Agnieszka Brachman

RPL Objective Function Impact on LLNs Topology and Performance

RPL is IPv6 Routing Protocol designed for Low Power and Lossy networks. RPL is a distance vector routing protocol that builds Directed Acyclic Graphs (DAGs), using implementation specific routing metrics and constraints. In the construction process of network topology, each node selects a set of potential parents towards the destination and associates itself to a preferred parent, basing on the outcome of Objective Function (OF). OF defines how one or more node and link metrics and constraints are used to compute the node rank.

Performance of AQM Routers in the Presence of New TCP Variants

In this paper, we study the performance of active queue management algorithms for packet queueing in Internet routers in the presence of new versions of the TCP congestion control mechanism. In particular, we compare the performance of tail drop, adaptive RED, AVQ, PI, REM and AN-AQM queueing in four TCP cases: (i) the classic New Reno protocol, (ii) the Sack protocol, (iii) the Fack protocol, (iv) the Cubic protocol. Apparently, the application of Fack and Cubic versions of TCP have (with some exceptions) minor impact on the basic performance characteristics (throughput and delay) of the routers queueing mechanism. However, application of Cubic TCP has often a positive impact on the stability of the routers queue size. As for the inter-flow fairness for different TCPs, the results are not univocal - both fairness improvement and degradation can be observed depending on the network congestion level.

Simulation Comparison of LEACH-Based Routing Protocols for Wireless Sensor Networks

Battery-powered nodes have limited energy reserves therefore applications and protocols used for WSNs, should be designed, concerning the optimized energy consumption in order to prolong the network lifetime. Data reception and transmission are the main energy consuming operations and they are regulated by the network layer, hence the routing protocol plays very important role in network optimization.

Profitability Analysis of PV Installation in Combination with Different Time-of-Use Strategies in Poland

Increasing the participation of energy originated from renewable sources is one of the most important issues for polish and EU economy. It is also required by all targets of the 2020 climate and energy package for EU. The usage of micro photovoltaic (PV) instalments for residential and commercial buildings in Poland has been increasing for several years. Introduction of the Renewable Energy Sources Act, will raise profitability of this type of installations even more. The paper presents an energetic and economical analysis of exemplary PV system for domestic production, under polish climatic and economic conditions. Moreover an overview of DSR strategies is presented, some of them are already available for customers, others require additional regulations or technology development.

On the Shortcoming of EDCA Queues in the Presence of Multiservice Traffic

The paper aims at depicting certain limitations of EDCA queues related to the different traffic classes. Through simulation, we show main flaws of identical, medium size, Drop Tail queues used by default for each class, with reference to different traffic category’s requirements. We propose some substitutes such as differentiated, basically smaller buffer sizes and Active Queue Management mechanisms that can be employed to improve the overall performance. We present a strategy for EDCA queues to maintain the desired quality of transmission for traffic belonging to different categories.

On the Performance of AQM Algorithms with Small Buffers

Packet buffers in routers play a major role in congestion control in existing Internet. They compensate for the incoming traffic bursts transmitted by aggressive TCP applications. The appropriate sizing of buffers is important for providing equilibrium between the high link utilization, the loss ratio and the queueing delay. There is a growing need for routers with small buffers in high speed networks. In this paper we investigate the performance of active queue management algorithms with very small buffers. In particular, we show, that the use of very small buffers does not influence throughput on bottlenecked links if mixed (TCP / UDP) traffic is involved. On the other hand a very small buffer may lead to degradation of the inter-flow fairness.

Scheduling Algorithms for Different Approaches to Quality of Service Provisioning

IP network provides only best effort delivery meaning, that data is transmitted at unspecified variable bit rate and delivery time is unknown, depending on the current traffic load. Nowadays, real-time traffic occupies significant percentage of the available bandwidth and Internet must evolve to support new applications. Therefore one of the main and crucial objective of the future Internet is to change best effort network into Quality of Service controlled network.

Towards a common benchmark in WiMAX environment

Recently Andrew et al. proposed the TCP Evaluation suite to provide a common test suite for researchers designing new TCP extensions and AQM mechanisms. It defines network topologies, simulation scenarios i.e. traffic characteristic as well as evaluation parameters to provide a common testbed for all new enhancements. The presented remarks determine the essential features of a simulation environment for different solutions in common networks.

A Program Suite for Distributed Simulation of Networks in Multi-core Environments

The ns-2 simulator is one of the most popular and widely used discrete event network simulators. Its usage of the general purpose Tcl scripting language accompanied with a wide range of networking technologies allows users to easily create complex and differentiated simulation scenarios. The main limitation of ns-2 is its lack of support for multiprocessing, especially considering that the multi-core environments have recently become tools of everyday use. In this paper we (a) propose a programming approach that allows running single-model simulations simultaneously on a multi-core systems using ns-2 and (b) present a set of software tools developed following the proposed convention. In addition, we describe a lightweight software scheduler extending the use of ns-2 on ad-hoc grid systems.