Juan Carlos Guerri

Personalized multimedia touristic services for hybrid broadcast/broadband mobile receivers

This paper presents the topology of a multimedia tourism service that targets mobile devices equipped with broadband and either multicast or broadcast access capabilities. Multicast / Broadcast access is used to handle the delivery of multimedia data to many simultaneous users in the service area. The solution adopted is based on existing standards for mobile TV services, but introducing features that enable the provision of generic multimedia services on top of mobile hybrid broadband and broadcast networks. Furthermore, this paper shows how to use standardized interfaces originally defined for interactive mobile TV broadcasting to build personalized mobile multimedia services that do not deal with TV contents or are not necessarily coupled to a mobile TV service bundle.

Analysis and Evaluation of Adaptive LDPC AL-FEC Codes for Content Download Services

This paper proposes the use of adaptive low density parity check (LDPC) application layer-forward error correction (AL-FEC) codes for content download services over erasure channels. In adaptive LDPC codes, clients inform the content download server of the losses they are experiencing. Using this information, the server makes forward error correction (FEC) parity symbols available to the client at an optimum code rate. This paper presents an analytical model of the proposed adaptive LDPC codes. The model is validated through measurements realized with an application prototype. In addition, results show the performance of these codes in different scenarios, compared to the performance of nonadaptive AL-FEC, optimum LDPC AL-FEC codes, and an almost ideal rateless code. Adaptive LDPC AL-FEC codes achieve download times similar to almost ideal rateless codes with less coding complexity, at the expense of an interaction channel between server and clients.

Feedback Flow Control with Hysteresial Techniques for Multimedia Retrievals

The objective of this paper is to demonstrate the advantages of using hysteresial techniques in flow control mechanisms. The work scenario consists of a server transmitting video information to a group of clients. Each client stores the information in a buffer and then plays it back at a set consumption rate. To avoid “overflow” or “underflow” in the buffer, the client sends control messages (feedbacks) to the server which order adjustments in the transmission rate. Hysteresial techniques allow the minimization of this signaling traffic, even when there are rapid fluctuations in the buffer occupation. As a first step, an analytical model is developed using Markovian processes. This produces expressions of the most relevant parameters and allows the evaluation of the proposed flow control mechanism. The Markovian model has been compared with the performance of a multimedia application for video distribution, running in a real scenario. The results show that the model represents qualitatively the real scenario and consequently validates the model usefulness.

JMFMoD: a new system for media on demand presentations

This article describes the main challenges of implementing a Java media on demand (MoD) system. The objective of this system is to offer a complete solution for creating multimedia presentations (audio, video, text, slides) and their synchronized reproduction on the client side. This system consists of the following elements: an authoring presentation tool, a standalone MoD server application, a Web integrated MoD client, a database containing all the available media presentations, and a proprietary protocol that provides all the functionality of a VCR stream control mechanism. The Java Media Framework library (JMF) and the RTP protocol for audio and video transmission were used as development tools.

A QoS-aware routing protocol with adaptive feedback scheme for video streaming for mobile networks

One of the major challenges for the transmission of time-sensitive data like video over mobile ad-hoc networks (MANETs) is the deployment of an end-to-end QoS support mechanism. Therefore, several approaches and enhancements have been proposed concerning the routing protocols. In this paper we propose a new QoS routing protocol based on AODV (named AQA-AODV), which creates routes according to application QoS requirements. We have introduced link and path available bandwidth estimation mechanisms and an adaptive scheme that can provide feedback to the source node about the current network state, to allow the application to appropriately adjust the transmission rate. In the same way, we propose a route recovery approach into the AQA-AODV protocol, which provides a mechanism to detect the link failures in a route and re-establish the connections taking into account the conditions of QoS that have been established during the previous route discovery phase. The simulation results reveal performance improvements in terms of packet delay, number of link failures and connection setup latency while we make more efficient use of the available bandwidth than other protocols like AODV and QAODV. In terms of video transmission, the obtained results prove that the combined use of AQA-AODV and the scalable video coding provides an efficient platform for supporting rate-adaptive video streaming.

