Dynamic link sleeping reconfigurations for green traffic engineering

The high volume of energy consumption has become a great concern to the Internet community because of high energy waste on redundant network devices. One promising scheme for energy savings is to reconfigure network elements to sleep mode when traffic demand is low. However, due to the nature of today's traditional IP routing protocols, network reconfiguration is generally deemed to be harmful because of routing table reconvergence. To make these sleeping network elements, such as links, robust to traffic disruption, we propose a novel online scheme called designate to sleep algorithm that aims to remove network links without causing traffic disruption during energy‐saving periods. Considering the nature of diurnal traffic, there could be traffic surge in the network because of reduced network capacity. We therefore propose a complementary scheme called dynamic wake‐up algorithm that intelligently wakes up minimum number of sleeping links needed to control such dynamicity. This is contrary to the normal paradigm of either reverting to full topology and sacrificing energy savings or employing on‐the‐fly link weight manipulation. Using the real topologies of GEANT and Abilene networks respectively, we show that the proposed schemes can save a substantial amount of energy without affecting network performance.     

Combined ICA and FCA Schemes for a Hierarchical Network

A combined idle channel assignment (ICA) and fixed channel assignment (FCA) scheme is proposed to improve the traffic performance in a hierarchical network. This dual-mode network integrates the Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes of the Universal Mobile Telecommunication System (UMTS) and Terrestrial Radio Access (UTRA) in a given cell. This approach includes a high traffic load area and a blocked area as an example to evaluate the traffic performance. The ICA threshold and network timeout period effects on the traffic performance of this integrated dual-mode network are also investigated. The analytical results show that the handoff failure probabilities of the integrated dual-mode network can be reduced significantly with a minimal increase in the new call blocking probability when the combined ICA and FCA scheme replaces the FCA scheme. The integrated dual-mode network using the combined ICA and FCA scheme also increases the carried traffic. The traffic performance improvements for non-uniformly generated new calls are more significant than those for uniformly generated new calls when the combined ICA and FCA scheme is used. An increase in the high ICA threshold will result in an increase in the total carried traffic and an increase in the new call blocking and handoff failure probabilities for higher-tiered and low-tiered systems located in the high traffic load area. The traffic performance was evaluated using the discrete time simulation method to validate the analysis results.     

Green optical backbone networks: virtual topology adaptation using a page rank‐based rating system

An energy‐aware virtual topology rating system is proposed in this work, which can be utilized as a tool during the virtual topology reconfiguration procedure in an optical backbone network in order to reduce its energy consumption. It is well known that maintaining a static virtual topology in Internet Protocol (IP)‐over‐Wavelength Division Multiplexing (WDM) networks is not energy‐efficient. To that end, virtual topology adaptation algorithms have been developed to adjust the virtual topology to the constantly fluctuating traffic load. While these algorithms achieve significant energy savings, further reduction on the total network energy consumption can be achieved through the proposed rating system. The proposed rating system is a modified version of the page rank algorithm, which ranks websites in the Internet based on their importance. The proposed rating system attributes ratings to lightpaths, which indicate the relative significance of a lightpath in the virtual topology in terms of energy consumption. The rating can be used during the routing procedure as an energy efficiency indicator, in order to increase the number of lightpaths that are deactivated from the reconfiguration mechanism and increase the utilization per lightpath. The proposed reconfiguration scheme (page rank‐based virtual topology reconfiguration) achieves up to 12% additional energy savings in comparison to an existing virtual topology reconfiguration algorithm at the cost of slightly increased average hop distance. Copyright © 2015 John Wiley & Sons, Ltd.     

A batched network coding scheme for wireless networks

Several wireless network coding schemes apply either inter-flow traffic or intra-flow traffic, but not both. This paper proposes a novel batched network coding scheme to deal with both inter-flow and intra-flow traffics, which attempts to combine the advantages of both network coding approaches. Based on the idea in the well-known network coding scheme COPE, our batched network coding scheme allows each node to make use of intra-flow network coding technique to improve the transmission reliability in a lossy environment, consequently obtaining higher throughput. Moreover, we also utilize the multiple-path transmitting scheme to further increase the throughput of wireless networks with low link delivery probability. Finally, using a simplified network topology model, we show theoretically that our proposed scheme outperforms COPE significantly, particularly when the link quality is low.     

