Improve Network Efficiency Research Articles

A Seamless Handoff Scheme with Access Point Load Balance for Real-Time Services Support in 802.11 Wireless LANs

IEEE 802.11 wirelesses LANs (WLANs) have been rapidly deployed in enterprises, public areas, and households. Voice-over-IP (VoIP) and similar applications are now commonly used in mobile devices over wireless networks. Recent works have improved the quality of service (QoS) offering higher data rates to support various kinds of real-time applications. However, besides the need for higher data rates, seamless handoff and load balancing among APs are key issues that must be addressed in order to continue supporting real-time services across wireless LANs and providing fair services to all users. In this paper, we introduce a novel access point (AP) with two transceivers that improves network efficiency by supporting seamless handoff and traffic load balancing in a wireless network. In our proposed scheme, the novel AP uses the second transceiver to scan and find neighboring STAs in the transmission range and then sends the results to neighboring APs, which compare and analyze whether or not the STA should perform a handoff. The initial results from our simulations show that the novel AP module is more effective than the conventional scheme and a related work in terms of providing a handoff process with low latency and sharing traffic load with neighbor APs.

A recursive, cell processing model for predicting freeway travel times

Travel time information influences driver behaviour and can contribute to reducing congestion and improving network efficiency. Consequently many road authorities disseminate travel time information on road side signs, web sites and radio traffic broadcasts. Operational systems commonly rely on speed data obtained from inductive loop detectors and estimate travel times using simple algorithms that are known to provide poor predictions particularly on either side of the peak period. This paper presents a new macroscopic model for predicting freeway travel times which overcomes the limitations of operational ‘instantaneous’ speed models by drawing on queuing theory to model the processing of vehicles in sections or cells of the freeway. The model draws on real-time speed, flow and occupancy data and is formulated to accommodate varying geometric conditions, the relative distribution of vehicles along the freeway, variations in speed limits, the impact of ramp flows and fixed or transient bottlenecks. Field validation of the new algorithm was undertaken using data from two operational freeways in Melbourne, Australia. Consistent with the results of simulation testing, the validation confirmed that the recursive model provided a substantial improvement in travel time predictions when compared to the model currently used to provide real-time travel time information to motorists in Melbourne.

Beyond rapid provisioning: Driving value-added services on control plane foundations

Optical control planes came to the forefront during the Internet boom of the late 1990s as the network operations solution of choice for emerging mesh architectures. However, in spite of the numerous advantages, their deployments in service provider networks have been below expectations. While the telecom downturn of the last few years is often blamed, we also posit that control planes lost some of their luster because the applications they were primarily marketed for — rapid provisioning for bandwidth-on-demand services and mesh restoration — failed to get the requisite traction in the marketplace. In this paper, we propose that the changed landscape notwithstanding, optical control planes still fulfill a critical role in the service provider network. We argue that an underlying control plane foundation, with its routing and signaling infrastructure, gives tremendous flexibility to the operator to build new value-added services that can significantly improve network efficiency. Consequently, once deployed, these novel services can provide alternate avenues for revenue and capital expenditure (CapEx) savings in the long term. To that end, we present two applications — link defragmentation for legacy traffic and Ethernet mesh restoration — that leverage virtual concatenation in next-generation synchronous optical network (SONET) standards. We highlight our implementation experiences and show that the underlying control plane infrastructure is key to a low overhead deployment. We quantify the savings and conclude that in the current environment, these new customizable value-added services provide a prudent strategy for increasing service provider traction, especially with respect to long-term CapEx savings.

Incentive Regulation for German Energy Network Operators

Germany's newly instituted energy regulator, the BNA, has created high hopes that new rules would not only improve network efficiency but also provide a level playing field in energy markets. But an analysis suggests that the proposed new regulatory methods are unlikely to meet these objectives without provoking economic and legal challenges.

