Providing and verifying advanced IP services in hierarchical DiffServ networks‐the case of GEANT

The differentiated services (DiffServ) framework is widely proposed as an efficient method for providing advanced IP services to large‐scale networks, with QoS requirements. However, the provisioning of such services in production networks has proved to be more difficult than initially expected, in defining, setting and verifying appropriate Service Level Agreements (SLAs). GEANT, the Gigabit core pan‐European research network, on a pilot basis introduced ‘Premium IP’ service, offering bounded delay and negligible packet loss to the European National Research & Education Networks (NRENs) that it interconnects. However, large scale provisioning of this new service requires the definition of efficient interaction procedures between administrative domains involved and methods for SLA monitoring. This paper focuses on these issues and presents the experience acquired from the early experiments in GEANT, as an example of hierarchical Gigabit multi‐domain environment, enabled with QoS provisioning to its constituent NRENs. This model scales more efficiently than the common peering Internet Service provider (ISP) commercial paradigm. Finally, we outline other options that promise QoS, such as Layer 2 VPNs in MPLS backbones, with non‐standard (yet) mechanisms. Copyright © 2004 John Wiley & Sons, Ltd.     

IP QoS across multiple management domains: practical experiences from pan-European experiments

GEANT is the pan-European 10 Gbs network interconnecting European national research and educational networks (NRENs). A Premium IP service based on the DiffServ EF PHB has been specified and implemented for this environment to provide quality of service to selected user groups on a Europe-wide scale. Basic features of Premium IP are described, and results from early experiments in the production networks of GEANT and the NRENs are presented. Next steps are proposed for achieving a fast and wide availability of Premium IP in the European research networks.     

Performance analysis of relative service using TCP‐aware marking and dynamic WRED

The implementation of successful assured forwarding (AF) services according to the DiffServ framework remains a challenging problem today, despite the numerous proposals for assured forwarding per‐hop‐behaviour (AF PHB) mechanisms and AF‐based service implementations. The interaction of the TCP and UDP traffic under an AF‐based service and a number of relative issues such as fairness among flows, achievable bandwidth guarantees and qualitative performance have been taken into consideration in this work in order to address the existing limitations. We propose two modules, the TCP‐window aware marker (TWAM) and the dynamic WRED (WRED) mechanism for implementing the differentiated services (DiffServ) AF PHB. We provide analytical models and an experimental evaluation in order to demonstrate how they succeed in enhancing the quality, improving the performance and easing the deployment of a production level AF‐based service. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance issues of bandwidth management in ATM networks

In our days, efficient management of the available network resources becomes a critical issue, both from a functional point of view (so that users can be provided with the bandwidth they need), and an economical point of view (so that carriers can satisfactorily and efficiently serve as many customers as possible and at the same time increase their revenue). In this paper we consider a bandwidth control scheme (i.e. managed bandwidth service) for an ATM network infrastructure which is applied to the Greek research and technology network (GRNET). We present some methods that we have tested (in a simulation setting) in order to increase the efficiency of the system and the utilization of the available bandwidth. More specifically, we consider a bandwidth‐resizing algorithm for virtual paths, in order to keep the allocated bandwidth very close to the bandwidth actually used. This leads to an increased number of accepted requests and better network utilization. We, also, use the simulation results in order to get an estimation of the effective bandwidth for VBR paths that can be used in call admission. Finally, we consider a semi‐offline scheme where requests are gathered and considered for acceptance in regular intervals. Simulation results show an increase in the utilization of resources. As a further improvement, we allow connections to be allocated a little before or after the time initially requested. This leads to further improvement in network utilization. All the improvement schemes were tested with the ATM‐TN simulator and the results look promising. Copyright © 2003 John Wiley & Sons, Ltd.     

Photostabilization of oxolinic acid in hydroxypropyl-β-cyclodextrins; implications for the effect of molecular self-assembly phenomena

Oxolinic acid (OXA) is a first-generation quinolone antibacterial agent, known to cause drug induced photosensitivity. In the present work its photoinduced degradation was monitored under simulated solar irradiation. The effect of photoprotecting agents on OXA stability was also assessed by drug complexation with hydroxypropyl-β-cyclodextrin (HPβCD). The complex was studied by UV-Vis and ¹H (2D) NMR Spectroscopy. A photostability indicating chromatographic method was developed and validated. Because OXA is insoluble in acidic solutions, and because an acidic solvent is necessary for successful chromatographic separation, a procedure was developed to pre-treat the sample. This method is suitable for the separation of degradation products from OXA and from each other. The method was also evaluated in the presence of HPβCD, in order to ensure that inclusion complexation did not generate inaccuracies. Investigation of OXA photodegradation profiles confirms first order kinetics and acceleration at higher initial sample concentrations. A 94% photostabilization upon complexation with HPβCD was achieved. Furthermore, molecular self association phenomena were determined by self titration experiments, using ¹H NMR Spectroscopy and suggestions were made for the photostabilization mechanism of cyclodextrins.     

HPLC determination of residual monomers released from heat-cured acrylic resins

HPLC was used to examine the leachability of three non-phthalic and four phthalic post-polymerized residual monomers from three commercially available heat-cured acrylic resins. Specimens of equal dimensions were constructed from each brand of material by following the standardized procedure and were stored under three different conditions, namely, distilled water, artificial saliva, and a binary mixture of ethanol/water. The resulting liquids provided samples for analysis by HPLC. Three different experiments were performed for each brand of acrylic and each storage condition in order to examine the effects of parameters, particularly time and temperature. The results obtained from this study suggest that a wide spectrum of residues diffuse out of the three examined acrylic resin materials. The non-phthalic compounds were leached at high concentrations, whereas all the phthalates examined exhibited different degrees of elusion commensurate with the storage condition, brand of material, and type of experiment. It seems that a significant quantity of non-phthalic and phthalic residues diffuse out of the acrylic resin materials examined. The main component extracted was methyl methacrylate, the level of which seems to be time-dependent and decreases for a period of up to 5 days when resins are stored in distilled water at room temperature.     

The effect of β-cyclodextrin on tenoxicam photostability, studied by a new liquid chromatography method; the dependence on drug dimerisation

Tenoxicam (TXM) is an effective anti-inflammatory and analgesic drug, which presents fast photochemical decomposition. In this work in an attempt to investigate the potential β-CD photostabilizing effect on TXM, the photodegradation rate of β-CD complexed drug was monitored under simulated solar irradiation from Xenon arc lamp. The photodegradation was studied at pH 7.5. A new stability indicating Liquid Chromatography method, for TXM in the presence of β-CD was used. According to the obtained results, in the case of free molecules increasing the concentration the photostability is enhanced. The effect of complexation with CDs on the photodegradation rate seems to vary depending on TXM initial concentration. At low TXM concentrations photodecomposition is retarded upon CD complexation, while at high concentrations the process is accelerated. Molecular dimerisation was studied by ¹H(1D) NMR and 2D NOESY experiments. 2D ROESY spectra of complexed molecule were evaluated in order to confirm the complexation. TXM dimers could be considered as a critical parameter affecting oxicams photostability, in combination with the already described ESIPT phenomenon.