Wireless Sensor Network consists of tens or thousands of sensor nodes scattered in a physical space and one or more Base stations or Sinks. Even thought developed for military applications now they find a wide variety of civilian applications also. Some of the applications are Target tracking, Animal monitoring, Vehicle monitoring. The need (or lack thereof) for reliability in a sensor network is firmly dependent upon the specific application the sensor network is used for. Some applications like re-tasking or reprogramming sensor nodes [upgrading software or algorithms, adding codes, scripts etc] over -the-air requires assured delivery of high-priority events to sinks. We believe that as the number of sensor network applications grows, there will be a need to build more powerful general-purpose hardware and software environments capable of reprogramming or retasking sensors to. / Wireless sensor network is a special form of wireless networks dedicated to surveillance and monitoring applications Reliability in wireless sensor network is application specific. The specific form of reliability might change from application to application. Our idea is to generate reliability based transport protocol that is customizable to meet the needs of emerging reliable data applications in sensor networks and is also adaptive when the nodes are mobile. In our approach, clusters are formed for minimizing energy dissipation. The nodes maintain a neighbor list to forward data and any changes in the local topology can trigger updates to a node’s neighbor list. If a node notices that its neighbor list has changed, it can spontaneously re-advertise all of its data thus providing reliable transport in mobility conditions also. Our approach has five phases-setup, relaying, relay initiated error recovery, selective status reporting and node supervising. Our simulation results prove that the proposed approach can outperform existing related techniques and is highly responsive to the various error and mobility conditions experienced in sensor networks.

In this thesis, a low overhead transport protocol for Linux networking is proposed. This proposed protocol is motivated by the observation that the transport protocol for Linux requires more than a single memory copy for both the receiving and transmission of a packet, which is essentially redundant. In this thesis, we show that all but one of the memory copies can be eliminated, thus reducing the number of memory copies to one and only one, which is in general referred to as zero copy.

