Reliable data delivery in low energy ad hoc sensor networks

Reliable delivery of data is a classical design goal for reliability-oriented collection routing protocols for ad hoc wireless sensor networks (WSNs). Guaranteed packet delivery performance can be ensured by careful selection of error free links, quick recovery from packet losses, and avoidance of overloaded relay sensor nodes. Due to limited resources of individual senor nodes, there is usually a trade-off between energy spending for packets transmissions and the appropriate level of reliability. Since link failures and packet losses are unavoidable, sensor networks may tolerate a certain level of reliability without significantly affecting packets delivery performance and data aggregation accuracy in favor of efficient energy consumption. However a certain degree of reliability is needed, especially when hop count increases between source sensor nodes and the base station as a single lost packet may result in loss of a large amount of aggregated data along longer hops. An effective solution is to jointly make a trade-off between energy, reliability, cost, and agility while improving packet delivery, maintaining low packet error ratio, minimizing unnecessary packets transmissions, and adaptively reducing control traffic in favor of high success reception ratios of representative data packets. Based on this approach, the proposed routing protocol can achieve moderate energy consumption and high packet delivery ratio even with high link failure rates. The proposed routing protocol was experimentally investigated on a testbed of Crossbow's TelosB motes and proven to be more robust and energy efficient than the current implementation of TinyOS2.x MultihopLQI

Traffic eavesdropping based scheme to deliver time-sensitive data in sensor networks

Due to the broadcast nature of wireless channels, neighbouring sensor nodes may overhear packets transmissions from each other even if they are not the intended recipients of these transmissions. This redundant packet reception leads to unnecessary expenditure of battery energy of the recipients. Particularly in highly dense sensor networks, overhearing or eavesdropping overheads can constitute a significant fraction of the total energy consumption. Since overhearing of wireless traffic is unavoidable and sometimes essential, a new distributed energy efficient scheme is proposed in this paper. This new scheme exploits the inevitable overhearing effect as an effective approach in order to collect the required information to perform energy efficient delivery for data aggregation. Based on this approach, the proposed scheme achieves moderate energy consumption and high packet delivery rate notwithstanding the occurrence of high link failure rates. The performance of the proposed scheme is experimentally investigated a testbed of TelosB motes in addition to ns-2 simulations to validate the performed experiments on large-scale network

Reliable routing scheme for indoor sensor networks

Indoor Wireless sensor networks require a highly dynamic, adaptive routing scheme to deal with the high rate of topology changes due to fading of indoor wireless channels. Besides that, energy consumption rate needs to be consistently distributed among sensor nodes and efficient utilization of battery power is essential. If only the link reliability metric is considered in the routing scheme, it may create long hops routes, and the high quality paths will be frequently used. This leads to shorter lifetime of such paths; thereby the entire network's lifetime will be significantly minimized. This paper briefly presents a reliable load-balanced routing (RLBR) scheme for indoor ad hoc wireless sensor networks, which integrates routing information from different layers. The proposed scheme aims to redistribute the relaying workload and the energy usage among relay sensor nodes to achieve balanced energy dissipation; thereby maximizing the functional network lifetime. RLBR scheme was tested and benchmarked against the TinyOS-2.x implementation of MintRoute on an indoor testbed comprising 20 Mica2 motes and low power listening (LPL) link layer provided by CC1000 radio. RLBR scheme consumes less energy for communications while reducing topology repair latency and achieves better connectivity and communication reliability in terms of end-to-end packets delivery performance

Cost effective RISC core supporting the large sending offload

The Ethernet speed has increased sending and receiving frames from 40 to 100 Gbps after the IEEE P802.3ba released. The industry and academia have focused scaling up the TCP/IP protocol processing for 40-100 Gbps. LSO is a de facto standard, which is offloaded to network interface for sending packets up to 10 Gbps. It not clears whether a network interface can support such function for new 40-100 Gbps. The widely use of the hardware-based NIC such as the use of a fully customized logic based network interface can be due to the following reasons; Still it is not clear whether the General Purpose Processor (GPP) can provide the processing required for high-speed line beyond the 10 Gbps. Also, the limit of the GPP's clock in supporting the processing of network interfaces. However, using a RISC core engine for offloading the LSO function can deliver some important features to network interfaces design, such as simplicity, scalability, shorter developing cycle time. In this paper, we have investigated using a specialized RISC core to process the LSO functions for TCP/IP and UDP/IP for high-speed communications rate up to 100 Gbps. To achieve this, we have enhanced the LSO algorithm to scale it to 100 Gbps. A fast DMA is used to support transferring data in the network interface. The LSO processing methodology on the network has presented. In addition, the RISC's performance and data movements for high communication rate up to 100 Gbps have been measured. A 148 MHz RISC core can support the sending-side processing for up to 100 Gbps transmission speed for the TCP/IP and UDP/IP protocol when the MTU is applied (1500 bytes). A DMA with 3759 MHz is required to eliminate the idle cycles while transferring data over the 64-bit local bus

Student perceptions of flipped learning

Flipped learning has been the subject of significant hype and attention but descriptions of the development and the evaluation of this pedagogical model are lacking. Flipped learning is an inverted teaching approach where students learn the basics via short videos at home, then come to class to complete challenges and clarify any misunderstandings. This paper describes how an IT unit was delivered using the flipped learning approach. A survey was used to determine how students perceived flipped learning. Students were generally positive about the approach, particularly the convenience and flexibility of the flipped videos. Although face to face teaching time was reduced in this flipped learning implementation, students felt that they interacted more with their instructors and peers. Students felt strongly positive to walkthroughs and were mixed as to the need for the instructors face. Significant efforts to produce high quality and engaging videos were made, but the survey suggested that students learnt the most during tutorial time. The relative importance of interactive tutorials is congruent with a large body of research and pedagogical approaches advocating the importance of active student-centred learning

