This paper proposes a defragmentation scheme using reroutable backup paths in toggled-based quasi 1+1 path protected elastic optical networks (EONs) to improve the efficiency of defragmentation and suppress the fragmentation effect. The proposed scheme can reallocate spectrum slots of backup paths and reroute of backup paths. The path exchange function of the proposed scheme makes the primary paths become the backup state while the backup paths become the primary. This allows utilization of the advantages of defragmentation in both primary and backup paths. We formulate a static spectrum reallocation problem with rerouting (SSRR) in the toggled-based quasi 1+1 path protected EON as an integer linear programming (ILP) problem. The decision version of SSRR is proven to be an NP-complete problem. A heuristic algorithm is introduced to solve the problem for large networks networks where the ILP problem is not tractable. For a dynamic traffic scenario, an approach that suppresses the fragmentation considering rerouting and path exchanging operations is presented. We evaluate the performances of the proposed scheme by comparing it to the conventional scheme in terms of dependencies on node degree, processing time of network operations and interval time between scheduled defragmentations. The numerical results obtained from the performance evaluation indicate that the proposed scheme increases the traffic admissibility compared to the conventional scheme.

Adaptive and flexible network control technology is considered essential for efficient network resource utilization. Moreover, such technology is becoming a key to cost-effectively meet diverse service requirements and accommodate heavier traffic with limited network resources; demands that conventional static operation cannot satisfy. To address this issue, we previously studied dynamic network control technology for large-capacity network services including on-demand broad bandwidth provisioning services and layer-one VPN. Our previous study introduced a simple weighting function for achieving fairness in terms of path length and proposed two dynamic Make Before Break Routing algorithms for reducing blocking probability. These algorithms enhance network utilization by rerouting existing paths to alternative routes while completely avoiding disruption for highly reliable services. However, the impact of this avoidance of service disruption on blocking probability has not been clarified. In this paper, we propose modified versions of the algorithms that enhance network utilization while slightly increasing disruption by rerouting, which enable us to elucidate the effectiveness of hitless rerouting. We also provide extensive evaluations including a comparison of original and modified algorithms. Numerical examples demonstrate that they achieve not only a high degree of fairness but also low service blocking probability. Hitless rerouting is achieved with a small increase in blocking probability.

This paper proposes an IP fast rerouting method which can be implemented in OpenFlow framework. While the current IP is robust, its reactive and global rerouting processes require the long recovery time against failure. On the other hand, IP fast rerouting provides a milliseconds-order recovery time by proactive and local restoration mechanism. Implementation of IP fast rerouting is not common in real systems, however; it requires the coordination of additional forwarding functions to a commercial hardware. We propose an IP fast rerouting mechanism using OpenFlow that separates control function from hardware implementation. Our mechanism does not require any extension of current forwarding hardware. On the contrary, increase of backup routes becomes main overhead of our proposal. We also embed the compression mechanism to our IP fast rerouting mechanism. We show the effectiveness of our IP fast rerouting in terms of the fast restoration and the backup routes compression effect through computer simulations.

IP fast rerouting has widely been studied for realizing millisecond-order recovery on pure IP networks. This paper proposes IP fast rerouting using backup topologies against concurrent double failures. The main issue in recovering from multiple failures is avoiding forwarding loops. To avoid forwarding loops, we propose a deterministic forwarding algorithm, which estimates the concurrently occurring failures from the packet header information. We also propose an efficient backup topology design algorithm which is both loop-free and which reduces the number of backup topologies. Our key idea is preparing the adequate diversity of backup routes for arbitrary source and destination pairs by combination of backup topologies. For efficient computation of diverse routes, we propose a similarity comparison-based algorithm between the original topology and the backup topologies. Our algorithm can achieve nearly optimal loop-free restoration from double failures on realistic topologies without explicit failure notification.

Telecommunications networks have become an important social infrastructure, and their robustness is considered to be a matter of social significance. Conventional network planning methods are generally based on the maximum volume of ordinary traffic and only assume explicitly specified failure scenarios. Therefore, present networks have marginal survivability against multiple failures induced by an extraordinarily high volume of traffic generated during times of natural disasters or popular social events. This paper proposes a telecommunications network planning method based on probabilistic risk assessment. In this method, risk criterion reflecting the degree of risk due to extraordinarily large traffic loads is predefined and estimated using probabilistic risk assessment. The probabilistic risk assessment can efficiently calculate the small but non-negligible probability that a series of multiple failures will occur in the considered network. Detailed procedures for the proposed planning method are explained using a district mobile network in terms of the extraordinarily large traffic volume resulting from earthquakes. As an application example of the proposed method, capacity dimensioning for the local session servers within the district mobile network is executed to reduce the risk criterion most effectively. Moreover, the optimum traffic-rerouting scheme that minimizes the estimated risk criterion is ascertained simultaneously. From the application example, the proposed planning method is verified to realize a telecommunications network with sufficient robustness against the extraordinarily high volume of traffic caused by the earthquakes.

We consider the problem of computing the optimal swap edges of a shortest-path tree. This problem arises in designing systems that offer point-of-failure shortest-path rerouting service in presence of a single link failure: if the shortest path is not affected by the failed link, then the message will be delivered through that path; otherwise, the system will guarantee that, when the message reaches the node where the failure has occurred, the message will then be re-routed through the shortest detour to its destination. There exist highly efficient serial solutions for the problem, but unfortunately because of the structures they use, there is no known (nor foreseeable) efficient distributed implementation for them. A distributed protocol exists only for finding swap edges, not necessarily optimal ones. We present two simple and efficient distributed algorithms for computing the optimal swap edges of a shortest-path tree. One algorithm uses messages containing a constant amount of information, while the other is tailored for systems that allow long messages. The amount of data transferred by the protocols is the same and depends on the structure of the shortest-path spanning-tree; it is no more, and sometimes significantly less, than the cost of constructing the shortest-path tree.