This thesis contributes toward the design of a reliable and energy-efficient transport system for Wireless Sensor Networks. Wireless Sensor Networks have emerged as a vital new area in networking research. In many Wireless Sensor Network systems, a common task of sensor nodes is to sense the environment and send the sensed data to a sink node. Thus, the effectiveness of a Wireless Sensor Network depends on how reliably the sensor nodes can deliver their sensed data to the sink. However, the sensor nodes are susceptible to loss for various reasons when there are dynamics in wireless transmission medium, environmental interference, battery depletion, or accidentally damage, etc. Therefore, assuring reliable data delivery between the sensor nodes and the sink in Wireless Sensor Networks is a challenging task. The primary contributions of this thesis include four parts. First, we design, implement, and evaluate a cross-layer communication protocol for reliable data transfer for data streaming applications in Wireless Sensor Networks. We employ reliable algorithms in each layer of the communication stack. At the MAC layer, a CSMA MAC protocol with an explicit hop-by-hop Acknowledgment loss recovery is employed. To ensure the end-to-end reliability, the maximum number of retransmissions are estimated and used at each sensor node. At the transport layer, an end-to-end Negative Acknowledgment with an aggregated positive Acknowledgment mechanism is used. By inspecting the sequence numbers on the packets, the sink can detect which packets were lost. In addition, to increase the robustness of the system, a watchdog process is implemented at both base station and sensor nodes, which enable them to power cycle when an unexpected fault occurs. We present extensive evaluations, including theoretical analysis, simulations, and experiments in the field based on Fleck-3 platform and the TinyOS operating system. The designed network system has been working in the field for over a year. The results show that our system is a promising solution to a sustainable irrigation system. Second, we present the design of a policy-based Sensor Reliability Management framework for Wireless Sensor Networks called SRM. SRM is based on hierarchical management architecture and on the policy-based network management paradigm. SRM allows the network administrators to interact with the Wireless Sensor Network via the management policies. SRM also provides a self-control capability to the network. This thesis restricts SRM to reliability management, but the same framework is also applicable for other management services by providing the management policies. Our experimental results show that SRM can offer sufficient reliability to the application users while reducing energy consumption by more than 50% compared to other approaches. Third, we propose an Energy-efficient and Reliable Transport Protocol called ERTP, which is designed for data streaming applications in Wireless Sensor Networks. ERTP is an adaptive transport protocol based on statistical reliability that ensures the number of data packets delivered to the sink exceeds the defined threshold while reducing the energy consumption. Using a statistical reliability metric when designing a reliable transport protocol guarantees the delivery of adequate information to the users, and reduces energy consumption when compared to the absolute reliability. ERTP uses hop-by-hop Implicit Acknowledgment with a dynamically updated retransmission timeout for packet loss recovery. In multihop wireless networks, the transmitter can overhear a forwarding transmission and interpret it as an Implicit Acknowledgment. By combining the statistical reliability and the hop-by-hop Implicit Acknowledgment loss recovery, ERTP can offer sufficient reliability to the application users with minimal energy expense. Our extensive simulations and experimental evaluations show that ERTP can reduce energy consumption by more than 45% when compared to the state-of- the-art protocol. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended Wireless Sensor Network is increased. In Wireless Sensor Networks, sensor node failures can create network partitions or coverage loss which can not be solved by providing reliability at higher layers of the protocol stack. In the final part of this thesis, we investigate the problem of maintaining the network connectivity and coverage when the sensor nodes are failed. We consider a hybrid Wireless Sensor Network where a subset of the nodes has the ability to move at a high energy expense. When a node has low remaining energy (dying node) but it is a critical node which constitutes the network such as a cluster head, it will seek a replacement. If a redundant node is located in the transmission range of the dying node and can fulfill the network connectivity and coverage requirement, it can be used for substitution. Otherwise, a protocol should be in place to relocate the redundant sensor node for replacement. We propose a distributed protocol for Mobile Sensor Relocation problem called Moser. Moser works in three phases. In the first phase, the dying node determines if network partition occurs, finds an available mobile node, and asks for replacement by using flooding algorithm. The dying node also decides the movement schedule of the available mobile node based on certain criteria. The second phase of the Moser protocol involves the actual movement of the mobile nodes to approach the location of the dying node. Finally, when the mobile node has reached the transmission of the dying node, it communicates to the dying nodes and moves to a desired location, where the network connectivity and coverage to the neighbors of the dying nodes are preserved.

<p>In the last decade, we have seen an explosive growth in the deployment of multimedia applications on the Internet. However, the transport service provided over the Internet is not always feasible for these applications, since the network was originally designed for other types of applications. One way to better accommodate the service requirements of some of these applications is to provide a partially reliable transport service. A partially reliable transport service does not insist on recovering all, but just some of the packet losses, thus providing a lower transport delay than a reliable transport service. The work in this thesis focuses on the design, implementation, and evaluation of a partially reliable transport protocol called PRTP. PRTP has been designed as an extension to TCP in order to show that such a service could be effectively integrated with current protocol standards. An important feature of PRTP is that all modifications for PRTP are restricted to the receiver side, which means that it could be very easily deployed. The thesis presents performance results from various experiments on a Linux implementation of PRTP. The results suggest that transfer times can be decreased significantly when using PRTP as opposed to TCP in networks in which packet loss occurs. Furthermore, the thesis includes a study that investigates how users perceive an application that is based on a partially reliable service. Specifically, how users select the trade-off between image quality and latency when they download Web pages is explored. The results indicate that many of the users in the study could accept less than perfect image quality</p><p>if the latency could be shortened.</p>

