The impact of OBS burst aggregation on VBR performance

The constant and rapid expansion of the Internet at such a high rate has caused its traffic to double every four to six months. A large portion of this traffic is known to be multimedia and real time traffic, which has strict requirements in term of bandwidth, delay, jitter, and loss rate. Recent studies showed that constant bit rate (CBR) and variable bit rate (VBR) traffic can reduce both the transmission and storage costs for real time traffic. Other studies showed that optical burst switching (OBS) appears to be a promising switching technique for building the next-generation Internet infrastructure. In this paper, the compatibility between the requirements of CBR and VBR traffic and the services provided by the OBS networks are investigated. Initial finding shows that there is a need for quality of service (QoS) mechanisms to guarantee the CBR and VBR traffic characteristics and contract over OBS networks. This paper also discusses the issue of providing QoS over OBS network. The result of the study shows that the current QoS over OBS is insufficient for meeting the CBR and VBR traffic requirements if carried over the OBS networks. Nevertheless, it can be a motivation for further research.

Optical burst switching (OBS) network has been proposed as a novel network scheme which can realize IP over WDM and also been regarded as the trend of the next optical generation network. In OBS network, burst contention phenomena may often occur at the output data channel in core routers and the contention can bring on the data losing. Optical composite burst switching (OCBS) has been regarded as an efficient approach for the resolution scheme in burst contention, which segments and drops the header of contending burst, but OCBS may bring unfairness to burst dropping, this unfairness causes the OBS network can't well support quality of service (QoS). The previous works that focus on the resolution approaches for the unfairness have some limitations and also could bring unfairness to OBS network. An improved resolution approach has been proposed to solve the unfairness of burst segmentation and dropping in optical burst switching multi-hop network in this paper, this approach not only could maintain the advantage of conventional resolution approach, which could make the packets loss probability coherence in multi-hop network but also could decreases the data losing and increase the throughput for OBS network. At last, some simulations prove the validity of the proposed approach and it has the theoretic meaning to design the real OBS network in practice.

Variable bit rate (VBR) compressed video targeted at constant video quality is also known to exhibit significant and multiple-time-scale rate variabilities. The burstiness of such a compressed VBR video complicates the management and provisioning of network resources for ever increasing multimedia services. In a heterogeneous internetworking environment, a single service provider typically doesn't control the entire path from multimedia streaming server to the client buffer. In this paper we analyze bit rate variabilities exhibited by scalable video coding (SVC) encoded VBR stream and present optical burst switching (OBS) network as a mechanism for VBR transport across the core network. In our experimental evaluation we use OBS inherent bursitification feature at the edge node and evaluate its effectiveness towards smoothing and transport of VBR video stream. SVC encoded VBR video is transported over OBS test bed and OBS burst assembly parameters like time threshold and offset time are tuned for a smooth transport of SVC encoded VBR video stream. Experimental results reveal that for a proper burst assembly time, OBS transported VBR video stream has low inter-frame time intervals as well as a high peak signal to noise ratio (PSNR).

This paper considers the use of closed loop feedback control theoretic techniques to improve the performance of Optical Burst Switching (OBS) networks. In OBS networks, the Burst Loss Ratio (BLR) is the ratio between the lost bursts to the sent bursts. The BLR is used as a performance metric. The desired burst loss ratio depends on the application using the network. Some applications might tolerate more burst loss ratios than other applications. Higher network link utilization could be achieved by having more control over the burst loss ratio. Burstification rate is the rate of injecting bursts into the OBS network. In this paper, a novel technique to control the burst loss ratio in OBS networks is proposed. The technique is based on classical control theory approaches to tune the burstification rate in order to achieve a desired burst loss ratio to satisfy the application requirements. Extensive experiments show that the proposed technique achieves promising results. That is, the measured burst loss ratio hovers around the desired burst loss ratio and higher utilization is observed. Empirical approaches are used to identify the proposed model. The empirical model fits the OBS network by a value that did not fall below 75%.

