Dimitrios Loukatos

On the energy requirements of vertical handover operations: Measurement-based results for the IEEE 802.21 framework

The availability of multiple collocated wireless networks and the multi-radio capabilities of contemporary wireless terminals open the potential for optimized wireless connectivity over the heterogeneous wireless environment. Vertical Handover (VHO) operations play a central role in such a setting, enabling the dynamic association of wireless users with the most appropriate wireless networks among those available, towards improved effectiveness according to a host of relevant criteria. At the same time, the efficiency of executing the VHO operations themselves is also a factor affecting the overall system effectiveness. Although several aspects of VHO operations have been investigated in the literature, energy efficiency has not received so much attention yet. Towards closing this gap, the paper investigates the energy requirements associated with the execution of the VHO, by expressing the relevant operations as a sequence of elementary actions and determining the energy expenditure at the involved mobile node for each such action. The results address VHO operations compliant to the widely accepted IEEE 802.21 framework and were obtained through actual measurements taken on a prototype heterogeneous network testbed, employing Linux-powered mobile devices and making use of the Advanced Configuration and Power Interface (ACPI) subsystem for taking energy consumption measurements on them.

An efficient ATM traffic generator for the real-time production of a large class of complex traffic profiles

This paper presents an advanced architecture for a traffic generator capable of producing ATM traffic streams according to fully general semi-Markovian stochastic models. The architecture employs a basic traffic generator platform and enhances it by adding facilities for “driving” the cell generation process through high-level specifications. Several kinds of optimization are employed for enhancing the softwares speed to match the hardwares potential and for ensuring that traffic streams corresponding to models with a wide range of parameters can be generated efficiently and reliably. The proposed traffic generation procedure is highly modular. Thus, although this paper deals with ATM traffic, the main elements of the architecture can be used equally well for generating traffic loads on other networking technologies, IP-based networks being a notable example.

Extending an Open MPEG-4 Video Streaming Platform to Exploit a Differentiated Services Network

This paper describes extensions implemented on the MPEG4IP streaming platform, to exploit Differentiated Services. These extensions are based on concepts of proposed QoS frameworks and are implemented by exploiting platform communication capabilities. Within this context, a Packet-marking layer component is introduced performing packet Type of Service (ToS) marking. In the case of live streams, semantics are captured in real-time during encoding, and propagated to the transmission layer. In the case of preencoded streams, information about the semantics is included in the media file metadata and provided as hints to the streaming server. Furthermore, a Video Quality Study component enables the user to preview loss effects on a video stream before its transmission, by simulating packet losses during encoding. In this way new video quality metrics and packet marking algorithms can be investigated. The applicability of certain QoS policies on the extended platform is experimentally evaluated over a Differentiated Services testbed.

A versatile timing unit for traffic shaping, policing and charging in packet-switched networks

Timing has a key role in several traffic control functions encountered in modern packet-switched networks. In order to be effective, a timing unit must provide fine resolution, be simple to implement and scale well with the number of controlled traffic streams. This paper addresses the design, implementation and evaluation of a timing unit that can support accurate and efficient implementations of traffic shaping, policing and charging in packet-switched networks. The timing unit is implemented in hardware and, therefore, overcomes constraints associated with software-based timers. It accommodates a pool of independently-clocked timers and counters, organised in timing blocks, and, consequently, is able to support, in parallel, traffic streams with diverse timing requirements. The design supports shaping and policing through token buckets, leaky buckets and a scheme, variation of the token bucket, that aims at providing statistical quality of service guarantees by exploiting the effective rate concept. Charging is supported by dedicated counters that measure the utilization of the effective rate. The granularity of the timing unit is adjustable in run-time to adapt to changes in the rate parameters of the shaping and policing functions. The validation of the timing unit is done through the development of a prototype board consisting of programmable hardware and embedded software blocks. The temporal resolution of the timing unit and the advantages of the hardware/software co-design are experimentally evaluated.

Tools and Practices for Measurement-based Network Performance Evaluation

As networks and applications running on them become more complex, there is a need for an efficient framework supporting experimental performance evaluation based on real measurements. Towards this end, this paper presents: a) an advanced architecture for a traffic generation tool capable of producing complex traffic profiles, b) the architecture of a traffic analysis tool, and c) methods that allow for efficient monitoring and measurements of delay and loss-oriented metrics in packet networks. The effectiveness of these tools and the applicability of the measurement methodology are illustrated through experiments that evaluate the performance of vertical handovers between GPRS and WLAN networks.

A Network-Driven Architecture for the Multicast Delivery of Layered Video and a Comparative Study

Multicast multimedia distribution, despite the benefits it offers, features a number of unresolved issues, such as network and users heterogeneity. Layered stream organization has been considered as suitable to cope with these issues. In this paper we, initially, study proposed mechanisms for the multicast delivery of layered video streams, highlighting their principles and functionality. Most of them are suited for Best Effort networks, resulting in increased application complexity or sub-optimal performance. Based on the assumption that Quality of Service (QoS) will be probably deployed to the future Internet, we propose a simple, network-based architecture for the multicast delivery of layered video streams. The Differentiated Services (DiffServ) framework and content-aware packet marking are exploited in this architecture. We discuss, how the application defines priority layers within the video stream, while DiffSery copes with layer-aware packet dropping. Each video stream is delivered to a single multicast group and no application-level complexity is required. During congestion in nodes of the multicast tree, packets corresponding to lower priority layers are dropped first, thus protecting the most valuable video stream entities. Protocol extensions for coping with user heterogeneity and the problem of congestion from undelivered packets are also proposed. Finally, a qualitative comparison of all the aforementioned schemes is attempted.

Energy requirements of secure vertical handover operations in the 802.21a framework

IEEE 802.21 is a widely accepted standard providing a media-independent framework and services for enabling seamless handovers among heterogeneous wireless environments. The IEEE 802.21a standard complemented the original specification in an important direction, namely the provision of security mechanisms for handover-related signaling messages and services. However, although the new standard gives a detailed description of the incorporated security mechanisms and of the relevant changes to the structure of the signaling messages, it does not discuss the pros and cons of each security method, with respect to their energy efficiency. This work attempts to fill this gap, by providing simple yet descriptive analytical expressions for calculating the additional energy expended in mobile devices under handover due to the 802.21a security enhancements. These expressions are validated through measurements on a prototype heterogeneous network testbed. The results provide useful hints when choosing the appropriate protection method in devices with tight energy constraints.

An Open Framework for Propagating Qos Requirements of MPEG-4 Video Streams Over a Differentiated Services Network

In this paper, an open framework for implementing Quality of Service (QoS) mechanisms for qualitative guarantees, based on the semantics of MPEG-4 video streams, is introduced. The core of this framework is the open-source platform MPEG4IP, developed by Cisco, for streaming MPEG-4 audio/video streams over IP networks. This platform does not include explicit QoS mechanisms, and therefore certain extensions are studied and implemented providing the means to propagate QoS requirements of video streams over the network. These extensions concern both real-time encoded, and pre-encoded MPEG-4 video streams. The applicability of certain QoS policies based on theseQoS application extensions was experimentally evaluated over a laboratory-based Differentiated Services testbed.