Energy‐efficient multiple‐domain bidirectional scheme for G.hn applications

This paper presents an energy‐efficient relaying scheme for G.hn standard. We propose a multi‐domain bidirectional communication network with network coding at the physical layer in order to increase network coverage. The logical link control stack was also modified and supplemented with additional functionality. This reduces the power consumption in the network and enhances the performance while reducing collisions for inter‐domain network access. We consider domain selection to minimize the total energy consumption of the network and present optimal power allocation for the given QoS of each end node. Energy efficiency is evaluated in terms of transmit energy per bit for relay networks with bidirectional symmetric and asymmetric traffic flows. Simulation results show that the proposed multi‐domain bidirectional communication provides improved performance and higher energy savings than the single‐domain unidirectional network, especially in powerline communication channel, which is the worst medium of the three G.hn media. Finally, it was demonstrated that improved energy efficiency can be achieved with appropriate domain selection. Copyright © 2015 John Wiley & Sons, Ltd.     

Increasing the Link Utilization in IP over WDM Networks Using Availability as QoS

In this paper, we solve a mapping problem related to supporting two service classes that are differentiated based on their level of protection. The first class of service, called Fully Protected (FP), offers end-users a guarantee of survivability in the case of a single failure; all FP traffic is protected using either a 1:1 or 1 + 1 protection scheme at the WDM layer. The second class of service, called Best-Effort Protected (BEP), is not protected; instead restoration at the IP layer is provided. When a failure occurs, the network restores as much BEP traffic as possible, and thus BEP traffic does not receive any specific guarantees. The FP service class mimics what Internet users receive today. The BEP traffic is designed to run over the large amounts of unused bandwidth that exist in todays Internet. The motivation of this approach is to give carriers a mechanism for increasing the load carried on backbone networks without reducing the QoS received by existing customers. In order to support two such services, the logical links at the IP layer need to be carefully mapped onto primary and backup paths at the optical layer. We incorporate into our mapping problem a number of practical requirements that reflect constraints that carriers face and policies they want to enforce. For example, we allow the FP demand to be specified via a traffic matrix at the IP layer, we include an overprovisioning factor that specifies the portion of each link that must be left unused, and we incorporate a minimal fairness requirement on how the BEP traffic is allocated among connections. Our goal is to quantify how much BEP traffic can be carried in addition to the FP traffic, without impacting the protection quality of the FP traffic even in the case of failure, and without impacting the FP load. We provide two solutions, one is an optimal solution using an Integer Linear Program (ILP) model, and the other is an algorithm based on the Tabu Search (TS) methodology. Our heuristic algorithm allows us to solve this problem for large networks such as those spanning the continental US. We show that by having two such classes of service, the load on a network can be increased by a factor of 4–7 (depending upon the network). We illustrate that even with overprovisioning and fairness requirements (both of which reduce the total possible BEP load carried), we can still typically triple the total network load. We show that the location of the bottleneck can affect whether or not we see a difference in performance between 1:1 or 1 + 1 protection schemes. Our results illustrate the gain in terms of additional BEP load carried that can be obtained simply due to the upgrade of a single link. Our proposal provides carriers a new vehicle for generating revenue by extracting benefit from all the sources of unused bandwidth in networks.     

VoIP traffic in wireless mesh networks: a MOS‐based routing scheme

Support of Voice over Internet Protocol (VoIP) services in wireless mesh networks requires implementation of efficient policies to support low‐delay data delivery. Multipath routing is typically supported in wireless mesh networks at the network level to provide high fault tolerance and load balancing because links in the proximity of the wireless mesh gateways can be very stressed and overloaded, thus causing scarce performance. As a consequence of using multipath solutions, lower delay and higher throughput can be supported also when a given path is broken because of mobility or bad channel conditions, and alternative routes are available. This can be a relevant improvement especially when assuming that real‐time traffic, such as VoIP, travels into the network. In this paper, we address the problem of Quality of Service (QoS) support in wireless mesh networks and propose a multipath routing strategy that exploits the Mean Opinion Score (MOS) metric to select the most suitable paths for supporting VoIP applications and performing adaptive load balancing among the available paths to equalize network traffic. Performance results assess the effectiveness of the proposed approach when compared with other existing methodologies. Copyright © 2015 John Wiley & Sons, Ltd.     