In this study, we examine control-plane throughput in optical burst switching (OBS) networks with electronic header processing. In a large-scale OBS network, headers arrive to the burst scheduler at a very high rate. This can potentially cause overloading of the core-node control-processor and lead to data loss if headers are not processed in a timely manner. In this work, we examine the effect of control-plane congestion on the overall loss performance of OBS networks. We present preliminary results that show how this congestion can become the primary source of loss and can ultimately limit the throughput and the scalability of the OBS system if not properly accounted for when designing the OBS network.

The Scalable Video Coding (SVC) extension of H.264/AVC has higher compression efficiency and supports a wide range of scalability modes. But, due to invent of improved compression tools like motion compensated predictions and hierarchical B-frames, SVC suffers from higher bit rate variabilities as compared to the preceding encoders, making its network transport more challenging. Different mitigation techniques employed in the codecs, to eliminate such traffic variabilities, increase computational load as well as introduce extra coding delays. We propose a novel mechanism to use Optical Burst Switching (OBS) Network inherent capability of aggregating incoming packets at its ingress edge node for smoothing of SVC variable bit rate traffic thus resulting in efficient transport of SVC encoded VBR stream over the OBS core network and also reducing computational complexities of SVC codec.

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS Networks, called logical cascaded private subnet with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the OBS core node. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in OBS core node correspondingly. Due to the absence of wavelength conversion capabilities, we assign start wavelengths to both private subnets before network start operation. A new start wavelength assignment policy is proposed for the absence of wavelength conversion capabilities in the core node of OBS Networks. The analytical results clearly show that logical cascaded private subnet scheme can yield better performance in terms of block probability than traditional OBS Networks, and logical cascaded private subnet with start wavelength assignment policy has the potential to improve the block probability by more than one order of magnitude compared with traditional OBS Networks, helping reduce the performance gap with respect to full wavelength conversion.

This paper considers the use of closed loop feedback control theoretic techniques to improve the performance of optical burst switching (OBS) networks. In OBS networks, the burst loss ratio (BLR) is the ratio between the lost bursts to the sent bursts. The BLR is used as a performance metric. The desired burst loss ratio depends on the application using the network. Burstification rate is the rate of injecting bursts into the OBS network. In this paper, a novel technique to control the burst loss ratio in OBS networks is proposed. The technique is based on classical control theory approaches to tune the burstification rate in order to achieve a desired burst loss ratio to satisfy the application requirements. Extensive simulations on the NSFNET topology show that the proposed technique achieves promising results. That is, the measured burst loss ratio hovers around the desired burst loss ratio for all nodes.

Quality of Service differentiation is an open research issue in optical burst switching (OBS) networks. Most proposals assume full wavelength-conversion, but wavelength converters are still very complex and expensive, and accordingly limited and no wavelength conversion OBS networks are likely to be the most common scenarios. In this paper, we define and analyze the QoS Multiple Wavelength Simultaneous Transmission technique (QoS-MWST), a novel method for providing loss differentiation in OBS networks with limited or no wavelength-conversion capability. In QoS-MWST, multiple copies of each burst are simultaneously sent on different wavelengths, so as to increase the chances of data delivery, and loss differentiation is achieved by properly sending more copies of the higher-priority bursts. Through analysis and extensive simulation experiments, we demonstrate that QoS-MWST can provide loss differentiation in OBS networks without full wavelength-conversion capability more efficiently than other differentiation techniques proposed in the literature.

In optical burst switching (OBS) networks, class differentiation is achieved by assigning an adequately long offset time between a burst control packet (BCP) and a data burst (DB). Blocking probability is one of the main performance measures in OBS networks. Though the effects of length distribution of low-class burst and the ratio of arrival rates of low-class and high-class on high-class blocking probability have been studied, there has been no examination of the effects of the length of low-class on burst blocking probability. In this paper, we analyze loss performance of OBS network by examining the burst size of low-class bursts. When we vary the burst size of low-class burst from large to small, the evaluation results show that while the high-class blocking probability remains same, the low-class blocking probability decreases significantly. These results imply that it is important for OBS network designers to take into account the burst size of low-class to improve system performance in OBS networks

