A sink is a node in a sensor network that functions as a gateway and it gathers data from other nodes and sends the data over the Internet for further processing. However, a single sink cannot meet the demands of a sensor network for the Internet of Things (IoT) with heavy traffic. Although deploying multiple sinks can improve scalability and mitigate bottleneck problems, it is still challenging to use multiple sinks while keeping energy consumption down. Previous studies have addressed this issue using optimization techniques based on the assumption that the network converges to a steady state in terms of traffic load. We take a practical approach based on real-time changes in traffic load. This work introduces the concept ofdynamic sinks, a sensor device that can serve as an on-demand sink. We identify suitable metrics for decision mechanisms to activate/deactivate dynamic sinks and investigate three decision schemes, namely,autonomous,delegated, andcentralizedschemes. We also develop a protocol to disseminate the decisions. As a proof-of-concept, the dynamic sink protocol is implemented in Contiki. We evaluate tradeoffs between the packet delivery ratio (PDR) and energy consumption using emulated devices in the Cooja network simulator. The results show that setups with dynamic sinks can reduce energy consumption considerably at the expense of slightly lower PDR when compared to a setup with multiple permanent sinks.

This paper presents an outdoor IoT-based air quality monitoring testbed deployed in the city of Uppsala, Sweden. Our IoT sensing unit is designed and developed using low-cost hardware components and open source software, which makes it easy to replicate. We demonstrate that it can serve as an affordable solution for real-time measurements and has potential to complement traditional monitoring to cover larger areas. We use low-power communication based on IEEE 802.15.4, RPL, and MQTT, and achieve high end-to-end delivery ratio (>98%) in an outdoor setting. Moreover, we carry out network analysis of our testbed and provide detailed insights into its characteristics.

Data center networks (DCNs) are designed to be scalable, resilient, and tolerant to failures. This is achieved through redundancy of network devices and links. All devices and links are always operational, consuming full energy even when underutilized. Energy-aware routing (EAR) protocols leverage network-wide information to dynamically scale up or down network energy consumption according to utilization. However, many EARs are designed for networks of devices and links that are not energy-proportional, such as ElasticTree and VMPlanner. The advent of Energy Efficient Ethernet (EEE) brings new challenges into how EAR protocols are designed. In this paper, we propose Greener, an extension of ElasticTree to leverage the energy proportionality characteristics of EEE. We integrate the EEE energy model with the ElasticTree solution. Greener is designed for K-ary Fat-Tree multi-rooted topologies, to steer flows along the most energy-efficient paths and put into sleep mode unused switches and links. Simulation experiments of Greener in DCNs of different sizes and under varying traffic loads show that it brings significant improvements in energy savings. Moreover, Greener outperforms the benchmark ElasticTree executed on EEE-based DCNs by up to 10 percentage points of energy savings.

Telecommunication networks have been designed and deployed with over-provisioning and redundancy of resources to cope with traffic load during peak hours and quickly recover from failure. However, most of these resources are underutilized and in most of the time idle but consuming full energy. With the growing concern of energy waste and greenhouse gases (GHG), the network design principles tend to shift to allocate resources on-demand and be energy-efficient. In this paper, we analyze and evaluate the performance of two energy-saving techniques, namely Energy Saving TOPology control (ESTOP) for coordinated sleeping, and Energy Efficient Ethernet (EEE) for uncoordinated sleeping. Furthermore, we evaluate the potential of combining ESTOP and EEE considering that the reduced topologies obtained running ESTOP can substantially increase link utilization and the length of some paths and therefore degrade the performance of EEE. The evaluation was conducted in OMNet++ with realistic and synthetic networks under different traffic conditions. The results show that the energy conservation of the combination is significant when a lower value of the connectivity threshold is used during off-peak hours and a higher value is used during peak hours. ESTOP depends on the density of the topology and can save about 50% of energy.

