Kitsutaro Amano

A delay-constrained least-cost path routing protocol and the synthesis method

Real-time communication services will be one of the most promising future applications in both the B-ISDN and Internet. In addition, real-time traffic usually utilizes a significant amount of resources while traversing the network. Thus there is the need for routing mechanisms which are able to satisfy requirements of both real-time traffic and efficient management of network resources. Firstly we discuss an issue of routing of real-time traffic subject to each end-to-end delay constraint and a path cost. Then, we describe a key concept which is taken into consideration of the requirements simultaneously. Based on the requirements, a delay constrained least-cost path problem is formulated. Since the problem is NP-hard, a heuristic method is proposed to solve the problem. The heuristic method can always find a delay-constrained path between a source node and a destination node, if there is such a path. Based on the heuristic method, an outline of the synthesis method for the delay-constrained least-cost path routing protocol is also presented.

A parallel downloading method of coping with variable bandwidth

As a lot of programs and contents such as movie files are being delivered via the Internet, and copies are often stored in distributed servers in order to reduce the load on the original servers, to ease network congestion, and to decrease response time. To retrieve an object file, existing methods simply select one or more servers. Such methods divide a file into equal pieces whose size is determined a priori. This approach is not practical for networks that offer variable bandwidth. In order to more utilize variable bandwidth, we propose an adaptive downloading method We evaluate it by experiments conducted on the Internet. The results show that the new method is effective and that it will become an important network control technology for assurance.

TCP performance analysis on asymmetric networks composed of satellite and terrestrial links

As the Internet users increase, asymmetric networks which provide asymmetric bandwidth or delay for the uplink and downlink have become a great attraction. However asymmetric networks which use both terrestrial and satellite links at the same time have not been adequately investigated. Therefore, this paper proposes a new formula for TCP performance evaluation for the asymmetric networks. Using this evaluation formula, we calculate the throughput of TCP Reno over the asymmetric networks taking slow start into account. The calculation results are compared with the following: (1) the value based on an existing theoretical formula, (2) the outputs of simulation by NS (Network Simulator), and (3) the experimental results using VSAT (Very Small Aperture Terminal) satellite communication system for satellite links and the Internet for terrestrial links. As a result, it is shown that the new formula is more precise than the one already proposed.

PFTPD: an FTP proxy system to assure the freshness of files

As more software is being developed and distributed via the Internet, the number of accesses to file servers, such as FTP servers or WWW servers, is increasing. To reduce concentrated access to the original file server, mirror servers which have the same directories and files as the original server stores have been introduced. However, inconsistency among mirror servers and the original server is often observed because of transfer latency, traffic congestion on the network, and management policy of the mirror servers. Hence, we develop an intermediate FTP proxy server system PFTPD (Proxy FTP Daemon) which guarantees the freshness of files as well as dispersal of the access concentrated on the original FTP server. We found that the proposed system can disperse accesses to the mirror servers with a little overhead. This technology can assure that files are the latest version and adapt to heterogeneous network environments such as the Internet.

A protocol synthesis method for fault-tolerant multipath routing

Abstract This paper proposes a new synthesis method for generating fault-tolerant multipath routing protocols. The protocol is defined as fault-tolerant if messages can be rerouted by using another path when a communication channel fails. The routing protocols obtained adopt a multipath routing function, augmented with routing table, where each table stores the next nodes for multipath routing, and updates the tables according to the network topology changes. Additionally, the routing protocol can attain flexibility by the multipath routing mechanism in the sense that only a small amount of change is needed for the change of network topology. We also briefly describe an extension of the proposed method for generating multicast routing protocols.

An Internet auction method using decentralized selection servers

Internet auctions have got attention with the sensational diffusion of the Internet, because we are able to trade various goods for a desirable price. Many Internet auctions adopt the English auction The English auction is the mechanism to settle a successful bidder Conventional Internet auction systems are using one logical server called an auction server that is constructed with one or several servers. So, if simultaneous bids occur, the load of the auction server increases. Besides, when congestion at circumference of the auction server occurs, the response time will increase. We propose a new Internet auction method using decentralized selection servers which will reduce superfluous information derived from bidders. The proposed method tends to hold down the increase of the response time by lightening the processing load at an auction server and cutting down congestion around the auction server In order to evaluate the proposed method concisely, we assume a typical auction service and a network. We evaluate the proposed and the conventional methods by simulation experiments using a network simulator OPNET Modeler Consequently, it is shown that the proposed method is more scalable and can be deployed with smaller cost.

A synthesis method for fault-tolerant multicast routing protocol

Multicast communication services will be one of the most promising future applications, which include real-time flows, in both the B-ISDN and the Internet. Design of such multicast routing protocols is complex and difficult due to complicated requirements. The protocol is defined to be fault-tolerant if messages can be retransmitted when a message loss occurs. In this paper, we propose a new synthesis method for generating a fault-tolerant multicast routing prqtocol for a given service specification, a network topology, and a tree shaped route.

Resource reservation for multicast trees using multiagents

Multicast is a message delivery scheme from a source node to all nodes that belong to the given membership through a multicast tree. The paper discusses how source based multicast trees are set up such that the maximum damage due to failure of any link to the multicast trees is minimized. Then, the paper proposes a multiagent based method for finding such multiple source based multicast trees. The proposed method assumes that candidates of multicast tree rooted at each source node are given according to some criteria. Under this assumption, first, shared links in multiple multicast trees whose source nodes are different are recognized. Then, a multicast tree rooted at each source node is determined such that damage due to failure of a shared link is minimized. The proposed method has a potentially good adaptability for change of both network resources such as topology and link capacity and resource requirements such as source node, membership, and bandwidth of multicast trees.