The wireless LAN (WLAN) system based on IEEE802.11 uses multiple transmission rates to obtain improved communication quality according to the communication environment. Furthermore, the range of use of wireless LAN is rapidly expanding in daily life, and it has become an important infrastructure for safe and secure life. However, because the dynamic change in transmission rate depends on variation in the communication environment, it is difficult to implement this transmission rate model in typical simulators, making it impossible to sufficiently simulate the real environment using the existing transmission rate model. To address this issue, this study first evaluates the characteristics of transmission rate over the multi-rate environment using real machines. We then propose a transmission rate model for the multi-rate environment based on the experimental results. In this study, we show a transmission rate model using an advection-diffusion equation. Note that there is an effort to use Wi-Fi systems at the time of disaster. Our proposed model is useful for the design and the operation of such Wi-Fi systems. Next, our simulation results confirm that the proposed transmission rate model can replicate the performance achieved in the actual environment.

Wireless local area networks (WLAN) based on IEEE 802.11 usually employ carrier sense multiple access with collision avoidance (CSMA/CA) for media access control. In the CSMA/CA mechanism, data frame collisions often occur if the number of wireless terminals increases. This problem decreases the total throughput of terminals connected to the same access point. To address this problem, a media access control method based on the synchronization phenomena of coupled oscillators (SP-MAC) has been proposed. Previous studies have confirmed that SP-MAC can significantly decrease the number of data frame collisions and improve total throughput compared to CSMA/CA. However, the previous studies did not consider a QoS control based on SP-MAC. This study focuses on throughput as a QoS metric. This study proposes a control method to guarantee throughput based on SP-MAC. Furthermore, this study evaluates the effectiveness of the proposed method through simulation experiments. The simulation results demonstrate that the proposed method can control the throughput of each terminal without decreasing total throughput. Furthermore, this study shows that the proposed method can guarantee throughput for a specified terminal.

Public areas, such as train stations and airports, providing wireless Local Area Network (WLAN) services are increasing and expanding because of the rapid development of WLANs based on IEEE 802.11 standard. Moreover, because of the advances in smartphone tethering technology, portable access points (APs) such as mobile Wi-Fi routers are being utilized more frequently. Consequently, there are increasing circumstances where a user needs to select and connect to one of the many APs. AP selection significantly determines the quality of service of the subsequent communication session. Existing AP selection algorithms consider user movement but not AP movement. We propose an AP selection method that handles both types of movement effectively. Moreover, we show that the proposed method improves the throughput significantly compared to the existing method.

The technology of flow-based QoS control on wireless LANs is receiving a lot of attention. There are several QoS technologies that can provide bandwidth guarantees by using TCP congestion control (QoS-TCP) and MAC control (QoS-MAC). Unfortunately, since QoS-TCP runs on the end terminal, it is possible that QoS-TCP will attempt to guarantee bandwidth without the permission of the network administrator (e.g. a hotspot service provider). In such a case, it is possible that these flows compress the throughout of coexisting flows unfairly. That is, it is possible for a non-priority flow to claim to be a priority flow by using QoS-TCP without the permission of the network administrator. We call such flows greedy flows. The purpose of this study is restraining such greedy TCP flows by using QoS-MAC over the wireless LAN network. This study evaluates the performance of our proposal by using ns-2. Simulations show that the proposal can control the greedy flows by using a QoS-MAC.

Satellite link speeds are now increasing in unison with those of terrestrial links. For example, the maximum link speed of WINDS (Wideband Internetworking engineering test and Demonstration Satellite) which was launched on 2008 is 1.2 Gbit/s. WINDS is expected to support applications in education, medicine including telemedicine, and disaster countermeasures. Therefore, such satellite communication service is one of the key technologies for network assurance. TCP-STAR was proposed to improve the throughput over satellite Internet. However, no experimental evaluation of TCP-STAR over satellite links such as WINDS has been published. Therefore, this paper evaluates the performance of TCP-STAR by comparing with TCP-New Reno and TCP-Hybla over a network consisting of WINDS, HDR-VSAT, and portable VSAT. As a result, it is found that TCP-STAR and TCP-Hybla achieve better throughput when segment losses do not occur, while TCP-STAR achieves the best throughput when segment losses occur.

As a variety of communication devices emerging, we can easily install two or more communication interfaces on a PC or a PDA and make a multi-home environment. To utilize this multi-home environment effectively, SCTP (stream control transmission protocol) has been proposed and standardized. Extending functions of the original SCTP, a strategy which can adapt SCTP to real-time communications has been proposed. However, the typical existing strategy has not enough considered the switching conditions from the viewpoint of transmission delay, so there is room to improve them. In this paper, we clarify the drawbacks of the existing strategy and their influences on the performance. Then, we propose a new strategy of path switching to reduce the delay and to increase the amount of data successfully delivered. The effect of the proposed strategy is discussed and confirmed through experimental evaluations.

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.