Modern end-hosts are generally equipped with more than one network interfaces. IETF responded to proliferation of multi-homed end-hosts and proposed MPTCP to allow concurrent use of multiple interfaces in data transfers. Basically, MPTCP uses regular TCP flows (called as MPCTP subflows) to send/receive application data over multiple paths. This approach benefits from the strengths of TCP (e.g., its high deployment), but also suffers from its weaknesses (e.g., its vulnerability to reorderings). Scattering TCP data packets to multiple paths produces lots of reordered packets due to path delay differences. In that case, performance of MPTCP subflows decreases too much. Therefore, it is not possible to use per-packet load balancers on MPTCP subflow paths although there is a big potential to use them in current network architectures (e.g., they enable efficient utilization of network resources with low computational complexity and they decrease congestion occurences by shifting traffic to uncongested parts of networks). In this paper, we address this issue and make our previous transparent and light-weight TCP proxy proposal (ORTA, Outof-Order Robustness for TCP with Transparent ACK Intervention) MPTCP-aware. That is, ORTA now recognizes MPTCP subflows by observing the MPTCP options and makes them robust against reorderings as it made regular TCP flows. Our new proposal is called as ORTAM (ORTA with MPTCP support). ORTAM allows reorderings on MPTCP subflow paths so that access networks and/or Internet service providers (ISPs) are able to use per-packet load balancers without any concern about MPTCP performance degradation. ORTAM is implemented and tested in NS-2. In the simulation scenarios, MPTCP subflow path delays are selected to reflect real Internet path delay observations. Different levels of reorderings are generated on the MPTCP subflow paths and MPTCP performance is measured. As expected, MPTCP performance decreases sharply when regular TCP is used for MPTCP subflows and reorderings are generated on the subflow paths. On the other hand, ORTAM makes MPTCP subflows highly robust against reorderings. When ORTAM is used, MPTCP performance was unaffected by even high levels of reorderings on the MPTCP subflow paths. In addition, ORTAM supplies this reordering robustness with its transparency feature (i.e., it does not change TCP sender or receiver implementations) which makes it easy to deploy on access networks or edge ISPs.

The use of multiple paths in core networks for TCP traffic sounds promising as it suggests bandwidth aggregation, fault tolerance through redundancy, high resource utilization efficiency, reduced congestions, and increase in TCP throughput. In order to benefit from all these features, the load balancing approaches at different granularities (per-flow, per-destination, and per-packet) have to be applied. In order to promote use of per-packet load balancing in core networks, we already proposed a transparent TCP proxy called as ORTA (Out-of-Order Robustness for TCP with Transparent Acknowledgment Intervention). ORTA was introduced along with simulation results which were all promising and competing with the nontransparent approaches in the literature. However, network simulations may not reflect the real system performances because of the lack of precise and accurate model of the real systems. In this paper, ORTA is implemented as a netfilter module and emulation test results are presented. The results indicate that ORTA prevents TCP performance degradation caused by TCP packet reorderings. Moreover, ORTA has no degrading impact on TCP performance when packet reordering does not exist.

The idea to use multiple paths to transport TCP traffic seems very attractive due to its potential benefits it may offer for both redundancy and better utilization of available resources by load balancing. Fixed and mobile network providers employ frequently load-balancers that use multiple paths on either per-flow or per-destination level, but very seldom on per-packet level. Despite of the benefits of packet-level load balancing mechanisms (e.g., low computational complexity and high bandwidth utilization) network providers can’t use them mainly because of TCP packet reorderings that harm TCP performance. Emerging network architectures also support multiple paths, but they face with the same obstacle in balancing their load to multiple paths. Indeed, packet level load balancing research is paralyzed by the reordering vulnerability of TCP.A couple of TCP variants exist that deal with TCP packet reordering problem, but due to lack of end-to-end transparency they were not widely deployed and adopted. In this paper, we revisit TCP’s packet reorderings problem and present a transparent and light-weight algorithm, Out-of-Order Robustness for TCP with Transparent Acknowledgment (ACK) Intervention (ORTA), to deal with out-of-order deliveries.ORTA works as a transparent thin layer below TCP and hides harmful side-effects of packet-level load balancing. ORTA monitors all TCP flow packets and uses ACK traffic shaping, without any modifications to either TCP sender or receiver sides. Since it is transparent to TCP end-points, it can be easily deployed on TCP sender end-hosts (EHs), gateway (GW) routers, or access points (APs). ORTA opens a door for network providers to use per-packet load balancing.The proposed ORTA algorithm is implemented and tested in NS-2. The results show that ORTA can prevent TCP performance decrease when per-packet load balancing is used.

