:: Tutorials
Green Networking - A Tutorial

By Franco Davoli, DIST-University of Genoa, Italy


Great attention to energy efficiency is being dedicated in all Information and Communication Technology (ICT) sectors. In particular, besides data centers and mobile networks, where the concept already got a firm stand, fixed networks start to be structured and operated with energy saving goals in mind. Network operators and Internet Service Providers (ISPs) are motivated by the need to reduce both CO2 emissions and operational costs in terms of energy. Starting from the current network structure and trends, traffic profiles and service forecasts, the tutorial examines energy costs of ISPs and telcos, the sources of energy consumption in various network segments and devices, and the main approaches for its reduction. The potential savings achievable in the fixed network are pointed out, in the light of re-engineering, dynamic adaptation, and smart sleeping strategies. Some techniques are illustrated with reference to the structure of software routers and with the use of modeling and optimization. Standardization issues and current research projects are taken into consideration. Though the emphasis is mainly on cabled networks, green technologies in wireless networks and data centers are also briefly touched upon.

  • The Networking Context - Status and Trends
    • Protocol stack
    • Access, Metro and Core
    • Traffic profiles and breakdown
    • Examples from the TELIT network
  • Reasons for going green - The Carbon footprint
    • Embodied and Operational
    • Does the fixed network matter (in terms of consumption and OPEX)?
      • Some Data from Operators (Telcos and ISPs)
  • Breakdown of Energy Consumption
    • Routers
    • Ethernet Switches
    • DSLAMs
  • Taxonomy of Green Networking Approaches
    • Re-engineering
    • Dynamic Adaptation
    • Smart Sleeping
  • Potential Savings (or, is there room for network energy optimization?)
    • Data from 2015-2020 forecast of a Telecom operator
    • Effect of Green Technologies in Home, Access/Transport, Core
    • Overall potential savings
  • A Wrap-up on the Structure and Functionalities of Fixed Network Devices
    • Routers
      • Architecture, Data and Control Plane
      • Address Lookup, Forwarding
      • Software Routers
  • Dynamic Adaptation I - Link Protocols
    • Link Control: the Green Ethernet
      • Adaptive Link Ratee
      • IEEE 802.3az
  • Dynamic Adaptation II - Packet Processing Engine
    • Control actuation: the ACPI standard
    • Idle Logic
    • Power Scaling
  • Modeling and Optimization
    • Modeling Line Card Queues
    • Power-Performance Tradeoff
  • Standby and Virtualization
    • Proxying network presence
    • Data link layer virtualization
  • Network-Level Optimization
  • A glimpse on Green Wireless Networks and Data Centers
  • Ongoing Projects
  • Standardization
  • Research Challenges
  • About Speaker

    Franco Davoli received the "laurea" degree in Electronic Engineering in 1975 from the University of Genoa, Italy. Since 1990 he has been Full Professor of Telecommunication Networks at the University of Genoa, at the Department of Communications, Computer and Systems Science (DIST). His current research interests are in dynamic resource allocation in multiservice networks, wireless mobile and satellite networks, multimedia communications and services in distributed computing environments, and energy-efficient networking. In 2004 and 2011 he was Visiting Erskine Fellow at the University of Canterbury, Christchurch, New Zealand. He has been the Principal Investigator in a large number of research projects and has served in several positions in the Italian National Consortium for Telecommunications (CNIT), an independent research organization joining 37 universities all over Italy. He was one of the founders of the CNIT National Laboratory for Multimedia Communications in Naples, Italy, which he led for the term 2003-2004, and Vice-President of the CNIT Management Board for the term 2005-2007. He is a Senior Member of the IEEE.

    Quantitative discrete-event computer simulation as a credible paradigm of scientific investigations

    By Krzysztof Pawlikowski, University of Canterbury, Christchurch, New Zealand


    Advances of computer technology initiated in the twentieth century have resulted in adoption of discrete-event simulation as the most popular tool of performance evaluation studies of such complex stochastic dynamic systems as e.g. modern multimedia telecommunication networks. This wide-spread reliance on simulation studies raises the issue of credibility of results from such studies. This question needs to be answered before computer simulation can be objectively accepted as an independent, self-sufficient paradigm of scientific investigations.

    In this tutorial, having briefly overviewed the main necessary conditions of any trustworthy simulation study conducted for performance evaluation of stochastic dynamic systems, we will focus on one, the most efficient way of conducting of simulation studies, known as sequential simulation, i.e. simulation with on-line analysis of output data. The perils and pitfalls of such quantitative discrete-event computer simulation will be considered, together with its fast distributed version, known as Multiple Replications in Parallel (MRIP).

