Design and evaluation of protocols for wireless networks taking into account the interaction between transport and network layers.

We recognized two important shortcomings of the current TCP protocol: misinterpretation of delayed acknowledgments and competition among different TCP flows. In this dissertation, we propose to address these two issues by a use of novel protocol that uses immediate and delayed acknowledgment schemes and provides a coordination mechanism among independent TCP flows. We also address certain important issues that are related to the implementation of our proposed protocol: can we maintain the end-to-end semantics of TCP? Are there additional benefits that can be harvested if intermediate nodes with TCP protocol can be used? (Abstract shortened by UMI.)The Transmission Control Protocol (TCP) provides end-to-end data reliability and is the primary transport layer protocol for many applications such as email, web access, and file transfer. There has been a plethora of research activity that aims to improve the performance of TCP both in wired and wireless networks. Protocols for the computer networks have been very structured and layered to allow for easier upgrades and maintenance. The network layer protocol (e.g. IP) is independent and below the transport layer protocol (e.g. TCP). Our main goal in this dissertation is to examine the interaction and dynamics between the network layer protocols and TCP in the wireless environment.Towards this goal, we examined the network layer protocols in one-hop wireless (e.g. cellular networks) and multi-hop wireless, e.g. distributed Wi-Fi (Wireless Fidelity) networks. For each of these networks we, for the first time, propose transport layer protocols that take into account the interaction between the network layer and transport layer. For the one-hop wireless networks we have investigated analytical methods to determine the buffer requirements at base stations and estimate disruption time which is the time between two packet arrivals at the mobile host. We will show that the estimation of buffer requirements and disruption time is not only dependent on the wireless TCP scheme used, but also its interaction with the underlying network protocol. We also propose a comprehensive study of the effectiveness of wireless TCP and network protocols taking into account different networking environments that is decided on many factors such as mobility of senders and receivers, simplex and duplex communication among communicating peers, connection oriented and connection less communication at the network layer, rerouting schemes used after movement, and with and without hint handoff schemes

Proactive TCP mechanism to improve Handover performance in Mobile Satellite and Terrestrial Networks

Emerging standardization of Geo Mobile Radio (GMR-1) for satellite system is having strong resemblance to terrestrial GSM (Global System for Mobile communications) at the upper protocol layers and TCP (Transmission Control Protocol) is one of them. This space segment technology as well as terrestrial technology, is characterized by periodic variations in communication properties and coverage causing the termination of ongoing call as connections of Mobile Nodes (MN) alter stochastically. Although provisions are made to provide efficient communication infrastructure this hybrid space and terrestrial networks must ensure the end-to-end network performance so that MN can move seamlessly among these networks. However from connectivity point of view current TCP performance has not been engineered for mobility events in multi-radio MN. Traditionally, TCP has applied a set of congestion control algorithms (slow-start, congestion avoidance, fast retransmit, fast recovery) to probe the currently available bandwidth on the connection path. These algorithms need several round-trip times to find the correct transmission rate (i.e. congestion window), and adapt to sudden changes connectivity due to handover. While there are protocols to maintain the connection continuity on mobility events, such as Mobile IP (MIP) and Host Identity Protocol (HIP), TCP performance engineering has had less attention. TCP is implemented as a separate component in an operating system, and is therefore often unaware of the mobility events or the nature of multi-radios' communication. This paper aims to improve TCP communication performance in Mobile satellite and terrestrial networks.Comment: 5 pages, 2 figure

Enhanced FAST TCP by Solving Rerouting Problem

Delay-based congestion control algorithms inability to recognize increased RTT related to rerouting from increased RTT related to congestion is their most serious problem which has serious effect on their throughput. FAST TCP is one of delay-based TCP variants that although outperforms other TCP variants in high bandwidth-delay product networks, but suffers from several problems that inhere in its procedure to estimate trip delay. The most serious of these problems is rerouting. When rerouting occurs and round-trip time (RTT) of the new path is longer than RTT of the old path, the throughput of FAST TCP decreases sharply. Because FAST misinterprets the increased RTT as result of the network congestion and consequently decreases its own window size. This paper solves this problem by considering the relationship between sending rate and observed RTT. The simulation results show the effectiveness of proposed solution to solve rerouting problem while simultaneously preserves FAST TCP prominent primitive features