A Novel AP for Improving the Performance of Wireless LANs Supporting VoIP

Recently, wireless LANs based on the IEEE 802.11 standard have become popular and widely used, and Voice-over-IP (VoIP) is one of the most promising technologies to be used in mobile devices over wireless networks. Up-to-date, new technologies have improved, providing a high data rate to support various kinds of realtime applications. However, besides the need for higher data rates, seamless handoff is another important issue to be addressed in order to continue supporting real-time services across wireless LANs. In this paper we introduce a novel Access Point (AP) with two transceivers to improve network efficiency in terms of supporting seamless handoff and balancing the traffic load in a wireless network. In our proposed scheme, the novel AP will use the second transceiver to scan and find neighboring STAs in the transmission range and later send the result to its associate AP, which in turn compares and analyzes whether or not the STA should perform a handoff. The initial results from our simulations show the novel AP module is more effective than the conventional one in terms of providing a handoff process with low latency and support traffic load sharing with neighbor APs.

Supporting User Needs in a Network: A New Queue Management Technique

Traditional network-level Quality of Service (QoS) techniques are efficient from a network perspective, but they have not provided end-to-end QoS that is satisfactory to users. In this letter, a Coordinated Packet Discard scheme for the distribution of end-to-end QoS requirements into local loss constraints, as well as provision of local loss assurance is proposed. Experiments demonstrate its advantages on increasing QoS-satisfied user ratio and improving network efficiency.

Metrics for comparative analysis of operations competency

Improving network and service operations quality and efficiency to significantly reduce cost has become a business imperative for telecommunications service providers worldwide. However, one needs objective metrics by which to measure operations quality and efficiency and to facilitate comparison of them among service providers. This paper describes Total Operations Competency (TOC) metrics, a set of metrics designed to cover a comprehensive view of network and services operations. Although each metric is useful on its own, multiple metrics can also be used in combination to construct quantitative indicators for high-level business objectives. This paper also illustrates example applications of the metrics in business modeling and optimization.

LAMAN: Load Adaptable MAC for Ad Hoc Networks

In mobile ad hoc radio networks, mechanisms on how to access the radio channel are extremely important in order to improve network efficiency. In this paper, the load adaptable medium access control for ad hoc networks (LAMAN) protocol is described. LAMAN is a novel decentralized multipacket MAC protocol designed following a cross-layer approach. Basically, this protocol is a hybrid CDMA-TDMA-based protocol that aims at throughput maximization in multipacket communication environments by efficiently combining contention and conflict-free protocol components. Such a combination of components is used to adapt the nodes' access priority to changes on the traffic load while, at the same time, accounting for the multipacket reception (MPR) capability of the receivers. A theoretical analysis of the system is developed presenting closed expressions of network throughput and packet delay. By simulations, the validity of our analysis is shown and the performances of a LAMAN-based system and an Aloha-CDMA-based one are compared.

Media access using dynamic bandwidth system to improve satellite network uplink performance

AbstractThe paper describes a media access system for satellite network uplinks. The media access protocol is designed to support a range of low‐level protocols using a dual‐framing system, that is, there is a synchronous traffic subframe in which registered station requests are assigned fixed blocks or slots and an asynchronous traffic subframe for unregistered station random access on a contention basis. Slots for the registered stations are assigned through request to the satellite; the remaining frame time is assigned to unregistered stations. Capacity waste through contention resulting in collisions is minimized. The system uses dynamic bandwidth (bit rate) allocation for each channel, that is, the base frequency and bandwidth are changed for each channel at frame boundaries. The total bandwidth for the sum of all uplink channels is fixed. Channels that have low load based upon their request in a prior uplink frame are assigned lower bandwidth, while those with higher loading are provided larger bandwidth. By sharing bandwidth over channels at frame boundaries, overall network efficiency and fairness are significantly enhanced. Bandwidth allocation is decided in the satellite. It allocates sufficient bandwidth for all synchronous traffic and then commits the remaining bandwidth to asynchronous traffic. Here, the allocation for asynchronous traffic provides each channel with sufficient slots so that equal probability of success for stations sharing the channel can be expected. The combination of traffic assignment and bandwidth allocation provides significant improvement in overall network efficiency and fairness for all traffic types. The hardware implementation of media access for variable bandwidth sharing between channels use the concepts of Digital Software Radio. Copyright © 2003 John Wiley & Sons, Ltd.

