Josep Mangues-Bafalluy

Validation of the IEEE 802.11 MAC model in the ns3 simulator using the EXTREME testbed

We validate the IEEE 802.11 MAC layer model in ns3 by means of measurements on the EXTREME testbed. We consider different scenarios: communications within a single pair of nodes, multi-user communications using either VoIP or saturated traffic, and communications in the presence of hidden nodes. For each scenario we describe in detail our testbed and simulation setup, and compare the results provided by the ns3 simulator with the performance measured on the testbed.

EXTREME: combining the ease of management of multi-user experimental facilities and the flexibility of proof of concept testbeds

The experimental testbed for research enabling mobility enhancements (EXTREME) is being developed to allow researchers (i.e. users) of the CTTC to test networking algorithms and technologies in a close-to-real scenario. Basically, EXTREME development focuses on combining the ease of management of multi-user experimental facilities with the flexibility allowed by proof of concept testbeds. Its main goals are: 1) to reduce time from scenario conception by the researcher to the start of the measurements phase, 2) to provide an abstraction of the underlying physical resources to researchers so that they can focus on functionalities rather than low-level configuration issues of the machines, 3) to provide a generic framework to ease the realization and analysis of performance measurements and 4) to allow the rapid adoption and testing of new emerging technologies in a close-to-production environment. The main initial focus of EXTREME is on attaining these goals in wireless environments, which, in general, are more challenging than wired ones. This paper describes its design goals, current status, and some application scenarios where EXTREME has been used

A Survey on Routing Protocols that really Exploit Wireless Mesh Network Features

The design of a routing protocol that really exploits the specific features of a Wireless Mesh Network (WMN) still remains a challenge. The expected additional benefit, with respect to those that do not or cannot exploit them, is an increase in overall throughput supported by the network. The static and non-power constrained nature of backbone nodes allow offering some exploitable features towards this goal, such as multi-radio and multi-channel support, stability, and increased CPU and storage capabilities. Such features have a strong impact on the design of the routing scheme, which makes inefficient to port existing solutions from wired and other wireless networks. As a consequence, in recent years, many alternative routing protocols have been proposed for WMNs. This survey paper presents the current stateof- the-art of routing protocols specifically designed for WMNs that try to maximize the throughput transferred by the network. First, a classification of routing protocols is provided. Second, the routing architecture is decomposed into three major building blocks. Open research issues related to each building block are also discussed. And finally, the main characteristics of the building blocks for each relevant routing protocol in the taxonomy are summarized.

A self-organized Tracking Area List mechanism for large-scale networks of femtocells

In this paper we explore the concept of self-organized location management in large-scale networks of femtocells (NoFs). A NoF is a mesh network that provides multi-hop connectivity amongst femtocells and, in turn, to the Evolved Packet Core. One of the most challenging issues in NoFs is location management, i.e., the process of determining the location of a User Equipment (UE) in the network. Standard 3GPP location management mechanisms are not well suited for large-scale NoFs due to the overhead generated by frequent handovers and cell reselections. In this paper we propose a self-organized Tracking Area List (TAL) mechanism that seamlessly monitors the mobility state of each UE in order to adjust the size of its individual TAL dynamically. Analytical results show that our mechanism reduces location signalling traffic in the cellular network compared to standard 3GPP schemes. In addition, the self-organized TAL mechanism is fully compliant with 3GPP LTE Technical Specifications, which facilitates its implementation in a commercial scenario.

The CTTC 5G End-to-End Experimental Platform : Integrating Heterogeneous Wireless\/Optical Networks, Distributed Cloud, and IoT Devices

The Internet of Things (IoT) will facilitate a wide variety of applications in different domains, such as smart cities, smart grids, industrial automation (Industry 4.0), smart driving, assistance of the elderly, and home automation. Billions of heterogeneous smart devices with different application requirements will be connected to the networks and will generate huge aggregated volumes of data that will be processed in distributed cloud infrastructures. On the other hand, there is also a general trend to deploy functions as software (SW) instances in cloud infrastructures [e.g., network function virtualization (NFV) or mobile edge computing (MEC)]. Thus, the next generation of mobile networks, the fifth-generation (5G), will need not only to develop new radio interfaces or waveforms to cope with the expected traffic growth but also to integrate heterogeneous networks from end to end (E2E) with distributed cloud resources to deliver E2E IoT and mobile services. This article presents the E2E 5G platform that is being developed by the Centre Tecnol?gic de Telecomunicacions de Catalunya (CTTC), the first known platform capable of reproducing such an ambitious scenario.

