Abstract-Traditionally, energy efficiency aspects have been included in the wireless access network design space only in the context of power control aimed at interference mitigation and for the increase of the terminal battery lifetime. Energy consumption of network components has also, for a long time, not been considered an issue, neither in equipment design nor in network planning and management. However, in recent years, with the user demand increasing at nearly exponential pace and margins rapidly shrinking, concerns about energy efficiency have been raised, with the objective of reducing network operational costs (not to mention the environmental issues). Installing more energy-efficient hardware does not seem to fully solve the problem, since wireless access networks are almost invariably (over)provisioned with respect to the peak user demand. This means that efficient resource management schemes, which are capable of controlling how much of the network infrastructure is actually needed and which parts can be temporarily powered off to save energy, can be extremely effective and provide quite large cost reductions. Considering that most of the energy in wireless access networks is consumed in the radio part, dynamic provisioning of wireless access network resources is crucial to achieving energy-efficient operation. The consensus on this approach in the research community has been wide in the last Manuscript received September 6, 2013; revised March 13, 2014; accepted May 6, 2014 G. Koutitas and L. Tassiulas are with the Department of Computer Engineering and Telecommunications, University of Thessaly, Volos 38221, Greece (e-mail: george.koutitas@gmail.com; leandros@inf.uth.gr).S. Lambert, B. Lannoo, and M. Pickavet are with the Department of Information Technology, Ghent University iMinds, Gent 9000, Belgium (e-mail: sofie.lambert@intec.ugent.be; bart.lannoo@intec.ugent.be; mario.pickavet@ intec.ugent.be).A. Conte and I. Haratcherev are with Alcatel-Lucent Bell Labs, BoulogneBillancourt 92100, France (e-mail: alberto.conte@alcatel-lucent.com; ivaylo@alcatel-lucent.com; haratcherev@alcatel-lucent.com few years, and a large number of solutions have been proposed. In this paper, we survey the most important proposals, considering the two most common wireless access technologies, namely, cellular and WLAN. The main features of the proposed solutions are analyzed and compared, with an outlook on their applicability in typical network scenarios that also include cooperation between both access technologies. Moreover, we provide an overview of the practical implementation aspects that must be addressed to achieve truly energy-efficient wireless access networks, including current standardization work, and trends in the development of energy-efficient hardware.

Due to the requirements to provision a proper Quality of Service level in enterprise WLANs supporting both voice and data services the typical densities in the deployment of access points (APs) may exceed 4000 APs per square kilometer. While such density is necessary under heavy traffic conditions, it is obviously superfluous during the time of lower load -and dramatically excessive at night periods, with only marginal traffic intensity. We present a novel, aggressive approach for adjusting the AP density to the actual traffic conditions. In the limiting case of a very low traffic, we postulate keeping operational only a skeleton deployment, sufficient just to recognize that there is a station attempting an association. In this case additional APs can be powered up, in order to assure the requested connectivity, locally in this area. Using data from commercially available APs we estimate the potential of power saving in such an operation mode and relate it to the best approaches proposed so far.

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Abstract-Delay-based TCP variants continue to attract a large amount of attention in the networking community. Potentially, they offer the possibility to efficiently use network resources while at the same time achieving low queueing delay and virtually zero packet loss. One major impediment to the deployment of delay-based TCP variants is their inability to coexist fairly with standard loss-based TCP. In this paper we propose a simple strategy to make the fair coexistence possible and to ensure that delay-based flows will revert back to the delay-based operation when loss-based flows are no longer present. Analytical and ns-2 simulation results are presented to validate the proposed algorithm.

The Stream Control Transmission Protocol (SCTP) is a relatively recent general-purpose transport layer protocol for IP networks that has been introduced as a complement to the well-established TCP and UDP transport protocols. Although initially conceived for the transport of PSTN signaling messages over IP networks, the introduction of key features in SCTP, such as multihoming and multistreaming, has spurred considerable research interest surrounding SCTP and its applicability to different networking scenarios. This article aims to provide a detailed survey of one of these new features-multihoming-which, as it is shown, is the subject of evaluation in more than half of all published SCTP-related articles. To this end, the article first summarizes and organizes SCTP-related research conducted so far by developing a four-dimensional taxonomy reflecting the (1) protocol feature examined, (2) application area, (3) network environment, and (4) study approach. Over 430 SCTP-related publications have been analyzed and classified according to the proposed taxonomy. As a result, a clear perspective on this research area in the decade since the first protocol standardization in 2000 is given, covering both current and future research trends. On continuation, a detailed survey of the SCTP multihoming feature is provided, examining possible applications of multihoming, such as robustness, handover support, and loadsharing.