Physical layer characteristics of a wireless channel, which can be measured independently by the two communicating parties and yield near-identical results due to the channel reciprocity property, have been shown to be an important source of shared secrecy generation. Various types of channel state information (CSI), such as the received signal strength (RSS) and the channel impulse response (CIR) can be utilized for this purpose. Through periodic probing of the CSI, a continuous cycle of secret bit generation and key renewal can be maintained. However, many forms of wireless CSI inherently have substantial temporal correlation, which may hinder the secrecy generation process. Accordingly, various autocorrelation reduction (decorrelation) methods have been proposed, using either sub-sampling approaches that discard potentially valuable CSI data, or, computationally expensive transform domain approaches such as the Discrete Cosine Transform (DCT), Karhunen–Loeve Transform (KLT), and principal component analysis (PCA) that may not be feasible or desirable for resource and energy constrained devices. This paper proposes a low-complexity method for reducing the autocorrelation of the CSI measurements through a reordering of the data based on integer sequences such as the Fibonacci sequences, and applies it to various types of CSI data that represent both the individual path level CIR and the aggregate level multipath gain or RSS. We evaluate the performance of the method in three standard multipath ITU channel models. Fibonacci sequences are observed to be an effective means of decorrelating the channel measurement data, thereby eliminating the need for computationally intensive methods.

Physical-Layer (PHY) based secrecy has inherent advantages for generating symmetric keys in communication security, due to the reciprocity of the wireless communications channel. However, since noises are independently acquired and the communication channel is of half-duplex, the bit streams independently obtained from the PHY-layer by the two sides of a communications channel are usually not identical. This imperfection prevents the direct application of the PHY-layer secrecy for generating symmetric keys. In this paper, we propose a novel algorithm for dynamic symmetric key generation by utilizing the Golay code structure. The proposed algorithm achieves as much as 100% symmetric key generation rate when compared to the naive approach at a small extra computational cost. The performance of the proposed algorithm is evaluated using experimentally observed distribution of PHY-layer generated bit mismatches with MATLAB ITU channel models as the basis of a theoretical analysis. Our design is shown to provide a good trade-off between symmetric key generation rate and computational complexity without additional information leakage.

Due to lack of optical RAM buffers in fast optical switches (FOS), statistical multiplexing technologies using FOS like Optical Burst Switching (OBS) or Optical Packet Switching (OPS) are expected to have higher data losses than conventional electronic networks. Consequently, applications transferring data by means of TCP can suffer from a lower throughput. In this paper, we show that this low-throughput problem is mainly an artifact caused by the conventional TCP congestion control algorithms, and can be remedied by using a simple yet effective stop-and-wait congestion control algorithm instead, as long as the propagation delay between TCP source and TCP destination is small compared to the transmission time of an optical packet. We show that such a condition holds for a wide range of scenarios, including fat-tree-based data center networks. We also show that the throughput achieved in a FOS network using stop-and-wait can be the same as, or higher than that in an equivalent, conventional electronic network.

Achieving accurate and efficient fault localization in large transparent all-optical networks (TONs) is an important and challenging problem due to unique fault-propagation, time constraints, and scalability requirements. In this paper, we introduce a novel technique for optimizing the speed of fault-localization through the selection of an active set of monitors for centralized and hierarchically-distributed management. The proposed technique is capable of providing multiple levels of fault-localization-granularity, from individual discrete optical components to the entire monitoring domains. We formulate and prove the NP-completeness of the optimal monitor activation problem and present its Integer Linear Program (ILP) formulation. Furthermore, we propose a novel heuristic whose solution quality is verified by comparing it with an ILP. Extensive simulation results provide supporting analysis and comparisons of achievable alarm-vector reduction, localization coverage, and time complexity, for flat and hierarchically distributed monitoring approaches. The impact of network connectivity on fault localization complexity in randomly generated topologies is also studied. Results demonstrate the effectiveness of the proposed technique in efficient and scalable monitoring of transparent optical networks.

