The P2P-RPL Routing Protocol for IPv6 Sensor Networks: Testbed Experiments

International audienceAn important part of the foreseen Internet of Things consists in wireless sensor networks running adapted IPv6 protocols. Since the way sensors are scattered is generally unplanned and may evolve with time, a routing protocol is needed in order to provide paths across such networks. Efforts towards standardizing RPL, a routing protocol tar- geting sensor networks, have thus recently taken place. This paper analyzes some fundamental tradeoffs inherent to RPL, which enables the protocol to require smaller routing state than most other routing protocols. However, these tradeoffs are on the other hand an issue in several Home and Build- ing Automation use-cases, which require sensor to sensor communication - aside of communication from sensor to sink. RPL basically requires that all communication paths go through a central router (the sink), which provides severely suboptimal paths in these use-cases. In order to alleviate this, an extension of the protocol is proposed based on a reactive scheme that can provide shorter paths on-demand, without necessarily going through the sink. This paper then evaluates this extension via experiments on a sensor network testbed running RPL and its extension over IEEE 802.15.4 radio. These experiments confirm that the extension provides substantially shorter paths

A Definition of General Weighted Fairness and its Support in Explicit Rate Switch Algorithms

In this paper we give a general definition of weighted fairness and show how this can achieve various fairness definitions, such as those mentioned in the ATM Forum TM 4.0 Specifications. We discuss how a pricing policy can be mapped to general weighted (GW) fairness. The GW fairness can be achieved by calculating the $ExcessFairshare$ (weighted fairshare of the left over bandwidth) for each VC. We show how a switch algorithm can be modified to support the GW fairness by using the $ExcessFairshare$. We use ERICA+ as an example switch algorithm and show how it can be modified to achieve the general fairness. Simulations results are presented to demonstrate that the modified switch algorithm achieves GW fairness. An analytical proof for convergence of the modified ERICA+ algorithm is given in the appendix.Comment: Proceedings of ICNP'98, October199

Predicting TCP Throughput From Non-invasive Network Sampling

In this paper, we wish to derive analytic models that predict the performance of TCP flows between specified end-points using routinely observed network characteristics such as loss and delay. The ultimate goal of our approach is to convert network observables into representative user and application relevant performance metrics.The main contributions of this paper are in studying which network performance data sources are most reflective of session characteristics, and then in thoroughly investigating a new TCP model based on [1] that uses non-invasive network samples to predict the throughput of representative TCP flows between given end-points

Traffic Management for Satellite-ATM Networks

Various issues associated with "Traffic Management for Satellite-ATM Networks" are presented in viewgraph form. Specific topics include: 1) Traffic management issues for TCP/IP based data services over satellite-ATM networks; 2) Design issues for TCP/IP over ATM; 3) Optimization of the performance of TCP/IP over ATM for long delay networks; and 4) Evaluation of ATM service categories for TCP/IP traffic

On the photometric error calibration for the `differential light curves' of point-like Active Galactic Nuclei

It is important to quantify the underestimation of rms photometric errors returned by the commonly used \emph APPHOT algorithm in the \emph IRAF software, in the context of differential photometry of point-like AGN, because of the crucial role it plays in evaluating their variability properties. Published values of the underestimation factor, $\eta$, using several different telescopes, lie in the range 1.3 - 1.75. The present study aims to revisit this question by employing an exceptionally large data set of 262 differential light curves (DLCs) derived from 262 pairs of non-varying stars monitored under our ARIES AGN monitoring program for characterizing the intra-night optical variability (INOV) of prominent AGN classes. The bulk of these data were taken with the 1-m Sampurnanad Telescope (ST). We find $\eta$ = 1.54$\pm$0.05 which is close to our recently reported value of $\eta$ = 1.5. Moreover, this consistency holds at least up to a brightness mismatch of 1.5 mag between the paired stars. From this we infer that a magnitude difference of at least up to 1.5 mag between a point-like AGN and comparison star(s) monitored simultaneously is within the same CCD chip acceptable, as it should not lead to spurious claims of INOV.Comment: 20 pages, 3 figures and 1 table; accepted for publication in JAp

Extragalactic radio sources with sharply inverted spectrum at metre wavelengths

We present the first results of a systematic search for the rare extragalactic radio sources showing an inverted (integrated) spectrum, with spectral index $\alpha \ge +2.0$, a previously unexplored spectral domain. The search is expected to yield strong candidates for $\alpha \ge +2.5$, for which the standard synchrotron self-absorption (characterized by a single power-law energy distribution of relativistic electron population) would not be a plausible explanation, even in an ideal case of a perfectly homogeneous source of incoherent synchrotron radiation. Such sharply inverted spectra, if found, would require alternative explanations, e.g., free-free absorption, or non-standard energy distribution of relativistic electrons which differs from a power-law (e.g., Maxwellian). The search was carried out by comparing two sensitive low-frequency radio surveys made with sub-arcminute resolution, namely, the WISH survey at 352 MHz and TGSS/DR5 at 150 MHz. The overlap region between these two surveys contains 7056 WISH sources classified as `single' and brighter than 100 mJy at 352 MHz. We focus here on the seven of these sources for which we find $\alpha > +2.0$. Two of these are undetected at 150 MHz and are particularly good candidates for $\alpha > +2.5$. Five of the seven sources exhibit a `Gigahertz-Peaked-Spectrum' (GPS).Comment: 8 pages, 2 figures, accepted for publication in MNRA

A Performance Analysis of Point-to-Point Routing along a Directed Acyclic Graph in Low Power and Lossy Networks

International audienceThe ROLL working group at IETF is currently de- signing RPL, the Routing Protocol for Low power and lossy networks. RPL is based on organizing the nodes in a network in one or more directed acyclic graphs (DAGs) rooted at the popular/default destinations. The DAG structure naturally supports multipoint-to-point routing towards the DAG root and point-to-multipoint routing from the root towards the nodes. The point- to-point (P2P) routing mechanism specified in RPL requires a packet to travel upwards along the DAG until it is turned downwards by a node that knows the downward route along the DAG to the packet's destination. This up and down routing along the DAG may result in significantly suboptimal P2P routes. In this paper, we quantify the difference in terms of routing cost between DAG-based P2P routes and the shortest (or minimum cost) P2P routes available in a sample network topology and make the case for a better P2P routing solution in RPL

Routing Loops in DAG-based Low Power and Lossy Networks

International audienceDirected Acyclic Graphs (DAGs), rooted at popu- lar/default destinations, have emerged as a preferred mech- anism to provide IPv6 routing functionality in large scale low power and lossy networks, that include wireless sensor networks and those based on power line communication. A DAG maintains its acyclic nature by requiring that each DAG node must have a higher 'rank' than any of its DAG parents. While a node may decrease its DAG rank safely, increasing its DAG rank to add a new parent may result in a routing loop if the new parent is also a descendant in the DAG. In this paper, we first study via simulations the time required by the network to converge to a stable, loop-free state following a rank increase operation and the number of routing messages generated (the network 'churn') during this time. Then, we describe the precautionary measures that can be used to avoid routing loops and evaluate via simulations how these measures affect the time and churn involved in reaching a stable state following a rank increase operation