IoT technology is considered an essential imperative for Smart Grids (SGs). However, IoT devices have inherently limited responsiveness that may not be sufficient for a time critical SG with stringent demands on communication delay. In practice, it remains an outstanding problem to combine IoT technology with existing grids. To facilitate deployment of IoT-based grids in domestic environments, we propose IoT-grid, a programmable, small-scale, direct current (DC) grid, that can be easily implemented with low-power hardware with limited processing capacity. The proposed grid adopts relatively cheap DC-DC converters which not only provide high conversion efficiency but also accommodate existing small-scale DC power systems (e.g. solar panels). We then explore the communication aspects of IoT-grid, namely, control and monitoring functions. We observe that processing delays of IoT devices have large impact on IoT-grid, which cause a chain of control commands to take considerable longer time as the number of commands increases. To mitigate this problem, we propose a mechanism based on sending burst commands with scheduled responses. Our experimental results show that, in the presence of processing delays, this method can significantly reduce the overall response time.

This paper investigates OpenFlow performance, focusing on how the delay between switch and OpenFlow controller can impact the performance of a network. We use open-source controllers that support network virtualization to evaluate how such delay impacts ICMP, TCP and UDP traffic. We compare the controllers' flow set-up strategies and we conduct several experiments to compare their TCP and UDP performance. In ad-dition, we introduce a new metric to measure UDP packet losses at the beginning of the flow. The results of the measurements indicate that there are large differences in performance between controllers, and that performance depends on switch-controller delay and flow set-up strategy.

Advancements in today's technologies make it possible to offer competitive home-based healthcare services using software routers based on open source software combined with Commodity-Off-The-Shelf (COTS) hardware. In this paper, we propose resilient communication through multihoming for remote healthcare applications. The solution is based on Bidirectional Forwarding Detection (BFD) for fast failure detection and a customized rerouting operation. We investigate the tradeoff between short reaction times for rerouting and low probability of false alarms. This is challenging to achieve under high traffic loads since the load affects the BFD session which is formed to monitor the bidirectional forwarding capabilities. We propose a simple mechanism that provides fast failover and meanwhile maintains a very low probability of generating false alarms and unwanted rerouting decisions. The mechanism is based on allocation of system resources for processing BFD control messages, and we demonstrate through empirical results that BFD then can be used in software routers to provide average failover times within 200 ms.

In this paper we focus on how to use open source Linux software in combination with PC hardware to build high speed virtual routers. Router virtualization means that multiple virtual router instances will run in parallel on the same hardware. To enable this, virtual components are combined in the router's data plane. This can result in performance penalties. Furthermore, an overloaded virtual router can affect the performance of other virtual routers running in parallel. Achieving high performance and strong performance isolation in a virtualized environment is challenging. We investigate how hardware can help to achieve these goals in the Linux Namespaces environment. We propose a forwarding architecture for virtual routers based on multi-core hardware where virtual routers can run in parallel on different CPU cores. This reduces resource contention among virtual routers and results in improved performance and isolation. To enable this architecture, we find that hardware based I/O virtualization support is essential. We demonstrate this by making a comparison with a software based I/O virtualization approach. We also show that hardware assisted virtual routers can achieve better aggregate throughput than a non-virtualized router on a multi-core platform.

This paper addresses the challenges of reliably, and securely, extending a healthcare provider's network into the homes of its patients in order to provide Remote Patient Monitoring (RPM) services. It describes the Carenet Virtual Private Network (CVPN) solution, a multi-homed VPN solution implemented as a virtual device driver under Linux. We describe CVPN's architecture and implementation, motivating its design decisions. The initial experimental evaluation, of our proof-of-concept prototype, shows that CVPN's per packet overhead, forwarding delay, and fail-over time are reasonable for healthcare monitoring applications and time-sensitive synchronous communications.

A modern PC-based router can provide as competitive service as a specialized hardware router while offering more flexibility and possibility to extend beyond routing. We focus on a use case in which the PC-based router also functions as a server. In this paper, we propose a multi-core based architecture for a combined router/server that efficiently provides simultaneous packet forwarding and server processing. We improve the overall performance by creating a fast path for packet forwarding through caching flow entries in on-board classification hardware on the NIC. We propose a generic design based on multi-core processors and multi-queue network interface cards. We describe a prototype implementation and present an experimental evaluation of this design. We also devise a strategy for how to efficiently map packet forwarding and application processing tasks onto the multi-core architecture.

