Nestor Michael C. Tiglao

Efficient multimedia transmission in wireless sensor networks

Real-time multimedia data such as video are usually loss-tolerant but require timely delivery in order to be useful to the application. Loss recovery through the retransmission of lost data may introduce unacceptable delays, which is the reason why these data types are usually delivered with no transport layer reliability, using erasure coding and similar techniques to maximize data recovery at the receiver. However, in Wireless Multimedia Sensor Networks (WMSNs), these mechanisms are not enough to provide an acceptable image quality and, thus, reliable transport protocols adapted to these requirements are needed. This paper presents some mechanisms to improve multimedia transmissions in WMSNs when reliable transport layer protocols are used. They consist of assigning a budget of time for the sending of certain amount of information and estimating if the channel conditions allow to complete the transmission or not. If it is not likely to complete it, then the transmission is stopped, thus saving important energy resources in the sensors. We evaluate this approach by modifying the behavior of a previously proposed reliable transport protocol (DTSN). Our proposal, M-DTSN, improves DTSN flexibility by managing the trade-off between media quality and timely delivery for real-time multimedia data with some degree of loss-tolerance. The simulation results demonstrate that the advantages of M-DTSN for the transmission of multimedia data are quite significant when compared with the original DTSN protocol.

An analytical model for transport layer caching in wireless sensor networks

Reliable transport protocols have traditionally been designed to perform end-to-end error control transparently to the intermediate nodes (e.g., TCP). However, the resource constraints featured by Wireless Sensor Network (WSN) require a different paradigm where intermediate nodes are able to cache packets, retransmitting them on-demand in order to avoid incurring on costly end-to-end retransmissions. This paper presents an analytical model of end-to-end delivery cost for WSN reliable transport with intermediate caching. The model calculates the cost as the total number of physical layer transmissions using a probabilistic formulation that has been validated through network simulation. Although the model is based on a specific transport protocol (DTSN), the addressed mechanisms are more generic, allowing it to be easily adapted to other WSN transport protocols that also feature intermediate caching. Numerical results confirm the improved efficiency introduced by a transport layer with intermediate caching in comparison with end-to-end approaches that are based exclusively on MAC layer reliability. Different cache partitioning policies were tested, and it is shown that cache partitioning policies should take into account the network conditions experienced by concurrent flows, namely the status of the radio links and the flow lengths.

Real-time multimedia monitoring in large-scale wireless multimedia sensor networks: Research challenges

Wireless Sensor Networks (WSNs) have enjoyed dramatic developments over the last decade. The availability of CMOS cameras and microphones enlarged the scope of WSNs paving the way to the development of Wireless Multimedia Sensor Networks (WMSN). Among the envisaged WMSN applications, Real-time Multimedia Monitoring constitutes one of the most promising. However, the resource requirements of these applications place difficult challenges in terms of network lifetime and scalability. This paper starts by identifying the main characteristics and requirements of Real-time Multimedia Monitoring applications and then highlights key research directions that may help to overcome those challenges.

Cross-layer caching based optimization for wireless multimedia sensor networks

Traditional transport layer protocols have been designed to perform end-to-end error control transparently to the intermediate nodes (e.g., TCP). However, the resource constraints featured by Wireless Sensor Network (WSN) require a different paradigm where intermediate nodes are able to cache packets and if possible retransmit them on-demand to avoid incurring costly end-to-end retransmissions. Lately, wireless multimedia sensor network (WMSN) is being considered as a new research area whereby WSNs are targeted for the delivery of multimedia traffic. In this paper, we propose a NACK-based repair mechanism coupled with an adaptive MAC layer retransmission scheme in order to improve the performance of the transport protocols. Specifically, our goal is to be able to reduce real-time end-to-end delay while maintaining reliability and energy efficiency in the presence of high channel error rates. Our simulation results show that the ensemble of both mechanisms provides better good-put performance while simultaneously improving energy efficiency. Furthermore, the improved protocol also achieves lower deadline miss ratios which makes it suitable for multimedia transport. While we demonstrate the effectiveness of the mechanisms by incorporating them into the basic Distributed Transport for Sensor Networks (DTSN) protocol, they are generic enough to be applicable to other WSN transport protocols.