Satellite IP networks are characterized by high bit error rates, long propagation delays, low bandwidth feedback links, and persistent fades resulting from varying weather patterns. A new unicast transport protocol is designed to address all the above challenges. Two new algorithms, Jump Start and Quick Recovery, are presented to replace the traditional Slow Start algorithm and to recover rapidly from multiple segment losses within one window of data. The characteristics of satellite IP networks also distinguish satellite multicasting from multicasting in terrestrial wirelined networks. A reliable data multicast transport protocol, TCP-Peachtree, is proposed to solve the acknowledgment implosion and scalability problems in satellite IP networks. Developments in space technology are enabling the realization of deep space missions. The scientific data from these missions need to be delivered to the Earth successfully. To achieve this goal, the InterPlaNetary Internet is proposed as the Internet of the deep space planetary networks, which is characterized by extremely high propagation delays, high link errors, asymmetrical bandwidth, and blackouts. A reliable transport protocol, TP-Planet, is proposed for data traffic in the InterPlaNetary Internet. TP-Planet deploys rate-based additive-increase multiplicative-decrease (AIMD) congestion control and replaces the inefficient slow start algorithm with a novel Initial State algorithm that allows the capture of link resources in a very fast and controlled manner. A new congestion detection and control mechanism is developed and a Blackout State is incorporated into the protocol operation. Multimedia traffic is also one part of the aggregate traffic over InterPlaNetary Internet backbone links and it has additional requirements such as minimum bandwidth, smooth traffic, and error control. To address all the above challenges, RCP-Planet is proposed. RCP-Planet consists of two novel algorithms, i.e., Begin State and Operational State. The protocol is based on a novel rate probing mechanism and a new rate control scheme to update the media rate smoothly based on the observed rate for the probing sequence.

This thesis contributes toward the design of a reliable and energy-efficient transport system for Wireless Sensor Networks. Wireless Sensor Networks have emerged as a vital new area in networking research. In many Wireless Sensor Network systems, a common task of sensor nodes is to sense the environment and send the sensed data to a sink node. Thus, the effectiveness of a Wireless Sensor Network depends on how reliably the sensor nodes can deliver their sensed data to the sink. However, the sensor nodes are susceptible to loss for various reasons when there are dynamics in wireless transmission medium, environmental interference, battery depletion, or accidentally damage, etc. Therefore, assuring reliable data delivery between the sensor nodes and the sink in Wireless Sensor Networks is a challenging task. The primary contributions of this thesis include four parts. First, we design, implement, and evaluate a cross-layer communication protocol for reliable data transfer for data streaming applications in Wireless Sensor Networks. We employ reliable algorithms in each layer of the communication stack. At the MAC layer, a CSMA MAC protocol with an explicit hop-by-hop Acknowledgment loss recovery is employed. To ensure the end-to-end reliability, the maximum number of retransmissions are estimated and used at each sensor node. At the transport layer, an end-to-end Negative Acknowledgment with an aggregated positive Acknowledgment mechanism is used. By inspecting the sequence numbers on the packets, the sink can detect which packets were lost. In addition, to increase the robustness of the system, a watchdog process is implemented at both base station and sensor nodes, which enable them to power cycle when an unexpected fault occurs. We present extensive evaluations, including theoretical analysis, simulations, and experiments in the field based on Fleck-3 platform and the TinyOS operating system. The designed network system has been working in the field for over a year. The results show that our system is a promising solution to a sustainable irrigation system. Second, we present the design of a policy-based Sensor Reliability Management framework for Wireless Sensor Networks called SRM. SRM is based on hierarchical management architecture and on the policy-based network management paradigm. SRM allows the network administrators to interact with the Wireless Sensor Network via the management policies. SRM also provides a self-control capability to the network. This thesis restricts SRM to reliability management, but the same framework is also applicable for other management services by providing the management policies. Our experimental results show that SRM can offer sufficient reliability to the application users while reducing energy consumption by more than 50% compared to other approaches. Third, we propose an Energy-efficient and Reliable Transport Protocol called ERTP, which is designed for data streaming applications in Wireless Sensor Networks. ERTP is an adaptive transport protocol based on statistical reliability that ensures the number of data packets delivered to the sink exceeds the defined threshold while reducing the energy consumption. Using a statistical reliability metric when designing a reliable transport protocol guarantees the delivery of adequate information to the users, and reduces energy consumption when compared to the absolute reliability. ERTP uses hop-by-hop Implicit Acknowledgment with a dynamically updated retransmission timeout for packet loss recovery. In multihop wireless networks, the transmitter can overhear a forwarding transmission and interpret it as an Implicit Acknowledgment. By combining the statistical reliability and the hop-by-hop Implicit Acknowledgment loss recovery, ERTP can offer sufficient reliability to the application users with minimal energy expense. Our extensive simulations and experimental evaluations show that ERTP can reduce energy consumption by more than 45% when compared to the state-of- the-art protocol. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended Wireless Sensor Network is increased. In Wireless Sensor Networks, sensor node failures can create network partitions or coverage loss which can not be solved by providing reliability at higher layers of the protocol stack. In the final part of this thesis, we investigate the problem of maintaining the network connectivity and coverage when the sensor nodes are failed. We consider a hybrid Wireless Sensor Network where a subset of the nodes has the ability to move at a high energy expense. When a node has low remaining energy (dying node) but it is a critical node which constitutes the network such as a cluster head, it will seek a replacement. If a redundant node is located in the transmission range of the dying node and can fulfill the network connectivity and coverage requirement, it can be used for substitution. Otherwise, a protocol should be in place to relocate the redundant sensor node for replacement. We propose a distributed protocol for Mobile Sensor Relocation problem called Moser. Moser works in three phases. In the first phase, the dying node determines if network partition occurs, finds an available mobile node, and asks for replacement by using flooding algorithm. The dying node also decides the movement schedule of the available mobile node based on certain criteria. The second phase of the Moser protocol involves the actual movement of the mobile nodes to approach the location of the dying node. Finally, when the mobile node has reached the transmission of the dying node, it communicates to the dying nodes and moves to a desired location, where the network connectivity and coverage to the neighbors of the dying nodes are preserved.