  • Introduction to quantitative discrete-event computer simulation (basic terms and concepts)
  • Necessary conditions of credibility of simulation studies and the results of a recent survey of publications
  • Scientific Method as the basic criterion of credibility of research publications
  • The main guidelines for writing credible scientific publications reporting simulation results:
    • Sequential analysis of statistical errors of means and variances
    • Speeding up sequential analysis of statistical errors by MRIP
    • Pseudo-random number generators of the XXI century
  • Implementation of fast and automated on-line analysis of simulation results in Akaroa2.
  • About Speaker

    Krzysztof Pawlikowski is a Professor in Computer Science & Software Engineering at the University of Canterbury, in Christchurch, New Zealand. He received a Ph.D. degree in Computer Engineering from Gdansk University of Technology, Poland, and worked at that university until February 1983. The author of over 170 journal and conference papers and four books has given invited lectures at over 80 universities and research institutes in Asia, Australia, Europe and North America. He was the Alexander-von-Humboldt Research Fellow (Germany) in 1983-84 and 1999, and a Visiting Professor at universities in Austria, Australia, Italy, Germany and the USA. His research interests include discrete-event computer simulation, performance modelling of multimedia telecommunication networks, on-line statistical analysis and modelling of teletraffic, and applications of experimental networking facilities.

    Principles and applications of nano-spin semiconductor lasers

    By K Alan Shore , Bangor University, School of Electronic Engineering, Bangor, LL57 1UT, Wales, UK


    The tutorial will combine an outline of a design strategy for the achievement of room-temperature operation of electrically-injected metal-clad nano-spin VCSELs with a perspective on novel applications of such devices. The practical realization of such devices would represent the first application of the combined capabilities of three key technologies : plasmonics, spintronics and nano-technology. The presentation will include treatments of:

  • Wave-guiding properties of metal-clad semiconductor nano-lasers
  • Optical gain in semiconductor nano-lasers
  • Enhanced spontaneous emission effects in nano-lasers
  • Dynamical behaviour of nano-lasers
  • Prospects for the application of semiconductor nano-lasers
  • Rather subtle waveguiding effects arise in plasmonic lasers including the opportunity to significantly enhance the optical confinement factor. Exploitation of spintronic effects can enable reductions of up to 50 % in the lasing threshold current. The utilization of nanocavities gives access to Purcell- enhanced spontaneous emission for laser threshold reduction and, potentially, threshold-less lasing.

    A key aspect of electrically injected spin VCSELs is the process whereby injected spin-polarized are transported from the injecting contacts to the active region. This is principally a diffusion process, with an exponential depletion of the density of spin-electrons with distance from the injecting contact. On the other hand, the lowest order guided mode of the structure would typically have a maximum at the centre of the structure. This offers the possible disadvantage that the overlap between the guided mode of the laser cavity and the spin-polarized gain is not optimized.

    The impact of Purcell enhanced spontaneous emission on the modulation performance of nano- LEDS and nano-lasers has been examined and specifically it has been shown that the combination of enhanced optical confinement factor and enhanced spontaneous emission in metal- clad nano-lasers may have a detrimental effect on the dynamical behaviour of such lasers.

    In seeking novel applications of nano-spin lasers attention is given to the unique combination of features offered by these lasers and specifically their reduced active volumes and their provision of circularly polarized light emission. So for example, the latter is the key attribute which offers the means for imparting rotatory angular momentum via an optical torque. This would position the device for use as an actuator in optical MEMS/NEMS context. In the same context it is envisaged that an array of nano-spin lasers can be used to perform measurements of physical quantities ( such as magnetic fields ) to ultra-fine spatial resolution. Spin-polarized semiconductor lasers ,wherein dynamical switching of polarization states can be effected, offer new capabilities for optical communications, optical interconnects and other applications. Further opportunities for exploiting these devices will be presented.

    About Speaker

    Professor K Alan Shore graduated in mathematics from the University of Oxford, and obtained a PhD at University College, Cardiff, Wales, UK. He was a lecturer at the University of Liverpool ( 1979-1983) and then at the University of Bath where he became Senior Lecturer (1986 ), Reader (1990) and Professor (1995). In 1995 he was appointed to the Chair of Electronic Engineering, Bangor Univeristy where he has been Head of the School of Informatics and of the College of Physical and Applied Sciences. Between 2001 and 2008 he was the Director of 'Industrial and Commercial Optoelectronics ' (ICON ) a Welsh Development Agency Centre of Excellence. He was Chair of the Welsh Optoelectronics Forum 2006-2008 and has chaired the Photonics Academy for Wales since its establishment in 2005. From 2008-2011 he was chair of the Quantum Electronics Commission of the International Union of Pure and Applied Physics.

