A Distributed TDMA Slot Scheduling Algorithm for Spatially Correlated Contention in WSNs

In WSNs the communication traffic is often time and space correlated, where multiple nodes in a proximity start transmitting simultaneously. Such a situation is known as spatially correlated contention. The random access method to resolve such contention suffers from high collision rate, whereas the traditional distributed TDMA scheduling techniques primarily try to improve the network capacity by reducing the schedule length. Usually, the situation of spatially correlated contention persists only for a short duration, and therefore generating an optimal or suboptimal schedule is not very useful. Additionally, if an algorithm takes very long time to schedule, it will not only introduce additional delay in the data transfer but also consume more energy. In this paper, we present a distributed TDMA slot scheduling (DTSS) algorithm, which considerably reduces the time required to perform scheduling, while restricting the schedule length to the maximum degree of interference graph. The DTSS algorithm supports unicast, multicast, and broadcast scheduling, simultaneously without any modification in the protocol. We have analyzed the protocol for average case performance and also simulated it using Castalia simulator to evaluate its runtime performance. Both analytical and simulation results show that our protocol is able to considerably reduce the time required for scheduling

Julunga: A new Large-Scale Distributed Read-Write File Storage System for Cloud Computing Environments

We present in this paper the design of a large distributed file storage system called Julunga for cloud computing environments. Julunga is designed for federated data center environments where multiple numbers of data centers across the globe interconnect to each other and present a coherent single system view to end-users. In Julunga, the metadata, the namespace and the data blocks of the files are completely distributed with no hard limits on the number of files that can be accommodated in a single directory. Also, there is no physical limit on the size of a file. Julunga supports file of exabytes size with ease along with the number of concurrent users updating, reading and writing to the same file or a directory. The location of the data blocks of a file is determined by using functions, thus expunging the need for file allocation tables. Many new data structures and algorithms were designed earlier where locality and preferences of users are considered to provide optimal storage locations for files and metadata. We elaborate, in this paper, the design of fundamental building blocks of the distributed storage system and compare it with the designs of the earlier file storage systems

TRM-MAC: A TDMA-based reliable multicast MAC protocol for WSNs with flexibility to trade-off between latency and reliability

Multicast in wireless sensor networks (WSNs) is an efficient way to deliver the same data to multiple sensor nodes. Reliable multicast in WSNs is desirable for critical tasks like code updation and query based data collection. The erroneous nature of the wireless medium coupled with limited resources of sensor nodes, makes the design of reliable multicast protocol a challenging task. In this paper, we propose a framework for reliable multicast transmission in WSNs using TDMA-based channel access which works on top of a Multicast Spanning Tree (MST) rooted at the base station. The existing TDMA-based MAC protocols do not provide any mechanism to handle the collision and explosion of feedback messages, and therefore, they cannot be used in the proposed framework to support reliable multicast. To handle this issue, we propose a TDMA-based reliable multicast MAC (TRM-MAC) protocol for WSNs. The TRM-MAC protocol is parametric in the sense that it can be used to trade-off between reliability and delay performance, as per the requirement of the underlying applications. We have analyzed the TRM-MAC protocol to evaluate its delay and reliability performance at different packet loss rates, and have also compared its performance with those of others using simulation study. Both simulation and analytical results show that the TRM-MAC protocol considerably improves the performance of multicast communication in WSNs. (C) 2016 Elsevier B.V. All rights reserved

A Fast and Fault-Tolerant Distributed Algorithm for Near-Optimal TDMA Scheduling in WSNs