Automatic handover control for distributed load balancing in mobile communication networks

In this paper, we propose an auto-tuning of mobility algorithm in the mobile communication systems as a load balancing self-optimization use case. This paper presents a distributed approach in which the traffic load can be balanced systematically by utilizing the effective load information of neighboring cells. The proposed load balancing scheme detects a load imbalance in the network and resolves the problem automatically by controlling the handover parameter as a nonlinear function of the load difference. Based on control theory, we analyze the adaptive behavior of the proposed controller and derive condition for system stability. Results from asymptotic analysis and simulation indicate that the proposed local controller of each individual cell effectively achieves the global properties, such that the load difference in the network is stabilized globally within a predetermined threshold. Extensive simulation results also show that the proposed scheme outperforms the existing methods by reducing call blocking rate of the overloaded cells.     

On-demand power management for ad hoc networks

Battery power is an important resource in ad hoc networks. It has been observed that in ad hoc networks, energy consumption does not reflect the communication activities in the network. Many existing energy conservation protocols based on electing a routing backbone for global connectivity are oblivious to traffic characteristics. In this paper, we propose an extensible on-demand power management framework for ad hoc networks that adapts to traffic load. Nodes maintain soft-state timers that determine power management transitions. By monitoring routing control messages and data transmission, these timers are set and refreshed on-demand. Nodes that are not involved in data delivery may go to sleep as supported by the MAC protocol. This soft state is aggregated across multiple flows and its maintenance requires no additional out-of-band messages. We implement a prototype of our framework in the ns-2 simulator that uses the IEEE 802.11 MAC protocol. Simulation studies using our scheme with the Dynamic Source Routing protocol show a reduction in energy consumption near 50% when compared to a network without power management under both long-lived CBR traffic and on–off traffic loads, with comparable throughput and latency. Preliminary results also show that it outperforms existing routing backbone election approaches.     

A Drop and Throttle Flow Control Policy for Computer Networks

Store-and-forward packet switched networks are subject to congestion under heavy load conditions. In this paper a distributed drop and throttle flow control (DTFC) policy based on a nodal buffer management scheme is proposed. Two classes of traffic are identified: "new" and "transit" traffic. Packets that traveled over one or more hops are considered as transit packets. Packets that are candidates to enter the communication network are considered as new packets. At a given node if the number of allocated buffers is greater than a limit value, then new traffic is rejected, whereas transit traffic is accepted. Indeed, if the total buffer area is occupied, transit traffic is also rejected and, furthermore, it is dropped from the network. This policy is analyzed in the context of symmetrical networks. A queueing network model is developed whereby network throughput is expressed in terms of the traffic load, the number of buffers in a node and the DTFC limit value. Optimal policies where the limit value is a function of the traffic load are found to prevent network congestion. Furthermore, they achieve a very good network throughput even for loads fifty times beyond the normal operating region. Moreover, suboptimal, easy to implement fixed limit policies offer satisfactory results.     

A dynamic load-aware congestion control scheme in optical burst switching networks

The most important design goal in Optical Burst Switching (OBS) networks is to reduce burst loss resulting from resource contention. Especially, the higher the congestion degree in the network is, the higher the burst loss rate becomes. The burst loss performance can be improved by employing an appropriate congestion control. In this paper, to actively avoid contentions, we propose a dynamic load-aware congestion control scheme that operates based on the highest (called ‘peak load’) of the loads of all links over the path between each pair of ingress and egress nodes in an OBS network. We also propose an algorithm that dynamically determines a load threshold for adjusting burst sending rate, according to the traffic load in a network. Further, a simple signalling method is developed for our proposed congestion control scheme. The proposed scheme aims to (1) reduce the burst loss rate in OBS networks and (2) maintain reasonable throughput and fairness. Simulation results show that the proposed scheme reduces the burst loss rate significantly, compared to existing OBS protocols (with and without congestion control), while maintaining reasonable throughput and fairness. Simulation results also show that our scheme keeps signalling overhead due to congestion control at a low level.     

Power Savings in Packet Networks via Optimised Routing

This paper examines the use of a gradient-based algorithm for Quality of Service (QoS) and power minimisation in wired networks to result on reduced energy consumption. Two distinct schemes, conventional shortest-path routing and an autonomic algorithm energy aware routing algorithm (EARP) are investigated as the starting point for the gradient algorithm. Comparisons are conducted using the same network test-bed and identical network traffic under conditions where routers and link drivers are always kept on so as to meet the needs for network reliability in the presence of possible failures and unexpected overload. Since splitting traffic flows can increase jitter and the arrival of packets which are out of sequence, we also do not allow the same packet flow to be conveyed over multiple paths. In the experiments that we have conducted we observe that power consumed with the gradient-optimiser that is proposed in this paper is a few percent to 10% smaller than that consumed using shortest-path routing or EARP. Although the savings are small, they can be very significant for the Internet backbone as a whole over long periods of time, and further power savings may be obtained by judiciously putting to sleep equipment when it is under-utilised.     

