Providing scalable NH-diverse iBGP route re-distribution to achieve sub-second switch-over time

The role of BGP inside an AS is to disseminate the routes learned from external peers to all routers of the AS. A straightforward, but not scalable, solution, is to resort to a full-mesh of iBGP sessions between the routers of the domain. Achieving scalability in the number of iBGP sessions is possible by using Route Reflectors (RR). Relying on a sparse iBGP graph using RRs however has a negative impact on routers’ ability to quickly switch to an alternate route in case of a failure. This stems from the fact that routers do not often know routes towards distinct next-hops, for any given prefix.In this paper, we propose a solution to build sparse iBGP topologies, where each BGP router learns two routes with distinct next-hops (NH) for each prefix. We qualify such iBGP topologies as NH-diverse. We propose to leverage the “best-external” option available on routers. By activating this option, and adding a limited number of iBGP sessions to the existing iBGP topology, we obtain NH-diverse iBGP topologies that scale, both in number of sessions and routing table sizes. We show that NH diversity enables to achieve sub-second switch-over time upon the failure of an ASBR or interdomain link. The scalability of our approach is confirmed by an evaluation on a research and a Service Provider network.     

Radiotherapy, toxicity and dosimetry of copper-64-TETA-octreotide in tumor-bearing rats

The efficacy of 64Cu [T1/2 = 12.7 hr; beta+ (0.655 MeV; 19%); beta- (0.573 MeV; 40%)] as a radioisotope for radiotherapy has been recently established. Here we demonstrate that 64Cu-1,4,8,11 -tetraazacyclotetradecane-N,N',N",N'-tetraacetic acid (TETA)-octreotide, a somatostatin receptor ligand, inhibits the growth of CA20948 rat pancreatic tumors in Lewis rats at doses that cause minimal toxicity. METHODS: Tumor-bearing rats were administered a single 15 mCi (555 MBq) dose, a fractionated dose of 15 mCi given in 2-3 doses over 2-8 days, or control agents of buffer, unlabeled octreotide or 64Cu-labeled TETA. In certain experiments, blood was removed at times from 4-23 days post-treatment, and a complete blood count along with blood chemistry analyses were obtained. RESULTS: Tumor-growth inhibition was significantly greater in rats injected with a single 15 mCi dose than in rats injected with control agents (p < 0.05). Dose fractionation in two doses, either 1 or 2 days apart, induced significantly increased tumor-growth inhibition compared with rats given a single dose (p < 0.05). The only toxicity observed in treated rats was a decrease in the white blood cell count. This drop was more pronounced in rats treated with a single dose compared with those treated with a fractionated dose. Human absorbed doses of 64Cu-TETA-octreotide to normal organs were estimated from biodistribution data in Lewis rats, and these data indicate that radiotherapy with 64Cu-TETA-octreotide in humans would be feasible. CONCLUSION: Copper-64-TETA-octreotide is a promising radiopharmaceutical for targeted radiotherapy of somatostatin receptor-positive tumors.     

Interdomain traffic engineering with BGP

Traffic engineering is performed by means of a set of techniques that can be used to better control the flow of packets inside an IP network. We discuss the utilization of these techniques across interdomain boundaries in the global Internet. We first analyze the characteristics of interdomain traffic on the basis of measurements from three different Internet service providers and show that a small number of sources are responsible for a large fraction of the traffic. Across interdomain boundaries, traffic engineering relies on a careful tuning of the route advertisements sent via the border gateway protocol. We explain how this tuning can be used to control the flow of incoming and outgoing traffic, and identify its limitations.     

The Pass-Along Effect: Investigating Word-of-Mouth Effects on Online Survey Procedures

Email petitions to complete online surveys may be forwarded beyond the intended sample. We term this phenomenon the pass-along effect and investigate it as a factor that can influence the nature and size of survey samples in an online context. We establish the pass-along effect as a form of word-of-mouth communication and draw from the literature in this area to present and test a model of factors that influence the occurrence of this effect. The results of two studies provide empirical support for the existence and impact of the pass-along effect. Among the factors that lead to this effect are involvement and relationship with the survey topic, size of a participant's social network, and tie strength. The appropriateness of employing pass-along respondents as well as other implications for online sampling and survey research are discussed.     

A performance evaluation of BGP‐based traffic engineering

Many Internet Service Providers tune the configuration of the Border Gateway Protocol on their routers to control their traffic. Content providers often need to control their outgoing traffic while access providers need to control their incoming traffic. We show, by means of measurements and simulations, that controlling the flow of the incoming interdomain traffic is a difficult problem. For this purpose, we first rely on detailed measurements to show the limitations of AS‐Path prepending. Then, we show by using large‐scale simulations that the difficulty of controlling the flow of the incoming traffic lies in the difficulty of predicting which BGP route will be selected by distant Autonomous Systems (ASs). Copyright © 2005 John Wiley & Sons, Ltd.     

Local measurements of void fraction and liquid holdup in packed columns using X-ray computed tomography

A ‘tailor made’ computed X-ray tomographic scanner has been developed as a tool for the analysis of the distribution of gas, liquid and solid phases in packed columns. The very good spatial resolution of the scanner has first been assessed by the imaging of objects of known shape and size, called ‘physical’ phantoms. Images have then been realized on a 0.6 m diameter and 2 m height column packed with Cascade Mini-Ring 1A packing elements, which is a random polypropylene packing designed to be used in absorption columns. The solid phase distribution, leading to the void fraction distribution, has been analyzed on cross-section images of the dry packed column (without any liquid flowrate). The measured value of the bed void fraction is equal to the value provided by the manufacturer. The analysis of the axial profile of void fraction shows that the ‘end effect’ may be neglected, whereas the analysis of the radial profile evidences the existence of a non negligible ‘wall effect’. Images have then been carried out on the packed column irrigated by a liquid flowrate ranging between 0 and 6000 l h⁻¹ (0–6.10⁻³ m s⁻¹). Hold-up values have been measured in different cross-sections of the column and averaged in order to obtain the total hold-up value in the bed. The computed values are in very good agreement with those reported in the literature for similar packing. The dependence of the liquid hold-up on the liquid superficial velocity can be expressed in terms of a power law. The fitted value of the exponent, equal to 0.65, is in the range of exponent values found in correlations of the literature.