Extra Offset Time Research Articles

Efficient Predictable Probe of Optical Burst Switched For Wireless Feeler Bond

Optical Burst Switching (OBS) is a promising paradigm for high speed transmission of data. In OBS, a key problem is to schedule bursts with minimum loss. Single method is not sufficient to improve performance. So, our performance model includes some feasible methods to improve OBS performance without significantly increasing the implementation complexity. The methods are addition of simple fiber delay lines (FDLs), increasing random extra offset time, window based channel scheduling (WBS) and Burst Delay Feedback scheduling (BDFS). Additional FDLs can only eliminate the negative impact caused by the variation of the offset time between control packets and data bursts. The random extra offset time approach does not require any additional hardware in the nodes. WBS provides better throughput improvement when FDLs are used in the nodes to compensate the processing time. Finally Burst Delay Feedback Scheduling in addition with these methods can significantly improve OBS throughput and reduce transmission delay.

Traffic Control Based on Contention Resolution in Optical Burst

Traffic control based on contention resolution process (TCCR) is proposed in this study as a quality of service (QoS) mechanism to offer service level agreement (SLA) for optical burst switch (OBS). QoS of the high and the low priority classes are issued upon their SLA. The first one is defined for real time application as Internet protocol television (IP TV) and voice over Internet protocol (VoIP) while the other is for soft real–time service as Internet protocol remote terminal unit (IP RTU) based on IEC 86070–5–101/104 protocol. A combination of burst aggregation (BA), extra offset time, and fiber delay line (FDL) are utilized in TCCR to offer absolute service differentiation QoS to the high priority class. The experiments show TCCR can offer the high priority class of its satisfied SLA for both blocking probability and delay. It also relatively improves the performances of the low priority class bounded in its SLA because TCCR does not force to drop this class. The performances of TCCR are compared with the other techniques such as no class isolation and bandwidth allocation processes. The comparisons show TCCR gives the best solution of the defined SLA which enhances OBS performances and properly differentiates class of services.

Modeling analysis of deflection routing with FDLS to resolving contention problem in Obs networks

In Optical Burst Switching Network contention is one of the big problem. Contention occurs when more than one burst demand for same output wavelength channel in same time. The deflection routing, fiber delay line (FDL) and wavelength conversion are the methods used to resolve contention in OBS Networks. With deflection routing, contending bursts in send in another route rather than primary route towards it’s destination. In this case of wavelength conversion if any contentions occur then one of the burst’s wavelength have to be change from its current wavelength to another free wavelength channel. And, FDLs is usual used to provide an extra offset time for deflected burst since deflection route is commonly longer than primary one. This paper is propose a modeling analysis of deflection routing with FDLs using Queueing theory to resolving contention problem in OBS Network. Analysis results show that proposed model reduce blocking probability in comparison with models before.

A distributed backoff-channel deflection algorithm with load balancing for optical burst switching networks

Optical burst contention is one of the major factors that cause the burst loss in the optical burst switching (OBS) networks. So far, various contention resolution schemes have been proposed. Among them, the deflection path is more attractive due to its low requirement for optical buffer in capability and quantity. However, these deflection path algorithms do not consider the successful transmission rate of deflection traffic, and the deflection traffic's impacts on the original traffic of the deflection path are not concerned. Meanwhile, the offset-time deficit problem for deflected bursts is ignored. Therefore, in order to reduce the burst loss probability in OBS networks, a Distributed Backoff-channel DeFlection algorithm with load balancing, for short DBDF-LB, is proposed. It consists of two parts, that is, the deflection with load balancing and the backoff-channel buffering scheme. Firstly, from the perspective of the network-wide load balancing, the optimal deflection path, on which the contention-failure burst is deflected with the minimum hops and the least burst loss probability, is selected. Secondly, the extra offset-time for the deflected burst is provided through the backoff-channel scheme. Finally, by numerical simulations, compared with the classical shortest path deflection algorithm, the DBDF-LB can obviously reduce the burst loss probability, about 50%, with a little extra overhead.

