George Xylomenos - Academia.edu (original) (raw)

Papers by George Xylomenos

This article provides an overview of the multimedia broadcast/multicast service (MBMS) for univer... more This article provides an overview of the multimedia broadcast/multicast service (MBMS) for universal mobile telecommunications system (UMTS) networks. We first outline the features of UMTS networks as defined by the 3rd generation partnership project (3GPP) in order to provide a background for the discussion to follow. We then present the overall MBMS architecture, the services that it provides to the users and the differences between the broadcast and multicast options. The implementation details of MBMS are explained in terms of the modifications needed to the network, the new signaling procedures required and the impact of MBMS on the radio part of the network. We then describe how the security architecture of UMTS is used to support content protection and key distribution for MBMS groups. We evaluate the prospects of MBMS by comparing it first with IP multicast and then with DVB-H, considered by many to be the closest competitor of MBMS. Finally, we conclude with a discussion of the technical and business challenges still faced by MBMS.

Wireless Communications and Mobile Computing, 2008

Abstract A considerable body of evidence indicates that the use of reliable link layer protocols ... more Abstract A considerable body of evidence indicates that the use of reliable link layer protocols over error prone wireless links dramatically improves the performance of Internet protocols and applications. While traditional link layer protocols set their timeout values assuming that they fully control the underlying link, some wireless networks allow multiple link layer sessions to co-exist over the same link.

Abstract. Information-Centric Networking (ICN) has increasingly been attracting attention by the ... more Abstract. Information-Centric Networking (ICN) has increasingly been attracting attention by the research community. In ICN the center of attention becomes the information itself and not the endpoints as in today's IP networks. In this demonstration we present applications that we developed as proof of concepts for our ICN approach. A video streaming as well as a voice and a HTTP over publish/subscribe application that run on top of our ICN prototype will be demonstrated running in an international testbed.

Abstract—In this paper we explain how efficient delivery of real-time information can be supporte... more Abstract—In this paper we explain how efficient delivery of real-time information can be supported in the Publish Subscribe Internet (PSI), a network architecture proposal for the Future Internet. PSI departs from IP thinking with respect to the core abstractions made and the functional organization of the system. PSI places information at the heart of the network layer and decouples the forwarding, path formation and topology management functionalities.

Information-centric networking (ICN) is a paradigm that aims to better reflect current Internet u... more Information-centric networking (ICN) is a paradigm that aims to better reflect current Internet usage patterns by focusing on information, rather than on hosts. One of the most critical ICN functionalities is the efficient resolution/location of information objects ie, name resolution. The vast size of the information object namespace calls for a highly scalable and efficient name resolution approach.

Abstract The Internet is straining to meet demands that its design never anticipated, such as sup... more Abstract The Internet is straining to meet demands that its design never anticipated, such as supporting billions of mobile devices and transporting huge amounts of multimedia content. The publish-subscribe Internet (PSI) architecture, a clean slate information-centric networking approach to the future Internet, was designed to satisfy the current and emerging user demands for pervasive content delivery, which the Internet can no longer handle.

Abstract In this paper, we focus on the bootstrap operation of a publish/subscribe information ce... more Abstract In this paper, we focus on the bootstrap operation of a publish/subscribe information centric network. We consider a set of interconnected network nodes and describe how they organize themselves into a fully functional network by publishing and subscribing to control plane information. Network bootstrap includes establishing point-to-point communication between network elements, exchanging topological information and setting up the rendezvous system.

