Photonic crystal-based permutation switch for optical networks

We present, for the first time, the design of a low-cross talk scalable permutation switch employing photonic crystal ring resonators in an optical network. Through this novel approach, the transition between different states of the \(2 \times 2\) optical switch, as the basic element, is achieved by applying different operating wavelengths. Subsequently, the shuffling mechanisms in \(3 \times 3\) and \(4 \times 4\) optical networks are realized by controlling the position of photonics crystal ring resonators. Lowest cross talk levels of 6 and 5% are obtained for “bar” and “cross” switching states, respectively.     

Symbol-level reliable broadcasting of sensitive data in error-prone wireless networks

Reliable packet transmission over error-prone wireless networks has received a lot of attention from the research community. In this paper, instead of using simple packet retransmissions to provide reliability, we consider a novel retransmission approach, which is based on the importance of bits (symbols). We study the problem of maximizing the total gain in the case of partial data delivery in error-prone wireless networks, in which each set of bits (called symbols) has a different weight. We first address the case of one-hop single packet transmission, and prove that the optimal solution that maximizes the total gain has a round-robin symbol transmission pattern. Then, we extend our solution to the case of multiple packets. We also enhance the expected gain using random linear network coding. Our simulation results show that our proposed multiple packets transmission mechanism can increase the gain up to 60%, compared to that of a simple retransmission. Moreover, our network coding scheme enhances the expected total gain up to 15%, compared to our non-coding mechanism.     

CTAC: Control traffic tunneling attacks’ countermeasures in mobile wireless networks

Multihop wireless ad hoc and sensor networks open the door for great networking opportunities especially in scenarios where it is infeasible or expensive to deploy significant networking infrastructure. However, the open communication media and the lack of networking infrastructure make these networks vulnerable to a wide range of security attacks. A particularly devastating attack is the control traffic tunneling attack, where a malicious node records control traffic at one location and tunnels it to a colluding node, possibly far away, which replays it locally. One of the control traffic attacks’ incarnations is the wormhole attack that can be used to prevent route establishment by preventing nodes from discovering legitimate routes that are more than two hops away. These attacks have been addressed by many researchers, however, most of the presented work is either limited to static scenarios, require expensive hardware or suffer from high overhead and performance degradation. In this paper, we present a scalable countermeasure for the control traffic tunneling attack, called CTAC, which alleviates these drawbacks and efficiently mitigates the attack in both static and mobile networks. CTAC uses trusted nodes called cluster heads (CH) for global tracking of node locations and profile keeping. Local monitoring is used to detect and isolate malicious nodes locally. Additionally, when sufficient suspicion builds up at a CH, it enforces a global isolation of the malicious node from the whole network. The performance gain, the relatively low overhead, and the positive impact of CTAC on the data traffic fidelity are brought out through analysis and extensive simulation using ns-2. The results show that CTAC achieves higher detection ratio and faster isolation time while considerably decreases the overhead energy and the end-to-end delay compared to the state-of-the art schemes.     

Broadcasting with hard deadlines in wireless multihop networks using network coding

Broadcasting with network coding mixes packets to minimize the number of transmissions, which improves the energy efficiency of wireless networks. On the other hand, delaying the transmissions increases coding opportunities at intermediate nodes, but increases the delay of packets. In this paper, we consider these two contradicting factors and study the problem of minimizing the number of transmissions in wireless networks while meeting the deadline constraints. We show that this problem is NP‐complete; therefore, we provide a heuristic to solve it. First, we construct broadcasting trees, each of them rooted at one source. We then specify overlapping conditions based on the constructed trees, to determine the number of transmissions each node has to perform without the deadline constraints. Then, we partition the set of packets such that coding is performed among the packets of the same partition, which does not result in deadline misses. Linear coding may not be applicable in some wireless networks because of its computational complexity. For these networks, we propose three XOR coding approaches, which rely only on local neighborhood information. Simulation results show that our techniques not only reduce the number of transmissions but also allow the majority of nodes to receive the packets on time. Copyright © 2013 John Wiley & Sons, Ltd.     

Tuple switching network—When slower may be better

This paper reports an application dependent network design for extreme scale high performance computing (HPC) applications. Traditional scalable network designs focus on fast point-to-point transmission of generic data packets. The proposed network focuses on the sustainability of high performance computing applications by statistical multiplexing of semantic data objects. For HPC applications using data-driven parallel processing, a tuple is a semantic object. We report the design and implementation of a tuple switching network for data parallel HPC applications in order to gain performance and reliability at the same time when adding computing and communication resources. We describe a sustainability model and a simple computational experiment to demonstrate extreme scale application’s sustainability with decreasing system mean time between failures (MTBF). Assuming three times slowdown of statistical multiplexing and 35% time loss per checkpoint, a two-tier tuple switching framework would produce sustained performance and energy savings for extreme scale HPC application using more than 1024 processors or less than 6 hour MTBF. Higher processor counts or higher checkpoint overheads accelerate the benefits.     

Cross-layer optimization for wireless multihop networks with pairwise intersession network coding

For wireless multi-hop networks with unicast sessions, most coding opportunities involve only two or three sessions as coding across many sessions requires greater transmission power to broadcast the coded symbol to many receivers, which enhances interference. This work shows that with a new flow-based characterization of pairwise intersession network coding (coding across two unicast sessions), an optimal joint coding, scheduling, and rate-control scheme can be devised and implemented using only the binary XOR operation. The new scheduling/rate-control scheme demonstrates provably graceful throughput degradation with imperfect scheduling, which facilitates the design tradeoff between the throughput optimality and computational complexity of different scheduling schemes. Our results show that pairwise intersession network coding improves the throughput of non-coding solutions regardless of whether perfect/imperfect scheduling is used. Both the deterministic and stochastic packet arrivals and departures are considered. This work shows a striking resemblance between pairwise intersession network coding and non-coded solutions, and thus advocates extensions of non-coding wisdoms to their network coding counterpart.