Local voting: A new distributed bandwidth reservation algorithm for 6TiSCH networks
Introduction
Wireless Sensor Networks (WSNs) have advanced significantly in the past decades. The recent increase of connected devices has triggered countless Internet-of-Things (IoT) applications to emerge [1]. It is expected that 50 billion devices will be connected to the Internet by 2020 [2]. The so-called Industrial Internet-of-Things (IIoT) is modernizing various domains such as home automation, transportation, manufacturing, agriculture, and other industrial sectors.
Often IoT is realized through Low-power and Lossy Networks (LLNs), which consist of low complexity resource constrained embedded devices, that are interconnected using different wireless technologies.
The biggest challenges for enabling the pervasive deployment of IoT devices are the demand for high reliability and the limited energy supply for the nodes. These challenges are magnified with the increase of the number of network devices and the emergence of new applications with diverse requirements. As the deployment cases become more dense, and new applications and devices are added, the traffic patterns become more congested. In such conditions, it has been found that the network performance is determined by the ability of the network to distribute the resources (cells) among the competing links, in a way that maximizes efficiency [3].
Several communication standards have been defined supporting IoT connectivity. Among them the IEEE 802.15.4e standard defines the physical and the medium access control (MAC) layers for ultra-low power and reliable networking solutions for LLNs [4]. The protocol defines five MAC modes: Time Slotted Channel Hopping (TSCH), Deterministic and Synchronous Multi-channel Extension (DSME), Low Latency Deterministic Network (LLDN), Asynchronous Multi-Channel Adaptation (AMCA), and Radio Frequency Identification Blink (BLINK) [5]. In this work, the TSCH mode which is designed to allow IEEE 802.15.4 devices to support a wide range of applications, including industrial ones is studied. In industrial environments, the large metallic equipment causes multi-path fading and interference [6], and TSCH combats against them by combining channel hopping and time synchronization. The channel hopping allows transmissions between nodes to use different channels, while the slotted access enhances the reliability by synchronizing the nodes with a schedule and, thus, avoiding collisions.
In this paper, a distributed bandwidth allocation algorithm called Local Voting (LV) is proposed. It balances the load between the links in the network, where the load is defined as the ratio of the queue length plus new packet arrivals, over the number of allocated cells. LV was originally proposed in [3] in the context of wireless mesh networks. In this work the above algorithm is adapted for the link-based multi-channel environment of 6TiSCH networks. Through analysis and extensive performance evaluation it is shown here that by redistributing cells among the links, the maximum delay in the network can be reduced, and at the same time reliability and fairness is enhanced at a lower energy cost compared to scenarios where no load balancing takes place.
Most of the related works focus on ways to construct an optimal schedule between the links, without taking into consideration the optimal number of cells that should be allocated to each link. These works usually consider the On-The-Fly (OTF) bandwidth allocation algorithm [7]. Using the OTF algorithm, each node in the network estimates the number of cells that it requires for fulfilling its communication requirements by estimating the amount of new and forwarded traffic that it needs to transmit to its parent nodes. Then, the OTF module asks the 6top sublayer to add or remove cells, in order for the allocation to match this number if possible. However, the OTF algorithm does not consider the case where the requested number of cells exceeds the number of available cells, due to congestion. The nodes under OTF also do not consider the traffic requirements of the neighboring nodes, so there is no provision for cell redistribution to neighbors with higher bandwidth demands. Finally, the OTF algorithm tries to maintain a stable schedule by using a long-term average of the estimated throughput, which leads to inefficient allocation when the traffic patterns fluctuate. For these reasons we introduce LV algorithm that addresses the above limitations of OTF. We compare a thorough performance comparison between two versions of LV and OTF and Enhanced-OTF (E-OTF) [8]. Under LV, information about the queue lengths and the cell allocations are periodically diffused among neighboring nodes, which use this information to calculate the number of cells that should be allocated to each link based on the load of each interfering link. Equalizing the load throughout the congested areas in the network leads to better fairness in terms of load for LV compared to OTF and E-OTF. The performance evaluation also shows that LV provides similar performance in terms of delay to E-OTF with an energy consumption similar to OTF, making LV a promising distributed bandwidth allocation algorithm for 6TiSCH networks.
The rest of the paper is organized as follows. Section 3 summarizes the related works. In Section 4, the network model is formulated. Section 5 presents Local Voting algorithm. Extensive performance evaluation results are presented in Section 6, and Section 7 concludes the paper.
Section snippets
Technical background
The IETF 6TiSCH working group standardizes the protocol stack for IIoT [9]. It combines the high reliability and the low-energy consumption of IEEE 802.15.4e TSCH with the addressability and Internet integration capabilities of the Internet Protocol version 6 (IPv6). The communication in a 6TiSCH network is orchestrated by a schedule composed of cells, where each cell is identified by [slotOffset, channelOffset] [10]. The schedule specifies the channel (based on the channelOffset) and the time
6TiSCH scheduling protocols
Recently there have been many proposals for centralized and distributed solutions for TSCH scheduling in the literature. Centralized algorithms designate a specific scheduling entity that collects information about the network and adjusts the TSCH schedule to it. The first proposed centralized algorithm is Traffic Aware Scheduling Algorithm (TASA) [12], which builds a time/frequency collision-free schedule in a centralized manner. A master node collects information about the entire network
Network model and problem formulation
Our model considers a 6TiSCH network which has built a tree routing topology with one or multiple parents per node, using the Routing Protocol for Low-Power and Lossy Networks (RPL) [31]. For reader’s convenience, Table 1 summarizes the notation used throughout this paper.
