Antonio Cuevas

Qualitative robustness in abstract inference

Abstract Hampels concept of qualitative robustness (or stability) is applied to estimates of ‘generalized parameters’ (that is, estimates which take values in an abstract metric space). After a general introduction, the interest is focussed on three particular topics: 1. (a) Multivariate density estimates: We prove the incompatibility between robustness and consistency. As a consequence, a result of instability for kernel estimates is shown. A robust version of these estimates is also obtained. 2. (b) Estimation of the mean function of stochastic process with continuous trajectories on [0, 1]: The ‘sampling mean’ is proved to be unstable (thus, the situation is analogous to that of the parametric case). A general method for constructing robust estimates is given. 3. (c) Bayesian inference: The posterior distribution is considered as a generalized estimate taking values in the metric space of probability measures. We apply Hampels definition to this estimate and we show its instability under two specific Bayesian models. A discussion of the results is included in the last section.

The 'pure-IP' Moby Dick 4G architecture

Network operators, service providers and customers are players who have different interests and raise different requirements on the functionality of future mobile communication networks. However, some new capabilities, such as mobility, security, ubiquity and quality are spelled out by all, which means that there exist some fundamental mechanisms which are in fact needed in every network. This paper concentrates on critical elements of the network infrastructure which need to be deployed in 4G networks before services can be offered. In the paper we discuss these elements, and show how they can be combined to satisfy versatile service requirements. Furthermore, the paper shows how to combine these mechanisms of three traditionally quite separate architectures-for Authentication, Authorisation, Accounting and Charging (AAAC), for Mobility (Mobile IP with Fast Handover), and Quality-of-Service (QoS). A technology-independent paging concept is also integrated in this system. The resulting integrated system architecture is general and can be deployed in heterogeneous environments. Our implementation has recently been completed, validated and verified with applications such as data transfer, voice-over-IP, video streaming and real time concurrent gaming. This prototypical implementation incorporates TD-CDMA, 802.11 WLANs and Ethernet, and treats all transmission technologies as physical and data-link layers, while higher-level functions are supported in a uniform way with an all-IPv6-based signalling.

Usability and evaluation of a deployed 4G network prototype

This article presents a field evaluation of an IP-based architecture for heterogeneous environments that has been developed under the aegis of the Moby Dick project, covering UMTS-like (universal mobile telecommunications system) TD-CDMA (time division-code division multiple access) wireless access technology, wireless and wired LANs. The architecture treats all transmission capabilities as basic physical and data-link layers, and replaces all higher-level tasks by IP-based strategies. The Moby Dick architecture incorporates mobile IPv6, fast handovers, AAA-control (authentication, authorisation, accounting), charging and quality of service (QoS) in an integrated framework. The architecture further allows for optimised control on the radio link layer resources. It has been implemented and tested by expert users, and evaluated by real users on field trials with multiple services available.

Experimental Results with Forward Erasure Correction and Real Video Streaming in Hybrid Wireless Networks

In a heterogeneous MANET, based on wireless LANs linked together by satellite, the overall channel efficiency is impaired by multiple effects, because of multipath fading in the terrestrial segment and atmospheric fading on the satellite link. In this paper we address this issue by applying forward erasure correction codes (FZC) to MPEG-4 video sequences exchanged by the hosts of a hybrid network, made of a satellite link and a wireless LAN using 802.11b devices. A standard video streaming application runs on one end of the satellite link while, at the other end, a wireless ad hoc network receives the multicast video stream. This work aims at demonstrating the improvement in quality of service (QoS) of the video transmitted in the hybrid network. The main parameters measured are the packet loss, the delivery delay, and the overhead in bandwidth occupancy imposed by the use of FZC. The received video is then evaluated by using a MOS (mean opinion score) procedure

Extensions of AAA for future IP networks

The design of an extended and generic authentication, authorization, accounting, and charging architecture (AAAC Arch.) has been performed within the IST project MobyDick. In addition, this architecture has been implemented to address MobyDicks main objective: to facilitate the deployment of a ubiquitous mobile IPv6-based, quality-of-service (QoS)-aware infrastructure through a flexible and evolutionary AAAC Architecture. While the AAAC Arch. is based on the DIAMETER protocol, basic concepts developed cover session and services models, user profiles to allow for user mobility and QoS-aware authorization. Based on those basic building blocks for the extended AAAC Arch., the implementation of user registration, service authorization, metering, accounting, charging, and auditing is discussed. The paper closes with the presentation of the two trial sites used and their testbeds.

The challenges of IMS deployment at Telefonica Germany

The deployment of the IMS at Telefónica Germany (the third national integrated operator) went successfully live in early 2011. The IMS deployment required significant effort and targeted one of an operators main businesses: telephony. The lessons we learned, the opportunities we saw, and the challenges we had to face are described in this article. Furthermore, the evolution of the IMS in our network is discussed, and we describe, from our experience, some of the benefits and challenges the IMS can bring to an operator.

Cross System Engineering in Next Generation Networks

We present a study on planning and management in 4G networks. The deployment of next generation networks is driven by the proliferation and integration of radio access technologies. This will enable cooperation between access networks based on the reallocation of users across different systems. Inter-system user reallocation will open a new research field: cross system engineering. We break into this ambitious concept with a deep analysis of the impact of inter-system cooperation. The main goal of our study is to measure the cost of serving users that only have CDMA coverage and suffer outage because the cellular system is overloaded. An option to serve these users is to make space for them (in the CDMA network) by reallocating served CDMA users to an overlaid IEEE 802.11-based network. However, this reallocation process has associated costs such as impact on performance and signalling overhead. Thus, care is needed in making space in the cellular network. Our main contribution is the thorough analysis of inter-system user reallocation in 4G networks by simulating different reallocation strategies

Cross-Access Capacity and Performance in B3G Systems

The deployment of next generation networks (NGN) is a high priority for telecommunication operators. Future access networks will be based on a multi-access architecture, in which many independent radio access technologies will collaborate to offer a unified access platform for mobile users. In this scenario, it will be fundamental to control the interactions among the different systems (i.e. networks) in the best possible way. Therefore, it is urgent to develop tools that can assist network engineers in this complex task. This paper presents xCAT (Cross-access Capacity Analysis Tool) a tool that helps in the design and planning of next generation wireless networks. We also include results from a performed analysis focused on two typical situations in future wireless composite access networks: (1) inter-technology user reallocation and (2) network collocation. The experiments assess the impact of these interactions on the overall performance of NGN systems.

Transport resources reservation in IMS frameworks: Terminal vs. PDF driven

IMS is a good candidate to become the service platform for next generation networks (NGN). Among one of its key characteristics is the ability to keep the Internet paradigm of application and transport separation while designing interfaces between the two layers. In IMS there is an interaction between the CSCFs (call session control function), SIP proxies managing the application setup, and the PDF (Policy Decision Function), controlling the transport network. Still, the terminals have to perform the transport resource allocation (activating the PDP context). In future networks, a similar behavior is possible but also another approach can be followed: the PDF is in charge of allocating the transport resources between the terminals, allowing to reinforce the network control. In this paper we analyze and compare both approaches, including by resorting to simulation.