Vinod M. Vokkarane

Burst segmentation: an approach for reducing packet loss in optical burst switched networks

We address the issue of contention resolution in optical burst switched networks, and we introduce an approach for reducing packet losses which is based on the concept of burst segmentation. In burst segmentation, rather than dropping the entire burst during contention, the burst may be broken into multiple segments, and only the overlapping segments are dropped. The segmentation scheme is investigated by simulation in conjunction with a deflection scheme, and it is shown that segmentation with deflection can achieve a significantly reduced packet loss rate.

Prioritized burst segmentation and composite burst-assembly techniques for QoS support in optical burst-switched networks

We address the issue of providing quality-of-service (QoS) in an optical burst-switched network. QoS is provided by introducing prioritized contention resolution policies in the network core and a composite burst-assembly technique at the network edge. In the core, contention is resolved through prioritized burst segmentation and prioritized deflection. The burst segmentation scheme allows high-priority bursts to preempt low-priority bursts and enables full class isolation between bursts of different priorities. At the edge of the network, a composite burst-assembly technique combines packets of different classes into the same burst, placing lower class packets toward the tail of the burst. By implementing burst segmentation in the core, packets that are placed at the tail of the burst are more likely to be dropped than packets that are placed at the head of the burst. The proposed schemes are evaluated through analysis and simulation, and it is shown that significant differentiation with regard to packet loss and delay can be achieved.

Threshold-based burst assembly policies for QoS support in optical burst-switched networks

In this paper, we propose a threshold-based burst assembly scheme in conjunction with a burst segmentation policy to provide QoS in optical burst switched (OBS) networks. Bursts are assembled at the network edge by collecting packets that have the same QoS requirements. Once the number of packets in a burst reaches a threshold value, the burst is sent into the network. We investigate various burst assembly strategies which differentiate bursts by utilizing different threshold values or assigning different burst priorities to bursts that contain packets with differing QoS requirements. The primary objective of this work is to find the optimal threshold values for varous classes of bursts. We show through simulation that there is an optimal value of burst threshold that minimizes packet loss for given network parameters.

Absolute QoS differentiation in optical burst-switched networks

A number of schemes have been proposed for providing quality-of-service (QoS) differentiation in optical burst-switched (OBS) networks. Most existing schemes are based on a relative QoS model in which the service requirements for a given class of traffic are defined relative to the service requirements of another class of traffic. In this paper, we propose an absolute QoS model in OBS networks which ensures that the loss probability of the guaranteed traffic does not exceed a certain value. We describe two mechanisms for providing loss guarantees at OBS core nodes: an early dropping mechanism, which probabilistically drops the nonguaranteed traffic, and a wavelength grouping mechanism, which provisions necessary wavelengths for the guaranteed traffic. It is shown that integrating these two mechanisms outperforms the stand-alone schemes in providing loss guarantees, as well as reducing the loss experienced by the nonguaranteed traffic. We also discuss admission control and resource provisioning for OBS networks, and propose a path clustering technique to further improve the network-wide loss performance. We develop analytical loss models for the proposed schemes and verify the results by simulation.

Dynamic congestion-based load balanced routing in optical burst-switched networks

In optical burst-switched networks, data loss may occur when bursts contend for network resources. There have been several proposed solutions to resolve contentions in order to minimize loss. These localized contention resolution techniques react to contention, but do not address the more fundamental problem of congestion. Hence, there is a need for network level contention avoidance using load balanced routing techniques in order to minimize the loss. In this paper, we propose two dynamic congestion-based load balanced routing techniques to avoid congestion. Our simulation results show that the proposed contention avoidance techniques improve the network utilization and reduce the packet loss probability.