Network virtualization has been an important research topic for many years but still suffers from the lack of an abstraction level like the one present in virtualization of computing and storage. Our work in progress presented here proposes an architecture for such a network virtualization abstraction. It is deployed as a library, similar to libvirt in computer virtualization, with a unified interface towards the underlying network specific drivers. The architecture will allow management tools to be independent of the underlying technologies. In addition, it will enable programmatic and on-demand creation of virtual networks. A common set of calls is defined to instantiate different virtual networks, using a single node view to provide the user with a suitable abstraction of the network. We describe a prototype of our proposed architecture on top of an OpenFlow-enabled network. We demonstrate its feasibility for creating isolated virtual networks in a programmatic and on demand fashion.

OpenFlow is a promising technology that offers a flexible flow-based forwarding scheme based on multiple fields in the packet headers of different protocol layers. It provides a feasibility to adopt new network protocols and innovations thanks to a more flexible forwarding compared to traditional IP forwarding. In this paper, we propose an architectural design to improve lookup performance of PC-based OpenFlow switching in Linux using a standard commodity network interface card based on the Intel 82599 Gigabit Ethernet controller. We introduce a fast data path based on caching of flow table entries in on-board classification hardware on the NIC. We describe our design, and we present an experimental evaluation of its performance. Our results show that the throughput of our fast path gives over 40 percent higher throughput compared to the regular software-based OpenFlow switching.

In this paper, we propose an architectural design to improve lookup performance of OpenFlow switching in Linux using a standard commodity network interface card based on the Intel 82599 Gigabit Ethernet controller. We describe our design and report our preliminary results that show packet switching throughput increasing up to 25 percent compared to the throughput of regular software-based OpenFlow switching.

This paper presents a high-level overview of the CareNet Home Extension Project that aims to provide support for home-based healthcare for the elderly and outpatients. Details of a home networking environment based on a virtualized Residential Gateway (RG) are provided. The RG architecture is modular and scalable supporting the dynamic provision of third party services. This accommodates multiple independent stakeholders representing healthcare providers, Internet Services Providers (ISPs), and home automation system builders among others. Interoperability is guaranteed through adherence to open standards. Initial mechanisms facilitating the integration and consolidation of in-home systems, whilst providing a flexible framework for autonomous management, are described. This addresses issues of management and configuration of complex environments by individuals with little or no technical expertise. Finally, details of an initial implementation, in terms of architectural descriptions and enabling technological components, are outlined.

When the forwarding paths in an IP network change due to a link failure or a link weight modification, the forwarding tables in the routers may need to be updated. Each of these updates may cause transient loops if they are not performed in an appropriate order. In this paper, we propose an order to update the forwarding tables that avoids transient loops for non-urgent changes. The order is obtained by studying the changes in the forwarding tables, therefore it can be used in networks running any routing protocols, and for any type of forwarding path changes. After presenting the order, we prove that it is correct, and present an efficient algorithm to compute the order. Thereafter, we present several algorithms for performing forwarding table updates in accordance with the order. We also discuss how the update algorithms can be applied to both networks with centralized control and decentralized routing protocols. Finally, we study the update algorithms' performance on several network topologies and with varying parameter settings and for several types of forwarding path changes.

Dynamic synchronous transfer mode (DTM) is a broadband network architecture based on fast circuit-switching augmented with dynamic reallocation of resources. It provides a service based on multicast, multirate channels with short setup delay and supports applications with real-time requirements on quality of service as well as applications with bursty, asynchronous traffic. The paper describes the DTM architecture and its distributed resource management scheme. Performance analysis results from network simulations are presented. The analysis is performed with respect to throughput and access delay for two network topologies: a dual bus and a grid of dual buses. The effects of varying user requirements, internode distances and transfer size are studied for uniform traffic patterns. The results indicate that the overhead for establishing channels is low (a few hundred microseconds), which gives a high degree of utilization even for short transfers. The analysis also shows that when channels are established very frequently, the signaling capacity limits the performance.