In recent years, the virtual network (VN) for services by IP over WDM has been studied for the flexible and efficient use of network resources. The VNs are constructed by optical paths on the WDM network. Furthermore, by configuring VNs dynamically, resources which have been used for some VN at previous period can be allocated to another VN at the next period, which improves the utilization ratio of network resources. In this paper, we propose the SVN (Static Virtual Network configuration) method and the DVN (Dynamic Virtual network configuration) method for the VN configuration method. We formulate the MILP (Mixed Integer Linear Programming) for the SVN method and the DVN method and evaluate them from viewpoints of resource cost and availability by calculation experiments.

In recent years, multi-layer network (MLN) design methods have attracted great attentions of backbone carriers for their networks designs. In the MLN design, IP networks are constructed on optical path networks on the WDM (Wavelength Division Multiplexing) networks. In the MLN designs, the resilience against link failures is also required. The shared restoration method has been studied to achieve the resilience against link failures. In this method, the same wavelength is shared among plural optical paths, and the backup optical path is set up against link failure using the shared wavelength. In this paper, we formulate an Integer Liner Programming (ILP) for the MLN design using shared restoration method, and also propose a heuristic method for the MLN design. We evaluate these design methods from viewpoints of cost performance and calculation times and show the effectiveness of these design method.

Aggregated multicast methods have been proposed in order to reduce the size of routing tables in routers for multicast communications, where plural multicast sessions share a single multicast tree called Shared-Tree. STA (Scalable-Tree-Aggregation) method has been proposed as a Shared-Tree selection method, where a minimum size Shared-Tree has been selected among Shared-Trees which contain all destination nodes of a multicast session. In the STA method, the selected Shared-Tree sometimes contains invalid destination nodes for the multicast session and causes the unnecessary traffic load. In this paper, we proposed a novel Shared-Tree selection method which makes it possible to select smaller size Shared-Tree compared with the multicast session by a grafting method. By the grafting method, destination nodes not involved in the selected Shared-Tree can be connected to the Shared-Tree. We can expand the search range of Shared-Trees by the grafting method and select a Shared-Tree, destination nodes of which overlap those of the multicast session as many as possible. In our proposed selection method, Shared-Trees are selected by the measurement of overlapping degree, which indicates how many destination nodes in the multicast session overlap with those in Shared-Trees. Moreover, we introduce a replacement method for reducing the entry size of Shared-Trees. We evaluate our selection method by simulation experiments and show the effectiveness of our proposed method.

Recently a drastic increase of power consumption of network devices has been big problem in the green ICT field. In order to cope with this problem, some power saving method has been proposed, where traffic aggregations are executed and the powers of unnecessary links are turned off. In this method, every links are tried to be turned off and are checked whether traffic congestions are caused or not and whether network disconnections occur or not. However, this method causes frequent change of link on/off and induces network instabilities in the actual network environment, where traffic conditions change in real time. Moreover, in this method, since the shortest hop routing has been adopted, traffic congestions might occur in specific links. In this paper, in order to cope with these problems, we propose a High-Speed Topology Construction method, where an initial topology is constructed by a minimum spanning tree algorithm in order to maximize sleep links. When traffic congestions are caused, a proper link addition proposed in this paper is executed in order to resolve traffic congestions. We evaluate our proposed methods by simulation experiments and show its effectiveness.

We propose a scalable call admission control (CAC) scheme that avoids link congestion while maximizing the total admissible traffic of an IP backbone network. Our proposed scheme is scalable in the sense that it requires bandwidth reservation management only at ingress nodes instead of at every links in the core network. We have already evaluated the performance of admissible traffic in case where traffic observations are not executed at ingress nodes in the reference [1]. In this paper, in order to increase admissible traffic volumes, we newly formulate an LP problem in case where traffic observations are executed at ingress nodes for estimating offered traffic volumes between ingress and egress node pairs. We evaluated our proposed scheme for NSFNET and COST239 and showed that the total admissible traffic increases about 2.7 and 2.5 times more for NSFNET and COST239, respectively, compared with the case where traffic observations are not executed.