The time division multiple access (TDMA) based channel access mechanisms perform better than the contention based channel access mechanisms, in terms of channel utilization, reliability and power consumption, specially for high data rate applications in wireless sensor networks (WSNs). Most of the existing distributed TDMA scheduling techniques can be classified as either static or dynamic. The primary purpose of static TDMA scheduling algorithms is to improve the channel utilization by generating a schedule of smaller length. But, they usually take longer time to schedule, and hence, are not suitable for WSNs, in which the network topology changes dynamically. On the other hand, dynamic TDMA scheduling algorithms generate a schedule quickly, but they are not efficient in terms of generated schedule length. In this paper, we propose a novel scheme for TDMA scheduling in WSNs, which can generate a compact schedule similar to static scheduling algorithms, while its runtime performance can be matched with those of dynamic scheduling algorithms. Furthermore, the proposed distributed TDMA scheduling algorithm has the capability to trade-off schedule length with the time required to generate the schedule. This would allow the developers of WSNs, to tune the performance, as per the requirement of prevalent WSN applications, and the requirement to perform re-scheduling. Finally, the proposed TDMA scheduling is fault-tolerant to packet loss due to erroneous wireless channel. The algorithm has been simulated using the Castalia simulator to compare its performance with those of others in terms of generated schedule length and the time required to generate the TDMA schedule. Simulation results show that the proposed algorithm generates a compact schedule in a very less time

A media access and feedback protocol for reliable multicast over wireless channel

A link level reliable multicast requires a channel access protocol to resolve the collision of feedback messages sent by multicast data receivers. Several deterministic media access control protocols have been proposed to attain high reliability, but with large delay. Besides, there are also protocols which can only give probabilistic guarantee about reliability, but have the least delay. In this paper, we propose a virtual token-based channel access and feedback protocol (VTCAF) for link level reliable multicasting. The VTCAF protocol introduces a virtual (implicit) token passing mechanism based on carrier sensing to avoid the collision between feedback messages. The delay performance is improved in VTCAF protocol by reducing the number of feedback messages. Besides, the VTCAF protocol is parametric in nature and can easily trade off reliability with the delay as per the requirement of the underlying application. Such a cross layer design approach would be useful for a variety of multicast applications which require reliable communication with different levels of reliability and delay performance. We have analyzed our protocol to evaluate various performance parameters at different packet loss rate and compared its performance with those of others. Our protocol has also been simulated using Castalia network simulator to evaluate the same performance parameters. Simulation and analytical results together show that the VTCAF protocol is able to considerably reduce average access delay while ensuring very high reliability at the same time

An Efficient Distributed Group Key Management Algorithm

A key agreement protocol is an important part of a secure group communication system (SGCS) which provides secure message passing services to its members. Among the various distributed key agreement protocols proposed in the literature, the tree-based group Diffie-Hellman (TGDH) protocol is the most efficient in terms of the number of keys that need to be maintained at each member and distribution of DH exponentiation operations among group members. In TGDH, on a group change, the group members need to perform between one and $O(log_2\hspace{5 mm}n)$ exponentiation operations serially. Also, the messages that are passed during group key agreement must be authenticated using digital signatures. In this paper, we propose a key agreement protocol which minimizes the number of exponentiation operations at each member. The member join operation requires only three members to perform one or two exponentiation operations each while the member leave operation requires only two or five group members to perform one or two exponentiation operations each. This is achieved at the cost of $O(log_2\hspace{5 mm}n)$ causal messages per member leave operation

Improving the Energy Efficiency of a Clock Synchronization Protocol for WSNs using a TDMA-based MAC Protocol