Analysis of cache-based transport protocol at congestion in Wireless Sensor Networks

Consistent data delivery in constrained networks such as wireless sensor networks (WSN), which has a significant role in Internet of Things (IoT), is vital due to the high probability of packet loss, not only because of the unreliable channel but also from link and buffer congestions. Thus, a reliable transport protocol should be used. Data caching at intermediate nodes is one way of improving the reliability performance of transport protocols in WSNs. However, it is not yet known up to what extent data caching alone can alleviate congestion in WSNs. This study investigates and analyses how a cache-based transport protocol, that has no congestion control mechanism and has a fixed transmission window, performs under congestion states. The transport protocol, called DTSN, is evaluated under link and buffer congestion states and the optimal performance is determined in terms of goodput, transmission cost and cache hit metrics. The results of our analysis reveal that intermediate caching was able to perform significantly during congestions in WSN. However, the amount of traffic being sent and intermediate nodes cache memory should be taken into account. The optimum caching performance during link contentions is reached at higher transmission window and cache size values, while for buffer congestions, it is achieved at lower transmission window but higher cache size values, respectively. These values obtained can guarantee optimum usage of cache while ensuring congestion avoidance. In addition, the correlation that is established can serve as a basis for developing congestion window management for transport protocols in WSN that employ data caching.

Cache-based transport protocols in wireless sensor networks

Sensor nodes in Wireless Sensor Networks (WSNs) are battery-powered devices that consume energy during data transmission and processing. One of the most critical tasks in a sensor network is dealing with reliable end-to-end transmissions and optimizing the power consumption. WSNs are error prone due to the constrained nature of the nodes and the interference with other wireless technologies such as Wifi and Bluetooth. One possible way to minimize this problem is caching the data. Data caching is one technique of improving the performance of a transport protocol. Since a typical data transmission consumes more energy than processing in a sensor network, the use of caching enables quick access to data. Therefore, caching, if used efficiently, could reduce overall network traffic and hence bandwidth can be optimally utilized. Unfortunately, a systematic analysis of caching in WSNs was until now lacking. Given that WSNs are expected to play an important role in Machine Type Communications (MTC) and Internet of Things (IoT), the authors believe that now is time to collect the results of years of research on this important topic. This paper presents a comprehensive survey on the state-of-the-art cache-based transport protocols in wireless sensor networks. We classify the transport protocols by presenting a thematic taxonomy of the current cache management mechanisms in wireless sensor networks. Moreover, the critical aspects of the existing cache-ware schemes in sensor networks are analyzed to determine the strengths and weaknesses of such protocols. The similarities and differences of the transport protocols based on the important parameters, such as cache insertion/replacement policy, cache size requirement, cache location, cache partition, and cache decision are investigated in this paper. In addition to that, we discuss open research issues and challenges of cache-based transport protocols in wireless sensor networks. We strongly believe that this study can serve as a basis so that future implementations can choose the combination of caching mechanisms that best fits their target application scenario.

Transmission Window Optimization for Caching-Based Transport Protocols in Wireless Sensor Networks

Traditional transport protocols have been designed to perform end-to-end transmission and retransmission. In terms of choosing the optimal transmission window, previous works suggest a value based on the bandwidth-delay product (BDP). For wireless networks, the BDP value is related to the round-trip hop length. However, there exists a new class of transport protocols that use intermediate caching which can drastically improve the performance even in the presence of high packet error rates. In this paper, we show that using a window size related to the BDP could lead to sub-optimal performance for caching-based protocols. Furthermore, we present a heuristic for choosing the optimal transmission window such that the optimal value is related to the average cache size in the intermediate nodes.

