Karol Molnar

DiffServ-Based User-Manageable Quality of Service Control System

An efficient operation of modern network services in packet networks is often conditional on complex quality-of-service (QoS) support. Because of its relative simplicity the mechanism of differentiated services (DiffServ) has recently come to be the most widely used QoS support technology in IP networks. One of the biggest disadvantages of this mechanism is the inability to cooperate with end-stations and end-user applications. This paper introduces a solution which allows end-stations to automatically retrieve DiffServ- related information from a network. As a result, end-users can control traffic policing in the DiffServ domain provided the predefined traffic conditions are not violated.

Map-based direct position control system for wireless ad-hoc networks

Ad-hoc networking and mobility modelling are two very prospective research areas of modern network technologies. This paper is focused mainly on the possibilities of the map-based mobility modelling in OPNET Modeler simulation environment. The paper introduces a new simulation model which enables direct position control for mobile stations. This easily configurable and customizable system offers a promising and realistic solution to realistically model the movement of wireless stations and substitutes a testing in real environments. Since OPNET Modeler is a powerful simulation tool but it is not convenient for extensive mathematical operation, the MATLAB environment was used for calculations related to movement probabilities and destination coordinates. Both simulation environments were linked together by the MATLAB Engine library which allows external programs to access MATLAB functionalities. The proper function of system designed was evaluated by a simulation.

Advanced trajectory management techniques for mobile nodes in OPNET Modeler environment

The goal of each simulation is to get a situation with conditions approaching the real environment. The results obtained are more accurate and more in a line with network behaviour in real environment. One of the most important parameters of Mobile Ad hoc Networks (MANET) is the mobility of network nodes. Each mobile node may change its location with a specific rate depending on the time. The simulation environment OPNET Modeler enables to control a trajectory of each network station by several ways. This paper presents the possibility to control the movement of mobile node based on information about the route stored in the GPX file. This GPX file was originated from a simplified map source. The development process of the simulation scenario and obtained results are presented in this paper.

Architecture of a Universal Relation Data Source for Web Applications with Advanced Access Control and Simplified Migration

In enterprise systems many software operations over a database are implemented in a similar way. Systems always take care of correct storage of a data into appropriate tables, data integrity, multilingual support, locales, data validation etc. Data are often stored in a relational database management systems using SQL. SQL standard itself does not provide suitable support for wide range of operations which need to be implemented in almost all cases. Furthermore SQL implementation and triggers/stored procedures programming language differ between various systems. This leads to very difficult migration of software systems based on one database management system to another. Access control provided by the databases is not suitable for an application because users would be allowed to access a database but they must be allowed to access an application instead. Sometimes an application needs to design a more sophisticated access control system. This article deals with this topic and designs an architecture which universally solves all mentioned problem areas. Key benefits it brings are independency on any particular database management system, easy migration to another one and fast fully automatic lowlevel record based rights checking.

Evaluation of Quality-of-Service Support in MultiProtocol Label Switching

The technology of MultiProtocol Label Switching (MPLS) represents one of the most advanced ways how to optimize the packet-forwarding process in routers. In addition, MPLS also offers new possibilities of resource sharing, important from the point of view of service differentiation and quality of service (QoS) support. The aim of the paper is to present the results of our investigation into the efficiency of QoS support mechanisms available in MPLS for different traffic types. For this purpose several simulation scenarios were built to obtain a complex overview of the topic examined.

SNMP-based acquisition system for DiffServ parameters

Modern communication networks cannot get along without quality of service (QoS) assurance. QoS-support mechanisms offer preferential treatment for specific traffic classes that is required especially by real-time network applications. Unfortunately current QoS technologies have certain disadvantages and limitations and therefore they are not always able to guarantee the required QoS level. This paper introduces a quality of service support system that improves the most often used quality of service support technology called Differentiated Services (DiffServ). The system proposed utilizes the Simple Network Management Protocol (SNMP) for the acquisition of configuration information from the edge router of the DiffServ domain. This information is subsequently used to control the allocation of network resources within the QoS assurance process. In order to evaluate this system we used the OPNET Modeler simulation environment where we built a simulation scenario able to interact with real network components. For this purpose we implemented the SNMP protocol into the OPNET Modeler and used it for acquisition of management information, stored in the Management Information Base (MIB) of the network node. The paper describes in details the improved QoS-support mechanism and the simulation model able to cosimulate the behavior of both real and virtual network elements.

General architecture of grid framework with qos implementation

The sophisticated distribution of computing some difficult mathematical tasks between geographically scattered computers, connected into the so-called grids, offers to users the potential of using a processing power several times higher than that of a supercomputer or a cluster at a much lower price. A crucial problem of recent applications requiring the grid-based solution is that they are designed to solve one specific problem. The aim of this paper is to propose a universal Grid framework that will use a sophisticated aggregation method for distributed data processing. This framework should realize all repeating programmer operations automatically – e.g. data transfer and validation, security, authorization, etc. The user of this system should only insert desired algorithm and data for processing and the system will be able to solve any parallelized task automatically without additional programming.

Theoretical Analysis of EDCA Medium Access-Control Method in Simplified Network Environment

The IEEE 802.11e standard was designed to extend the basic WLAN access-control methods with QoS support. It is achieved by allowing the network administrators to tune several access-control related parameters. Our analysis is focused on the effect of these parameters on the probability of a station gaining access to the wireless medium. We provide a mathematical analysis in a simplified model with two stations, which were not in collision within the preceding contention.

Advanced access control system for multi-tier server applications

Server applications are one of the most important components of applications which use multi-tire architecture. These servers need to handle access of users. Access control logic is usually implemented directly inside an object which is responsible for performing required operations over the data. The object verifies access to its methods and permits or denies the operation. But systems usually consist of many such objects with different missions. All of these objects require similar access control system. This makes a greater overhead because access control verification must be coded inside all those objects. If in this approach a programmer forgets to verify some of required rights in the code then the system may encounter a forbidden data access. This article deals with that topic and designs a unified database layer working over relation databases. Benefits of this layer are strong simplification of the access control system and impossibility to access data without permissions.

Application Programming Interface offering classification services to end-user applications

There are several sophisticated and practically tested technologies supporting Quality of Service (QoS) through a communication network. On the other hand, the extension of QoS support towards end-user applications is quite rare. The Application Programming Interface (API) described in this paper represents a possibility how to extend QoS in this direction under the Microsoft Windows environment. The solution presented is closely related to the DiffServ technology, i.e. packet marking based on the type of the network service the packet was generated by.