During TCP/IP communications, MobileIP routing optimization functions causes out-of-order TCP packet sequences. To solve this problem, we propose a dynamic delayed ACK control scheme in which the wireless link-state management part notifies the upper TCP/IP layer of base-station hand-over, and at this time the TCP/IP layer sends dynamic delayed ACKs in response by using two-level-timer (i.e., hard-timer and soft-timer) processing. Simulation results confirm that applying dynamic delayed ACK control to MobileIP networks improves average throughput.

This paper describes a reduction algorithm for SW method which generates test sequences for communication systems. SW method is based upon the Finite State Machine (FSM). SW method uses a set of characterizing sequences and a state transition checking approach. This paper concentrates the characteristics of the SW sequences, and proposes the new derivation algorithm of characterizing sequences. Furthermore, Chinese Postman Tour and Extended Chinese Postman Tour is proposed to reduce redundancy of the SW sequences. This paper also presents an evaluation of this method in terms of an upper bound of the sequence length and generated test sequence length. The evaluation shows that the algorithm dramatically reduces the sequence length of the original method.

We describe a control scheme for wireless-link layers and the TCP/IP layers in which wireless link states, such as signal strength and transmission rate, are transparent to the upper network layers and govern the behavior of the upper layers. Monitoring and notifying functions for wireless link states are incorporated into mobile hosts, and prefetching functions for the mobility agent lists are added to the present MobileIP functionalities of the network layers. In addition, we give the mobile hosts functions for controlling the TCP advertised windows in the transport layers and give the base-stations buffering functions to deal with the variable signal strength of the wireless links. A simulation (using ns-2) of this control scheme shows that mobile agent can be switched at the network layers soon after base-station hand-over and that errors in packet routing, packet loss and communication throughput reduction can be avoided. Moreover, communications can be interrupted without having to shrink the size of the congestion windows of the TCP senders, which improves overall throughput.

This paper proposes a protocol verification tool where protocols are described in an extended Petri net and Horn clauses. The extended net model contributes to reduce state space in verification with hierarchical description. The model also includes timed and colored net. Horn clause enables protocol designers to grasp a protocol by the declarative semantics. They can describe non critical but mandatory portion of a protocol like error processing or abortion with Horn clauses. Protocols are verified through simulation. Protocol verification includes two methods, all-in-one and hierarchical methods. By the all-in-one method all description is translated into Prolong clause and simulated exhaustively, whereas by the hierarchical verification, simulation begins with the lowest layer and deduces sufficient conditions that give liveness and safeness of the net model. Then the layer is replaced by a simpler net model that is incorporated into the higher layer. The scheme is applied to an illustrative example of the Alternating Bit protocol to discuss its effectiveness.

Today, pedestrian navigation systems for mobile phones use 2-dimensional maps as a navigation media in general. But 3-dimensional maps or scenery images are easier to understand for users than 2-dimensional maps. To use 3-dimensional maps or scenery guidance, the measuring accuracy of user position is essential to understand guidance images. In this paper, we will present a pedestrian navigation system using real scenery photographs as a navigation media, and based on experiments we will report the evaluation result of influence of positioning accuracy on the understandability of navigation. It is shown that 3 meters or less error of positioning is tolerable for pedestrian navigation systems using scenery images.

It has been proposed that the collaborative working environments have been created by the computing assistance for human behaviors with the instructions of related information and items. The purpose of this study is to propose the collaboration mechanism and the environments constrained by the roles. The basic principle at issue in this studies is that all members should behave autonomously, and behave collaboratively with understanding the surrounding environments. We have already presented the Distributed Collaborative Computing architecture called Noah that has the concept of field with tupple space. On this mechanism, we designed the role-based cooperative work environments on the collaboration and coordination mechanism. We applied this mechanism to the typical models in the industrial system's domain.