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: Performance Enhancing Proxy; ABR; IP; Satellite; QoS; TCP. Includes bibliographical references (p.110-111).

In recent years, Internet and IP technologies have made inroads into almost every commu- nication market ranging from best-effort services such as email and Web, to soft real-time applications such as VoIP, IPTV, and video. However, providing a transport service over IP that meets the timeliness and availability requirements of soft real-time applications has turned out to be a complex task. Although network solutions such as IntServ, DiffServ, MPLS, and VRRP have been suggested, these solutions many times fail to provide a trans- port service for soft real-time applications end to end. Additionally, they have so far only been modestly deployed. In light of this, this thesis considers transport protocols for soft real-time applications. Part I of the thesis focuses on the design and analysis of transport protocols for soft real- time multimedia applications with lax deadlines such as image-intensive Web applications. Many of these applications do not need a completely reliable transport service, and to this end Part I studies so-called partially reliable transport protocols, i.e., transport protocols that enable applications to explicitly trade reliability for improved timeliness. Specifically, Part I investigates the feasibility of designing retransmission-based, partially reliable transport protocols that are congestion aware and fair to competing traffic. Two transport protocols are presented in Part I, PRTP and PRTP-ECN, which are both extensions to TCP for partial reliability. Simulations and theoretical analysis suggest that these transport protocols could give a substantial improvement in throughput and jitter as compared to TCP. Additionally, the simulations indicate that PRTP-ECN is TCP friendly and fair against competing congestion- aware traffic such as TCP flows. Part I also presents a taxonomy for retransmission-based, partially reliable transport protocols. Part II of the thesis considers the Stream Control Transmission Protocol (SCTP), which was developed by the IETF to transfer telephony signaling traffic over IP. The main focus of Part II is on evaluating the SCTP failover mechanism. Through extensive experiments, it is suggested that in order to meet the availability requirements of telephony signaling, SCTP has to be configured much more aggressively than is currently recommended by IETF. Fur- thermore, ways to improve the transport service provided by SCTP, especially with regards to the failover mechanism, are suggested. Part II also studies the effects of Head-of-Line Blocking (HoLB) on SCTP transmission delays. HoLB occurs when packets in one flow block packets in another, independent, flow. The study suggests that the short-term effects of HoLB could be substantial, but that the long-term effects are marginal.

