José Incera

Bit-level and packet-level, or Pollaczec-Khintchine formulae revisited

The construction of efficient compilers is very complex, since it has to contend with various optimization problems and depends on the characteristics of the architecture of the machine for which they generate code. Many of these problems are NP-hard. The genetics algorithms have been shown to be effective in the resolution of difficult problems, however, their use in compilation is practically nonexistent. In this paper we propose a solution to the problems of register allocation and instruction scheduling. We carry out an analysis of performance by comparing with the more traditional approaches for these problems and we obtain profits on the speed of the generated code varying between -2% and 26%.

A simulation study of the Adaptive RIO (A-RIO) queue management algorithm

Active queue management (AQM) algorithms are useful not only for congestion avoidance purposes, but also for the differentiated forwarding of packets, as is done in the DiffServ architecture. It is well known that correctly setting the parameters of an AQM algorithm may prove difficult and error-prone. Besides, many studies have shown that the performance of AQM mechanisms is very sensitive to network conditions. In this paper we present a detailed simulation study of an Adaptive RIO (A-RIO) AQM algorithm which addresses both of these problems. A-RIO, first introduced by Orozco and Ros (2003), draws directly from the original RIO proposal of Clark and Fang (1998) and the Adaptive RED (A-RED) algorithm described by Floyd et al. (2001). Our results, based on ns-2 simulations, illustrate how A-RIO improves over RIO in terms of stabilizing the queue occupation (and, hence, queuing delay), while maintaining a high throughput and a good protection of high-priority packets; A-RIO could then be used for building controlled-delay, AF-based services. These results also provide some engineering rules that may be applied to improve the behaviour of the classical, non-adaptive RIO.

FluidSim: a tool to simulate fluid models of high-speed networks

Abstract In this paper, we present a tool for the simulation of fluid models of high-speed telecommunication networks. The aim of such a simulator is to evaluate measures which cannot be obtained through standard tools in reasonable time or through analytical approaches. We follow an event-driven approach in which events are associated with rate changes in fluid flows. We show that under some loose restrictions on the sources, this suffices to efficiently simulate the evolution in time of fairly complex models. Some examples illustrate the utilization of this approach and the gain that can be observed over standard simulation tools.

A fairness study of the adaptive RIO active queue management algorithm

Active queue management (AQM) mechanisms manage queue lengths by dropping packets when congestion is building up; end-systems can then react to such losses by reducing their packet rate, hence avoiding severe congestion. They are also very useful for the differentiated forwarding of packets in the DiffServ architecture. Many studies have shown that setting the parameters of an AQM algorithm may prove difficult and error-prone, and that the performance of AQM mechanisms is very sensitive to network conditions. The adaptive RIO mechanism (A-RIO) addresses both issues. It requires a single parameter, the desired queuing delay and adjusts its internal dynamics accordingly. A-RIO has been thoroughly evaluated in terms of delay response and network utilization but no study has been conducted in order to evaluate its behaviour in terms of fairness. By way of ns-2 simulations, This work examines A-RIOs ability to fairly share the networks resources (bandwidth) between the flows contending for those resources. Using Jains fairness index as our performance metric, we compare the bandwidth distribution among flows obtained with A-RIO and with RIO.

FluidSim: A Tool to Simulate Fluid Models of High-Speed Networks

In this paper, we present a tool for the simulation of fluid models of high-speed telecommunication networks. The aim of such a simulator is to evaluate measures which could not be obtained through standard tools in a reasonable delay or through analytical approaches. We follow an event-driven approach in which events are associated only with rate changes in fluid flows. We show that, under some loose restrictions on the sources, this suffices to efficiently simulate the evolution in time of fairly complex models. Some examples illustrate the utilization of this approach and the gain that can be observed over standard simulation tools.

Custom tailored location based services: An IMS implementation

Digital convergence is becoming increasingly imortant to both network operators and end users. Network operators look to Next Generation Network (NGN) solutions to meet the ever growing user demand and to the IP Multimedia Subsystem (IMS) as a catalyzer for attractive and innovative services which aim at improving user Quality of Experience (QoE). IMS, presented as the first working implementation of a Service Delivery Platform (SDP), takes great strides to ease migration to NGN as well as help the network become transparent to the end user. Location Based Services (LBS) also play an important role in QoE by supplying relevant information on the users whereabouts directly enhancing their day-to-day activities. The combination of LBS within IMS holds great promise for future services where service delivery mimics a network responding directly to user activities. This helps dissolve the difference between the network and the User Equipment (UE), thus increasing user adoption through a transparent network and service delivery. This paper presents two personalized LBS implemented within an IMS test bed acting as a proof of concept for providing improved QoE on an IMS infrastructure as well as demonstrating that service creation is relatively easy to achieve in IMS.

Asterisk as a Public Switched Telephone Network Gateway for an IMS test bed

Network operators are in the process of adopting the IP Multimedia Subsystem (IMS) as their main underlying infrastructure which will in turn be used as a Service Delivery Platform (SDP). This process requires the migration of current services to their IMS counterparts, as well as a compatibility layer enabling successfull communication between IMS and other network infrastructures. Any and all functionality within IMS is normally available through an Application Server (AS). This paper presents an implementation of a Public Switched Telephone Network (PSTN) Gateway which is able to successfully interface with an IMS test bed. Consequently, it also allows calls to be placed between IMS and other Voice over IP (VoIP) providers. The gateway is enabled as an AS with the help of Asterisk.