An Adaptive Mechanism for Optimal Content Download in Wireless Networks

This paper presents an adaptive mechanism for improving the content download in wireless environments. The solution is based on the use of the file delivery over unidirectional transport (FLUTE) protocol in multicast networks, which reduce considerably the bandwidth when there are many users interested in the same contents. Specifically, the system proposed reduces the average download time of clients within the coverage area, thus improving the Quality of Experience. To that extent, clients send periodically feedback messages to the server reporting the losses they are experiencing. With this information, the server decides which is the optimum application layer-forward error correction (AL-FEC) code rate that minimizes the average download time, taking into account the channel bandwidth, and starts sending data with that code rate. The system proposed is evaluated in various scenarios, considering different distributions of losses in the coverage area. Results show that the adaptive solution proposed is very suitable in wireless networks with limited bandwidth.

Multimedia group synchronization approach for one-way cluster-to-cluster applications

Nowadays, many multimedia cluster-to-cluster applications exist, such as 3D tele-immersion (3DTI), computer-supported collaborative workspaces (CSCWs), distributed multimedia presentations (DMP)…. All these applications have sophisticated data transport requirements due to the use of multiple, semantically related flows of information. A synchronization mechanism must be used to synchronize the playout of the streams, regardless of the number of receivers and the number of streams played on the receiver clusters. In this paper, we present a new solution for multimedia group synchronization in such applications. Rather than base the solution on the definition of a new synchronization protocol (as other authors do), we base it on small modifications or extensions to RTP/RTCP standard protocols already used in most multimedia applications. Due to this, the overload introduced by the approach is minimal. The suitability of the approach was evaluated in a real one-way cluster-to-cluster application, with satisfactory results.

A closer look at a content delivery network implementation

Success in Internet applications involves user interactions whose quality is mainly affected by the application response time. Content delivery networks (CDNs) have shortly appeared as a distributed solution that serves the content at a faster rate as compared to contacting a centralized server. Their effectiveness of this network have been shown in large companies such as Akamai and Speedera. However, there is currently a certain gap about the implementation issues of this technology, and only the architectural designs and performance reports are published. This article tries to describe a CDN from a different point of view that pays more attention on the implementation process of the CDN.

Evaluation of Background Push Content Download Services to Mobile Devices Over DVB Networks

This paper proposes a multicast content download service based on the use of residual network capacity to push multimedia content to available local storage in personal multimedia devices. The service under study is based on the FLUTE protocol. Specifically, FLUTE packets fill the spare capacity in the IP tunnels reserved for the primary streaming service (opportunistic insertion). The paper also evaluates the use of application layer-forward error correction (AL-FEC) parity to overcome transmission errors, object multiplexing to send the most popular multimedia contents more frequently and cache management policies that consider user preferences to keep in storage the most useful items. The service has been evaluated through simulations and measurements performed with an application prototype based on the DVB-H standards. The results show that AL-FEC enables the use of residual capacity for background content download services. In turn, AL-FEC, as well as object multiplexing, improves the relation between the number of content items and the overall access time. Moreover, results show that high percentages of requests can be served from the local cache of the service, provided that it is possible to estimate the popularity of content items and the user preferences.

A mobile device application applied to low back disorders

Many muscular function assessments require the monitoring of muscular activity in different environments. This can happen in the gymnasium during a training session or while practising a sport; at work, where movements and specific actions are executed; at school, where the child adopts an incorrect posture, or even while we walk. In this paper, we propose a system to allow the assessment of the muscular condition in any of these environments in a comfortable and simple way for the patient and using the advances in wireless communications. Just a wireless biomonitor (we have used the ME6000 biomonitor, a medical portable equipment of very small dimensions) and one PDA or mobile phone with wireless interface are needed. The medical device is configured from the mobile device. Then, wireless communications are used to transmit online the electromyographic signals registered by the medical equipment to a mobile device. The specific protocol used by the medical device is implemented to carry out the communication. There are two ways to configure the system: offline and online. In offline mode, once all the information is received, it is sent to a server using a connection to the Internet instead of the online way, where this information is sent simultaneously. The server includes a background application to process the information in real-time with the aim to evaluate the function of the muscle during the exercise and to establish healthy behaviours for the patient. Then, this information can be consulted by the specialist and also by the client using the PDA or mobile phone to show the report. A prototype of this system has been developed and implemented. The system has been evaluated by a preliminary usability, reliability, feasibility and communication performance study.