Controlled use of excess backbone bandwidth for providing new services in IP-over-WDM networks

We study an approach to quality-of-service (QoS) that offers end-users the choice between two service classes defined according to their level of transmission protection. The fully protected (FP) class offers end-users a guarantee of survivability in the case of a single-link failure; all FP traffic is protected using a 1:1 protection scheme at the wavelength-division multiplexing (WDM) layer. The best effort protected (BEP) class is not protected; instead restoration at the IP layer is provided. The FP service class mimics what Internet users receive today. The BEP traffic is designed to run over the large amounts of unused bandwidth that exist in today's Internet. The goal is to increase the load carried on backbone networks without reducing the QoS received by existing customers. To support two such services, we have to solve two problems: the off-line problem of mapping logical links to pairs of disjoint fiber paths, and an on-line scheduling problem for differentiating packets from two classes at the IP layer. We provide an algorithm based on a Tabu Search meta-heuristic to solve the mapping problem, and a simple but efficient scheduler based on weighted fair queueing for service differentiation at the IP layer. We consider numerous requirements that carriers face and illustrate the tradeoffs they induce. We demonstrate that we can successfully increase the total network load by a factor between three and ten and still meet all the carrier requirements.     

An energy‐efficient clustering approach for collaborative data forwarding in heterogeneous MANET

Mobile ad hoc network consists of a group of mobile nodes that can communicate with each other without any infrastructure. Clustering of the mobile nodes ensures efficient use of available bandwidth and high network throughput. Various clustering schemes are developed to improve the energy efficiency and lifetime of the network. However, there is an increase in the energy consumption with the increase in the number of clusters for forwarding data. This paper presents an energy‐efficient clustering approach for collaborative data forwarding in mobile ad hoc network. The cluster head (CH) is selected based on the processing capability of the nodes and link connection metrics. The CH receives the data from the server and forwards the data to the member nodes at a corresponding data rate of the nodes. Data offloading technique manages the data traffic in the network. The CH rejoining approach enables load balancing in the network. The proposed clustering approach achieves a significant reduction in the energy consumption and data traffic and improvement in the throughput rate through stable routing.     

Radio versus backhaul bottlenecks: an integrated quality of service provisioning approach for small cell gateways

Small cell traffic is expected to experience a continuous increase during the upcoming years, and thus, backhauling challenges should be timely addressed. Regardless the fact that radio resource management continues to be a major research problem in coexisting heterogeneous wireless networks, a mentality shift is observed in the research community towards dealing with wired backhaul bottleneck situations, too. Hence, specific small cell network deployments such as the one considered in this paper have to adopt an integrated quality of service provisioning approach. A femtocell utilizing an existing internet protocol (IP) infrastructure has usually to share the backhaul capacity with several IP networks. As these networks do not provide an efficient admission control process, the capacity allocated to the femtocell can fluctuate unpredictably over time. As a remedy, we propose a scheme for small cells' efficient integration (SCEI) in the IP infrastructure. SCEI is able to manage the total incoming traffic load and continuously adjust the distribution of the backhaul capacity among the existing networks. Simulation results show that SCEI provides significantly higher utilization of the backhaul capacity and more resilience regarding quality‐of‐service‐related metrics in overload state situations compared with state‐of‐the‐art hybrid partitioning techniques. Finally, this work also provides hints on ways that SCEI concepts can be applicable in more future Internet and small cell network deployment variants. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance evaluation of dynamic routing based on the use of satellites and intelligent networks

