Masashi Sugano

Fault tolerant packet-switched network design and its sensitivity

Reliability and performance for telecommunication networks have traditionally been investigated separately in spite of their close relation. A design method integrating them for a reliable packet switched network, called a proofing method, is presented. Two heuristic design approaches (max-average, max-delay-link) for optimizing network cost in the proofing method are described. To verify their effectiveness and applicability, they are compared numerically for three example network topologies. The sensitivity of these two methods is examined with respect to changes in traffic demand and in link reliability. The design sensitivity to variation of input data is examined by changing the predicted probability of link failure, and by increasing the network traffic over the predicted value. The resulting analysis shows relative insensitivity of solutions generated by the two design methods to input data. >

Improving TCP handoff performance in Mobile IP based networks

Mobile IP has been designed to support host mobility over the Internet. In this paper, we show that in most cases the smooth handoff by the route optimization of the Mobile IP standard cannot prevent degradation of TCP performance in events of handoffs, although it was originally intended to reduce the number of packets dropped during a handoff. We also show that in utilizing the route optimization extension, the TCP performance sometimes becomes worse even than the case of the base Mobile IP, if its smooth handoff fails to avoid losses of four or more packets during a handoff. To resolve such problems without sacrificing the scalability in Mobile IP based networks, we propose a buffering of packets at a Base Station (BS). We modify the route optimization extension in order to support packet buffering at the BS, which only requires minor changes. Finally, we discuss some problems occurring when recovering the packets dropped during a handoff by the buffering method, and propose our solution. The proposed buffering method makes handoffs be transparent to transport layer protocols by recovering lost packets during a handoff.

Performance Evaluation and Improvement of an Ad Hoc Wireless Network

An ad hoc wireless network is a self-organized network system. In this system, wireless terminals autonomously construct a multi-hop network which maintains its structural information by exchanging network information with some neighbor terminals. In such a network, the network topology changes frequently due to an unsettled wireless environment. Flexible Radio Network (FRN), one of the products applying ad hoc wireless network system, adopts an original protocol that provide a multiple routes management and a packet retransmission ability against packet transmission errors. This system has been in use in recent years. In this paper, we first evaluate its performance through simulations of data-link protocol and routing protocol to clarify its basic properties, and then we discover some problems on these protocols that degrade the performance. Furthermore, we propose some performance improvement techniques, simulate them, and then show how they improve the system performance.