On TCP Performance over Multi-Hops Satellite Constellations

Taleb, Tarik,Kato, Nei,Nemoto, Yoshiaki 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-

TCP is the most widely used transport protocol on today's Internet. A large part of its success is due to its ability to probe for unused bandwidth while also backing off its transmission rate upon detection of network congestion. Despite the fact that several mechanisms have been presented in recent literature to improve TCP, there remain some vexing attributes that impair TCP's performance. In this paper, we address the issue of the efficiency and fairness of TCP in multi-hops satellite constellations. We mainly focus on the effect of the change in flow count on TCP behavior. In case of handover occurrence, a TCP sender mat be forced to share a new set of satellites with other users resulting in a change of flow count. Our work argues that the TCP rate of each flow should be dynamically adjusted to the available bandwidth when the number of flows, competing for a single link, changes over time. We show through simulations that our fair share scheme improves fairness by guaranteeing a fair progression in window size for each flow, decreases the number of losses, and makes better utilization of the bottleneck link.

A Traffic Congestion Avoidance Scheme for LEO Satellite Networks by Using Traffic Detour Technique

Mashimo, Daisuke,Taleb, Tarik,Jamalipour, Abbas,Kato, Nei,Nemoto, Yoshiaki 통신위성우주산업연구회 2005 Joint Conference on Satellite Communications Vol.2005 No.-

Given that wired network infrastructure is not yet ready in more than half of the world, satellite networks attrack attention as an important choice to build global communication networks. Satellite networks must deal by a communication demand of different quantity in every area due to most of the world people live around the equator or in middle latitude area. In addition, distribution of traffic becomes more unbalanced due to population density is different in a city and a district. As a result, the congestion occurs in some satellites, while others are not used at all. The problem about traffic engineering in satellite networks can be solved by scattering traffic over underutilized links. Therefore, this paper proposes a traffic congestion avoidance scheme using Traffic Detour Technique (TDT) which is based on traffic information about a satellite of next hop on the remainder of the path to the destination. The satellite where traffic was concentrated transmits a signaling packet to its neighboring satellites to decrease their sending rate before congestion occurs or packets drop. Neighboring satellites follow it and look for alternate paths of the others which do not include the satellite where a problem occurred. The performance of the proposed scheme is evaluated by simulations. And from the results, this scheme achieves a better traffic distribution and decreases the number of packet drops.

Supporting Context-Aware Applications for Eldercare

Bottazzi, Dario,Taleb, Tarik,Guizani, Mohsen,Hafid, Abdelhakim Senhaji The Korea Institute of Information and Commucation 2011 Journal of communications and networks Vol.13 No.2

Extended life expectancy and a decrease in fertility rates are dramatically increasing the number of seniors who will eventually need professional care assistance. Although there is no clear technical solution to this problem, recent advances in ubiquitous computing offer opportunities to assist elders in their residence, thus reducing the need for professional assistance in special facilities. There have been several studies, but current solutions tend to address specific issues and cannot be easily extended, updated, and customized to meet the complex and evolving requirements of eldercare assistance. This study aims to bridge this gap, and this paper presents a context-management framework, called awareness for pervasive environments (APE), that provides easily customizable support for the development of ubiquitous eldercare services and applications.

ELB in IP/NGEO Satellite Constellations: Issues and Solutions

Mashimo, Daisuke,Taleb, Tarik,Hashimoto, Kazuo,Nemoto, Yoshiaki,Kato, Nei 통신위성우주산업연구회 2006 Joint Conference on Satellite Communications Vol.2006 No.-

To ensure an intelligent engineering of traffic over satellite networks, the authors have recently proposed a routing protocol dubbed Explicit Load Balancing (ELB). The protocol enables neighboring satellites to explicitly exchange information on their congestion status. A satellite that is about to get congested requests its neighboring satellites to decrease their data forwarding rates. In response, the neighboring satellites search for less congested paths that do not include the satellite in question and communicate a portion of data, primarily destined to the satellite, via the retrieved paths. While transmitting packets of the same flow over different links helps to better distribute the traffic over the satellite constellation, and accordingly alleviates congestion and avoids packet drops, it leads to the reception of packets in an out-of-order manner at the receiver side. In case of TCP, this phenomenon results in the transmission of duplicate acknowledgments, unnecessarily halves the congestion window of TCP, and ultimately degrades the throughput. As a remedy to this issue, we suggest that receivers refer to the Time-to-Live (TTL) field of packet headers to judge whether the out of order in the reception of packets is due to congestion or simply to changes in the communication path. Furthermore, as packets have to traverse more hops in ELB, delay-sensitive applications may get affected by the extra delay due to hops. To cope with such an issue, we consider the use of differentiated services we classify users into a number of classes, namely delay sensitive, throughput-sensitive, and best effort. Via simulations, we demonstrate the efficiency of ELB in such environments.

Enhancements of T-REFWA to Mitigate Link Error-Related Degradations in Hybrid Wired/Wireless Networks

Nishiyama, Hiraki,Taleb, Tarik,Nemoto, Yoshiaki,Jamalipour, Abbas,Kato, Nei The Korea Institute of Information and Commucation 2006 Journal of communications and networks Vol.8 No.4

With the on-going wireless access technologies, the Internet has become accessible anytime anywhere. In wireless networks, link errors significantly degrade the performance of the transmission control protocol (TCP). To cope with this issue, this paper improves the recently-proposed terrestrial REFWA (T-REFWA) scheme by adding a new error recovery mechanism to its original design. In the T-REFWA scheme, senders are acknowledged with appropriate sending rates at which an efficient and fair utilization of network resources can be achieved. As the feedback values are computed independently of link errors, senders can keep transmitting data at high rates even in case of link error occurrences. Using this feature, the proposed error recovery mechanism can achieve high throughput in environments with high bit error rates. The throughput is further improved by disabling the exponential back-off algorithm of TCP so that long idle times are avoided in case of link errors. We show through simulations that the proposed method improves TCP performance in high bit error rates. Compared with several TCP variants, the proposed error recovery scheme exhibits higher link utilization and guarantees system fairness for different bit error rates.

Supporting Context-Aware Applications for Eldercare

Dario Bottazzi,Tarik Taleb,Mohsen Guizani,Abdelhakim Senhaji Hafid 한국통신학회 2011 Journal of communications and networks Vol.13 No.2

Extended life expectancy and a decrease in fertility rates are dramatically increasing the number of seniors who will eventually need professional care assistance. Although there is no clear technical solution to this problem, recent advances in ubiquitous computing offer opportunities to assist elders in their residence,thus reducing the need for professional assistance in special facilities. There have been several studies, but current solutions tend to address specific issues and cannot be easily extended, updated, and customized to meet the complex and evolving requirements of eldercare assistance. This study aims to bridge this gap, and this paper presents a context-management framework, called awareness for pervasive environments (APE), that provides easily customizable support for the development of ubiquitous eldercare services and applications.