Exploiting Location Awareness for Scalable Location-Independent Object IDs

We are building a wide-area location service that tracks the current location of mobile and replicated objects. The location service should support up to 10 12 objects on a worldwide scale. To support this huge number of objects, the workload of the location service is distributed over multiple hosts. Our load distribution method is unique in that it is aware of the (geographical) location of the hosts it uses. By using this location knowledge when distributing the workload, the distribution mechanism enforces locality of operations in the location service. Enforcing locality minimizes the use of global network resources by the location service and thereby enhances its scalability. We also show how this location-aware load distribution mechanism can be implemented. 1 Introduction Objects provide an easy way to model both applications and system services. It is therefore easy to understand that the use of objects as a design and implementation method has become popular, for example..

Supporting Effective Caching in a Wide-Area Distributed Location Service.

Abstract. Globe is a wide-area distributed system that supports mobile objects. To track and locate objects, we use a worldwide distributed location service, implemented as a search tree. An object registers its current position by storing its address in a nearby leaf node of the tree. This knowledge propagates up to the top of the tree, so every object can be found from the root. Remote objects can cache the location of an object. However, if the object moves, the cache entry is no longer valid. In this paper, we show how caching can be made to work effectively even in the presence of mobile objects. vrije Universitei

Characterizing Internet Performance to Support Wide-area Application Development.

To help in our wide-area application development, we have done an informal study of the relation between wide-area latency, the number of routers, and geographical distance between Internet sites. We did this by performing ping and traceroute measurements between 19 sites distributed across the globe. Contrary to our expectation there is almost no correlation between distance, latency, and number of routers in the current Internet. To help further studies of these characteristics the problems of this pilot project are also described. 1 Introduction When developing an application, it is important to have accurate knowledge of the characteristics of the environment in which the application is to run. This is especially true for wide-area applications since their performance (or lack thereof) will depend heavily on these characteristics. Obvious characteristics for wide-area networks are latency and bandwidth. Knowledge of these characteristics will be used not only when designing a wid..

Sound production in the collared dove: a test of the "whistle" hypothesis

The mechanism of sound production in the collared dove Streptopelia decaocto was studied to test the validity of the 'whistle' model and to analyze the role of vocal tract resonances. In this study, the vocalizations of six male adult doves were recorded both in normal air and in a mixture of 80 % helium and 20 % oxygen (heliox). Depending on the way in which the syrinx operates, the spectral structure of the vocalizations is expected to show specific changes in heliox. The effects of heliox differed substantially depending on the type of vocal element. Except for a significant decrease in amplitude, unmodulated elements, i.e. elements with a constant frequency, were relatively unaffected by heliox. In contrast, modulated elements, i.e. elements with an abrupt increase in frequency, showed a gradual increase in frequency with increasing helium concentration. This specific increase in frequency stopped when the modulation frequency was 1.5 times the base frequency, even when the helium concentration was increased further. In some individuals, a frequency band of half the base frequency was also observed. In general, the proportion of modulated elements also showed a significant decrease. The lack of change in the fundamental frequency of the unmodulated elements and in the base frequency of the modulated elements indicates that these vocalizations are not produced like a whistle. It is more likely that they are the result of vibration of the syringeal membranes. Generally, vocal tract resonances do not play an active role in the modification of vocalizations, although they might enhance the fundamental frequency passively. The results suggest that the almost pure tonal vocalizations are produced as such in the syrinx and undergo limited modification when passing through the vocal tract. The effect of heliox on the modulation frequency suggests (1) that different sound-producing mechanisms may underlie different types of vocalizations, and (2) that resonance properties of the vocal system may be involved in the production or modification of the modulation frequency.Animal science

A Scalable Implementation for Human-Friendly URIs

Abstract. In the Web, Uniform Resource Identifiers (URIs) are used to name resources. The most common form of URI, the Uniform Resource Locator (URL) has, unfortunately, some scalability problems. In this paper, we proposes the use of Human-Friendly Names (HFNs) to solve these scalability problems. HFNs are high-level names that allow (human) users to easily deal with names. We also describes a scalable HFN-to-URL resolution mechanism. This mechanism is based on the existing Domain Name System (DNS) and the Globe Location Service. To gain experience and validate our ideas, we have implemented our HFN resolution scheme

The distributed ASCI supercomputer project

The Distributed ASCI Supercomputer (DAS) is a homogeneous wide-area distributed system consisting of four cluster computers at different locations. DAS has been used for research on communication software, parallel languages and programming systems, schedulers, parallel applications, and distributed applications. The paper gives a preview of the most interesting research results obtained so far in the DAS project