Overlay networks are widely used for locating and disseminating information, by means of custom r... more Overlay networks are widely used for locating and disseminating information, by means of custom routing and forwarding on top of the underlying network. Distributed Hash DHT) based overlays provide flexibility coupled with good scalability and load balancing properties. However, this comes at the cost of inefficient routing, caused by the lack of adaptation to the underlying network: current DHT designs often overlook physical network proximity, administrative boundaries and inter-domain routing policies, or a combination thereof. In this paper we show how to construct a DHT-based overlay network that takes all these aspects into account. Based on the Pastry distributed object location and routing substrate and the Canon paradigm, we developed H-Pastry, an overlay DHT scheme that harvests the scalability and load balancing features of flat DHT designs, while also adapting to the underlying network topology, administrative structure and routing policies. We evaluate the performance characteristics of the proposed scheme through an extensive set of detailed simulations over realistic inter-network topologies. Our results show that H-Pastry substantially improves routing by reducing both overlay path stretch (by up to 50%) and routing policy violations (by up to 67%), compared to the canonical Chord DHT. In addition, the canonical design of H-Pastry keeps traffic within administrative boundaries as far as possible, while also creating excellent opportunities for the support of caching and multicast.

Abstract In this paper we focus on the issue of transferring diverse kinds of information through... more Abstract In this paper we focus on the issue of transferring diverse kinds of information through information-centric networks (ICNs). We argue that the one request per packet mode of operation suggested in the early development of ICN applications is not a good fit for some types of traffic, such as media streams and real-time notifications. To efficiently deliver all kinds of information, we argue that an ICN should not only identify information by its name, it should also be aware of the nature of its traffic.

2013 International Conference on Computing, Networking and Communications (ICNC), 2013

20th International Conference on Advanced Information Networking and Applications - Volume 1 (AINA'06), 2006

A considerable body of evidence indicates that the use of reliable link layer protocols over erro... more A considerable body of evidence indicates that the use of reliable link layer protocols over error prone wireless links dramatically improves the performance of Internet protocols and applications. While traditional link layer protocols set their timeout values assuming that they fully control the underlying link, some wireless networks allow multiple link layer sessions to co-exist over the same link. Since the optimal timeout values for a reliable link layer protocol depend on the available bandwidth, with dynamic link sharing such a protocol should ideally adapt its timeout values accordingly. We have thus designed an Adaptive Selective Repeat protocol that modifies its timeout values based on the policy used by TCP. We compare the performance of Web Browsing over Selective Repeat when using our adaptive timeout scheme with a range of parameters, against a manually tuned fixed timeout version. Our measurements show that these adaptive timeout policies outperform the fixed one, regardless of the level of contention, and that the best adaptive timeout policy in this setting is not the one used by TCP.

Proceedings of the ACM SIGCOMM workshop on Information-centric networking - ICN '11, 2011

In this paper we focus on the issue of transferring diverse kinds of information through informat... more In this paper we focus on the issue of transferring diverse kinds of information through information-centric networks (ICNs). We argue that the one request per packet mode of operation suggested in the early development of ICN applications is not a good fit for some types of traffic, such as media streams and real-time notifications. To efficiently deliver all kinds of information, we argue that an ICN should not only identify information by its name, it should also be aware of the nature of its traffic. We classify information traffic types based on two characteristics: a) reliable vs. unreliable transfer and b) real-time vs. on-demand delivery. The combination of these two characteristics leads to three broad categories: a) channels, b) on-demand documents and c) real-time documents. To handle all traffic types, we propose two extensions to the CCN architecture: Persistent Interests and Reliable Notifications. We describe how these additions, together with a careful selection of information names, can efficiently support these three categories of information traffic types.

The Radio Link Control (RLC) protocol, used in Universal Mobile Telecommunication System (UMTS) n... more The Radio Link Control (RLC) protocol, used in
Universal Mobile Telecommunication System (UMTS) networks,
is one of the most advanced and complex link layer protocols.
Among its notable features are the absence of retransmission
timers, which makes it tolerant to contention for the link, and
the ability to abandon persistently lost frames, which makes it
suitable for reliable transport layers. In order to assess whether it
makes sense to use RLC with non-UMTS wireless links, especially
in the face of the enhanced error recovery offered by TCP with
the Selective Acknowledgment (SACK) option, we implemented
it in the ns-2 simulator and measured the throughput achieved
by File Transfer and Web Browsing over RLC, either with or
without contention from a Media Distribution application. While
we found that RLC adapts well to the available bandwidth,
providing considerable performance gains with random losses,
with bursty losses RLC hardly improved upon TCP SACK.