Caching Based Transport Optimization for Wireless Multimedia Sensor Networks

Traditional transport layer protocols have been designed to perform end-to-end error control transparently to the intermediate nodes (e.g., TCP). To address the severe resource constraints featured by Wireless Sensor Networks (WSN), new paradigms have been developed such as intermediate caching where intermediate nodes are able to cache packets and if possible retransmit them on-demand to avoid incurring costly end-to-end retransmissions. Lately, Wireless Multimedia Sensor Network (WMSN) has been considered as a new research area whereby WSNs are targeted for the delivery of multimedia traffic. In this paper, we propose a NACK-based repair mechanism coupled with an adaptive MAC layer retransmission scheme in order to improve the performance of caching-based WMSN transport protocols. Specifically, our goal is to be able to reduce real-time end-to-end delay while maintaining reliability and energy efficiency in the presence of high channel error rates. Our simulation results show that the ensemble of both mechanisms provides better good put performance while simultaneously improving energy efficiency. Furthermore, the improved protocol also achieves lower deadline miss ratios making it suitable for multimedia transport. While we demonstrate the effectiveness of the mechanisms by incorporating them into the basic Distributed Transport for Sensor Networks (DTSN) protocol, they are generic enough to be applicable to other WSN and WMSN transport protocols.

Improving reliable data transport in wireless sensor networks through dynamic cache-aware rate control mechanism

Data delivery in low power and lossy networks like Wireless Sensor Networks (WSN), which has a significant role in Internet of Things (IoT), is vital due to the high probability of packet loss due to wireless and constrained environment. Data caching and transmission rate control are independent ways of improving the performance of transport protocols in WSN by immediately responding to packet losses in the network. However, a suitable rate control for cache-based transport protocols is not yet investigated. This work developed a dynamic cache-aware rate control algorithm that uses a transmission window rate as a function of cache size allocation used by intermediate nodes and utilizes cache elimination policy to notify packet losses in the network. A baseline cache-based transport protocol called DTSN+ is used to implement the rate control algorithm and evaluated under different network scenarios. Results show that the cache-aware approach improves the performance of the baseline transport protocol during high level of packet losses in the network in terms of cache utilization especially at lower cache size value. The algorithm also obtained outstanding throughput, transmission time and fairness performance as compared with original DTSN+ and DTC protocols. In the future, these results can serve as an underlying support in designing a new cache-aware congestion control framework that can be integrated in a transport protocol to mitigate packet losses in WSN.

Towards a taxonomy of cache-based transport protocols in wireless sensor networks

Sensor nodes in Wireless Sensor Networks (WSNs) are battery-powered devices that consume energy during data transmission and processing. One of the most critical tasks in a sensor network is to deal with optimizing the power consumption. One possible way to minimize this problem is caching the data. Data caching is a promising technique for improving the performance of transport protocols in terms of reliability in most sensor applications. Since, a typical data transmission consumes more energy than processing in a sensor network, the use of caching enables quick access to data. Therefore, caching, if used efficiently, could reduce overall network traffic and hence bandwidth can be optimally utilized. Unfortunately, a systematic treatment of caching in WSNs was until now lacking. Given that WSNs are expected to play an important role in Internet of Things (IoT) and wireless sensing applications, the authors believed that now is time to collect the results of years of research on this important topic. This paper presents a thematic taxonomy of the current cache management mechanisms of transport protocols in wireless sensor networks. The similarities and differences of the transport protocols based on the important parameters, such as cache insertion/replacement policy, cache size requirement, cache location, cache partition, and cache decision are investigated in this paper. In addition to that, we discuss open research issues and challenges of implementing intermediate caching to various sensor deployment. In the future, this study can be a basis so that future implementations can choose the combination of caching mechanisms that best fits their target in the field of instrumentation and measurements, especially in WSN applications.