Network topology

About: Network topology is a research topic. Over the lifetime, 52259 publications have been published within this topic receiving 1006627 citations.

Theoretical Results on Base Station Movement Problem for Sensor Network

Abstract: The benefits of using mobile base station to prolong sensor network lifetime have been well recognized. However, due to the complexity of the problem (time-dependent network topology and traffic routing), theoretical performance limit and provably optimal algorithms remain difficult to develop. This paper fills this important gap by contributing theoretical results regarding the optimal movement of a mobile base station. Our main result hinges upon a novel transformation of the joint base station movement and flow routing problem from time domain to space domain. Based on this transformation, we first show that if the base station is allowed to be present only on a set of pre-defined points, then we can find the optimal time span for the base station on each of these points so that the overall network lifetime is maximized. Based on this finding, we show that when the location of the base station is un-constrained (i.e., can move to any point in the two-dimensional plane), we can develop an approximation algorithm for the joint mobile base station location and flow routing problem such that the network lifetime is guaranteed to be at least (1-epsiv) of the maximum network lifetime, where epsiv can be made arbitrarily small depending on required precision.

Configuring BlueStars: multihop scatternet formation for Bluetooth networks

Abstract: Describes a protocol for the establishment of multihop ad hoc networks based on Bluetooth devices. The protocol proceeds in three phases: device discovery, partitioning of the network into Bluetooth piconets, and interconnection of the piconets into a connected scatternet. The protocol has the following desirable properties: it is executed at each node with no prior knowledge of the network topology, thus being fully distributed. The selection of the Bluetooth masters is driven by the suitability of a node to be the "best fit" for serving as a master. The generated scatternet is a connected mesh with multiple paths between any pair of nodes, thus achieving robustness. Differently from existing solutions, no extra hardware is required to run the protocol at each node and there is no need for a designated node to start the scatternet formation process. Simulation results are provided which evaluate the impact of the Bluetooth device discovery phase on the performance of the protocol.

Detection of Topology Errors by State Estimation

Abstract: In modern energy management systems (EMS), there are two types of measurement data collected by the SCADA (supervisory control and data acquisition) system, namely, status data of breakers and switches, and analog data of real and reactive power flows, injections, and bus voltages. The status data are used to determine real-time topology of the network. The analog data are used to determine line and transformer loading and voltage profile. These data are noisy due to measurement errors, communication noise, missing data, etc. In addition to simple checking of the analog data locally, in most modern EMS, state estimation is used to process these data globally to correct errors in the raw analog measurement data. In this paper, the use of global information in state estimation to correct errors in the direct measurements of the status data is proposed and conditions for detectability of errors are analyzed. The telemetered data of breaker and switch status are processed in the EMS computer to determine the present network topology of the system, and this function is called network topology processor. Errors in status data will show up as errors in the network topology. Sasson et al and Dy Liacco et al used a tree search algorithm for the network topology processor. The method is widely used in practice. Bonanomi et al proposed a sequential search method through the network graph. Recently Lugtu et al suggested the approach of using state estimation results for topology error detection.

Network Coding-Based Broadcast in Mobile Ad-hoc Networks

Abstract: Broadcast operation, which disseminates information network-wide, is very important in multi-hop wireless networks. Due to the broadcast nature of wireless media, not all nodes need to transmit in order for the message to reach every node. Previous work on broadcast support can be classified as probabilistic (each node rebroadcasts a packet with a given probability) or deterministic approaches (nodes pre-select a few neighbors for rebroadcasting). In this paper, we show how network-coding can be applied to a deterministic broadcast approaches, resulting in significant reductions in the number of transmissions in the network. We propose two algorithms, that rely only on local two-hop topology information and makes extensive use of opportunistic listening to reduce the number of transmissions: 1) a simple XOR-based coding algorithm that provides up to 45% gains compared to a non-coding approach and 2) a Reed-Solomon based coding algorithm that determines the optimal coding gain achievable for a coding algorithm that relies only on local information, with gains up to 61% in our simulations. We also show that our coding-based deterministic approach outperforms the coding-based probabilistic approach presented in (C. Fragouli et al, 2006).

On reliability-optimized controller placement for Software-Defined Networks

Abstract: By decoupling control plane and data plane, Software-Defined Networking (SDN) approach s i m p l i f i e s network management and speeds up network innovations. These benefits have led not only to prototypes, but also real SDN deployments. For wide-area SDN deployments, multiple controllers are often required, and the placement of these controllers becomes a particularly important task in the SDN context. This paper studies the problem of placing controllers in SDNs, so as to maximize the reliability of SDN control networks. We present a novel metric, called expected percentage of control path loss, to characterize the reliability of SDN control networks. We formulate the reliability-aware control placement problem, prove its NP-hardness, and examine several placement algorithms that can solve this problem. Through extensive simulations using real topologies, we show how the number of controllers and their placement influence the reliability of SDN control networks. Besides, we also found that, through strategic controller placement, the reliability of SDN control networks can be significantly improved without introducing unacceptable switch-to-controller latencies.