for optical packet switching (OPS) under limited packet sorting. Three schemes, which are able to sort newly arrived packets based on packet’s length as well as capability of finding the minimum buffer occupancy, are analyzed and compared. Results show that all three proposed schemes could improve OPS performance considerably in terms of probability of packet loss (PPL) and probability of information loss (PIL). In addition, the simulation results show that not all the newly arrived packets need to be sorted in order to obtain minimum packet loss probability. Since the amount of packets and thus the packet processing time is significant in OPS, it is possible that not all the packets can be processed using one of the buffering strategies. An important finding of this paper is that if only 10% of the packets are sorted, the PPL is comparable to the minimum packet loss value obtained when 100% of the packets are sorted.     

Demonstration of 10 Gbit Ethernet/Optical-Packet Converter for IP Over Optical Packet Switching Network

We developed novel network interfaces, for example 10 Gbit Ethernet to 80 Gbit/s optical-packet (10 GbitE–80 GbitOP) or 80 Gbit/s optical-packet to 10 Gbit Ethernet (80 GbitOP–10 GbitE) converters (collectively called as 10 GbitE/80 GbitOP converters), to connect optical packet switching (OPS) networks with IP technology-based networks. By using newly developed arrayed burst-mode optical packet transmitters/receivers together, the 10 GbitE–80 GbitOP converter at the ingress edge node of the OPS network encapsulates an IP packet into an $80(8lambdatimes 10) {rm Gbit/s}$ dense wavelength division multiplexing (DWDM)-based optical packets and generates an optical label based on a lookup table and the destination addresses of the IP packet. The 80 GbitOP–10 GbitE converter at the egress edge node decapsulates the IP packet from the optical packet and generates a 10 GbitE frame accommodating the IP packet according to a lookup table. By using these network interface devices and OPS system based on multiple optical label processing, we achieved, for the first time, 74-km single-mode fiber transmission, switching, and buffering of $80(8lambdatimes 10) {rm Gbit/s}$ DWDM-based optical packets encapsulating almost 10 Gbit/s IP packets with error-free operation (IP packet loss rate $≪ 10^{-6}$).      

Experimental demonstration of OCDMA traffic over optical packet switching network with hybrid PLC and SSFBG en/decoders

The transmission of coherent optical code division multiple access (OCDMA) traffic over optical-code-based optical packet switching (OPS) network has been proposed and successfully demonstrated in experiment. Full function of the OPS node has been successfully demonstrated in the experiment with coherent OCDMA traffic. A hybrid using planar lightwave circuit and superstructured fiber Bragg grating en/decoder for packet label and OCDMA-payload encoding/decoding has been verified as well. Error-free (<10/sup -12/) transmissions have been achieved for the 10- and 40-Gb/s payload data and up to two OCDMA channels.     

Packet Pacing in Small Buffer Optical Packet Switched Networks

In the absence of a cost-effective technology for storing optical signals, emerging optical packet switched (OPS) networks are expected to have severely limited buffering capability. To mitigate the performance degradation resulting from small buffers, this paper proposes that optical edge nodes “pace” the injection of traffic into the OPS core. Our contributions relating to pacing in OPS networks are three-fold: first, we develop real-time pacing algorithms of poly-logarithmic complexity that are feasible for practical implementation in emerging high-speed OPS networks. Second, we provide an analytical quantification of the benefits of pacing in reducing traffic burstiness and traffic loss at a link with very small buffers. Third, we show via simulations of realistic network topologies that pacing can significantly reduce network losses at the expense of a small and bounded increase in end-to-end delay for real-time traffic flows. We argue that the loss-delay tradeoff mechanism provided by pacing can be instrumental in overcoming the performance hurdle arising from the scarcity of buffers in OPS networks.      

Multi-wavelength switching in IP optical nodes adopting different buffering strategies

The paper addresses the topic of long-haul optical networking for the provision of large-bandwidth IP services. A class of optical packet switching architectures is considered which adopts an arrayed wavelength grating device as packet router. The architecture performs slotted packet switching operations and fully exploits the wavelength routing capabilities by allowing multi-wavelength switching. Fiber delay lines are used to perform optical packet buffering, which accomplishes either input queueing or shared queueing. Here a thorough performance evaluation is carried out with different buffering configurations and the effect of various switch parameters on traffic performance is studied.     