Rapid fault identification and localization in optical networks are crucial due to high data rates. These problems are more challenging than in traditional electronic networks because of optical transparency. In a transparent optical network which does not regenerate optical signals, a fault may propagate to various parts of the network from the origin, and multiple alarms can be generated for a single failure. In order to reduce the number of redundant alarms, simplify fault localization, and reduce the fault localization time, the number and location of fault monitors that are turned on should be optimized for a given network. In this paper, we formulate a problem on the optimal activation of network monitoring devices and propose a solution approach. First, we provide a brief summary of available physical-layer monitoring devices, and then present a scheme for optimal monitor activation. We show the NP-completeness of the problem and present a mixed-integer-linear-program (MILP) formulation of it. We also present a heuristic, whose performance is evaluated through comparisons with the solutions to the MILP, as well as a naive monitor activation approach.

We consider an IP/MPLS over WDM network, in which label switched routers (LSRs) in the IP/MPLS layer are interconnected through optical cross-connects (OXCs) in the optical core network (WDM layer) providing an end-to-end wavelength routing capability. In this paper, we study a dynamic label switched path (LSP) routing problem for the three different network models of the IP/MPLS over WDM network, namely, Overlay, Augmented, and Peer models. For the overlay model, we propose two algorithms: ECF_OVLY and MLH_OVLY. In ECF_OVLY, a network always tries to use existing capacity first, whereas in MLH_OVLY, a network finds a path with the minimum number of logical hops for an LSP request. We also propose, for the augmented model, two simple and efficient dynamic LSP provisioning algorithms, called MCPI_AUG and DCPI_AUG, utilizing different type/amount of summarized capacity information from the WDM layer, namely Minimum CaPacity Information (MCPI) and Detailed CaPacity Information (DCPI). We compare the proposed algorithms with the existing algorithms available for the overlay [1] and peer [2], [3] models. The algorithms are compared and evaluated using two key performance measures: LSP blocking probability and network (lightpath) utilization. Simulation results show that at low loads with a limited number of ports available in the network, DCPI_AUG achieves an order of magnitude better blocking performance than the algorithm in [2] and outperforms the one in [3] by more than three times. It also achieves higher network utilization than the one in [2] by more than 10 % and the one in [3] by 2-7 % depending on the traffic load. Considering the small amount of information that is exchanged between the layers in the augmented model, these results suggest that the augmented model can be a practically good compromise between the overlay and peer models.

Traffic grooming is an essential functionality of WDM optical networks to provision multi-granularity subwave-length connections. Depending on the number of lightpaths allowed in a connection route, traffic grooming can be classified as single-hop traffic grooming (SH-TG) and multi-hop traffic grooming (MH-TG). MH-TG is more general and resource-efficient than SH-TG, because it allows connections from different source-destination pairs to share the bandwidth of a lightpath. In this paper, we propose a MH-TG algorithm, namely the fixed-order multi-hop (FOMH) grooming algorithm, based on the fixed-alternate routing approach. We introduce the grooming node selection (GNS) problem in MH-TG and propose three grooming policies, namely exhaustive sequential (ES), limited-hop sequential (LHS) and load sharing (LS) policies, to address the GNS problem. Given that the analysis of MH-TG is a relatively unexplored area, we propose an analytical model to evaluate the blocking performance of MH-TG using FOMH and the LS grooming policy. To address the multi-layered routing and multi-rate connection characteristics of traffic grooming, we introduce a novel multi-level decomposition approach in our analytical model which decomposes traffic at four different levels, namely alternate path, connection route, lightpath and link levels. The Erlang fixed-point approximation method is used to solve the analytical model. Numerical results show that analytical results matches well with simulation results. We also evaluate the effect of the grooming policies, the number of virtual hops (lightpaths) within a connection route and the number of alternate paths on the performance of the grooming algorithm.

This paper studies the effects of the sub-carrier grouping on the scheduling problem in a wireless network with multiple carriers. In particular, the authors consider the trade-offs between the size of the sub-carrier groups and the link throughput for various sub-carrier grouping models, with each corresponding to a different level of CSI tracking and system design complexity. The paper assumes that a single user is communicating with the base station using the entire sub-carriers. This assumption is motivated by the OFDM, which uses multiple carriers in order to benefit from the frequency selective fading introduced by spreading the information bits over the entire signal band. An offline dynamic programming algorithm for finding an optimal solution for the case of spectrum- and time-perfect estimates is also presented. The performance can potentially be improved by using high-level modulation on the sub-carriers with good channel conditions.