Base station sharing is currently considered one of the most promising solutions for reducing the energy consumption costs of cellular networks. This paper presents a game theoretic framework for the study of such cooperative solutions where different mobile network operators (MNOs) decide to switch off subsets of their base stations during off-peak hours and roam their traffic to the remaining stations. The solution is based on a detailed optimization framework that determines exactly which base stations should remain active and how much traffic each one of them should serve, so as to maximize the aggregate energy savings. Accordingly, using the axiomatic Shapley value rule, it is determined how the benefits from the cooperation, i.e., the cost savings, should be dispersed among the cooperating MNOs. It is proved that this coalitional game with transferrable utilities has a nonempty core, and thus there exists a cooperation solution that incentivizes the participation of all operators. Moreover, using a thorough numerical analysis, it is shown that the benefits achieved with the implementation of the cooperation strategy depend mainly on the power consumption characteristics of the MNOs, which in turn are related to the number, type, and technology of their base stations. Overall, the energy savings are found to be most sensitive to the technology of the used base stations, and more precisely to the no-load base station energy consumption which defines the energy waste in a network.

The past years have witnessed a significant increase in the number of WLANs deployed in most of the enterprises, campuses and public areas to provide high-speed Internet connectivity. These WLANs typically consist of APs densely installed to assure enough capacity to meet users demand during the peak period of activity. At the same time, it translates into a serious energy wastage during low-utilization periods, when capacity is not needed at the APs. To reduce this wastage, many proposed solutions consist of adapting the active capacity to the actual needs, introducing switching strategies able to turn on and off the APs. The effectiveness and potential benefit of these strategies strongly depend on the user behavior and traffic patterns. In this paper, we focus our analysis on the real usage characteristics of a dense WLAN (such as users' behavior and users' mobility patterns) in a university campus and evaluate potential energy savings and benefits achievable when introducing AP on/off switching strategies. We discuss different strategies, in which decisions are based either on: (1) historical behavior in the campus, or on (2) current AP utilization. In addition, considering the large overlapping coverage available in dense WLANs, we investigate users' mobility patterns to derive further improvements to AP switching strategies. The results show that, due to the repetitiveness of users' patterns and large differences in WLAN usage between days and nights, as well as between weekdays and weekends, large savings of up to 40% can be easily achieved. Moreover, by fine-tuning the strategies in different areas of the campus, additional savings are possible. The deployment of these strategies leads to energy saving and, as a practical consequence, to a remarkable reduction of electricity costs.

Power wastage in dense WLANs is a challenging problem. In order to reduce the power wastage, AP switching on/off strategies have been developed, aiming at decreasing the number of active APs (according to the traffic conditions). The efficiency of such strategies is strongly dependent on the efficiency of detecting WLAN users communication attempts, as a trigger for switching on the inactive APs. We demonstrate that such a communication attempts can be efficiently identified even for SNR values far below thresholds needed for frame reception. We present a signal-detection-based approach and verify its efficiency experimentally.

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 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.

Cellular networks have been traditionally dimensioned to fulfill the desired quality of service (QoS) requirements at all times, and consequently their deployment has been planned to meet the expected peak of the user demand. However, with the user demand recently increasing at exponential pace, concerns about the cellular networks energy consumption have been raised. In response, energy-efficient resource management schemes have been proposed, which take into account energy consumption, and control how much of the network infrastructure is actually needed at different times, and how much can be temporarily powered off to cut energy consumption. Since most of the energy consumed in cellular networks is used by base stations (BSs), algorithms for managing BSs seem to be the most urgent development to achieve energy-efficient operation. This paper provides a quick overview of the BS management techniques that were recently proposed for cellular networks. In addition, an outlook on real implementation aspects, including current commercial products, and trends in the development of energy-efficient hardware is also given.

IEEE 802.11 WLANs are currently one of the most popular wireless technologies, but their immediate success results in dense deployments and high demand of user traffic. This in turn leads to decrease in throughput and poor spectrum utilization. Especially in the 2.4 GHz ISM band, where the spectrum is a very scarce resource, all available WLAN channels should be exploited in the best possible way to achieve higher utilization. One way to reach this goal is the usage of partially overlapping channels (POC). Most of the previous work related to POC is based on two major studies addressing 802.11 b, but none of them evaluates the POC behavior in the 802.11 g networks. Moreover, most of the previous results are based on simulations. The main contribution of this work is an experimental evaluation of POC in 802.11g networks. In this paper we confirm quantitatively that 802.11b reacts as expected from the previous studies, while 802.11 g reacts entirely different to the presence of adjacent channel interference. That leads to the conclusion that the usage of POC for 802.11g is not recommended.

Aimed at answering important questions about the energy demand of current telecom infrastructure and the design of sustainable and energy-efficient future networks, the research of a number of European partners is brought together in the TREND project. In this paper we present the achievements of the Work Package coordinating the experimental activities of the project - WP4. Although not presenting a completely finished portrait yet, the results shown help building a better global view on the “big picture” in the field of energy-efficient networking.