The error prone nature of wireless links often necessitates the use of a link layer protocol to e... more The error prone nature of wireless links often necessitates the use of a link layer protocol to ensure acceptable application performance. While traditional link layers assume that they fully control the link, in most emerging wireless networks many sessions may dynamically share the link due to the presence of multiple contending users and/or applications. Such networks require link layers that can automatically adapt to bandwidth variations, offering good performance regardless of contention. To this end, we discuss two adaptive protocols, an Adaptive Selective Repeat (ASR) protocol that dynamically modifies its retransmission timeouts, and the Radio Link Control (RLC) protocol used by UMTS, an advanced protocol without retransmission timers. To assess the applicability of each approach, we measure the throughput achieved by File Transfer and Web Browsing over both protocols, with or without contention from a Media Distribution application, as well as the delay induced by these protocols to the contending application. Our results indicate that the complexity of RLC is not justified by its performance, as ASR nearly always outperforms it.

Information-centric networking constitutes an alter-native to the conventional, IP-based internet... more Information-centric networking constitutes an alter-native to the conventional, IP-based internetworking, with in-formation being identified rather than the host where it resides (which is the case for IP networking). This approach appears to be very promising for the next generation Internet. However, many challenges and critical issues remain to be addressed, asso-ciated with the range of applications that can be supported by the new architectures. Specifically, it is unclear whether information-centric networking abstractions can support conversational ap-plications which are very important in the Internet, and even more important in other telecommunication networks. In light of those reflections, we present the design, prototype implementation and performance evaluation of a simple voice application for the Publish-Subscribe Internet architecture developed in PSIRP and now being further refined in PURSUIT, two EU FP7 research projects on clean slate Future Internet design. Index...

We present preliminary work on a sensor-based system that we are currently implementing with the ... more We present preliminary work on a sensor-based system that we are currently implementing with the aim of monitoring the health of the elderly and people with special needs. The system functions both inside and outside the home of the monitored individuals, using sensors and GPS-enabled cellular phones. Its objective is to first learn the daily behavior of the monitored individuals, and then detect changes in their routines and health status, providing alerts and a preliminary diagnosis as quickly as possible when something out of the ordinary occurs.

10th International Conference on Heterogeneous Networking for Quality, Reliability, Security and Robustness, 2014

INTRODUCTION The current strong drive towards Internet access via mobile terminals, makes the inc... more INTRODUCTION The current strong drive towards Internet access via mobile terminals, makes the inclusion of wireless systems such as Cellular Communications (CC) and Wireless Local Area Networks (WLAN) into the mainstream Internet very desirable. CC and WLAN systems however raise a multitude of performance issues, since environmental conditions and terrestrial obstructions and reflections lead to high and unpredictable error rates. CC and WLAN systems mostly share the characteristics of traditional wireless systems (satellite and terrestrial microwave), such as high error rates. They also share some of the characteristics of wired systems, such as low physical layer propagation delays. As a result, in order to improve their performance, a synthesis of techniques for enhancing the performance of both wired and wireless links is required, that will also take into account the requirements of the TCP/IP protocol suite. In this chapter we present the characteristics and performance limitati

In this paper, we focus on the bootstrap operation of a publish/subscribe information centric net... more In this paper, we focus on the bootstrap operation of a publish/subscribe information centric network. We consider a set of interconnected network nodes and describe how they organize themselves into a fully functional network by pub-lishing and subscribing to control plane information. Network bootstrap includes establishing point-to-point communication between network elements, exchanging topological information and setting up the rendezvous system. We showcase the network's publish/subscribe service with a complete example.

Wireless Communications and Mobile Computing, 2008

2013 International Conference on Computing, Networking and Communications (ICNC), 2013

20th International Conference on Advanced Information Networking and Applications - Volume 1 (AINA'06), 2006

Proceedings of the ACM SIGCOMM workshop on Information-centric networking - ICN '11, 2011

10th International Conference on Heterogeneous Networking for Quality, Reliability, Security and Robustness, 2014