Rute C. Sofia

User-provided networks: consumer as provider

This article describes and characterizes an emerging type of user-centric wireless network model, here named a user-provided network, where the end user is at the same time a consumer and a provider of Internet access. A discussion of challenges these new models face is also provided.

A Cross-Layer Fast Handover Scheme For Mobile WiMAX

The Mobile WiMAX standard (IEEE 802.16e-2005) brings wireless broadband to a new level due to the support of nomadism. Still, handover latency in Mobile WiMAX is an issue that may affect real-time continuity of application sessions. This is partially due to the Layer 2 scanning/ranging, as well as the network re-entry procedure, which may result in a latency of hundreds of milliseconds, far exceeding the requirement of typical real-time services (e.g., 150 ms for Voice over IP). In this paper, we describe a mechanism which incorporates information from several OSI Layers to speed up the Layer 2 handover. We show by means of simulations that this new mechanism can decrease the handover latency significantly, to less than 100 ms in most cases.

Dynamic and User-Centric Network Selection in Heterogeneous Networks

The use of multiple interfaces to access heterogeneous networks is becoming a strong reality to end-users. Hence one realistic problem is how to select a specific access interface (and consequently network) as well as how to perform smooth and seamless handover among different types of technologies. In this paper we propose a dynamic and user-centric network selection and decision process which optimizes handover across heterogeneous networks. A satisfaction degree function (SDF) is used to evaluate, according to users predefined criteria, available networks and select the best one(s) according to such criteria. The criteria consider incorporating user policies and information from several OSI layers, including dynamic network status and application requirements. Numerical results show that the proposed network selection process results in the choice of the best network according to the users choices.

A survey of advanced ethernet forwarding approaches

The higher transmission rates currently supported by Ethernet lead to the possibility of expanding Ethernet beyond the local area network scope, bringing it into the core of large scale networks, of which a metropolitan area network (MAN) is a significant example. However, originally Ethernet was not devised to scale in such environments: its design does not contemplate essential requirements of larger and more complex networks, such as the need for resilience, scalability, or even integrated control features. Furthermore, its spanning-tree based forwarding results in slow convergence and weak resource efficiency. Specifically focusing on Ethernets forwarding behaviour, this survey covers solutions that enhance the Ethernets path computation, allowing it to scale in larger, more complex environments. General notions concerning the application of Ethernet in Metro areas are also provided, as a specific example of Ethernets application in large scale networks.

Always acyclic distributed path computation

Distributed routing algorithms may give rise to transient loops during path recomputation, which can pose significant stability problems in high-speed networks. We present a new algorithm, Distributed Path Computation with Intermediate Variables (DIV), which can be combined with any distributed routing algorithm to guarantee that the directed graph induced by the routing decisions remains acyclic at all times. The key contribution of DIV, besides its ability to operate with any routing algorithm, is an update mechanism using simple message exchanges between neighboring nodes that guarantees loop-freedom at all times. DIV provably outperforms existing loop-prevention algorithms in several key metrics such as frequency of synchronous updates and the ability to maintain paths during transitions. Simulation results quantifying these gains in the context of shortest path routing are presented. In addition, DIVs universal applicability is illustrated by studying its use with a routing that operates according to a nonshortest path objective. Specifically, the routing seeks robustness against failures by maximizing the number of next-hops available at each node for each destination.

Moving towards a socially-driven internet architectural design

This paper provides an interdisciplinary perspective concerning the role of prosumers on future Internet design based on the current trend of Internet user empowerment. The paper debates the prosumer role, and addresses models to develop a symmetric Internet architecture and supply-chain based on the integration of social capital aspects. It has as goal to ignite the discussion concerning a socially-driven Internet architectural design.

A characterization of mobility management in user-centric networks

Mobility management is a key aspect to consider in future Internet architectures, as these architectures include a highly nomadic end-user which often relies on services provided by multi-access networks. In contrast, todays mobility management solutions were designed having in mind simpler scenarios and requirements from the network and where roaming could often be taken care of with previously established agreements.With a more dynamic behavior in the network, and also with a more prominent role from the end-user, mobility management has to deal with additional requirements derived from new Internet paradigms. To assist in understanding such requirements and also how to deal with them, this paper proposes a starting point to dismantle current mobility management notions. Our contribution is an initial proposal on defining mobility management in concrete functional blocks, their interaction, as well as a potential grouping which later can assist in deriving novel and more flexible mobility management architectures.

A Discussion on Developing Multihop Routing Metrics Sensitive to Node Mobility

This paper is focused on a discussion of parameters and heuristics that are expected to assist multihop routing in becoming more sensitive to node mobility. We provide a discussion concerning existing and a few proposed parameters. Moreover, the work also discusses two new heuristics based on the notion of link duration. The heuristics are compared based on a meaningful set of scenarios that attain different mobility aspects.

Distributed path computation without transient loops: an intermediate variables approach

Paths with loops, even transient ones, pose significant stability problems in networks. As a result, much effort has been devoted over the past thirty years to designing distributed algorithms capable of avoiding loops. We present a new algorithm, Distributed Path Computation with Intermediate Variables (DIV), that guarantees that no loops, transient or steady-state, can ever form. DIVs novelty is in that it is not restricted to shortest paths, can easily handle arbitrary sequences of changes and updates, and provably outperforms earlier approaches in several key metrics. In addition, when used with distance-vector style path computation algorithms, DIV also prevents counting-to-infinity; hence further improving convergence. The paper introduces DIV and its key properties. Simulation quantifying its performance gains are also presented.

An investigation of inter-domain control aggregation procedures

Current quality of service models such as those embodied in the differentiated services proposal, rely on data path aggregation to achieve scalability. Data path aggregation bundles into a single aggregate multiple flows with the same quality requirements, hence decreasing the amount of state to be kept. A similar scalability concern exists on the control path, where the state required to account for individual reservations needs to be minimized. There have been several proposals aimed at control path aggregation, and the goal of the paper is to expand on these works in an attempt to gain a better understanding of the various parameters that influence the efficiency of different approaches. In particular, we focus on inter-domain control aggregation, and compare an autonomous system (AS) sink-tree based approach with two examples of a shared AS segment based approach, in terms of the amount of state kept, both per AS and per edge router Our main contributions are in providing a greater understanding into the design of efficient control path aggregation methods.