We consider an IP/MPLS over WDM network, in which label switched routers (LSRs) in the IP/MPLS layer are interconnected through optical cross-connects (OXCs) in the optical core network (WDM layer) providing an end-to-end wavelength routing capability. In this paper, we study a dynamic label switched path (LSP) provisioning problem for the three different network models of the IP/MPLS over WDM network, namely, overlay, augmented, and peer models. For the overlay model, we propose an algorithm, called MLH/spl I.bar/OVLY, in which a network finds a path with the minimum number of logical hops for an LSP request. We also propose, for the augmented model, a simple and efficient dynamic LSP provisioning algorithm, called CAPA/spl I.bar/AUG, utilizing summarized capacity information from the WDM layer. We compare the proposed algorithms with the existing algorithms available for the overlay and peer models, and also provide an in-depth analysis of the algorithms. The algorithms are compared and evaluated using two key performance measures: LSP blocking probability and network (lightpath) utilization. Simulation results show that at low loads with a limited number of ports available in the network, CAPA/spl I.bar/AUG achieves an order of magnitude better blocking performance and outperforms all other algorithm. Considering the small amount of information that is exchanged between the layers in the augmented model, these results suggest that the augmented model can be a practically good compromise between the overlay and peer models.

This paper considers the problem of providing quality-of-protection (QoP) classes and improving the failure-recovery time performance in dense wavelength-division-multiplexing (DWDM) networks that use mesh-based path restoration schemes with capacity sharing. We focus on the signaling process required for reconfiguring the nodes along the preplanned restoration paths, and propose a novel approach for reducing the restoration time and meeting the QoP requirements by coordinating the setup procedures for the backup paths through scheduling. We present priority-based online scheduling algorithms that are amenable to distributed implementation for the problems of: 1) minimizing the worst case restoration time and 2) maximizing the number of connections that meet their QoP-class-specific restoration time deadlines. We also present mixed-integer-linear-program (MILP) formulations for both problems for comparison purposes. The online scheduling methods that we propose use simple connection and/or class-specific information and can be easily implemented with minor modifications to the currently proposed signaling protocols. We apply these methods to signaling protocols that require cross-connect configurations at different nodes to be done in sequence as in the current generalized multiprotocol label switching specification, as well as signaling protocols that allow cross-connect configurations to be done in parallel. It is shown that in both cases, significant performance improvements are achievable through scheduling in terms of both the QoP grades that can be supported and the restoration times, with both the MILP solutions and the heuristics. The improvement in restoration time and restorability through our heuristics can be quite high (e.g., increase from a network restorability performance of 40% to a network restorability of 88%, and a 12% reduction in worst case restoration time).

We consider an IP/MPLS-over-WDM overlay network, which an IP/MPLS service layer exists independently over a WDM transport network. In the overlay model, two adjacent layers communicate with each other only through a pre-defined user-network interface (UNI) and the WDM topology information is not available to the service layer. In this paper, we concentrate on network design with a fault tolerance mechanism provided only in the IP/MPLS service layer in which the label-switched path (LSP) protection takes into account both node failures in the IP/MPLS service layer and failures in the WDM transport layer. In this design problem, the service layer must decide how lightpaths or logical links should be provisioned and how primary and backup LSPs should be routed in a cost-effective manner, such that failures do not affect both LSPs simultaneously. We formulate this survivable IP/MPLS overlay network design problem as a mixed integer linear program (MILP). Since the MILP is computationally intractable for large networks, we solve it only for a small network and present the optimal solution found by CPLEX 7.5, a commercial MILP solver. In order to find efficient solutions in larger networks we propose a heuristic algorithm that performs near-optimally in the cases studied. we then compare total costs for LSP protection from WDM link failures and LSR failures may not be much more expensive than protection from LSR failures only.