Quantitative analysis of the effects queuing has on a CCID3 controlled DCCP flow

While the Data Congestion Control Protocol (DCCP) shows much promise at becoming a protocol of choice for real-time applications in the future, there are relatively speaking, only a small number of academic papers purporting to its performance and its various nuances. This paper will describe the effects queuing and in particular queue sizes have on DCCP when CCID3 is selected as the congestion control mechanism. From results obtained through the experimentation described in this paper, a clear trade-off between packet loss rates and packet latency values was found to occur when different queue sizes were employed on the experimental network. It was found that employing small fixed sized queues on the network led to lower packet latencies but higher volumes of packet loss as a result of the queue size reaching its maximum threshold more frequently. Alternatively when large queue sizes were used, the number of packet loss events reduced significantly however, packet latency values increased. In addition to showing this impending trade-off empirically, this paper describes ways in which this phenomenon could potentially be exploited to allow DCCP to offer applications with a more tailored form of transportation protocol based on their particular needs

Measuring the reliability of 802.11 WiFi networks [forthcoming]

Over half of the transmission time in WiFi networks is dedicated to ensuring that errors are corrected or detected. Despite these mechanisms, many studies have concluded that frame error rates vary. An increased understanding of why frames are lost is a pragmatic approach to improving real world 802.11 throughput. The potential beneficiaries of this research, include rate control algorithms, Modulation and Coding Schemes, simulation models, frame size selection and 802.11 configuration guidelines. This paper presents a measurement study of the factors which correlate with packet loss in 802.11 WiFi. Both passive and active approaches were used to investigate how the frame size, modulation and coding scheme and airtime effect the loss rate. Overall, packet errors were high, but the size of frames were not a major determinant of the loss rate. The loss rate decreased with the airtime but at substantially lower rates than those suggested in simple packet error models. Future work will further try to isolate and investigate specific errors, such as head on collisions in the preamble

Measuring the reliability of 802.11 WiFi networks

Over half of the transmission time in WiFi networks is dedicated to ensuring that errors are corrected or detected. Despite these mechanisms, many studies have concluded that frame error rates vary. An increased understanding of why frames are lost is a pragmatic approach to improving real world 802.11 throughput. The potential beneficiaries of this research, include rate control algorithms, Modulation and Coding Schemes, simulation models, frame size selection and 802.11 configuration guidelines. This paper presents a measurement study of the factors which correlate with packet loss in 802.11 WiFi. Both passive and active approaches were used to investigate how the frame size, modulation and coding scheme and airtime effect the loss rate. Overall, packet errors were high, but the size of frames were not a major determinant of the loss rate. The loss rate decreased with the airtime but at substantially lower rates than those suggested in simple packet error models. Future work will further try to isolate and investigate specific errors, such as head on collisions in the preamble

Reliable routing for low-power smart space communications

Smart Space (SS) communications has rapidly emerged as an exciting new paradigm that includes ubiquitous, grid, and pervasive computing to provide intelligence, insight, and vision for the emerging world of intelligent environments, products, services and human interaction. Dependable networking of a smart space environment can be ensured through reliable routing, efficient selection of error free links, rapid recovery from broken links and the avoidance of congested gateways. Since link failure and packet loss are inevitable in smart space wireless sensor networks, we have developed an efficient scheme to achieve a reliable data collection for smart spaces composed of low capacity wireless sensor nodes. Wireless Sensor Networks (WSNs) must tolerate a certain lack of reliability without a significant effect on packet delivery performance, data aggregation accuracy or energy consumption. In this paper we present an effective hybrid scheme that adaptively reduces control traffic with a metric that measures the reception success ratio of representative data packets. Based on this approach, our proposed routing scheme can achieve reduced energy consumption while ensuring minimal packet loss in environments featuring high link failure rates. The performance of our proposed routing scheme is experimentally investigated using both simulations and a test bed of TelosB motes. It is shown to be more robust and energy efficient than the network layer provided by TinyOS2.x. Our results show that the scheme is able to maintain better than 95% connectivity in an interference-prone medium while achieving a 35% energy saving

LBR: Load balancing routing algorithm for wireless sensor networks

Homogeneous wireless sensor networks (WSNs) are organized using identical sensor nodes, but the nature of WSNs operations results in an imbalanced workload on gateway sensor nodes which may lead to a hot-spot or routing hole problem. The routing hole problem can be considered as a natural result of the tree-based routing schemes that are widely used in WSNs, where all nodes construct a multi-hop routing tree to a centralized root, e.g., a gateway or base station. For example, sensor nodes on the routing path and closer to the base station deplete their own energy faster than other nodes, or sensor nodes with the best link state to the base station are overloaded with traffic from the rest of the network and experience a faster energy depletion rate than their peers. Routing protocols for WSNs are reliability-oriented and their use of reliability metric to avoid unreliable links makes the routing scheme worse. However, none of these reliability oriented routing protocols explicitly uses load balancing in their routing schemes. Since improving network lifetime is a fundamental challenge of WSNs, we present, in this chapter, a novel, energy-wise, load balancing routing (LBR) algorithm that addresses load balancing in an energy efficient manner by maintaining a reliable set of parent nodes. This allows sensor nodes to quickly find a new parent upon parent loss due to the existing of node failure or energy hole. The proposed routing algorithm is tested using simulations and the results demonstrate that it outperforms the MultiHopLQI reliability based routing algorithm