Network survivability is defined as the ability of a network keeping connected under failures and/or attacks. In this paper, we propose two stochastic models; binomial model and negative binomial model, to quantify the network survivability and compare them with the existing Poisson model. We give mathematical formulae of approximate network survivability for respective models and use them to carry out the sensitivity analysis on model parameters. Throughout numerical examples it is shown that the network survivability can change drastically when the number of network nodes is relatively small under a severe attack mode which is called the Black hole attack.

A wireless sensor network is comprised of a large number of battery-limited sensor nodes communicating with unreliable radio links. The nodes are deployed in an ad hoc fashion and a reverse multicast tree is formed in the target domain. The sink node disseminates a query and collects responses from the sensors over pre-established links. Survivability in wireless sensor networks reflects the ability of the network to continue to detect events in the case of individual node failures. We present a sender initiated path switching algorithm that enables the immediate sender to change the packet's route dynamically when its parent on the reverse path is down. The overall effect of path switching on the survivability is analyzed as a measure of reliable event delivery. Using independent battery capacities, an analytical model of a multihop network is derived. The model is used to predict the maximum network lifetime in terms of total transmitted messages; which is in turn used to verify the correctness of our simulations. The results have revealed that dynamic path switching has a better performance than static multipath routing and salvaging schemes. It has also been shown that the proposed approach enhances reliability up to 30% in some topologies.

The self-healing capability against network failure is one of indispensable features for the B-ISDN infrastructure. One problem in realizing such self-healing backbone network is the inefficient utilization of the large spare capacity designed for the failure-restoration purpose since it will be used only in the failure time that does not occur frequently. "Pool-capacity" is the concept that allows some VPs (virtual paths) to efficiently utilize this spare capacity part. Although the total capacity can be saved by using the "Pool Capacity," it is paid by less reliability of VPs caused by the emerging influence of indirect-failure. Thus, this influence of indirect-failure has to be considered in the capacity designing process so that network-designers can trade off the saving of capacity with the reliability level of VPs in their self-healing networks. In this paper, Damage Rate:DR which is the index to indicate the level of the influence caused by indirect-failure is defined and the pool-capacity design scheme with DR consideration is proposed. By the proposed scheme, the self-healing network with different cost (pool-capacity) can be designed according to the reliability level of VPs.

Network survivability against various unexpected failures is one of indispensable technologies for the B-ISDN infrastructure. Self-healing algorithm is the technique to automatically restore the failed VP's (virtual paths) in the backbone ATM network. Since the B-ISDN transports various kinds of traffic with various levels of priority (Grade of Service: GoS), the effective self-healing algorithm should orderly restore the failed VP's based on the priority of their traversing traffic. This paper proposes the priority based restoring self-healing algorithm, which realizes the priority based restoring function by the two-timer mechanisms and a simple capacity reserving protocol. The simulation results show that the proposed algorithm can schedule the restoration process so that the failed VP's with higher priority are restored before the others with lower priority. In addition, the significant improvement in restoration speed for the highest priority traffic class has been achieved.

In this paper, we propose a new design method to construct the highly reliable ATM network based on the virtual path (VP) concept. Through our method, we can guarantee a network survivability, by which we mean that connectivity between every pair of two end nodes is assured even after the failure, and that quality of service (QoS) requirements of each VC connection are still satisfied. For achieving a reliable network, every VP connection between two end nodes is equipped with a secondary VP connection such that routes of primary and secondary VPs are established on completely disjoint physical paths. Our primary objective of the current paper is that the construction cost of the VP-based network with such a survivability is minimized while the QoS requirement of traffic sources in fulfilled. For this purpose, after all the routes of VPs are temporarily established by means of the shortest paths, we try to minimize the network cost through (1) the alternation of VP route and (2) the separation of a single VP into several VPs, and optionally through (3) the introduction of VCX nodes. Through numerical examples, we show how the increased cost for the reliable network can be sustained by using our design method.