A Cross Layer Solution to Address TCP Intra-flow Performance Degradation in Multihop Ad hoc Networks

Incorporating the concept of TCP end-to-end congestion control for wireless networks is one of the primary concerns in designing ad hoc networks since TCP was primarily designed and optimized based on the assumptions for wired networks. In this study, our interest lies on tackling the TCP instability and in particular intra-flow instability problem since due to the nature of applications in multihop ad hoc networks, connection instability or starvation even for a short period of time can have a negative impact on the Quality of Service and may not be acceptable for the end user. Through a detailed analysis, it will be shown that the main causes of TCP intra-flow instability lies in overloading the network by sending more packets than the capacity of the channel. Based on this, the paper proposes a novel cross layer solution called “TCP Contention Control” that dynamically adjusts the amount of outstanding data in the network based on the level of contention experienced by packets as well as the throughput achieved by connections. The simulation results show TCP Contention Control can drastically improve TCP stability over 802.11 multihop ad hoc networks

Performance evaluation of channel selection algorithm for multi-channel MAC protocol in ad hoc networks

This thesis aims to provide an approach that is to investigate channel selection algorithm for increasing the performance of ad hoc networks. Although our channel selection algorithms are very simple, multi-channel MAC protocol that employs our channel selection algorithms are effective for increasing the performance of ad hoc networks.学位記番号：工博甲47

Offered load and stability controls in multi-hop wireless networks.

Ng Ping-chung.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.Includes bibliographical references (leaves 71-72).Abstracts in English and Chinese.Chapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Overview and Motivation --- p.1Chapter 1.2 --- Background of Offered Load Control --- p.2Chapter 1.3 --- Background of Stability Control --- p.3Chapter 1.4 --- Organization of the Thesis --- p.4Chapter Chapter 2 --- Performance Problems and Solutions --- p.6Chapter 2.1 --- Simulation Set-up --- p.6Chapter 2.2 --- High Packet-Drop Rate --- p.7Chapter 2.3 --- Re-routing Instability --- p.8Chapter 2.3.1 --- Hidden-Node Problem --- p.8Chapter 2.3.2 --- Ineffectiveness of Solving Hidden-Node Problem with RTS/CTS …… --- p.9Chapter 2.4 --- Solutions to High-Packet Loss Rate and Re-routing Instability --- p.10Chapter 2.4.1 --- Link-Failure Re-routing --- p.11Chapter 2.4.2 --- Controlling Offered Load --- p.13Chapter 2.5 --- Verification of Simulation Results with Real-life Experimental Measurements --- p.14Chapter Chapter 3 --- Offered Load Control --- p.16Chapter 3.1 --- Capacity Limited by the Hidden-node and Exposed-node Problems --- p.16Chapter 3.1.1 --- Signal Capture --- p.18Chapter 3.1.2 --- Analysis of Vulnerable Period induced by Hidden Nodes --- p.20Chapter 3.1.3 --- Analysis of Vulnerable Period induced by Exposed Nodes --- p.21Chapter 3.1.4 --- Sustainable Throughput --- p.22Chapter 3.2 --- Capacity Limited by Carrier Sensing Property --- p.23Chapter 3.3 --- Numerical Results --- p.26Chapter 3.4 --- General Throughput Analysis of a Single Multi-hop Traffic Flow --- p.29Chapter 3.5 --- Throughput Analysis on Topologies with Variable Distances between Successive Nodes --- p.31Chapter Chapter 4 --- Discussions of Other Special Cases --- p.33Chapter 4.1 --- A Carrier-sensing Limited Example --- p.33Chapter 4.2 --- A Practical Solution to Improve Throughput --- p.34Chapter Chapter 5 --- Achieving Fairness in Other Network Topologies --- p.36Chapter 5.1 --- Lattice Topology --- p.36Chapter Chapter 6 --- Stability Control --- p.39Chapter 6.1 --- Ad-hoc routing protocols --- p.39Chapter 6.2 --- Proposed scheme --- p.40Chapter 6.2.1 --- Original AODV --- p.41Chapter 6.2.2 --- AODV with Proposed Scheme --- p.42Chapter 6.2.2.1 --- A Single Flow in a Single Chain of Nodes --- p.43Chapter 6.2.2.2 --- Real-break Case --- p.44Chapter 6.3 --- Improvements --- p.45Chapter Chapter 7 --- Impacts of Data Transmission Rate and Payload Size --- p.48Chapter 7.1 --- Signal Capture --- p.48Chapter 7.2 --- Vulnerable region --- p.50Chapter Chapter 8 --- Performance Enhancements in Multiple Flows --- p.53Chapter 8.1 --- Impacts of Re-routing Instability in Two Flow Topology --- p.53Chapter 8.2 --- Impacts of Vulnerable Periods in Multiple Flow Topologies --- p.55Chapter 8.2.1 --- The Vulnerable Period induced by Individual Hidden-terminal Flow --- p.57Chapter 8.2.2 --- The Number of Hidden-terminal Flows --- p.58Chapter 8.2.3 --- Correlation between Hidden-terminal Flows --- p.60Chapter Chapter 9 --- Conclusion --- p.63Chapter Appendix A: --- General Throughput Analysis of a Single Multi-hop Traffic Flow --- p.67Chapter A.l --- Capacity Limited by Hidden-node and Exposed-Node --- p.67Chapter A.1.1 --- Sustainable Throughput --- p.68Chapter A.2 --- Capacity Limited by Carrier Sensing Property --- p.68Bibliography --- p.7