Grid-distributed visualizations using connectionless protocols

The NERSC and Lawrence Berkeley National Laboratory visualization group has developed the Visapult tool to attack grand challenge problems. Visapult is a distributed, parallel, volume rendering application that leverages parallel computation and high-performance networking resources that are on the same scale as the supercomputers generating the data. We've improved Visapult's effectiveness using aggressive network tuning and network protocol modifications. In particular, we used a new connectionless user datagram protocol (UDP) to improve network efficiency from a 25 to 88 percent line rate increase for multigigabit networks. This connectionless protocol also dramatically reduces the latency of network event delivery, improving the responsiveness of wide area distributed interactive graphics applications as compared to transmission control protocol (TCP) streams. We believe that this UDP protocol, as well as transport encodings and algorithms that can tolerate loss gracefully, will become a fundamental component of future grid visualization architectures.

Toward Secure and Resilient Interdependent Infrastructures

A new megainfrastructure is emerging from the convergence of energy ~including the electric grid, water, oil and gas pipelines!, telecommunications, transportation, Internet and electronic commerce. Furthermore, in the electric power industry and other critical infrastructures, new ways are being sought to improve network efficiency and eliminate congestion problems without seriously diminishing reliability and security. Maintaining reliability, security, and robustness of critical national and international infrastructures is becoming increasingly challenging and a comprehensive strategy is needed to prepare for the diverse threats posed by the evolving spectrum of destabilizers. Such a strategy should both increase protection of vital industry assets and ensure the public that they are well protected. All the infrastructure industries in the United States, and to a significant extent in many other nations, have multiple ownership and management and they operate with only a minimum of regulation by the national government. The international infrastructure is operated by a combination of national governments, national corporate entities, and increasingly by multinational corporations. Only treaties whose enforcement depends heavily on the goodwill and cooperation of all parties, regulate the behavior of these heterogeneous organizations. There is also the effect of deregulation and economic factors and the impact of policies and human performance. As recent events in the United States, specifically California, have shown the network is becoming increasingly stressed. Whether the capacity or safety margin will exist to support anticipated demand is in question. The complex systems used to relieve bottlenecks and clear disturbances during periods of peak demand are at great risk of serious disruption, creating a critical need for technological improvements. Thus these infrastructures are increasingly vulnerable to failures cascading through and between them. A key concern is the avoidance of widespread network failure due to cascading and interactive effects. Management of disturbances in all infrastructures, along with prevention of cascading effects throughout and between networks, requires a basic understanding of true system dynamics, as well as effective distributed control so that to halt cascading effects proactively, or at least after a disturbance, enable parts of the networks to remain operational and even automatically reconfigure themselves. Given economic, societal, quality-of-life issues, and the everincreasing interactions among infrastructures, science and technology has a major role to play and create innovative solutions. Although the immediate and critical goal is to avoid widespread network failure, the longer-term vision is to enable adaptive and

The architecture of HORNET: A packet-over-WDM multiple-access optical metropolitan area ring network

To cost-effectively address the phenomenal demand for bandwidth in the metropolitan area, the Optical Communications Research Laboratory at Stanford University and Sprint Advanced Technology Laboratories have developed a novel architecture for a large-scale metropolitan area network (MAN). The network, which is called HORNET, is a packet-over-WDM multiple-access network featuring the use of fast-tunable transmitters and a novel “CSMA/CA” media access protocol to improve network efficiency well beyond that of today’s solution. This paper presents the design and implementation of the network architecture and gives an analytical discussion of its advantages.

A virtual path routing algorithm for ATM networks based on the equivalent bandwidth concept

The coexistence of a wide range of services with different quality of service (QoS) requirements in today's networks makes the efficient use of resources a major issue. It is desirable to improve network efficiency by adaptively assigning resources to services that have different bandwidth demands. Implementing Broadband Integrated Services Digital Networks (B-ISDN) therefore requires a network control scheme that can handle bursty traffic with unexpected fluctuations. The Asynchronous Transfer Mode (ATM) technology provides this flexibility by virtualizing network resources through the use of the virtual path (VP) concept. In this study, a method for designing a VP-based ATM network is proposed. The developed heuristic design algorithm applies VP routing and separation techniques to minimize the maximum link utilization under processing delay constraints. Each link is assigned a weight that reflects its current utilization. Using these weights, the VPs on highly utilized links are rerouted to less congested physical paths. The algorithm makes use of the equivalent bandwidth concept, which provides an efficient method to estimate capacity requirements of connection requests such that QoS requirements are met. The quality of the solutions achieved by the proposed method is compared to several competitors under varying network topologies and traffic conditions. The observations on the algorithm performance show that the developed method is able to facilitate an efficient use of network resources through the introduction of VPs.