DragonNet: a robust mobile internet services system for long distance trains

Wide range wireless networks often suffer from annoying service deterioration due to ever-changing wireless environments. This is especially the case with passengers on long-distance trains (LDT, such as intercity, interprovincial, and international commuter trains) connecting to the Internet. To improve the service quality of wide-area wireless networks, we present the DragonNet system and protocol with practical implementations. The DragonNet system is a chained gateway that consists of a group of interlinked DragonNet routers running the DragonNet protocol for node failure amortization across the long stretching router chain. The protocol makes use of the spatial diversity of wireless signals when not all spots on a surface see the same level of radio frequency radiation. In the case of an LDT of around 500 meters, it is highly possible that some of the DragonNet routers in the gateway chain still see sound signal quality when the LDT is partially blocked from the wireless Internet. The DragonNet protocol fully utilizes this feature to amortize single-point router failure over the whole router chain by intelligently rerouting traffic on failed ones to sound ones. We have implemented the DragonNet system and tested it in real railways over a period of three months. Our results have pinpointed two fundamental contributions of the DragonNet protocol. First, DragonNet significantly reduces the average temporary communication blackout (i.e., no Internet connection) to 1.5 seconds compared with 6 seconds without the DragonNet protocol. Second, DragonNet nearly doubles the aggregate system throughput compared with gateway without running the DragonNet protocol

Study of Reliable Data Communication in Wireless Sensor Networks

A distributed wireless sensor network consists of numerous tiny autonomous sensing nodes deployed across a wide geographical area. These sensor nodes self organize and establish radio communication links with the neighboring nodes to form multi-hop routing paths to the central base station. The dynamic and lossy nature of wireless communication poses several challenges in reliable transfer of data from the sensor nodes to the sink. There are several applications of sensor networks wherein the data collected by the sensors in the network are critical and hence have to be reliably transported to the sink. An example of such an application is sensors with RFID readers mounted on them to read tag information from the objects in a factory warehouse. Here, the tag information recorded by the RFID reader is a critical piece of information which may not be available at a later point of time and hence has to be reliably transported to the sink. We study the various issues and analyze the design choices proposed in literature in addressing the challenge of sensors-to-sink reliable data communication in such applications. A cross-layer based protocol with MAC layer retransmissions and NACK (Negative Acknowledgment) based rerouting of data packets is developed to overcome link failures and provide reliability. The protocol is implemented on TinyOS and the performance of NACK based rerouting protocol in terms of percentage successful message reception is compared with NACK based retransmission protocol by running simulations on TOSSIM. The NACK based rerouting protocol provides greater reliability under different metrics like varying network size, network traffic and percentage of failed links in the network

Quality of experience-centric management of adaptive video streaming services : status and challenges

Video streaming applications currently dominate Internet traffic. Particularly, HTTP Adaptive Streaming ( HAS) has emerged as the dominant standard for streaming videos over the best-effort Internet, thanks to its capability of matching the video quality to the available network resources. In HAS, the video client is equipped with a heuristic that dynamically decides the most suitable quality to stream the content, based on information such as the perceived network bandwidth or the video player buffer status. The goal of this heuristic is to optimize the quality as perceived by the user, the so-called Quality of Experience (QoE). Despite the many advantages brought by the adaptive streaming principle, optimizing users' QoE is far from trivial. Current heuristics are still suboptimal when sudden bandwidth drops occur, especially in wireless environments, thus leading to freezes in the video playout, the main factor influencing users' QoE. This issue is aggravated in case of live events, where the player buffer has to be kept as small as possible in order to reduce the playout delay between the user and the live signal. In light of the above, in recent years, several works have been proposed with the aim of extending the classical purely client-based structure of adaptive video streaming, in order to fully optimize users' QoE. In this article, a survey is presented of research works on this topic together with a classification based on where the optimization takes place. This classification goes beyond client-based heuristics to investigate the usage of server-and network-assisted architectures and of new application and transport layer protocols. In addition, we outline the major challenges currently arising in the field of multimedia delivery, which are going to be of extreme relevance in future years