Bandwidth and Buffer Tradeoffs in Optical Packet Switching

Recognizing the difficulties in buffering or slowing data in all-optical networks, optical packet switching (OPS) may be viable if buffers are small, at the cost of some inefficiency in link utilization. In this paper, the authors consider a new single-node OPS model that focuses on a set of output wavelengths in a certain link and consider the set of input wavelengths that transmits packets competing for the set of output wavelengths. Using this model, an exact solution and an accurate and scalable approximation, based on reduction of the state-space to a single direction, are provided for packet-loss probability and mean queueing delay. Tradeoffs between optical buffering capacity and link utilization for cases with and without wavelength conversion are studied and discussed     

Performance characteristics of cascaded delay‐line node architectures in single‐path interconnection networks

Internally buffered multistage interconnection network architectures have been widely used in parallel computer systems and large switching fabrics. Migration from electrical domain to optical domain has raised the necessity of developing node architectures with optical buffers. Cascaded fibre delay line architectures can be seen as possible realizations of output and shared buffering in a 2 × 2‐switching element. These approaches can be used as buffered node architecture in a Banyan like interconnect. In this paper, we investigate and compare these approaches by using simulation methods. Different performance metrics, such as normalized throughput, average packet delay, packet loss rate and buffer utilization have been used under uniform and non‐uniform traffic models. Results show that the TC‐chain node Banyan network offer an improved normalized throughput and average packet delay performances under both traffic models without disrupting first‐in‐first‐out order of arrivals. The switched delay‐line requires fewer switching elements than TC and TTC architectures but at the cost of high packet delay. Copyright © 2004 John Wiley & Sons, Ltd.     

The study of QoS guarantee in the optical burst switching internet backbone

Optical switching technology can be categorized into optical circuit switching (OCS), optical packet switching (OPS) and optical burst switching (OBS). OCS is suitable for large amounts of data transmission; however, the channel utilization is inefficient when the traffic flows are intermittent. OPS can be easily adapted to any higher layer and is suitable for bursty traffic, but it requires a highly complex technology and optical buffer. The new switching paradigm, OBS, can provide higher bandwidth utilization and meanwhile avoid the complexity in OPS technology.In this paper, we investigate how the quality of service (QoS) can be guaranteed and reliable transmission can be supported in the OBS-based Internet backbone. We propose the adjustable-time-counter-based (ATCB) burst assembly and the non-real time packet retransmission mechanisms and apply them in the ingress router of the OBS Internet backbone to guarantee the quality of real time applications and lossless requirement of non-real time services. Moreover, traffic shaped is performed for real time packets in the egress router so that the real time property is preserved with a low jitter. Simulation results show that the burst blocking probability using the ATCB burst assembly is improved, compared with the time-counter-based (TCB) and burst-length-threshold-based (BLTB) mechanisms. The delay, loss and jitter of real time service conform to the QoS requirement. Meanwhile, the delay of non-real time service also falls in the acceptable range.     

Flow Routing and its Performance Analysis in Optical IP Networks

Optical packet-switching networks deploying buffering, wavelength conversion and multi-path routing have been extensively studied in recent years to provide high capacity transport for Internet traffic. However due to packet-based routing and switching, such a network could result in significant disorder and delay variation of packets when they are received by end users, thus increasing the burstiness of the Internet traffic and causing higher-layer protocol to malfunction. This paper addresses a novel routing and switching method for optical IP networks — flow routing, and its facilitating protocol. Flow routing deals with packet-flows to reduce flow corruption due to packet out-of-order, delay variation and packet loss, without using complicate control mechanism. Detailed performance analysis is given for output-buffered optical routers adopting flow routing. Two flow-oriented discarding techniques, i.e., flow discard (FD) and early flow discard (EFD), are discussed. Compared with optical packet-switching routers, a remarkable improvement of good-throughput is obtained in the optical flow-routers, especially under high congestion periods. We conclude that EFD behaves as a robust technique, which is more tolerant than FD to the change of traffic and transmission system factors.     

High-capacity multiservice optical label switching for the next-generation Internet

This article presents an optical label switching technology geared toward the next-generation Internet, and highlights its promising potential to accommodate packet, burst, and circuit traffic in a unified optical layer. In particular, we provide detailed discussions on an architecture design for a high capacity optical label switching router by considering enabling optical technologies. In pursuit of an effective contention resolution scheme, we investigate an end-to-end solution by incorporating a traffic shaping function at the network edge with wavelength, time, and space dimensions contention resolution in the core network. Experimental results indicate that this scheme is capable of achieving very low packet loss rates. Furthermore, due to its natural compatibility with GMPLS architecture, optical label switching has great potential for a seamless upgrade of today's optical networks toward the next generation Internet.     

Routing Strategies to Minimize Packet Loss in an Optical Packet Switched Network with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. We study optical packet switches with recirculating fiber delay line (FDL) buffers. Through simulation, we have assessed the logical performance of a single optical packet router (OPR), focusing on packet loss rate (PLR). By verifying that our scheduling algorithm does not alter the traffic profile characteristics from in- to output, we illustrate how the single node results can be used to assess network-wide performance. We use the capability of assessing end-to-end PLRs to develop network-wide routing algorithms designed to minimize the maximal PLR occurring in the network. In case studies on pan-European networks, we first compare two algorithm variants and thereafter we compare the PLR-based routing algorithm with both load balancing and shortest path routing. While load balancing achieves PLRs that are multiple orders of magnitude lower than shortest path routing, the PLR-based algorithm can reach PLRs up to two orders of magnitude better. The improvement in PLR comes at the price of only a small increase in used bandwidth (a few percent). Subsequently we show that the discussed PLR-based routing algorithm can be easily extended to multiple priorities. By introducing multiple priorities we can keep the loss rates for high priority traffic very low. However, it may lead to an increase of the obtained minimal max-PLR value for low priority traffic. But as we prove this increase to be limited, the cost of introducing multiple priorities is small.     