We propose novel tree construction algorithms for multicast communication in photonic networks. Since multicast communications consume many more link resources than unicast communications, effective algorithms for route selection and wavelength allocation are required. We propose novel tree construction algorithms called the weighted Steiner tree (WST) algorithm and the composite weighted Steiner tree (CWST) algorithm. Since the proposed Weighted Steiner Tree algorithm takes account of the number of wavelengths available for each link, this algorithm can select those links which have larger number of available wavelengths. By using this link selection technique, this algorithm can accept many more multicast requests than other multicast tree construction algorithms. However, under certain delay constraints, the blocking characteristics of the proposed weighted Steiner tree algorithm deteriorate since some light paths between source and destination use long hops and cannot satisfy the delay constraint. In order to adapt the approach to the delay-sensitive environments, we have devised the composite weighted Steiner tree algorithm comprising the weighted Steiner tree algorithm and the Dijkstra algorithm for use in a delay constrained environment such as an IPTV application. In this paper, we also give the results of simulation experiments which demonstrate the superiority of the proposed composite weighted Steiner tree algorithm compared with the distributed minimum hop tree (DMHT) algorithm, from the viewpoint of the light-tree request blocking probability.

Dynamic routing and wavelength assignment (RWA) is an attractive method for the efficient use of network resources in all-optical networks. We present a novel fixed alternate routing method referred to as overlap-degree aware (ODA) routing in all-optical network. The authors believe that in order to minimize the blocking probability, it is important to consider not only the consumption of wavelength resources but also the existence of the other flows when a routing decision is made. Our simulation results show that our new routing algorithm outperforms fixed-alternate routing (FAR) and weighted least congestion routing (WLCR) from the viewpoint of call blocking probability.

We propose a novel routing algorithm for reverse proxy servers, called adaptive loud balancing content address hashing (AH), and evaluate the performance of the proposed routing algorithm compared with that of the content address hashing (SH) and the hash and slide (HS) routing algorithms. The proposed AH routing algorithm calculates the popularity of pages in the load balancer using an LFU caching technique and periodically makes a popularity list. Using this popularity list, the proposed routing algorithm selects a reverse proxy server as follows. When the requested page appears in the popularity list, the request is routed according to the round robin method; otherwise, it is routed according to the content address hashing method. We evaluate and compare the AH, SH and HS routing algorithms by simulation experiments from the viewpoints of load balancing, consumed cache space and cache hit rate. Simulation experiments show that the proposed AH routing algorithm achieves almost the same degree of load balancing as the HS algorithm and the same cache hit rate as the SH algorithm, for reverse proxy servers in various web site environments.

A mechanism for specifying distributed communication software is proposed. Using this mechanism, each process is specified by three types of constraints: an event to a process is decomposed into event elements and distributed to relevant processes in accordance with decomposing constraints; each process independently performs actions by its functional constraints; and the output is determined by superposing constraints as a superposing result of each process action. Because the functional constraints are independent of other processes, they can be made up of reusable components. To facilitate specifying the decomposing and superposing constraints, a language based on constraint-oriented logic programming is developed. The authors also propose a constraint evaluation system which executes reasoning rules to obtain outputs from input events and knowledge of constraints. The bound/unbound concept of event variables is employed to implement the execution control of each constraint evaluator. Using plain old telephony service and call waiting service as examples, the advantages of the mechanism and the evaluation system are shown.>

The conventional go-back-NARQ is modified so as to be applicable to point-to-multipoint communication by using a control block that indicates the occurrence of retransmission to all the receivers. This paper also presents a "tandem error control scheme," in which the up-link and the down-links use separate go-back-NARQ's. The throughput efficiency of the tandem go-back-NARQ is analyzed. Specifically, the mathematical formula for the throughput efficiency is obtained for cases in which there is a single receiver. The throughput efficiencies of these schemes are also evaluated by simulation.