We develop a non-concurrent single-failure occurring model, a restoration scheme based on adaptively-decided sub-lightpath rerouting algorithm is then proposed, which aims to achieve better service guaranty with less network status information.

The crucial handover elements in wireless ATM networks are handover delay and handover efficiency. Since the research about the handover in wireless ATM has until now focused mainly on minimizing handover delay, the results have shown the inefficiency of network resources. In broadband wireless ATM networks, handover efficiency is critical to network capacity. In this paper, we propose a new handover scheme based on a partial path rerouting scheme called the delay limited best-fit backtracking scheme. The scheme searches for the crossover switch that limits handover delay and at the same time maximizes handover efficiency. It uses a new crossover switch searching method, which is an adaptive backtracking searching method that uses a best-fit search manner, to search for the optimal crossover switch that satisfies the given crossover switch condition. We evaluated the performance of proposed handover scheme, and show that the suggested scheme can improve handover efficiency more than other handover schemes.

This letter addresses the issue of RSVP path management in IP micro-mobility networks. We describe efficient RSVP QoS paths with a minimal impact to the existing protocol and underlying routing infrastructure. The goal of this letter is to reduce RSVP path reservation restoration latency and unnecessary control traffic caused by mobility events. We thus propose a RSVP branch-path rerouting scheme at a crossover router (CR) under IP micro-mobility networks. We show that this scheme could give a good tradeoff between the resource reservation cost and the link usage during the lifetime of a RSVP connection.

Since each ATM virtual path (VP) contains bundles of virtual channels (VCs), a VP layer network can serve as a server layer and each VC layer network can be a client layer. Therefore the effective VC service provisioning depends completely on the reliability of the VP layer network. We propose the ATM virtual path (VP) management framework with dynamic routing and rerouting schemes in a hierarchical transport network. The routing algorithm aims to provide the globally optimal route in a hierarchical network environment from the perspectives of maximization of network resource utilization and satisfaction of the end user's QoS requirement. The rerouting algorithm guarantees network survivability in the event of network faults or performance degradations. We also propose the implementation model of the ATM virtual path network management system (VP-NMS). Lastly, we evaluate the routing and rerouting performance for a real network, the High Speed Information Network (HSIN) of Korea Telecom.

In QoS networks, routing algorithms for QoS traffic have to provide the transmission path satisfying its QoS requirement while achieving high utilization of network resources. Therefore, server-based QoS routing algorithms would be more effective than distributed routing ones which are very common on the Internet. Furthermore, we believe that rerouting function enhances the advantage of their algorithms in which an already accepted flow with established path is replaced on some other path in order to accept newly arriving transmission request if it can not be accepted without doing so. Thus in this paper, we will propose a rerouting algorithm with the server-based QoS routing and evaluate its performance in terms of the blocking probability by computer simulation. In addition, we will investigate the impact of the amount of traffic with high-priority on the performance in some network topologies. Through some simulation results, we also discuss some issues arising in improving the effectiveness of rerouting.

Design and evaluation of a high-performance switch architecture for free-space photonic switching systems is described. The switch is constructed of 22 switching elements and employs special multistage interconnection patterns. The connection setup algorithm and the control procedure at the switching elements are based on a "rerouting algorithm." Performance analysis shows that the blocking probability of the switch is easily controlled by increasing the number of switching stages. Example implementations of this switch are shown in which birefringent plates, polarization controllers, etc. are used.

Design and evaluation of a high-performance switch architecture for free-space photonic switching systems is described. The switch is constructed of 22 switching elements and employs special multistage interconnection patterns. The connection setup algorithm and the control procedure at the switching elements are based on a "rerouting algorithm."" Performance analysis shows that the blocking probability of the switch is easily controlled by increasing the number of switching stages. Example implementations of this switch are shown in which birefringent plates, polarization controllers, etc. are used.

This paper describes the design and evaluation of a high-performance multicast ATM switch and its feasibility study, including its 40 Gbit/s LSI packaging. The multicast switch is constructed using a serial combination of rerouting networks and employs an adapted Boolean interval-splitting scheme for a generalized self-routing algorithm. Analysis and computer simulation results show that the cell loss probability is easily controlled by increasing the number of switching stages. It is shown that the switch configuration can be transformed into other patterns to be built from banyan-based subnetworks of arbitrary size for LSI packaging. It is also shown that an LSI chip integrating an 88 banyan-based subnetwork using 0. 25-µm CMOS/SIMOX technology can attain a 40-Gbit/s switching capability.

This paper proposes implementation methods of fast ATM layer protection switching function. The main problem in attaining fast ATM protection is the number of connections in one transmission path. The transmission delay of the signal for protection negotiation procedure is relatively less than the processing time in the end nodes. Therefore shortening of the processing time in the nodes is a crucial factor for fast rerouting. This paper focuses on this point and presents some suitable implementations on ATM nodes for fast protection switching. These architectures can attain protection time of less than 50 ms after the detection of a failure at an end node. The key is load-sharing of the hardware and firmware. This paper also sums up the effectiveness of ATM protection and the current situation of standardization in ITU-T SG13.

The paper presents the improvement of out new approach to optimize the process parameter variation, device heat and wire parasitics for analog LSI design by explicitly incorporating various performance estimations into objective functions for placement and routing. To minimize these objective functions, the placement by the simulated annealing method, and maze routing are effectively modified with the perfomance estimation. The improvement results in the excellent performance driven layout for the large size of analog LSIs.