Performance Improvement Methods for Burst-Switched Networks

In this paper, we present a performance model of optical burst switching (OBS) that can explain the degradation of OBS throughput performance when the control packet processing time increases. We then use the proposed performance model to investigate three feasible methods to improve OBS performance without significantly increasing the implementation complexity: addition of simple fiber delay lines (FDLs), random extra offset time, and window-based channel scheduling (WBS). Additional FDLs can eliminate the negative impact caused by the variation of the offset time between control packets and data bursts. The random extra offset time approach does not require any additional hardware and computational capability in the nodes. If higher computational capability is available, WBS in general can provide better throughput improvement than that of random extra offset time when FDLs are used in the nodes to compensate the processing time. Simulation results show that a combination of the proposed methods can significantly improve OBS performance.

Joint resource and network scheduling with adaptive offset determination for optical burst switched grids

Optical burst switching (OBS) is a promising technology for optical grids with short-lived and interactive data communication requirements. On the other hand, burst losses are in the nature of the OBS protocol and these losses severely affect the grid job completion times. This paper first proposes a joint grid resource and network provisioning method to avoid congestion in the network in order to minimize grid job completion times. Simulations show that joint provisioning significantly reduces completion times in comparison to other methods that perform network provisioning after grid scheduling. An adaptive extra offset based quality of service (QoS) mechanism is also proposed in order to reduce grid burst losses in case of network congestion. Results show that this adaptive mechanism significantly reduces grid completion times by exploiting the trade-off between decreasing loss probability and increasing delay introduced by the extra offset time.

A general resource assignment scheme for successful transmission in optical burst switched networks

This work proposes a general resource assignment strategy for Optical Burst Switched networks to avoid burst losses. Given a set of communications and the associated paths defined by a routing, we propose a wavelength assignment scheme in which contentions can always be solved or avoided by delaying properly the transmission of some (perhaps all) data bursts. Two mechanisms are defined for this purpose. One is based on adding a suitable extra-offset time to each burst transmission (static approach). The other consists of adding the additional delay, only when contention occurs in an intermediate node of the network, by using a single fiber delay line (dynamic approach). In both cases, the additional delay is independent of the link lengths. Moreover, we resort to Linear Programming (LP) methods to compute the number of wavelengths needed to serve a given traffic matrix. Some examples show that the proposed method gives optimal or near-optimal solutions. This strategy works in either synchronous or asynchronous transmission environments. Moreover, the burst arriving and length distributions can be of general type.

Modelling and performance evaluation of optical burst switched node with deflection routing and dynamic wavelength allocation

In this paper the effect of dynamic wavelength allocation (DWA) scheme implementation to the OBS node performance is investigated. We have developed the mathematical model of an OBS node in order to evaluate the burst blocking probability. It is proposed to allocate a part of total wavelength capacity to be used by deflected bursts only. The results obtained from the model show that if the number of allocated wavelengths is dynamically adapted to the deflected burst traffic intensity, the total blocking probability and deflected burst blocking probability significantly decrease. Concerning to the hardware requirements the implementation of deflection routing needs the limited optical FDL buffer incorporation, to provide the deflected burst with the extra offset time. Also, control logic for burst scheduler needs to be upgraded to perform the dynamic wavelength allocation for deflected bursts. .

FEC-Based Reliable Transmission for Multiple Bursts in OBS Networks

SUMMARY In this paper, we consider consecutive burst transmission with burst loss recovery based on Forward Error Correction (FEC) in which redundant data is transmitted with multiple bursts. We propose two burst generation methods: Out-of Burst Generation (OBG) and In-Burst Generation (IBG). The OBG generates a redundant burst from redundant data, while the IBG reconstructs a burst from an original data block and a part of the redundant data. For both methods, the resulting bursts are transmitted consecutively. If some bursts among the bursts are lost at an intermediate node, the lost bursts can be recovered with the redundant data using FEC processing at the destination node. We evaluate by simulation the proposed methods in a uni-directional ring network and NSFNET, and compare the performances of the proposed methods with the extra-offset time method. Numerical examples show that the proposed methods can provide a more reliable transmission than the extra-offset time method for the OBS network where the maximum number of hops is large. Moreover, it is shown that the end-to-end transmission delay for our proposed methods can be decreased by enhancing the FEC processor or by increasing the number of FEC processors.

