Muhammed Ali Aydin

Performance Study of OBS Reservation Protocols

This paper presents a comparison of reservation protocols used in optical burst switches (OBS) with quality of service (QoS). In terms of performance criteria, byte loss rate, end-to-end delay and access delay are considered. A 2-state MMPP(Markov modulated Poisson process) traffic generator on a 14-node mesh network topology illustrating NSFNET is chosen as the testbed. This topology is simulated using NS2 network simulation platform. Bursts are created using a hybrid model that takes into account both timeout and maximum length methods. In edge and core nodes, there are different QoS mechanisms such as explicit tear down and priority based queuing. Simulation results have shown that JIT (just in time) algorithm is not as successful as JET (just enough time) and horizon when the network is highly loaded. However, JET algorithm produces better performance than other reservation protocols while considering QoS.

A new dynamic bandwidth allocation algorithm based on online-offline mode for EPON

In parallel with the enormous spread of Internet usage, the tendency of users for high capacity applications (HDTV, Online Games, P2P File Transfer) are rising. This increase in needs of data communication, compel the service providers to act to end users better than before. At this point, Passive Optical Networks (PONs) distinguish in access network solutions due to its capability of carrying high amount of data over longer distances. Although they are still in development, existing electronic based data communication techniques (ADSL, double twisted copper telephony systems like VDSL, cable modem coaxial cable CATV systems) can operate over short distances and have large amount of energy consumption. In this paper, basic schemes of dynamic bandwidth allocation algorithms on EPON have been presented and a novel online-offline based method called hcDBA (Half Cycling Dynamic Bandwidth Allocation) has been introduced. In addition, hcDBA algorithm has been improved with early prediction mechanism (p-hcDBA). By the simulation studies, it has been investigated that hcDBA algorithm performs better than existing mechanism in terms of byte loss ratio and access delays criteria. p-hcDBA also improved the performance in terms of access delay. In this study, we stated that when the bandwidth increases the prediction approached has more impact of the overall performance.

Performance Study of New OBS Channel Scheduling Algorithms in a Multiservice Network

This paper presents a comparative study between JET (Just Enough Time) and a number of new preemptive channel scheduling algorithms in Optical Burst Switching (OBS) with QoS (Quality of Service) requirement. In terms of performance criteria, loss rate in byte, access delay and end-to-end delay are considered. A 2-state MMPP (Markov Modulated Poisson Process) traffic generator on a 14-node mesh network topology illustrating NSFNET is designed as the testbed. NS2 Network Simulation tool is used for our tests. Bursts are created using a hybrid model that takes into account both timeout and maximum length threshold mechanisms. In core and edge nodes, in order to satisfy QoS requirements two mechanisms such as Regulative Wavelength Grouping (RWG) and priority based queuing are used. RWG mechanism, where the number of wavelengths for each traffic class is arranged for adjusting the burst drop probability of traffic classes under a specific threshold value, is used for providing priority levels in core nodes. In priority based queuing, bursts are sent according to their priority order, in edge nodes. Simulation works have shown that our preemptive channel scheduling algorithms give better results compared to the other studied algorithms while considering QoS.

A circular chain intrusion detection for cloud computing based on improved AdjointVM approach

Cloud computing has recently emerged and gained momentum to implement existing networks and data centers in a new architecture to enable services in a timely manner. Although it offers tremendous opportunities, there are some major challenges, such as security, that must be solved for efficient usage. Confidentiality is one of the most important points of information security especially in financial, governmental and military usage. In this paper, we propose a hybrid approach for cloud computing to protect cloud users from the untrusted cloud providers and untrusted employees. The proposed approach is built as an improvement on an existing model, which is called AdjointVM. In this model, it is aimed to overcome one of the weakest points of AdjointVM model, the defenselessness of the protection architecture, and to build a more secure cloud environment for users. In AdjointVM, to protect the VM, there have to be two configured VMs: the protected VM and the protector VM. These VMs are connected in a circular chain to monitor intrusions. Unlike AdjointVM, in which the number of running VMs is proportional to the number of VMs that have to be protected, in the proposed model, this number remains the same, and this results in a decrease in the capital expenditure (capex).

Circular chain VM protection in AdjointVM

Cloud computing is a demanding subject and its fans are increasing day by day in the private or corporate areas. Confidentiality is the most important point of information security with respect to integrity and availability in cloud computing especially in financial, governmental and military usage. An Intrusion Detection System (IDS) service increases the clouds security level. In this paper, a hybrid approach is introduced that can be used in cloud computing to protect cloud users from the untrusted cloud providers or untrusted employees in a circular chain protection model. This model is proposed over an existing model, AdjointVM, which uses three types of technologies (trusted computing, host-based IDS, virtual machine monitor based IDS) to tackle external and internal threats in cloud systems. The proposed model claims to overcome one of the weakest points of AdjointVM model, and aims to build a more secure cloud environment for the users by adding additional security mechanism between VMs. In the proposed model, responsibility of confidentiality is not giving up only to the providers or cloud administrators, a VM can protect another VM in a circular manner and this results a chain structure and constructs a circular structure to enhance global security of the system. At the same time, users can also manage and monitor their own confidentiality by themselves.

