Javier de Santiago Fernández

Reliable Partial Replication of Contents in Web Clusters: Getting Storage without losing Reliability

Traditionally, distributed Web servers have used two strategies for allocating files on server nodes: full replication and full distribution. While full replication provides a highly reliable solution, it limits storage capacity to the capacity of the smallest node. On the other hand, full distribution provides higher storage capacity at the cost of lower reliability. A hybrid solution is partial replication where every file is allocated to a small number of nodes. The most promising architecture for a partial replication strategy is the Web cluster architecture. However, Web clusters present a big flaw from reliability perspective as they contain a single point of failure. To correct this flaw, in this paper we present a modified architecture: the Web cluster with distributed Web switch. Reliability of Web clusters is evaluated for different replication strategies. System evaluations show that our proposal leads to a highly reliable solution with high scalability.

Assessment of Exposure from Wi-Fi Devices

In the last decade the number of wireless devices operating at the frequency band of 2.4 GHz has increased in several settings, such as: healthcare, occupational and household. The working conditions of a Wi-Fi module have been analyzed. The levels of electromagnetic (EM) field in near field conditions were measured inside an anechoic chamber with a specific absorption rate (SAR) fully automated test system, DASY5PRO. The obtained results were compared with the levels set by international regulations to analyze the exposure to EM fields. In close areas to the device, the obtained electric field levels show that local exposure can reach the most restrictive value of 3 V/m that is established in the International Electrotechnical Commission Standard of Electromedical Devices.