Service Differentiation Scheme Using Two Horizons for Horizon Based OBS Networks

We propose a service differentiation scheme for optical burst switching (OBS) with the scheduling algorithm Horizon. In the proposed scheme, in addition to the latest horizon used in the conventional Horizon, we introduce the second latest horizon and use them for reservation preemption. Burst priority order is perfectly guaranteed according to the burst class information informed by its control packet if the arrival time of the burst is later than the second latest horizon and earlier than the latest horizon. Since the extra offset time is no longer needed for service differentiation, the burst blocking probability and the data latency will be reduced. We assume a multi-hop network with ring topology where bursts traverse five intermediate nodes, and evaluate the performance in terms of the end-to-end and hop-by-hop burst blocking probabilities. Simulation results show that the proposed scheme can achieve service differentiation with smaller blocking probability than the extra-offset-time-based scheme with Horizon. Furthermore, we show that the proposed scheme preserves service differentiation even in multi-hop environments.

Providing absolute differentiated services for optical burst switching networks: loss differentiation

The provision of absolute differentiated services for optical burst switching (OBS) networks based on dynamic wavelength assignment is investigated. Unlike existing quality of service (QoS) schemes, such as buffer-based and offset-time based ones, the proposed dynamic virtual lambda partitioning (DVLP) scheme does not mandate any buffer or extra offset time, but can achieve absolute service differentiation between classes. This new DVLP scheme shares wavelength resources based on several different class priorities in an efficient and QoS guaranteed manner. Furthermore, DVLP is robust: this means that each traffic class, with a loss probability conforming to the target value, continues to receive the required QoS, despite the presence of misbehaving packets, such as bursty arrival traffic. The conditions in which the DVLP scheme is feasible are stated, and the performance results are given for the proposed scheme, which effectively guarantees the target loss probability of each traffic class, both in Poisson and self-similar traffic environments.

Providing absolute QoS through virtual channel reservation in optical burst switching networks

This paper proposes a new absolute QoS differentiation scheme call Virtual Channel Reservation (VCR) scheme for Optical Burst Switching (OBS) networks. The scheme provides worst case guarantee on the drop probability of higher priority classes. In existing literature, there are very few contributions that support efficient absolute QoS guarantee in OBS networks, which is critical for burst drop sensitive applications. The service differentiation among each priority class in VCR is achieved by applying the concepts of virtual channel reservation and pre-emption, rather than by implementing optical buffer or extra offset time. Pre-emption in OBS literature often means the discard of a scheduled burst or a burst in service. One potential side effect of pre-emption, however, is bandwidth under utilization in multi-node scenarios. To address this problem, we also contribute a new informing header (i-header) mechanism. Simulations are conducted to evaluate the performance of VCR, both with and without i-headers. Results show that VCR without i-headers is able to meet the absolute QoS requirements in both single-node and multi-node scenarios. In addition, the introduction of i-header effectively reduces downstream bandwidth wastage caused by pre-emption in the multi-node scenario. The contribution of VCR and i-header are significant for the following practical reasons. First, VCR does not use optical buffers or extra offset time to achieve service differentiation; hence long end-to-end delay problems will not arise. Second, VCR conforms theoretically to the Conservation Law; hence as far as overall drop probability is concerned, VCR will outperform other QoS techniques like Guard Channel (GC) and JET QoS schemes. The last statement will be verified both theoretically and by the many simulation scenarios presented in the paper.

Absolute priority just-enough-time scheme for absolute quality of service in optical-burst-switching networks

We propose an extension of the popular priority just-enough-time (PJET) system in optical-burst-switched networks to provide absolute quality-of-service (QoS) differentiation. PJET is a simple QoS protocol that provides relative service differentiation by means of an extra offset time given to higher-priority bursts. By the innovative use of fiber delay lines (FDLs) and an accompanying token algorithm, we are able to achieve an absolute QoS technique that provides a worst-case loss probability for the guaranteed traffic. This absolute PJET technique is similar to the PJET scheme in that it conforms to the conservation law at high loads. This means that the drop probability of low-priority bursts is kept to a minimum. This is a significant advantage over existing absolute QoS techniques that employ intentional dropping or wavelength reservation, which does not conform to the conservation law.