An optical router with multistage management functions for asynchronous optical packet switching network

An optical router with multistage distributed management features for the asynchronous optical packet switching (OPS) network is presented, which can improve switching capacity and all-optical scalability. A compact recycling-fiber-delay-line (Rec-FDL) based collision resolution mechanism is proposed to resolve the contentions for asynchronous and variable length optical packets. The analysis models of stabilities, packet loss rates (PLR) and average packet waiting latencies (PWL) for the router are developed based on the timer based optical packet assembly algorithm. The simulation shows that PLR and PWL for a 400-byte optical packet transmitted in the 32 wavelengths dense wavelength division multiplexing (DWDM) system equal to 3.48 × 10⁻⁴ and 0.072 ns, respectively. The non-blocking switching can be realized for the packets with lengths less than the buffer granularity of the Rec-FDL, and the optimized performance for the proposed router can be obtained through properly selecting of the system parameters.     

光总线交换网络输出排队两级缓冲结构与性能分析

为了解决核心路由器高速无阻塞光总线交换网络体系结构中的高速大容量分组缓冲这一关键技术难题,本文提出了基于SRAM技术和DRAM技术相结合的输出排队分组两级缓冲结构及相关LBF-MMA存储器管理算法,并利用实测的网络流量数据对该缓冲技术的性能进行了仿真分析.分析表明,两级缓冲结构较好地解决了光总线交换网络中分组缓冲高速度与大容量之间的矛盾,对高速路由器技术的发展也具有一定的指导意义.     

The impact of synchronization on the performance of FDL buffers

Circumventing the speed bottleneck of electronic switching, novel switching approaches like optical burst switching (OBS) and optical packet switching (OPS) handle the switching of bursts (or packets) in backbone nodes optically, and include a set of fiber delay lines (FDLs) for optical buffering. While previous work acknowledges the performance difference between optical FDL buffers and electronic RAM buffers, the important role of synchronization herein has received little attention to date.     

Constrained and Unconstrained overspill routing in optical networks: a detailed performance evaluation

In this article, we present a detailed performance evaluation of a hybrid optical switching (HOS) architecture called Overspill Routing in Optical Networks (ORION). The ORION architecture combines (optical) wavelength and (electronic) packet switching, so as to obtain the individual advantages of both switching paradigms. In particular, ORION exploits the possible idle periods of established lightpaths to transmit packets destined to the next common node, or even directly to their common end-destination. Depending on whether all lightpaths are allowed to simultaneously carry and terminate overspill traffic or overspill is restricted to a sub-set of wavelengths, the architecture limits itself to constrained or un-constrained ORION. To evaluate both cases, we developed an extensive network simulator where the basic features of the ORION architecture were modeled, including suitable edge/core node switches and load-varying sources to simulate overloading traffic conditions. Further, we have assessed various aspects of the ORION architecture including two basic routing/forwarding policies and various buffering schemes. The complete network study shows that ORION can absorb temporal traffic overloads, as intended, provided sufficient buffering is present. We also demonstrate that the restriction of simultaneous packet insertions/extractions, to reduce the necessary interfaces, do not deteriorate performance and thus the use of traffic concentrators assure ORION’s economic viability.     

On wavelength-converted optical routers employing flow routing

Optical networks have been extensively investigated in recent years to provide high capacity for the Internet traffic. Among them the optical packet-switching network deploying buffering, wavelength conversion and multipath routing could be the most suitable one. It cannot only provide high capacity transport for Internet traffic but also achieve high utilization of the network resources. However due to the packet-oriented routing and switching, such a network can result in a large amount of packets out-of-order, packet loss and/or with various delays upon arriving at end systems, causing TCP flows that comprise those packets corrupted. Large amount of corrupted flows can increase the burstiness of the Internet traffic and cause higher-layer protocol to malfunction. This paper presents a novel routing and switching method for optical IP networks-flow routing. Without using a complicate control mechanism flow routing deals with packet-flows to reduce the amount of corrupted flows. The performance of the wavelength-converted optical flow router is investigated, based on a novel analytical model. A performance metric, i.e., good-throughput, is used, measuring the ratio of the amount of packets comprised in the noncorrupted flows to total amount of packets. Comparing with optical packet-switching routers, a remarkable improvement of good-throughput can be obtained by using optical flow routers. More important, using wavelength conversion can greatly improve the good-throughput of optical flow routers.