A dynamic routing scheme for public switched telephone networks is introduced which employs satellite broadcast to distribute network load data. The proposed network architecture closely resembles the IN (Intelligent Network) architecture, whereby the IN SCPs (Service Control Points) serve as so‐called Routing Control Points (RCPs). The key functions of an RCP are (i) to execute the routing algorithm and issue routing instructions in response to routing queries it receives from its associated switches for calls which overflow from the default network links, and (ii) to monitor and evaluate the pattern of received routing queries to obtain an estimate for the traffic loads present in each RCP's domain of associated switches. Satellite broadcast is used to distribute the load information among all RCPs in the network in a periodic fashion. This paper also reports on the results of extensive call‐by‐call simulations. The objective of the simulations was to validate this new routing scheme and compare its performance with well‐known existing schemes. Real traffic and network data as measured in the Austrian PSTN were used in the simulations. The main results are that, under all realistic network and traffic conditions including link and node failures, the proposed scheme yields lower blocking rates and significantly less routing and crankback attempts than the existing dynamic routing schemes. Note that this is achieved in the absence of any load measurements within the switches. As regards the periodic satellite based RCP‐RCP broadcast for the PSTN studied, it was shown that an update period of 10 seconds yields an excellent routing performance which is close to the limit of a vanishing update period. This revised version was published online in June 2006 with corrections to the Cover Date.     

Performance Evaluation of a Power Management Scheme for Disruption Tolerant Network

Disruption tolerant network (DTN) is characterized by frequent partitions and intermittent connectivity. Power management issue in such networks is challenging. Existing power management schemes for wireless networks cannot be directly applied to DTNs because they assume the networks are well-connected. Since the network connectivity opportunities are rare, any power management scheme deployed in DTNs should not worsen the existing network connectivity. In this paper, we design a power management scheme called context-aware power management scheme (CAPM) for DTNs. Our CAPM scheme has an adaptive on period feature that allows it to achieve high delivery ratio and low delivery latency when used with Prophet, a recently proposed DTN routing scheme. Via simulations, we evaluate the performance of the CAPM scheme when used with the Prophet routing scheme in different scenarios e.g. different traffic load, node speeds and sleep patterns. Our evaluation results indicate that the CAPM scheme is very promising in providing energy saving (as high as 80%) without degrading much the data delivery performance.     

Throughput increase in packet forwarding engines using adaptive block-selection scheme

We propose a new approach for using the block-selection scheme to increase the search throughput in a multi-block TCAM-based packet forwarding engine. While the existing methods try to counter and forcibly balance the inherent bias of the Internet traffic, our method takes advantage of it hence improving flexibility of table management and scalability towards high rates of change in traffic bias. This approach also offers higher throughput than the current art.     

Lighting fibers in a dark network

We consider the problem of network design in transparent, or clear channel, optical networks associated with wavelength-division multiplexing (WDM). We focus on the class of traffic engineering models known as routing, wavelength, and capacity assignment problems. Here, in contrast to traditional networks, traffic flow paths must also be assigned an end-to-end wavelength. This additional requirement means that there can be an increased cost associated with optimal capacity allocations for such WDM-flows. In general, this can be arbitrarily worse than traditional network designs. We argue that in order to evaluate the benefit of different switch technologies, a good benchmark is to measure the increase in costs purely in terms of link capacity, we call this the cost of transparency. Experimental research shows that this cost is small in multifiber networks with modest switching functionality at the nodes. We present theoretical justification for why this occurs, and prove that in multiwavelength multifiber transparent networks the cost of transparency all but disappears if there is moderate traffic load. Our arguments are based on efficient heuristics that may also be useful for more complex network optimizations. This suggests that the cost savings from using wavelength converters is significant only in young networks with relatively few fibers lit. Such savings may, thus, be small relative to the initial capital expense involved in installing wavelength conversion.     

Lightpath Re-optimization in mesh optical networks

Intelligent mesh optical networks deployed today offer unparalleled capacity, flexibility, availability, and, inevitably, new challenges to master all these qualities in the most efficient and practical manner. More specifically, demands are routed according to the state of the network available at the moment. As the network and the traffic evolve, the lightpaths of the existing demands becomes sub-optimal. In this paper we study two algorithms to re-optimize lightpaths in resilient mesh optical networks. One is a complete re-optimization algorithm that re-routes both primary and backup paths, and the second is a partial re-optimization algorithm that re-routes the backup paths only. We show that on average, these algorithms allow bandwidth savings of 3% to 5% of the total capacity in scenarios where the backup path only is re-routed, and substantially larger bandwidth savings when both the working and backup paths are re-routed. We also prove that trying all possible demand permutations with an online algorithm does not guarantee optimality, and in certain cases does not achieve it, while for the same scenario optimality is achieved through re-optimization. This observation motivates the needs for a re-optimization approach that does not just simply look at different sequences, and we propose and experiment with such an approach. Re-optimization has actually been performed in a nationwide live optical mesh network and the resulting savings are reported in this paper, validating reality and the usefulness of re-optimization in real networks.