Impact of transient CSMA/CA access delays on active bandwidth measurements

WLAN devices based on CSMA/CA access schemes have become a fundamental component of network deployments. In such wireless scenarios, traditional networking applications, tools, and protocols, with their built-in measurement techniques, are usually run unchanged. However, their actual interaction with the dynamics of underlying wireless systems is not yet fully understood. A relevant example of such built-in techniques is bandwidth measurement. When considering WLAN environments, various preliminary studies have shown that the application of results obtained in wired setups is not straightforward. Indeed, the contention for medium sharing among multiple users inherent to CSMA/CA access schemes has remarkable consequences on the behavior of and results obtained by bandwidth measurement techniques. In this paper, we focus on evaluating the effect of CSMA/CA-based contention on active bandwidth measurement techniques. As a result, it presents the rate response curve in steady state of a system with both FIFO and CSMA/CA-based contending cross-traffic. We also find out that the distribution of access delay shows a transient regime before reaching a stationary state. The duration of such transient regime is characterized and bounded. We also show how dispersion-based measurements that use a short number of probing packets are biased measurements of the achievable throughput, the origin of this bias lying on the transient detected in the access delay of probing packets. Overall, the results presented in this paper have several consequences that are expected to influence the design of bandwidth measurement tools as well as to better understand the results obtained with them in CSMA/CA links.

Experimental analysis of VoIP call quality support in IEEE 802.11 DCF

In recent years the interest in supporting voice over IP (VoIP) services over wireless local area networks (WLANs) based on IEEE 802.11 standard is growing. A key issue on this topic is to understand how well the 802.11 can support quality of service (QoS) for VoIP services. Recently ITU-T has released the E-model recommendation to evaluate voice quality perceived by users. In this paper we present via experimental trials with commercial equipments, the relationship between the E-model and network metrics like packet, delay, jitter and packet loss in order to find the optimal working point for a WLAN supporting VoIP applications. Result analysis shows how packet loss is the metric with major influence on quality degradation for the considered scenarios. Following these results, we select packet loss ratio (PLR) as the fundamental parameter to determine the voice call quality. Finally, we introduce a procedure to compute PLR in the wireless stations based on parsing the sequence number field in the RTP header.

VoIP Performance in SIP-Based Vertical Handovers Between WLAN and GPRS/UMTS Networks

This paper experimentally analyzes the handover performance of VoIP sessions in a wireless overlay of 802.11 WLANs and GPRS/UMTS networks when mobility is handled at the application layer by SIP. It also assesses the impact of handovers on the VoIP call quality perceived by the user by means of the extended E-model. The study reveals that good performance values are achieved when handing over from GPRS/UMTS to WLAN. Additionally, acceptable quality is obtained for handovers from WLAN towards UMTS. On the other hand, unacceptable values are achieved when moving towards GPRS. The main reason is the delay experienced by SIP messages when traversing the cellular network.

Traffic and Mobility Management in Networks of Femtocells

A deployment of femtocells that is harmonic with its environment is a challenging issue. In this respect, interference management has traditionally been in the spotlight. However, architectural improvements for efficient femtocell deployments, despite being equally relevant, have received less attention. This paper presents a system architecture conceived for efficiently deploying femtocells in the form of Networks of Femtocells (NoFs). In this scenario, a group of femtocells in the same administrative domain cooperate towards a global performance improvement. Key to this improvement is the introduction of a new entity called Local Femto Gateway (LFGW) and the modifications in the femtocells in the local network. This allows offloading a high volume of control and data traffic from the core network of the mobile operator to the functional entities in the NoF. In particular, this paper focuses on building blocks related to traffic and mobility management. A two-level routing approach is discussed. The highest level is carried out by the mobile network layer. It is in charge of (1) determining the communication endpoints in the form of GPRS Tunneling Protocol (GTP) tunnel endpoint IDs, and (2) forwarding packets between tunnels belonging to the same Evolved Packet System (EPS) bearer at the appropriate nodes. Solutions for efficient handoff, local breakout, and local location management are presented for this level of routing. On the other hand, the lowest-level routing is carried out by the transport network layer. This level is in charge of finding the path between the above endpoints by efficiently using the local transport network that interconnects the femtocells in the NoF. A distributed routing solution for a large-scale, all-wireless network of femtocells is also presented. Overall, these architectural improvements render NoFs a promising approach for efficient traffic management in large-scale femtocell deployments, hence making them a scalable solution.

Monitoring wireless networks: performance assessment of sniffer architectures

This paper assesses the performance of wireless sniffers built using off-the-shelf hardware and software. Such an analysis tool is commonly found in wireless testbeds given its low cost. The goal of this study is to provide a framework to assess the performance of measurements obtained using this popular tool. Among various contributions, the study shows the importance of precisely checking the behavior of the hardware used for communications and for monitoring in order to validate the traces obtained. It also presents a methodology to assess the performance of wireless sniffers based on obtaining a correlation factor between traces captured by independent devices. The paper reveals, in addition, a new type of loss in sniffer captures, the saturation loss, that completes previous work on this topic. Finally, the paper also studies the behavior of architectures using several sniffers in a single computer. It reveals how, again in this case, the hardware chosen is critical to obtain desired performance.