The idea of using multiple paths to transport TCP traffic seems very attractive due to the potential benefits it may offer. Despite a solid theoretical background and quite substantial implementation attempts, none of the provided proposals was successful enough to fully establish its mark. Therefore, this paper presents and develops a novel approach to carry TCP traffic over multiple paths. The main features of the proposed architecture include: (1) end-to-end transparency, (2) autonomy of the operation (protocol stack transparency), and (3) interoperability with different operating systems (OSs). To demonstrate the potential of the presented architecture, experimental results are provided in one of possible application scenarios, a high capacity local mesh backbone network with bottleneck gateway links.

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.

This draft complements the work of MPTCP by defining a TCP Splitter/ Combiner Architecture (SCA) that enables non-MPTCP-capable single-homed hosts to benefit from the multiple paths within Internet by means of performance enhancing proxies (PEPs) placed in the access networks. SCA Proxies (SCAPs) make use of multiple paths in a way which is completely transparent to end-hosts. Since the existence of the SCAPs is shielded from the TCP end-points, they can be deployed in the Internet as well as on the end-systems.

This document describes the different categories of traffic management scenarios including problem statements. Subsequently the requirements are derived for a traffic engineering architecture within the evolved packet system.

This paper presents NMLab, a proposal of new co-simulation framework for Matlab and ns-2 targeted for networked control systems. NMLab enables to combine flexible and powerful numerical operations together with a realistic support for a wide range of up-to-date communication protocols, and permits simulating networking scenarios of high grade of complexity. At the same time the proposed solution is kept simple. The capabilities of NMLab are illustrated through a series of experiments, using as an example the academic version of the pendulum on a cart.

This paper presents and develops a novel delay-based additive increase, multiplicative decrease (AIMD) congestion control algorithm. The main features of the proposed solution include: 1) low standing queues and delay in homogeneous environments (with delay-based flows only); 2) fair coexistence of delay- and loss-based flows in heterogeneous environments; 3) delay-based flows behave as loss-based flows when loss-based flows are present in the network; otherwise they revert to delay-based operation. It is also shown that these properties can be achieved without any appreciable increase in network loss rate over that which would be present in a comparable network of standard TCP flows (loss-based AIMD). To demonstrate the potential of the presented algorithm, both analytical and simulation results are provided in a range of different network scenarios. These include stability and convergence results in general multiple-bottleneck networks and a number of simulation scenarios to demonstrate the utility of the proposed scheme. In particular, we show that networks employing our algorithm have the features of networks in which RED AQM's are deployed. Furthermore, in a wide range of situations (including high-speed scenarios), we show that low delay is achieved irrespective of the queueing algorithm employed in the network, with only sender-side modification to the basic AIMD algorithm.

Handling mobility at the transport layer is a promising approach to achieve seamless handover in the context of heterogeneous wireless access networks. In particular, features such as multihoming and dynamic address reconfiguration provided by mobile SCTP (mSCTP) protocol are among the key enablers for handover support at the transport layer. This paper investigates the applicability of Concurrent Multipath Transfer (CMT) to distribute data among two end-to-end paths of a mSCTP association during handover transition process. To that end, the principles of the mSCTP-CMT design are given, emphasizing the consequences of such a sender-introduced reordering and its congestion control implications in a handover scenario. The proposed mSCTP-CMT handover scheme is benchmarked with a pure mSCTP handover scheme. Provided analysis indicates the possible application area of mSCTP-CMT, taking into account not only handover scenario parameters (dwelling time, available bandwidth ratio and round-trip time), but also the most important constraint of such a design: receiver buffer (rbuf) size. Rbuf size proves to be the major limiting factor shrinking significantly possible mSCTP-CMT application scope, yet not excluding definitively the proposed idea.

Handling mobility at the transport layer is a promising approach to achieve seamless handover in the context of heterogeneous wireless access networks. In particular, features such as multihoming and dynamic address reconfiguration provided by mobile SCTP (mSCTP) protocol are among the key enablers for handover support at the transport layer. This paper investigates the applicability of Concurrent Multipath Transfer (CMT) to distribute data among two end-to-end paths of an mSCTP association during the handover transition process. To that end, the principles of the mSCTP-CMT design are given, emphasizing the consequences of a sender-introduced reordering and its effect on congestion control. The proposed mSCTPCMT handover scheme is benchmarked with two other handover schemes, namely mSCTP and SCTP failover-based. Provided analysis indicates the possible application area of mSCTP-CMT, taking into account not only handover scenario parameters (dwelling time, available bandwidth ratio and round-trip time), but also an important design constraint: receiver buffer (rbuf) size. Rbuf size proves to be a major limiting factor shrinking significantly, yet not excluding mSCTP-CMT's application scope.