A major concern in optical burst-switched (OBS) networks is contention, which occurs when more than one bursts contend for the same data channel at the same time. Due to the bufferless nature of OBS networks, these contentions randomly occur at any degree of congestion in the network. When contention occurs at any core node, the core node drops bursts according to its dropping policy. Burst loss in OBS networks significantly degrades the throughput of TCP sources in the local access networks because current TCP congestion control mechanisms perform a slow start phase mainly due to contention rather than heavy congestion. However, there has not been much study about the impact of burst loss on the performance of TCP over OBS networks. To improve TCP throughput over OBS networks, we first introduce a dropping policy with burst retransmission that retransmits the bursts dropped due to contention, at the ingress node. Then, we extend the dropping policy with burst retransmission to drop a burst that has experienced fewer retransmissions in the event of contention at a core node in order to reduce the number of events that a TCP source enters the slow start phase due to contention. In addition, we propose to limit the number of retransmissions of each burst to prevent severe congestion. For the performance evaluation of the proposed schemes, we provide an analytic throughput model of TCP over OBS networks. Through simulations as well as analytic modeling, it is shown that the proposed dropping policy with burst retransmission can improve TCP throughput over OBS networks compared with an existing dropping policy without burst retransmission.

From the network layer perspective, the problem of burst losses is one of the most challenging problems which restrain the development of optical burst switching (OBS) networks. Indeed, OBS is a buffer-less technology and the consequent lack of guarantees for data delivery may affect significantly the quality of service (QoS) perceived by end users. To overcome these obstacles, dedicated network mechanisms and design methods are required for QoS provisioning in the network. With this end in view, in this paper, we present a traffic engineering (TE) approach to support the end-to-end traffic delivery with absolute QoS guarantees, in terms of burst losses, in an OBS network. We focus on the establishment of explicit routing paths and minimum allocation of wavelength resources in network links under the requirement that certain absolute level of burst loss probability for a given set of traffic demands is guaranteed. In this paper, we call such an off-line problem the virtual topology (VT) design problem. Since the VT design problem is NP-complete, as an alternative to the mixed integer linear programming formulation, we develop a local search heuristic algorithm to solve it. Moreover, we focus on a dynamic OBS network scenario, where the offered traffic is subject to a change. In this context, we propose an on-line VT maintenance mechanism that is responsible for traffic admission control and adaptation of the VT to traffic changes. Eventually, proposed algorithms and mechanisms for the TE-driven end-to-end QoS approach are verified both numerically and by means of network simulations for a number of network scenarios.

The main weakness of OBS (Optical Burst Switching) networks is the difficulty to support different types of traffic requiring several performance constraints. This paper focuses on the design and the performance evaluation of efficient cognitive OBS protocols that pave a way to the multi-service context. We present a graphical probabilistic model to avoid and resolve contention inside the OBS network. In order to efficiently exploit the available bandwidth while respecting QoS requirements, we highlight our complete framework using closed/open loop feedback control theoretic techniques to improve OBS networks performance.

Since Transmission Control Protocol (TCP) is the dominant protocol on the Internet and optical burst switching (OBS) networks represent the optical transmission solution that can meet future high bandwidth requirements, TCP and OBS networks represent a possible combination for the next-generation Internet. However, a problem with this combination model is that operations at the OBS layer need to be controlled so that false congestion detection at the TCP layer is minimised. Considering the combination of TCP Vegas and OBS, congestion detection at the TCP layer is based on the round-trip time (RTT), where congestion is detected if the current RTT exceeds a given RTTmax. The extra delay may be due to some actual loss, but it may also be due to the extended execution time caused by some OBS layer operations. Therefore, reducing the time of operations at the OBS layer will reduce false congestion detection at the TCP layer. This paper investigates the impact of reducing the buffering time at the ingress node on the false congestion detection rate at the TCP layer. The reduction of the burst buffering time is accomplished by nesting the offset time in the assembly time. The simulation results and analysis show that the transmission efficiency in TCP Vegas over OBS networks is significantly improved; the throughput remains high, and the delivery success rate is significantly increased compared to the conventional buffering mode.

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, which has a considerable impact on network performance, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS networks, called logical cascaded private subnet (LCPN) with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the core node in OBS Networks. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in the core node correspondingly. A new start wavelength assignment policy is proposed for the absence of (full) wavelength conversion capabilities in the core node of OBS Networks. The performance study indicates that, our new scheme is robust under self-similar traffic and wavelength continuity constraint.