Generalized burst assembly and scheduling techniques for QoS support in optical burst-switched networks

We address the issue of providing differentiated services to IP packets over an optical burst switched core network, and we introduce a new approach for assembling packets into a burst. In this technique, a composite burst is created by combining packets of different classes into the same burst. The packets are placed from the head of the burst to the tail of the burst in order of decreasing class. The performance of this approach is enhanced by using a burst segmentation technique in which, during burst contention, only the packets in the tail of a burst are dropped. We describe a generalized model for burst assembly and burst scheduling, and we propose several composite burst assembly methods. We observe that having multiple classes of packets in a burst performs better than having a single class of packets in a burst.

A Survey of Advance Reservation Routing and Wavelength Assignment in Wavelength-Routed WDM Networks

Traditionally, research on routing and wavelength assignment over wavelength-routed WDM networks is concerned with immediate reservation (IR) demands. An IR demand typically does not specify a holding time for data transmission and the start time of the data transmission is assumed to be immediate (i.e. when the connection request arrives). The concept of advance reservation (AR) has recently been gaining attention for optical networks. An AR demand typically specifies information about the start of the data transmission or a deadline, as well as the holding time of the transmission. AR has several important applications for both wide-area networks and Grid networks. For example, AR can be used for adjusting virtual topologies to adapt to predictable peak hour traffic usage. It can be used to provide high-bandwidth services such as video conferencing and in Grid applications requiring the scheduled distribution of large files and for co-allocation of network and grid resources. AR can also be beneficial to the network by allowing the network operator to better plan resource usage and therefore increase utilization. Knowledge of the holding time can lead to more optimal decisions for resource allocation. This translates to better quality of service for users. In this paper we provide a comprehensive survey of the past and current work on advance reservation for optical networks. There have been many variations of the advance reservation concept proposed, so we will also provide a broad classification. In addition to the survey, we will discuss what we believe are important areas of future work and open challenges for advance reservation on optical networks.

Analysis of TCP over optical burst-switched networks with burst retransmission

Due to the bufferless nature of OBS networks, random burst losses may occur, even at low traffic loads. For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network, leading to serious degradation of the TCP performance. In this paper, we reduce random burst losses by a burst retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can then reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We analyze the TCP throughput when OBS networks employ the burst retransmission scheme and develop a simulation model to validate the analytical results. Based on our simulation results, we show that an OBS layer with burst retransmission provides an improvement of up to ten times the TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-out based retransmissions when the OBS retransmission scheme is used

Segmentation-based nonpreemptive channel scheduling algorithms for optical burst-switched networks

One of the key components in the design of optical burst-switched nodes is the development of channel scheduling algorithms that can efficiently handle data burst contentions. Traditional scheduling techniques use approaches such as wavelength conversion and buffering to resolve burst contention. In this paper, we propose nonpreemptive scheduling algorithms that use burst segmentation to resolve burst contentions. We propose two segmentation-based scheduling algorithms, namely, nonpreemptive minimum overlapping channel (NP-MOC) and NP-MOC with void filling (NP-MOC-VF), which can significantly reduce the loss experienced in an optical burst-switched network. We further reduce packet loss by combining burst segmentation and fiber delay lines (FDLs) to resolve contentions during channel scheduling. We propose two types of scheduling algorithms that are classified based on the placement of the FDL buffers in the optical burst-switched node. These algorithms are referred to as delay-first or segment-first algorithms. The scheduling algorithms with burst segmentation and FDLs are investigated through extensive simulations. The simulation results show that the proposed algorithms can effectively reduce the packet-loss probability compared to existing scheduling techniques. The delay-first algorithms are suitable for applications that have higher delay tolerance and strict loss constraints, while the segment-first algorithms are suitable for applications with higher loss tolerance and strict delay constraints.

Prioritized routing and burst segmentation for QoS in optical burst-switched networks

In this paper we apply the concepts of burst segmentation and priority-based deflection routing algorithms to provide differentiated services in optical burst-switched networks. The high-priority bursts have significantly lower losses and delay then the low-priority bursts, and the policies which incorporate deflection tend to perform better than the policies with limited deflection or no deflection.