Encarna Pastor

A virtualized platform for analyzing LTE broadcast services

Nowadays, users are demanding access to video content anytime and anywhere. LTE broadcast services and video streaming services can reduce the resources used by telecommunication companies to give access to video content and open up new business opportunities. In this context, testbeds and simulation tools can help in the analysis of the different parameters that need to be considered in the deployment of video services based on LTE. In this paper, we describe the design and implementation of an open-source virtualized platform that supports both LTE broadcast services and video streaming services. The testbed is being used both over real LTE networks and LTE network emulations to analyze the performance of video streaming services and to validate new proposals.

A model to evaluate MBSFN and AL-FEC techniques in a multicast video streaming service

In a multicast video streaming service over a cellular network, the same content is sent to a mass audience using a common channel. However, users belonging to the same multicast channel perceive different characteristics of the radio channel. Moreover, in wireless environments, the radio interface introduces an important level of interference and noise, resulting in a high rate of transmission errors. Therefore, a protection of the information is needed at each receiver using Forward Error Correction (FEC) schemes, which allow the recovery of the lost packets sending redundancy together with the payload. FEC solutions can be used in combination with other techniques to overcome the existing limitations of the mobile network, in particular, the use of a single-frequency network to prevent the effect of destructive signal interference. This paper analyzes the performance of a video streaming service comparing different FEC schemes, Raptor and RaptorQ codes, where some system parameters can be tuned in a single-frecuency network.

Reducing Latency for Multimedia Broadcast Services Over Mobile Networks

Multimedia services over mobile networks pose several challenges, such as the efficient management of radio resources or the latency induced by network delays and buffering requirements on the multimedia players. In Long Term Evolution (LTE) networks, the definition of multimedia broadcast services over a common radio channel addresses the shortage of radio resources but introduces the problem of network error recovery. In order to address network errors on LTE multimedia broadcast services, the current standards propose the combined use of forward error correction and unicast recovery techniques at the application level. This paper shows how to efficiently synchronize the broadcasting server and the multimedia players and how to reduce service latency by limiting the multimedia player buffer length. This is accomplished by analyzing the relation between the different parameters of the LTE multimedia broadcast service, the multimedia player buffer length, and service interruptions. A case study is simulated to confirm how the quality of the multimedia service is improved by applying our proposals.

Analysis of the impact of FEC techniques on a multicast video streaming service over LTE

In a multicast video streaming service the same multimedia content is sent to a mass audience using only one multicast stream. In multicast video streaming over a cellular network, due to the nature of the multicast communication, from a source to multiple recipients, and due to the characteristics of the radio channel, different for each receiver, transmission errors are addressed at the application level by using Forward Error Correction (FEC) techniques. However, in order to protect the communication over the radio channel, FEC techniques are also applied at the physical layer. Another important technique to improve the communication of the radio channel is the use of a single-frequency network. This paper analyzes the performance of a video streaming service over a cellular network taking into account the combined impact of different factors that affect the transmission, both the physical deployment of the service and the two levels of FEC.

New strategies for learning computer networks

This paper describes experiences in computer networking education with a large number of students based on two kinds of learning activities: personalized exercises and hands-on experiments using virtualization tools. Using an example of each kind of activity the paper explains the process of creating the activity, the software tools that have been developed to support them in the context of a Learning Management System and the impact of the activities in the learning process.

Using multimedia communication technologies in distance learning

This paper describes pilot experiences of distance learning using videoconference over the public Integrated Services Digital Network (ISDN). Graduate and postgraduate courses of the Technical University of Madrid (Telecommunication Engineers) form the educational scenario chosen for the experiences. Several phases were defined to carry out the experiments, each one centred around different students/subjects profiles. The first phase has been recently finished and it has been evaluated with interesting results from a pedagogical point of view. Organisational, technical and economical aspects has also been evaluated with the aim of extending these experiences to a larger scale.

Seamless Mobile Multimedia Broadcasting Using Adaptive Error Recovery

Multimedia services over mobile networks present several challenges, such as ensuring a reliable delivery of multimedia content, avoiding undesired service disruptions, or reducing service latency. HTTP adaptive streaming addresses these problems for multimedia unicast services, but it is not efficient from the point of view of radio resource consumption. In Long-Term Evolution (LTE) networks, multimedia broadcast services are provided over a common radio channel using a combination of forward error correction and unicast error recovery techniques at the application level. This paper discusses how to avoid service disruptions and reduce service latency for LTE multimedia broadcast services by adding dynamic adaptation capabilities to the unicast error recovery process. The proposed solution provides a seamless mobile multimedia broadcasting without compromising the quality of the service perceived by the users.

QoE-Based Analysis of DASH Streaming Parameters Over Mobile Broadcast Networks

Multimedia services over mobile networks are subject to multiple factors that affect the quality of experience (QoE) perceived by users. In a long term evolution (LTE) multimedia broadcast service, these factors are initial delay, technical quality of multimedia content, and service disruptions. However, there is a lack of QoE models to enable QoE measurement. We propose to use video mean opinion score as a new and objective QoE model that is in the process of standardization, and we show how it can be applied to LTE multimedia broadcast services for QoE assessment. The results obtained are useful to better understand the impact of several service parameters on perceived quality. By applying this assessment methodology, it is possible to determine the most adequate service parameters for a specific LTE broadcast deployment.

A Collaborative Environment Integration Layer for Activity Orientation

This paper proposes the creation of an architectural layer for integration of all the resources and members participating in a given collaborative activity into a unified framework which is referred as the collaborative environment integration layer (CEIL). This layer is considered a necessary step for integrating with open standards all the collaborative resources or components into a tightly coupled collaborative environment which implements activity orientation. The proposal considers two architectural elements. The first element is the collaborative environment description language (CEDL), which is the formal language for describing all the elements and associated parameters relevant for modeling and managing a collaborative environment. The second one is the collaborative environment management interface (CEMI), which is the unified interface which provides uniform management and configuration of the collaborative components of an environment. This layer includes accurate descriptions of the virtual organizations associated to collaborative activity, including participants, roles, rights, hierarchies, etc being able to model the variety of existing virtual organization models

DASH Adaptation Algorithm Based on Adaptive Forgetting Factor Estimation

The wide adoption of multimedia service-capable mobile devices, the availability of better networks with higher bandwidths, and the availability of platforms offering digital content has led to an increasing popularity of multimedia streaming services. However, multimedia streaming services can be subject to different factors that affect the quality perceived by the users, such as service interruptions or quality oscillations due to changing network conditions, particularly in mobile networks. Dynamic Adaptive Streaming over HTTP (DASH), leverages the use of content-distribution networks and the capabilities of the multimedia devices to allow multimedia players to dynamically adapt the quality of the media streaming to the available bandwidth and the device characteristics. While many elements of DASH are standardized, the algorithms providing the dynamic adaptation of the streaming are not. The adaptation is often based on the estimation of the throughput or a buffer control mechanism. In this paper, we present a new throughput estimation adaptation algorithm based on a statistical method named Adaptive Forgetting Factor (AFF). Using this method, the adaptation logic is able to react appropriately to the different conditions of different types of networks. A set of experiments with different traffic profiles show that the proposed algorithm improves video quality performance in both wired and wireless environments.