Enhancing TCP Performance in Mobile Ad Hoc Network Using Explicit Link Failure Notification (ELFN)

The dynamics and the unpredictable behaviour of a wireless mobile ad hoc network results in the hindrance of providing adequate reliability to network connections. Frequent route changes in the network relatively introduce incessant link failures which eventually degrade TCP performance considerably. In this research, we are going to study the potential improvement of TCP performance when Explicit Link Failure Notification is implemented as opposed to the standard TCP mechanism. ELFN modifies the ‘slow start’ mechanism that is used in standard TCP so that the throughput achieved from the network can be maximized

Experimenting with commodity 802.11 hardware: overview and future directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.This work has been partly supported by the European Community through the CROWD project (FP7-ICT-318115) and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919).Publicad

Fairness issues in multihop wireless ad hoc networks

Ph.DDOCTOR OF PHILOSOPH

Transport protocols for multi hop wireless networks

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

Cross-layer optimizations in multi-hop ad hoc networks

Unlike traditional wireless networks, characterized by the presence of last-mile, static and reliable infrastructures, Mobile ad Hoc Networks (MANETs) are dynamically formed by collections of mobile and static terminals that exchange data by enabling each other's communication. Supporting multi-hop communication in a MANET is a challenging research area because it requires cooperation between different protocol layers (MAC, routing, transport). In particular, MAC and routing protocols could be considered mutually cooperative protocol layers. When a route is established, the exposed and hidden terminal problems at MAC layer may decrease the end-to-end performance proportionally with the length of each route. Conversely, the contention at MAC layer may cause a routing protocol to respond by initiating new routes queries and routing table updates. Multi-hop communication may also benefit the presence of pseudo-centralized virtual infrastructures obtained by grouping nodes into clusters. Clustering structures may facilitate the spatial reuse of resources by increasing the system capacity: at the same time, the clustering hierarchy may be used to coordinate transmissions events inside the network and to support intra-cluster routing schemes. Again, MAC and clustering protocols could be considered mutually cooperative protocol layers: the clustering scheme could support MAC layer coordination among nodes, by shifting the distributed MAC paradigm towards a pseudo-centralized MAC paradigm. On the other hand, the system benefits of the clustering scheme could be emphasized by the pseudo-centralized MAC layer with the support for differentiated access priorities and controlled contention. In this thesis, we propose cross-layer solutions involving joint design of MAC, clustering and routing protocols in MANETs. As main contribution, we study and analyze the integration of MAC and clustering schemes to support multi-hop communication in large-scale ad hoc networks. A novel clustering protocol, named Availability Clustering (AC), is defined under general nodes' heterogeneity assumptions in terms of connectivity, available energy and relative mobility. On this basis, we design and analyze a distributed and adaptive MAC protocol, named Differentiated Distributed Coordination Function (DDCF), whose focus is to implement adaptive access differentiation based on the node roles, which have been assigned by the upper-layer's clustering scheme. We extensively simulate the proposed clustering scheme by showing its effectiveness in dominating the network dynamics, under some stressing mobility models and different mobility rates. Based on these results, we propose a possible application of the cross-layer MAC+Clustering scheme to support the fast propagation of alert messages in a vehicular environment. At the same time, we investigate the integration of MAC and routing protocols in large scale multi-hop ad-hoc networks. A novel multipath routing scheme is proposed, by extending the AOMDV protocol with a novel load-balancing approach to concurrently distribute the traffic among the multiple paths. We also study the composition effect of a IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF), used to reduce the effects of self-contention among frames at the MAC layer. The protocol framework is modelled and extensively simulated for a large set of metrics and scenarios. For both the schemes, the simulation results reveal the benefits of the cross-layer MAC+routing and MAC+clustering approaches over single-layer solutions