A Dynamic Energy Efficient Optical Line Terminal Design for Optical Access Network

Computer networks are one of the major slices of the global energy consumption. Since 2009, a couple of standards have been developed for energy conservation in passive optical networks. These standards and most of the researches are based on improvements on Optical Network Unit side. In this study, a novel energy efficiency algorithm, which is based on coupling two Optical Line Terminal to reduce energy consumption in central office, is proposed. Our design employs optical switches and amplifiers to create a switch-box, which is under control of both Optical Line Terminal pairs.

A framework for modeling and implementing QoS-aware load balancing solutions in WiFi hotspots

Access Point (AP) selection in WiFi hotspots is driven by stations and it is based on the measured strongest RSSI (Received Signal Strength Indicator) level: any station connects to the AP that provides the higher physical data rate. Although simple and effective in low crowded scenarios with low-medium traffic load, this strategy performs inefficiently when the number of mobile users is high and their distribution among APs is unbalanced, i.e. when network congestion becomes an issue. Load Balancing (LB) solutions aim at solving this problem by enforcing the connection of stations to the AP having either the smallest number of associated stations or the lowest traffic load. However, LB solutions do not account for traffic priorities or, when they consider them, they do not deal with the joint configuration of QoS (Quality of Service) and LB parameters. In this study we present a framework for modeling, analyzing and designing QoS-aware LB solutions. The proposed framework assumes that stations implement the Enhanced Distributed Channel Access (EDCA) mechanism of the IEEE 802.11e standard. Moreover, in order to make the framework concrete, we assume that the QoS goal is the weighted fair allocation of wireless resources. However, the framework is not restricted to this goal and can be easily extended in order to deal with a different cost function. The proposed framework is validated through simulations in a typical indoor LB scenario. The results show that the model is effective in capturing network performance and in designing LB solutions that account for traffic priorities and the configuration of QoS parameters.

A performance comparison of OPS with variable-size packets and OBS

This article presents a comparative study between Optical Burst Switching (OBS) and Optical Packet Switching (OPS) with variable-size packets on mono-service and multi-service network with Quality of Service (QoS) support. In terms of performance criteria, loss rate in byte and access delay are considered. A 2-state Markov Modulated Poisson Process (MMPP) traffic generator is used. A 14-nodes mesh network topology illustrating NSFNET and a ring topology are designed as the testbed. NS2 Network Simulation tool is used for our tests. According to the simulation results, we have seen that in both mono-service and multi-service networks, OPS is better than OBS under low traffic loads. However, OBS performs better than OPS in mono-service networks and low priority service classes under high traffic loads. In this study, we have shown that choosing one of these two switching technologies (OPS or OBS) in the future depends on the traffic load and the topology of network, together with the considered service differentiation scheme.

Regulative Wavelength Grouping Approach for QoS in OBS Networks

In this study, a wavelength grouping approach has been proposed for core nodes in OBS in order to control byte drop rates for different classes of traffic. Preemptive Channel Scheduling Algorithm (PCSA) has been used for channel scheduling in OBS. In terms of performance criteria, loss rate in bytes is considered. A 2-state MMPP (Markov Modulated Poisson Process) traffic generator on a 14-node mesh network topology illustrating NSFNET is designed as the testbed. NS2 Network Simulation tool is used for our tests. In OBS algorithms, bursts are created using a hybrid model that takes into account both timeout and maximum length threshold mechanisms. In nodes, in order to satisfy QoS requirements, priority based queuing and Regulative Wavelength Grouping (RWG) are used. In priority based queuing, packets (bursts) are sent according to their priority order. RWG mechanism, where the number of wavelengths for each traffic class is arranged for adjusting the packet drop probability of different classes of client traffic under a specific threshold value, is used for providing priority levels. According to the simulation studies, RWG algorithm gives better results in OBS for high priority traffic performance.

A performance comparison according to number of wavelengths and topologies on PCSA reservation mechanism for OBS

A performance comparison according to different number of wavelengths and topologies on OBS has been studied in this paper. Preemptive Channel Scheduling Algorithm (PCSA) has been used as reservation mechanism in OBS. In terms of performance criteria, loss rate in bytes, access delay and end-to-end delay are considered. A 2-state MMPP (Markov Modulated Poisson Process) traffic generator is used. Four different types of Mesh and Ring topologies are used. NS2 Network Simulation tool is used for our tests. In OBS algorithms, bursts are created using a hybrid model that takes into account both timeout and maximum length threshold mechanisms. In nodes, in order to satisfy QoS requirements, priority based queuing and Regulative Wavelength Grouping (RWG) are used. In priority based queuing, packets (bursts) are sent according to their priority order. In this study, the effects of generated traffic according to the topologies and the effects of increased number of wavelengths are shown by access delays. According to the simulation studies, the success of byte drop rate increases while the number of wavelengths increases. The results that obtained on mesh topologies are better than the results of ring topologies according to our simulation results.