    His research work has been principally in the area of semiconductor optoelectronic device design and experimental characterisation with particular emphasis on nonlinearities in laser diodes and semiconductor optical waveguides. He has authored or co-authored more than 880 contributions to archival journals, books and technical conferences. With Prof Deb Kane he co-edited the research monograph 'Unlocking Dynamical Diversity'. He co-founded and acts as Organiser and Programme Committee Chair for the international conference on Semiconductor and Integrated Optoelectronics ( SIOE ) which , since 1987, has been held annually in Cardiff, Wales, UK. He has been a programme member for several OSA conferences and was a co-organiser of a Rank Prize Symposium on Nonlinear Dynamics in Lasers held in the Lake District, UK in August 2002. He chaired the Education and Training in Optics and Photonics ( ETOP) conference held in Technium OpTIC,Wales in July 2009.

    He was a visiting researcher at the Center for High Technology Materials,University of New Mexico,Albuquerque , in 1987.He received a Royal Society Travel Grant to visit universities and laboratories in Japan in July 1988. In 1989 he was a visiting researcher at the Huygens Laboratory, Leiden University,The Netherlands.During the summers of 1990 and 1991 he worked at the Teledanmark Research Laboratory and the MIDIT Center of the Technical University of Denmark, Lyngby. He was a guest researcher at the Electrotechnical Laboratory Tsukuba, Japan in 1991. In 1992 he was a visiting professor at the Department of Physics ,University de les Illes Balears, Palma-Mallorca,Spain. He was a visiting lecturer in the Instituto de Fisica de Cantabria, Santander,Spain in June 1996 and 1998 and a visiting researcher in the Department of Physics, Macquarie University, Sydney, Australia in 1996, 1998,2000, 2002 , 2005 and 2008. In July/August 2001 he was a visiting researcher at the ATR Adaptive Communications Laboratories, Kyoto, Japan. From July- December 2010, he held a Japan Society for the Promotion of Science ( JSPS ) Invitation Fellowship in the Ultrafast Photonics Group, Graduate School of Materials Science,Nara Institute of Science and Technology ( NAIST , Nara, Japan. His current research interests include the dynamics of vertical cavity semiconductor lasers ,applications of nonlinear dynamics in semiconductor lasers and the design of nano-spin semiconductor lasers.


    Wireless Mesh Networks – A Tutorial

    By Ulf Körner, Lund University, Sweden


    For more than a decade, we have heard that the concept of Wireless Mesh Networks (WMNs) has emerged as a very promising technology for fast and cost-efficient deployments of wireless access networks combining the benefits of cellular networks and those of Wireless Local Area Networks (WLANs). I think one has to agree to that setting up a WMN is quite cheap compared to other technologies and normally it is done rather fast. But is it a good technology, concept or as one may say a good paradigm? Does it provide good performance in terms of desired throughputs and delays? Is it scalable to cover large cities with one and the same WMN? Is this technology, that is built on unstable wireless link characteristics and a multi-hop forwarding operation, really robust?

    The WMN paradigm is built upon a number of existing technologies from other fields say the IEEE802.11 WLAN standard, on ad hoc network protocols, on MANET technologies, etc. While it for long has been a very hot topic within academia, which in turn has lead to that the concept of today’s WMNs differs significant from that of yesterday, we today also find a number of commercial products and deployments in parallel with academia built test beds. Besides, standardization has taken place also for this technology.

    This tutorial, will address a number of issues like:

  • Introduction to Wireless Mesh Networks
  • WMN design challenges
  • The family of wireless ad hoc, mesh and sensor networks and their relations
  • Multi-channel multi-radio contra single-channel WMNs
  • The concept of self- (-healing, -organized, -configuring, ..) when it comes to WMNs
  • WMN QoS
  • Routing protocols for WMNs
  • WMN standards
  • Some experimental test beds
  • WMNs tomorrow
  • About Speaker

    Ulf Körner currently holds the Professor chair in Communications Systems at Lund University, Sweden. There he also obtained his PhD in electrical engineering in 1982 as well as his docent degree (habilitation) in Communications Systems in 1985. He has spent a number of sabbaticals abroad not at least several times at North Carolina State University, Raleigh, NC, USA. From 1995 to 1998 he was the Dean of Electrical Engineering and Computer Engineering at Lund University. He has been the Principle Investigator for several national and international research projects. His areas of research interests are communication network architectures and protocols, performance modeling and evaluation. During the last years his research has been focused on wireless systems, especially on ad hoc and mesh networking, on WLAN technologies and on “Beyond 3/4G technologies”. Dr. Körner is the author of several books, serves in several journal editor boards and has a publication list of more than 100 papers published in journals and at conferences with peer reviews. He has served in numerous technical program committees for international conferences and in many cases acted as program chair/co-chair.

    For more than 10 years Prof. Körner served as a member of the Board of Directors of the Post and Telecommunications Agency in Sweden, which is the regulating body there. He has also for years been in the board of directors for a number of larger communication technology companies and been co-founder for a couple of startup companies.


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