To support bursty traffic on the Internet (and especially WWW) efficiently, optical burst switching (OBS) is proposed as a way to streamline both protocols and hardware in building the future gener...

Optical burst switching (OBS) - a new paradigm for an optical Internet

Next-generation high-speed Internet backbone networks will be required to support a broad range of emerging applications which may not only require significant bandwidth, but may also have strict quality of service (QoS) requirements. Furthermore, the traffic from such applications are expected to be highly bursty in nature. For such traffic, the allocation of static fixed-bandwidth circuits may lead to the over-provisioning of bandwidth resources in order to meet QoS requirements. Optical burst switching (OBS) is a promising new technique which attempts to address the problem of efficiently allocating resources for bursty traffic. In OBS, incoming data is assembled into bursts at the edges of the network, and when the burst is ready to be sent, resources in the network are reserved only for the duration of the burst. The reservation of resources is typically made by an out-of-band one-way control message which precedes the burst by some offset time. By reserving resources only for the duration of the burst, a greater degree of utilization may be achieved in the network. This book provides an overview of optical burst switching. Design and research issues involved in the development of OBS networks are discussed, and approaches to providing QoS in OBS networks are presented. Topics include: - Optical burst switching node and network architectures - Burst assembly - Signaling protocols - Contention resolution - Burst scheduling - Quality of service in OBS networks

Optical Burst Switched Networks

Optical burst switching (OBS) is a promising paradigm for the next-generation Internet. In OBS, a key problem is to schedule bursts on wavelength channels whose bandwidth may become fragmented with the so-called void (or idle) intervals with both fast and bandwidth efficient algorithms so as to reduce burst loss. To date, only two scheduling algorithms, called Horizon and LAUC-VF, have been proposed, which trade off bandwidth efficiency for fast running time and vice versa, respectively. In this paper, we propose several novel algorithms for scheduling bursts in OBS networks with and without fiber delay lines (FDLs). In networks without FDLs, our proposed Min-SV algorithm can schedule a burst successfully in O(logm) time, where m is the total number of void intervals, as long as there is a suitable void interval. Simulation results suggest that our algorithm achieves a loss rate which is at least as low as the best previously known algorithm LAUC-VF, but can run much faster. In fact, its speed can be almost the same as Horizon (which has a much higher loss rate). In networks with FDLs, our proposed batching FDL algorithm considers a batch of FDLs simultaneously to find a suitable FDL to delay a burst which would otherwise be discarded due to contention, instead of considering the FDLs one by one. The average search time of this algorithm is therefore significantly reduced from that of the existing sequential search algorithms.

Efficient channel scheduling algorithms in 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.

/pdf/segmentation-based-nonpreemptive-channel-scheduling-48u70vs10f.pdf

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

In this paper, we evaluate and enhance the performance of a Forward Error Correction (FEC) scheme for IEEE 802.11 Medium Access Control (MAC). A novel retransmission combining technique is proposed to enhance the performance of the MAC-level FEC scheme.,We also identify the problem with the IEEE 802.11a physical (PHY) layer when it is used with the MAC-level FEC. A new PHY frame format, backward compatible with the original format, is proposed to resolve the problem. Finally, we analytically evaluate the error performance of the MAC-level FEC, and its enhanced performance via retransmission combining and new 802.11a PHY frame format in AWGN environment. Additionally, we present and discuss the results from simulations using TCP/UDP traffic in more realistic channel environments.

IEEE 802.11 MAC-Level FEC scheme with retransmission combining

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.

Absolute QoS differentiation 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.

/pdf/generalized-burst-assembly-and-scheduling-techniques-for-qos-3mzj9u5cao.pdf

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

A number of schemes have been proposed to support QoS in optical burst-switched (OBS) networks. Most schemes only support relative QoS differentiation instead of absolute QoS guarantee. However, absolute QoS differentiation is a basic requirement for many delay and loss sensitive applications. In this paper, we propose two mechanisms for providing absolute QoS differentiation in OBS networks, an early drop mechanism, which selectively drops non-guaranteed traffic, and a wavelength grouping mechanism, which manages wavelengths for guaranteed traffic. We show that the combination of these two mechanisms not only outperforms other schemes in providing loss guarantees, but also improves the loss performance of non-guaranteed traffic.

/pdf/early-drop-and-wavelength-grouping-schemes-for-providing-3ebiers77c.pdf

Early drop and wavelength grouping schemes for providing absolute QoS differentiation in optical burst-switched networks

There have been several schemes proposed to provide relative differentiated service in OBS. One such scheme is the proportional QoS scheme. However, to meet the requirements of a wide variety of applications, the backbone OBS network must provide absolute QoS differentiation. There is no work in the literature to provide support for this crucial QoS model. We propose an absolute QoS model in the backbone network with admission control and resource provisioning at the edge nodes and with loss guarantee at each core node. We also propose two approaches to guarantee worst-case loss probability at the core nodes: early drop by threshold (EDT) and early drop by span (EDS). We compare the performance of these proposed approaches with the proportional QoS scheme. Simulation results showed that the EDS outperforms EDT and the proportional QoS scheme in providing loss guarantee and also reduces the loss of other non-guaranteed traffic.

http://ieeexplore.ieee.org/iel5/8691/27532/01226697.pdf

Early drop scheme for providing absolute QoS differentiation in optical burst-switched networks

Several schemes have been proposed recently in the literature for providing absolute QoS differentiation in OBS networks, such as early drop and wavelength grouping schemes. However, these schemes only provide loss guarantees at a per-hop level. In this paper, we propose a path clustering technique to implement these per-hop schemes over an entire network. The path clustering technique provides a solution to prioritizing the traffic based on hop-distances between source and destination pairs. We develop an analytical model for obtaining the optimal path clustering for a given network. By using the path clustering technique, we can improve the end-to-end loss performance of nonguaranteed traffic, and also provide absolute end-to-end loss probability of guaranteed traffic.

/pdf/path-clustering-an-approach-to-implement-absolute-qos-4cysa10r2w.pdf

Path clustering: an approach to implement absolute QoS differentiation in optical burst-switched networks

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