A mobile wireless ad hoc network (MANET) consists of a group of mobile nodes communicating wirelessly with no fixed infrastructure. Each node acts as source or receiver, and all play a role in path discovery and packet routing. MANETs are growing in popularity due to multiple usage models, ease of deployment and recent advances in hardware with which to implement them. MANETs are a natural environment for multicasting, or group communication, where one source transmits data packets through the network to multiple receivers. Proposed applications for MANET group communication ranges from personal network apps, impromptu small scale business meetings and gatherings, to conference, academic or sports complex presentations for large crowds reflect the wide range of conditions such a protocol must handle. Other applications such as covert military operations, search and rescue, disaster recovery and emergency response operations reflect the "mission critical" nature of many ad hoc applications. Reliable data delivery is important for all categories, but vital for this last one. It is a feature that a MANET group communication protocol must provide. Routing protocols for MANETs are challenged with establishing and maintaining data routes through the network in the face of mobility, bandwidth constraints and power limitations. Multicast communication presents additional challenges to protocols. In this dissertation we study reliability in multicast MANET routing protocols. Several on-demand multicast protocols are discussed and their performance compared. Then a new reliability protocol, R-ODMRP is presented that runs on top of ODMRP, a well documented "best effort" protocol with high reliability. This protocol is evaluated against ODMRP in a standard network simulator, ns-2. Next, reliable multicast MANET protocols are discussed and compared. We then present a second new protocol, Reyes, also a reliable on-demand multicast communication protocol. Reyes is implemented in the ns-2 simulator and compared against the current standards for reliability, flooding and ODMRP. R-ODMRP is used as a comparison point as well. Performance results are comprehensively described for latency, bandwidth and reliable data delivery. The simulations show Reyes to greatly outperform the other protocols in terms of reliability, while also outperforming R-ODMRP in terms of latency and bandwidth overhead.

More and more so-called soft real-time traffic is being sent over IP-based networks. The bursty, data-limited traffic pattern as well as the latency requirements from this traffic present challenges to the traditional communication techniques, designed for bulk traffic without considering latency. To meet the requirements from soft real-time traffic, in particular from telephony signaling, the Stream Control Transmission Protocol (SCTP) was designed. Its support for connectivity to multiple networks, i.e., multihoming, provides robustness and opens up for concurrent multipath transfer (CMT) over multiple paths. Since SCTP is a general transport protocol, it also enables for handover of media sessions between heterogeneous networks. Migrating an ongoing session to a new network, as well as CMT with minimal latency, requires tuning of several protocol parameters and mechanisms. This thesis addresses latency reduction for soft real-time traffic using SCTP multihoming from three perspectives. The first focus is on latency for signaling traffic in case of path failure, where a path switch, a failover, occurs. We regard quick failure detection as well as rapid startup on the failover target path. The results indicate that by careful parameter tuning, the failover time may be significantly reduced. The second focus in the thesis is on latency for signaling traffic using CMT. To this end, we address sender-side scheduling. We evaluate some existing schedulers, and design a dynamic stream-aware scheduler. The results indicate that the dynamic stream-aware scheduler may provide significantly improved latency in unbalanced networks. Finally, we target multihomed SCTP to provide for handover of a media session between heterogeneous wireless networks in a mobile scenario. We implement a handover scheme and our investigation shows that SCTP could provide for seamless handover of a media session at walking speed. / So-called soft real-time traffic may be sent over IP-based networks. The bursty, data-limited traffic pattern and the latency requirements from this traffic present a challenge to traditional communication techniques. The Stream Control Transmission Protocol (SCTP), with support for multihoming, was designed to better meet the requirements from soft-real time traffic. Multihoming provides for robustness and for concurrent multipath transfer (CMT) as well as for handover of sessions between heterogeneous networks. Still, to meet the timeliness requirements, tuning of protocol parameters and mechanisms is crucial. This thesis addresses latency reduction for soft real-time traffic using SCTP multihoming. The first focus is on signaling traffic in case of path failure, where a path switch, a failover, occurs. We show that careful parameter tuning may reduce the failover time significantly. The second focus is on signaling traffic using CMT. We address sender-side scheduling and show that dynamic stream-aware scheduling may reduce latency when data is transmitted over asymmetric network  paths. The third focus is multihomed SCTP for handover between heterogeneous networks, where we show that SCTP could provide for seamless handover of a media session at walking speed. / <p>Paper 3 (Efficient Scheduling to Reduce Latency...) ingick i avhandlingen som manuskript med samma namn.</p>