Christoph M. Gauger

Evaluation of Reservation Mechanisms for Optical Burst Switching

Summary In this paper, we give an overview and classification of optical burst switching schemes and present burst reservation concepts. The performance of various basic reservation mechanisms proposed in literature is compared. Furthermore, a new analysis is introduced that allows to calculate the loss probabilities of a two-class system based on the reservation mechanism just-enough-time (JET) for arbitrary offsets. Finally, a variety of new results is presented including the dependence of burst loss probabilities on offset, burst length distribution, and interarrival distribution.

Hybrid optical network architectures: bringing packets and circuits together

In recent years hybrid optical network architectures, which employ two or more network technologies simultaneously, were proposed. They aim at improving the overall network design by combining the advantages of different technologies while avoiding their disadvantages. In order to structure this developing research field, we classify such hybrid architectures based on the degree of interaction and integration of the network technologies. Also, we discuss the three classes and their main representatives regarding key characteristics, performance benefits, and realization complexity. Finally, we highlight two hybrid architectures and show their key benefits compared to the respective non-hybrid architectures through a dimensioning case study

Dimensioning of FDL Buffers for Optical Burst Switching Nodes

Optical burst switching (OBS) is a promising candidate for a more dynamic optical layer in the context of IP over WDM. Although buffering is not mandatory for the functionality of OBS, even simple FDL buffers can improve burst loss probability. In this paper, we first discuss principal buffer architectures and reservation schemes for fiber delay line (FDL) buffers. Then, we investigate key design parameters of FDL buffers like FDL delay, buffer architecture and total number of buffer ports. Finally, we introduce and evaluate strategies for distributing a given number of buffer ports over all FDL’s of a feed-forward buffer.

Does burst assembly really reduce the self-similarity?

Recently, the question has been heavily discussed whether burst assembly in edge nodes of optical burst switching (OBS) networks reduces self-similarity of traffic. Our performance evaluation by analysis and simulation shows that in most cases self-similarity remains unchanged.

Optimized Combination of Converter Pools and FDL Buffers for Contention Resolution in Optical Burst Switching

Optical burst switching (OBS) has attracted interest as a transport network architecture for the future optical Internet. As OBS relies on statistical multiplexing efficient contention resolution is a key issue in order to achieve a low burst loss probability. First, this paper discusses options and key design parameters for contention resolution in OBS. Then, it evaluates the performance of OBS nodes which employ shared wavelength converter pools and simple fiber delay line (FDL) buffers. Finally, optimized strategies for the order of probing a wavelength converter pool and an FDL buffer for contention resolution are presented and compared. It is shown that these strategies can be used to optimize performance for a given, for example, minimal cost, dimensioning of the wavelength converter pool and the FDL buffer.

Performance of converter pools for contention resolution in optical burst switching

Optical burst switching (OBS) has recently attracted increasing interest as a network architecture for the future optical Internet. In OBS, efficient contention resolution is a key issue. This paper investigates the performance of shared converter pools for contention resolution in OBS. First, key design parameters for contention resolution in OBS nodes which employ wavelength converters and simple fiber delay line (FDL) buffers are discussed. Then, the performance of a converter pool is evaluated for a Poisson and a self-similar traffic model. Depending on load and node dimensioning, the number of wavelength converters can be reduced by 50-75%. Finally, different converter usage strategies for the combination of a converter pool and an FDL buffer are presented and compared. A strategy that prefers FDLs over converters for contention resolution can reduce burst loss probability for converter pools with a small number of converters.

Comparison of contention resolution strategies in OBS network scenarios

Optical burst switching (OBS) has attracted interest as a transport network architecture for the future optical Internet. As OBS relies on statistical multiplexing efficient contention resolution is a key issue in order to achieve a low burst loss probability. Basically, contentions can be resolved by wavelength conversion, deflection routing and delaying the burst in a fiber delay line or a combination of these schemes. This paper compares the basic and combined contention resolution strategies in two reference core network scenarios with respect to burst loss probability and end-to-end transfer delay. We show that the effectiveness of those contention resolution schemes highly depends on the load offered to the network and the dimensioning of specific nodes and links. For high load, contention resolution schemes applying deflection routing have an end-to-end transfer time increase in the order of 10-60% depending on the scheme.

Trends in optical burst switching

Optical burst switching (OBS) has been proposed in the late 1990s as a novel photonic network architecture directed towards efficient transport of IP traffic. OBS aims at cost-efficient and dynamic provisioning of sub-wavelength granularity by optimally combining electronics and optics. Optical bursts cut through intermediate nodes, i.e., data stays in the optical domain at all times, while the control information is signaled out-of-band and processed electronically. In contrast to optical packet switching, OBS aggregates and assembles packets electronically into bursts of variable length according to destination and QoS class at the edge of the network. This paper surveys current trends in OBS and discusses proposed solutions for burst reservation and scheduling, burst assembly, contention resolution and QoS provisioning as well as design and scalability of OBS nodes. Also, it looks at the question of the optimal burst size, which has been around from the very beginning of OBS, based on recent trends and results. On the one hand, burst size and burst characteristics are influenced by client layer traffic and burst assembly scheme. On the other hand burst size and burst characteristics have an impact on network performance and node architectures. Finally, consequences of burst durations in the microsecond and millisecond range are presented and compared.

Modeling and performance evaluation of iSCSI storage area networks over TCP/IP-based MAN and WAN networks

This paper provides a concise modeling and performance evaluation of the iSCSI storage area network (SAN) architecture and protocol. SANs play a key role in business continuity, enterprise-wide storage consolidation and disaster recovery strategies in which storage resources are most often distributed over many distant data center locations. In the future, SAN traffic will be transported over IP-based networks, e.g., enterprise virtual private networks, to benefit from converged networks and save cost. In these scenarios, the impact of end-to-end delay and QoS of broadband networks on SAN performance is critical and has to be well understood by IT departments when deploying IP-storage solutions and network operators when designing transport network services for SAN applications. In this context, we propose models for iSCSI write requests over TCP/IP networks, e.g., as used in asynchronous mirroring applications. In addition to the analysis for individual requests we present - to the best of our knowledge for the first time - the evaluation of an iSCSI session under a realistic request traffic model with and without interleaving. We analyze the throughput and total request write times for different network dimensions, i.e., round-trip times, and QoS levels, processing delays in the iSCSI layer as well as request characteristics

Limits of effective throughput of optical burst switches based on semiconductor optical amplifiers

Both signal degradation and burst losses limit the effective throughput of optical burst switches. These limitations are analyzed for different burst switch architectures, bit rates, and numbers of fibers and wavelengths.