Future transport network architectures

The architecture of today's long distance transmission networks, which we call the baseline architecture, is a complex and multilayered hierarchy of TDM circuits. One premise of the baseline architecture is that restoration from network failures is provided mostly by SONET/SDH rings. This article presents an alternative architecture that uses ATM and optical layer cross-connect technology for TDM services. Using a sophisticated set of network design tools developed at AT&T Labs-Research, we show that the alternative architecture offers dramatic capital savings and improved network efficiency over the baseline architecture. Most of this savings can be attributed to use of OLXC mesh network restoration, which makes more efficient use of capacity than SONET/SDH rings, and use of ATM switching for transport of TDM circuits, which consolidates the numerous TDM equipment layers inherent to the baseline architecture. In addition, motivated by the rapid growth of IP services, we analyze in the alternative architecture whether to provide restoration for IP services in the IP layer itself, by rerouting packets over precalculated restoration paths with MPLS, or to alternatively provide restoration of failed IP layer links in the OLXC layer. One potential advantage of IP layer restoration is that network operators may choose to only restore a fraction of the services, in particular the priority services, affected by a network failure. This article gives some methodology of how to determine this fraction at which IP layer restoration is cost-competitive with OLXC restoration.

A 2.5 Gb/s ATM switch chip set

The design and implementation of two application specific integrated circuits used to build an ATM switch are described. The chip set is composed of the CMC which is an input/output processor of ATM cells implemented on a BICMOS 0.7 /spl mu/m technology and the ICM, a 0.7 /spl mu/m CMOS IC, that performs cell switching at 68 MHz. The ATM switch exploits parallelism and segmentation to perform 2.5 Gb/s switching per input/output. The main advantage of the high-speed link rates in the range of Gb/s, is the exploitation of statistical gain with bursty high peak rate sources. Another feature of the high speed ATM switches is that the number of interface devices and stages is reduced on an ATM network. To demonstrate the usefulness of the switch, an evaluation of the network efficiency improvement by using statistical gain is presented in the paper.

Resource management with virtual paths in ATM networks

A virtual path connection (VPC) is a labelled path which can be used to transport a bundle of virtual channel connections (VCCs) and to manage the resources used by these connections. The virtual network is organized as a collection of VPCs which form a VPC, or logical, overlay network. If the VPCs are permanent or semi-permanent and have reserved capacity, establishing new VCCs requires simple connection admission decisions at the VPC terminators of existing VPCs. This would enable faster connection establishment since transit nodes are not involved in the connection setup. The virtual path concept also allows the possibility of segregating traffic types according to quality of service requirements. However, the extent to which VPC provisioning is able to improve network efficiency is dependent on the resource management decisions that determine the VPC topology and capacity allocations. The article surveys resource management using virtual paths in an ATM network. Of interest are techniques which modify the VPC topology and capacity assignments in order to adapt to changing traffic conditions and possible network failures. The resource management activities employed to facilitate such adaptation can be categorized by the timescale on which they operate. On the shortest timescale are strategies for dynamically making minor changes to the VPC topology or capacity assignments. On a somewhat longer timescale are strategies for making more widespread modifications to the VPC overlay network. This would be appropriate for traffic changes based on time of day and for recovering from network failures. Finally, on an even longer timescale, strategies may be employed to design a general VPC overlay network, to be used at startup or after major network upgrades. Solutions to VPC resource management for each of these timescales are discussed.

Servicing and Real-Time Control of Networks With Dynamic Routing

The design of a network for dynamic routing is made using the forecasted network loads. Load uncertainties arising from errors in the forecast and from daily variations in network load give rise to reserve or idle network capacity not immediately needed by current network demands. The reserve capacity can be reduced by the use of more flexible dynamic routing methods, which allow routing flexibility to help control network flow under load uncertainties. We illustrate techniques for changing network routing patterns in planned and demand servicing to counteract the effects of forecast errors. Included in the benefits are a reduction in both reserve capacity, estimated to be about 5 percent of network first cost, and in trunk rearrangements. We also present call-by-call simulation results for real-time routing enhancements to the basic routing algorithms. The real-time routing algorithms use dynamic trunk reservation techniques, and the simulation results illustrate the improvement in network efficiency and performance under normal daily load variations, network overloads, and network failures.