Clock synchronization protocols in wireless sensor networks (WSNs) provide a uniform notion of time which is required by both system as well as application level programs of WSNs. Since nodes have limited energy, it is required that the energy consumed by the clock synchronization protocols is as minimum as possible. Synchronous clock synchronization protocols execute their clock synchronization process at each node, roughly during the same real-time interval, called synchronization phase. The energy consumed by these protocols depends on the duration of the synchronization phase and how frequently the synchronization phase is executed. Hence, to minimize the energy consumption by each node, the duration of synchronization phase should be as small as possible, and the interval between consecutive synchronization phases as large as possible. Due to different drift rates of the clocks, the synchronization phases at different nodes drift apart and special techniques are required to keep them in sync. Keeping synchronization phases at neighbouring nodes in sync helps to reduce the synchronization phase. In this paper, we propose a novel technique using TDMA-based MAC protocol to keep the synchronization phases at neighbouring nodes in sync much more tightly than the existing techniques. We have applied the technique in the improved weighted-average based clock synchronization (IWICS) protocol to reduce the synchronization phase considerably and the modified TDMA-based IWICS protocol is named TIWICS protocol. This reduction in energy consumption is achieved without reducing the synchronization accuracy. Simulation results obtained using Castalia network simulator and the experimental results obtained using a testbed of WSN consisting of a few TelosB motes confirm the effectiveness of the approach

A TDMA-Based Energy Aware MAC (TEA-MAC) Protocol for Reliable Multicast in WSNs

Multicast in wireless sensor networks (WSNs) is an efficient way to spread the same data to multiple sensor nodes. It becomes more effective due to the broadcast nature of wireless link, where a message transmitted from one source is inherently received by all one-hop receivers, and therefore, there is no need to transmit the message one by one. Reliable multicast in WSNs is desirable for critical tasks like code updation and query based data collection. The erroneous nature of wireless medium coupled with limited resource of sensor nodes, makes the design of reliable multicast protocol a challenging task. In this work, we propose a time division multiple access (TDMA) based energy aware media access and control (TEA-MAC) protocol for reliable multicast in WSNs. The TDMA eliminates collisions, overhearing and idle listening, which are the main sources of reliability degradation and energy consumption. Furthermore, the proposed protocol is parametric in the sense that it can be used to trade-off reliability with energy and delay as per the requirement of the underlying applications. The performance of TEA-MAC has been evaluated by simulating it using Castalia network simulator. Simulation results show that TEA-MAC is able to considerably improve the performance of multicast communication in WSNs

A survey of cloud storage facilities

There are many applications such as software for processing customer records in telecom, patient records in hospitals, email processing software accessing a single email in a mailbox etc. which require to access a single record in a database consisting of millions of records. A basic feature of these applications is that they need to access data sets which are very large but simple. Cloud computing provides computing requirements for these kinds of new generation of applications involving very large data sets which cannot possibly be handled efficiently using traditional computing infrastructure. In this paper, we describe storage services provided by three well-known cloud service providers and give a comparison of their features with a view to characterize storage requirements of very large data sets as examples and we hope that it would act as a catalyst for the design of storage services for very large data set requirements in future. We also give a brief overview of other kinds of storage that have come up in the recent past for cloud computing

A distributed TDMA slot scheduling algorithm for spatially correlated contention in WSNs

In wireless sensor networks (WSNs) the communication traffic is often time and space correlated, where multiple nodes in a proximity start transmitting at the same time. Such a situation is known as spatially correlated contention. The random access methods to resolve such contention suffers from high collision rate, whereas the traditional distributed TDMA scheduling techniques primarily try to improve the network capacity by reducing the schedule length. Usually, the situation of spatially correlated contention persists only for a short duration and therefore generating an optimal or sub-optimal schedule is not very useful. On the other hand, if the algorithm takes very large time to schedule, it will not only introduce additional delay in the data transfer but also consume more energy. To efficiently handle the spatially correlated contention in WSNs, we present a distributed TDMA slot scheduling algorithm, called DTSS algorithm. The DTSS algorithm is designed with the primary objective of reducing the time required to perform scheduling, while restricting the schedule length to maximum degree of interference graph. The algorithm uses randomized TDMA channel access as the mechanism to transmit protocol messages, which bounds the message delay and therefore reduces the time required to get a feasible schedule. The DTSS algorithm supports unicast, multicast and broadcast scheduling, simultaneously without any modification in the protocol. The protocol has been simulated using Castalia simulator to evaluate the run time performance. Simulation results show that our protocol is able to considerably reduce the time required to schedule