Journal of High Speed Networks

Evaluation of the availability and unavailability of optical connections is necessary for WDM optical networks to make efficient use of optical resources. Network providers will not be welling to upgrade their current protection plans unless these protection strategies are carefully investigated, providing them with optimal tradeoffs between the required protection degree and the corresponding cost. In this paper, a mathematical model based on the combinatorial and probability theories is developed to evaluate the availability and unavailability of protected optical connections in WDM networks employing M:N dedicated protection. This model works with any number of working and protected paths. Several numerical tests have been performed and their results are presented to investigate the availability and unavailability degrees for different number of working and protection paths. Moreover, we use Monte-Carlo simulation to verify the correctness of our mathematical model. Simulation results confirm not only the correctness of the proposed model but also its potential accuracy. The proposed analytical model provides an efficient tool for network providers to assess the anticipated improvement in the network availability by upgrading their survivability schemes to higher protection classes.

We propose a network scheme with Admission Control (AC) for TCP flows, which can provide different minimum throughputs and isolation between flows. It is built with simple mechanisms without per-flow state, per flow signaling or per-flow processing in the core. The whole scheme uses a small set of packet classes, with a different discarding priority assigned to each one. The AC is implicit, edge-to-edge and based on per-aggregate throughput measurements. The out packets of the aggregation of accepted flows (i.e., the packets that correspond to the flows' extra throughput) act as a probing flow to test if the throughput in the network path is enough to satisfy the flow's request. Then signaling packets carry the per-aggregate throughput measurement from the egress to the ingress, where the AC decision is made. Through simulation we show that the scheme guarantees the requested minimum throughput to accepted flows and achieves a good utilization of resources.

In a heterogeneous system, processor and network failure are inevitable and can have adverse effect on the complex applications executing on the systems. To reduce the rate of these failures, matching and scheduling algorithms should take into account the objectives of minimizing schedule length (makespan) and reducing the probability of failure. Equitable distribution of workload over resources contributes in reducing the probability of failure. The Heterogeneous Earliest Finish Time (HEFT) algorithm has been proved as a performance effective task scheduling algorithm, addressing the objective of minimizing makespan. Reliable Dynamic Level Scheduling (RDLS) algorithm is a bi-objective scheduling algorithm that maximizes the reliability more effectively. Though the reliable version of HEFT algorithm (RHEFT) considers failure rate in scheduling decision, the improvement in reliability is less, compared to that of RDLS. To overcome this deficiency, we propose to incorporate the task–processor pair finding step of RDLS in HEFT algorithm, since it meets both the objectives of minimizing the makespan and maximizing the reliability. We define the load on a processor as the amount of time the processor is engaged in completing the scheduled subtasks. In this paper, a modification to the HEFT is proposed as a new algorithm called Improved Reliable HEFT (IRHEFT) for minimizing the schedule length, balancing the load and maximizing the reliability of schedule. The algorithm is compared for its performance with RDLS algorithm for randomly generated task graphs and a real application task graph.

The Internet multicast capabilities have been used in enormous number of groups through the Internet. However, IP multicast does not deploy any mechanisms to secure the multicast messages in these groups. A lot of research efforts have been done to secure multicast messages. The idea behind the multicast security is to share a symmetric key between group members to encrypt/decrypt the multicast messages and to change this key after any membership change. The main re-keying problem is how to exchange the new group key between the group members in a scalable and secure way. In this paper we present a new multicast re-keying approach that is based on dividing the whole group into smaller subgroups. Each subgroup in turn is organized in a logical key hierarchy tree, and each subgroup member has the inverse key values of the other members in his subgroup in order to make the subgroup re-keying in a scalable and secure way. This decomposition, the proposed approach, which is named as Key Inverse Re-keying (KIR), reduces the multicast complexity from O(n) to O(log ₂m) where n is the total number of the whole group members and m is the number of members in each subgroup. The performance of KIR is compared with that of other group re-keying approaches to prove its effectiveness. The comparison is undertaken according to the computational overhead, communication overhead, storage overhead, and message size. The results show that KIR enhances the group performance in terms of computational overhead and communication overhead especially at the leave operation which represents a big problem for most of the previous group re-keying protocols.

In this paper, we propose a novel approach to finding and predicting anomalous network states based on a flow monitoring mechanism. We assume that number of active flows can show a real network state. Moreover, the dependence between flow number and link utilisation allows us to derive an equation for the confidence interval on high-loaded network links. Experiments have been conducted that confirmed the basic position of the model and identified the anomaly network states. A software package based on this model has been created that allows the prevention of DDoS attacks. For successful operation of this software the number of active flows that single IP address can generate has been analysed.