The communication in the network can be modeled by a graph where is the set of all nodes and E is the set of edges that represent the communication symmetric links between the nodes. Data is gathered over
Local voting bandwidth allocation algorithm
Each source node ni, where ni ∈ VT and ni ≠ n0, has a queue with packets to be transmitted to the root through a parent node, which is a one-hop neighbor of the node ni. The internal scheduling on the queue is first-come-first-serve. A cell is allocated to link (i, j) so that node ni transmits a packet to nj as it is given in Eq. (2).
The state of link (i, j), where at the beginning of frame is described by three characteristics:
- •
is the number of packets (queue length)
Performance evaluation
). It retrieves statistics from the 6top sublayer about the list of neighboring links, the queue length of each link, and the number of scheduled cells per link. Not all of these statistics were available in the reference implementation so the 6top sublayer had to be modified to accommodate the additional parameters for LV.
Conclusions
We proposed a new distributed bandwidth allocation algorithm called Local Voting which balances the load between links in 6TiSCH networks. The algorithm calculates the number of cells to be added or released by 6top while considering the collision-free constraints. In this way, it adapts the schedule to the network conditions in 6TiSCH networks, equalizes the load in congested areas, that as expected provides efficient resource allocation. We showed that optimal schedules are maximal and
CRediT authorship contribution statement
Dimitrios J. Vergados: Conceptualization, Methodology, Software, Data curation, Writing - original draft, Visualization. Katina Kralevska: Conceptualization, Methodology, Validation, Writing - original draft, Visualization. Yuming Jiang: Conceptualization, Validation, Writing - review & editing. Angelos Michalas: Conceptualization, Validation, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Dimitrios J. Vergados was born in 1980, and is currently an Assistant Professor at the Department of Informatics, University of Western Macedonia, Greece, and also a post-doctoral researcher at the School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Greece. He received his PhD and his B. Engineering degrees from the school of Electrical and Computer Engineering, NTUA in 2009 and 2003 respectively. He has been employed in research projects and as a
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Dimitrios J. Vergados was born in 1980, and is currently an Assistant Professor at the Department of Informatics, University of Western Macedonia, Greece, and also a post-doctoral researcher at the School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Greece. He received his PhD and his B. Engineering degrees from the school of Electrical and Computer Engineering, NTUA in 2009 and 2003 respectively. He has been employed in research projects and as a Visiting Lecturer in several universities in Greece and Norway. His research interests include distributed systems, wireless networks, simulation modeling, scheduling algorithms, multihop networks, and smart-grids. He has authored several publications in these areas.
Katina Kralevska was born in 1987 in Skopje, Republic of Macedonia. She received her B.Sc. degree in 2010 and her M.Sc. degree in 2012 in Telecommunications from Ss. Cyril and Methodius University-Skopje, Macedonia. She was awarded a Ph.D. in December 2016 from Norwegian University of Science and Technology (NTNU). In 2017 she was a postdoctoral researcher at the Department of Information Security and Communication Technology, NTNU and in 2018 she became an Associate Professor at the same department. Since 2019 she is Deputy Head of Department of Information Security and Communication Technology. Her research interests include coding theory, mobile and wireless communications and blockchain. She is an author of more than 25 scientific publications and more than 8 inventions.
Yuming Jiang received his BSc from Peking University, China, in 1988, MEng from Beijing Institute of Technology, China, in 1991, and PhD from National University of Singapore, Singapore, in 2001. He worked with Motorola from 1996 to 1997. From 2001 to 2003, he was a Member of Technical Staff and Research Scientist with the Institute for Infocomm Research, Singapore. From 2003 to 2004, he was an Adjunct Assistant Professor with the Electrical and Computer Engineering Department, National University of Singapore. From 2004 to 2005, he was with the Centre for Quantifiable Quality of Service in Communication Systems (Q2S), Norwegian University of Science and Technology (NTNU), Norway, supported in part by the Fellowship Programme of European Research Consortium for Informatics and Mathematics (ERCIM). He visited Northwestern University, USA from 2009 to 2010, and Columbia University, USA from 2015 to 2016. Since 2005, he has been a full Professor at NTNU. He was Co-Chair of IEEE Globecom2005 - General Conference Symposium, TPC Co-Chair of 67th IEEE Vehicular Technology Conference (VTC) 2008, General/TPC Co-Chair of International Symposium on Wireless Communication Systems (ISWCS) 2007-2010, General Chair of IFIP Networking 2014 Conference, and Chair of the first International Workshop on Network Calculus and Applications (NetCal 2018). He is an author of the book “Stochastic Network Calculus”. His research interests are the provision, analysis and management of quality of service (QoS) guarantees in communication networks. In QoS evaluation, his focus has been on developing models and investigating their properties for (stochastic) network calculus, and also on applying the (stochastic) network calculus theory to performance guarantee analysis of wireless networks and time-sensitive networking.
Angelos Michalas is professor in the Department of Informatics of the University of Western Macedonia (UOWM), Greece. His research interests focus on the design and performance evaluation of wireless and wired broadband communication networks, mobile ad-hoc networks, network management and QoS/QoE provisioning, distributed systems and algorithms, cloud computing, intelligent mobile agent technology and multi-agent systems. He is the author of over 91 peer-reviewed publications in these areas. Prof. Michalas serves as a reviewer and as a technical program committee member in a number of international journals and conferences.