Manuel Ricardo

Cross-layer design in 4G wireless terminals

The classical TCP/IP layered protocol archi- tecture is beginning to show signs of age. In order to cope with problems such as the poor performance of wireless links and mobile termi- nals, including the high error rate of wireless network interfaces, power saving requirements, quality of service, and an increasingly dynamic network environment, a protocol architecture that considers cross-layer interactions seems to be required. This article describes a framework for further enhancements of the traditional IP- based protocol stack to meet current and future requirements. Known problems associated with the strictly layered protocol architecture are summarized and classified, and a first solution involving cross-layer design is proposed.

FlowMonitor: a network monitoring framework for the network simulator 3 (NS-3)

When networking researchers meet the task of doing simulations, there is always a need to evaluate the value of such models by measuring a set of well known network performance metrics. However, simulators in general and NS-3 in particular, require significant programming effort from the researcher in order to collect those metrics. This paper reports a contribution for NS-3 consisting of a new flow monitoring module that makes it easier to collect and save to persistent storage a common set of network performance metrics. The module automatically detects all flows passing through the network and stores in a file most of the metrics that a researcher might need to analyze about the flow, such as bitrates, duration, delays, packet sizes, and packet loss ratio. The value of this module is demonstrated using an easy to follow example. It is also validated by comparing the measurements of a simple scenario with the expected values. Finally, the performance of flow monitoring is characterized and shown to introduce small overheads.

XCP for shared-access multi-rate media

The eXplicit Control Protocol (XCP) was developed to overcome some of the limitations of TCP, such as low utilization in high bandwidth delay product networks, unstable throughput, large queue build-up, and limited fairness. XCP, however, requires that each queue controller in a path knows the exact capacity of its link. In shared access media, e.g. IEEE 802.11, knowing the actual capacity of the channel is a difficult task.In this paper we propose modifications to the XCP algorithm that enable the utilization of XCP even when the capacity of a link is unknown. These modifications are validated through simulation.We also present the results of a comparison between the performance of the modified XCP and TCP, where XCP controlled flows result more stable, fairness increases, and the network delay becomes lower. In addition, as the bandwidth delay product increases, XCP is able to maintain near-maximum utilization while TCP decreases utilization.

A fast algorithm for computing minimum routing cost spanning trees

Communication networks have been developed based on two networking approaches: bridging and routing. The convergence to an all-Ethernet paradigm in Personal and Local Area Networks and the increasing heterogeneity found in these networks emphasizes the current and future applicability of bridging. When bridging is used, a single active spanning tree needs to be defined. A Minimum Routing Cost Tree is known to be the optimal spanning tree if the probability of communication between any pair of network nodes is the same. Given that its computation is a NP-hard problem, approximation algorithms have been proposed. We propose a new approximation Minimum Routing Cost Tree algorithm. Our algorithm has time complexity lower than the fastest known approximation algorithm and provides a spanning tree with the same routing cost in practice. In addition, it represents a better solution than the current spanning tree algorithm used in bridged networks.

Fast prototyping of network protocols through ns-3 simulation model reuse

Abstract In the networking research and development field, one recurring problem faced is the duplication of effort to write first simulation and then implementation code. We posit an alternative development process that takes advantage of the built in network emulation features of Network Simulator 3 (ns-3) and allows developers to share most code between simulation and implementation of a protocol. Tests show that ns-3 can handle a data plane processing large packets, but has difficulties with small packets. When using ns-3 for implementing the control plane of a protocol, we found that ns-3 can even outperform a dedicated implementation.

Dynamic and automatic interworking between personal area networks using composition

Next generation communication networks will be characterized by the coexistence of multiple technologies and user devices in an integrated fashion. The increasing number of devices owned by a single user will lead to a new communication paradigm: users owning multiple devices that form cooperative networks, and networks of different users that communicate with each other, e.g., acquiring Internet access through each other. In this communication scenario no user intervention should be required and technology should seamlessly adapt to the users context, preferences, and needs. In this paper we address one of those scenarios, interworking between personal area networks, using legacy technologies and the Ambient Network and network composition concepts, herein explained. We argue that new functionalities should be introduced to enable effortless use of legacy technologies in such dynamic and heterogeneous environments

Monitoring emerging IPv6 wireless access networks

Foreseeing a future where IPv6 and mobile terminals play an important role in public access communication networks, this article introduces a monitoring system capable of identifying relevant traffic flows and tracking them while terminal equipment moves between network attachment points. The mobile flows are characterized and represented so that individual users and flows can perceive the quality of service they receive, and operators can have global traffic views of their heterogeneous access networks.

Explicit Congestion Control Algorithms for Time Varying Capacity Media

Explicit congestion control (XCC) is emerging as one potential solution for overcoming limitations inherent to the current TCP algorithm, characterized by unstable throughput, high queuing delay, RTT-limited fairness, and a static dynamic range that does not scale well to high bandwidth delay product networks. In XCC, routers provide multibit feedback to sources, which, in turn, adapt throughput more accurately to the path bandwidth with potentially faster convergence times. Such systems, however, require precise knowledge of link capacity for efficient operation. In the presence of variable-capacity media, e.g., 802.11, such information is not entirely obvious or may be difficult to extract. We explore three possible algorithms for XCC which retain efficiency under such conditions by inferring available bandwidth from queue dynamics and test them through simulations with two relevant XCC protocols: XCP and RCP. Additionally, preliminary results from an experimental implementation based on XCP are presented. Finally, we compare our proposals with TCP and show how such algorithms outperform it in terms of efficiency, stability, queuing delay, and flow-rate fairness.

Support of IP QoS over UMTS networks

The paper presents an end-to-end quality of service (QoS) architecture suitable for IP communications scenarios that include UMTS access networks. The rationale for the architecture is justified and its main features are described, notably the QoS management functions on the terminal equipment, the mapping between IP and UMTS QoS parameters and the negotiation of these parameters.

End-to-end delay estimation using RPL metrics in WSN

Critical monitoring applications can use wireless sensor networks to transport delay sensitive data. This data may demand bounded delays in order to be considered useful by the receiver. In these cases, an accurate and real-time estimation of the end-to-end delay could be used to anticipate the data usefulness prior to sending it. A novel real-time and end-to-end delay estimation mechanism is proposed in this paper, which considers processing times and two new RPL metrics. Results show that our proposal is more accurate than the ETT-based solution for delay estimation, and it does not significantly degrade the network performance.