Showing papers in "IEEE Network in 2005"

BGP routing policies in ISP networks

Abstract: The Internet has quickly evolved into a vast global network owned and operated by thousands of different administrative entities. During this time, it became apparent that vanilla shortest path routing would be insufficient to handle the myriad operational, economic, and political factors involved in routing. ISPs began to modify routing configurations to support routing policies - goals held by the router's owner that controlled which routes were chosen and which routes were propagated to neighbors. BGP, originally a simple path vector protocol, was incrementally modified over time with a number of mechanisms to support policies, adding substantially to the complexity. Much of the mystery in BGP comes not only from the protocol complexity, but also from a lack of understanding of the underlying policies and the problems ISPs face that are addressed by these policies. In this article we shed light on goals operators have and their resulting routing policies, why BGP evolved the way it did, and how common policies are implemented using BGP. We also discuss recent and current work in the field that aims to address problems that arise in applying and supporting routing policies.

FAST TCP: from theory to experiments

Abstract: We describe a variant of TCP, called FAST, that can sustain high throughput and utilization at multigigabits per second over large distances. We present the motivation, review the background theory, summarize key features of FAST TCP, and report our first experimental results.

Performance analysis and enhancements for IEEE 802.11e wireless networks

Abstract: The IEEE 802.11 WLAN legacy standard cannot provide QoS support for multimedia applications. Thus, considerable research efforts have been carried out to enhance QoS support for 802.11. Among them, 802.11e is the upcoming QoS-enhanced standard proposed by the IEEE working group. This article describes in detail the new QoS features of 802.11e based on the latest version of the standard draft. We investigate the performance of 802.11e through computer simulations. Using simple examples, we show the effectiveness of adaptive schemes under the 802.11e framework.

The IEEE 802.11g standard for high data rate WLANs

Abstract: Continuous WLAN public acceptance comes with increasing demand for provision of higher data rates. Building on this context, the IEEE published the IEEE 802.11g standard for providing data rates of up to 54 Mb/s at the 2.4 GHz band. This article presents the new features of IEEE 802.11g and, using an open source C++-based simulation tool, evaluates both the performance and effectiveness of these features compared to the older IEEE 802.11 standard versions.

Modeling the routing of an autonomous system with C-BGP

Abstract: Today, the complexity of ISPs' networks make it difficult to investigate the implications of internal or external changes on the distribution of traffic across their network. In this article we explain the complexity of building models of large ISPs' networks. We describe the various aspects important to understanding the routing inside an AS. We present an open source routing solver, C-BGP, that eases the investigation of changes in the routing or topology of large networks. We illustrate how to build a model of an ISP on a real transit network and apply the model on two "what-if" scenarios. The first scenario studies the impact of chances in the Internet connectivity of a transit network. The second investigates the impact of failures in its internal topology.

Admission control in IEEE 802.11e wireless LANs

Abstract: Although IEEE 802.11 based wireless local area networks have become more and more popular due to low cost and easy deployment, they can only provide best effort services and do not have quality of service supports for multimedia applications. Recently, a new standard, IEEE 802.11e, has been proposed, which introduces a so-called hybrid coordination function containing two medium access mechanisms: contention-based channel access and controlled channel access. In this article we first give a brief tutorial on the various MAC-layer QoS mechanisms provided by 802.11e. We show that the 802.11e standard provides a very powerful platform for QoS supports in WLANs. Then we provide an extensive survey of recent advances in admission control algorithms/protocols in IEEE 802.11e WLANs. Our survey covers the research work in admission control for both EDCA and HCCA. We show that the new MAC-layer QoS schemes and parameters provided in EDCA and HCCA can be well utilized to fulfill the requirements of admission control so that QoS for multimedia applications can be provided in WLANs. Last, we give a summary of the design of admission control in EDCA and HCCA, and point out the remaining challenges.

Call admission control for QoS provisioning in 4G wireless networks: issues and approaches

Abstract: This article presents a survey on the issues and the approaches related to designing call admission control schemes for fourth-generation wireless systems We review the state of the art of CAC algorithms used in the traditional wireless networks The major challenges in designing the CAC schemes for 4G wireless networks are identified These challenges are mainly due to heterogeneous wireless access environments, provisioning of quality of service to multiple types of applications with different requirements, provisioning for adaptive bandwidth allocation, consideration of both call-level and packet-level performance measures, and consideration of QoS at both the air interface and the wired Internet To this end, architecture of a two-tier CAC scheme for a differentiated services cellular wireless network is presented The proposed CAC architecture is based on the call-level and packet-level QoS considerations at both the wireless and wired parts of the network A performance analysis model for an example CAC scheme based on this architecture is outlined, and typical numerical results are presented

Understanding 802.11e contention-based prioritization mechanisms and their coexistence with legacy 802.11 stations

Abstract: The IEEE 802.11e task group has reached a stable consensus on two basic contention-based priority mechanisms to promote for standardization: usage of different arbitration interframe spaces and usage of different minimum/maximum contention windows. The goal of this article is to provide a thorough understanding of the principles behind their operation. To this purpose, rather than limit our investigation to high-level (e.g. throughput and delay) performance figures, we take a closer look at their detailed operation, also in terms of low-level performance metrics (e.g., the probability of accessing specific channel slots). Our investigation on one hand confirms that AIFS differentiation provides superior and more robust operation than contention window differentiation. On the other hand, it highlights performance issues related to the coexistence between 802.11e contention-based stations with legacy 802.11 stations, and provides guidelines for the 802.11e parameter settings when such a coexistence is the goal.

An overview of scheduling algorithms in MIMO-based fourth-generation wireless systems

Abstract: In this article an overview of the scheduling algorithms proposed for fourth-generation multiuser wireless networks based on multiple-input multiple-output technology is presented. In MIMO systems a multi-user diversity gain can be extracted by tracking the channel fluctuations between each user and the base station, and scheduling transmission for the "best" user. Based on this idea, several opportunistic scheduling schemes that attempt to improve global capacity or satisfy users with different QoS requirements have been proposed. Transmit beamforming procedures aimed at increasing the channel fluctuations have been proposed. The simultaneous exploitation of both spatial and multi-user diversity is not straightforward; however, it may be achieved by a refined selection of the "best" user. In addition, a multiple access gain can be obtained from a simple SDMA/TOMA system. Finally, several resource allocation schemes are discussed for this hybrid multiple access system.

Resource management for QoS support in cellular/WLAN interworking

Abstract: To provide mobile users with seamless Internet access anywhere and anytime/ there is a strong demand for interworking mechanisms between cellular networks and wireless local area networks in the next-generation all-IP wireless networks. In this article we focus on resource management and call admission control for QoS support in cellular/WLAN interworking. In specific, a DiffServ interworking architecture with loose coupling is presented. Resource allocation in the interworking environment is investigated/ taking into account the network characteristics, vertical handoff, user mobility, and service types. An effective call admission control strategy with service differentiation is proposed for QoS provisioning and efficient resource utilization. Numerical results demonstrate the effectiveness of the proposed call admission control scheme.

Open issues in interdomain routing: a survey

Abstract: This article surveys several research challenges in interdomain routing. We introduce and describe these challenges in a comprehensible manner, along with a review of the most compelling contributions and ongoing research efforts addressing each of the exposed issues. During this analysis we identify the relation between these research challenges and now they influence each other. We also present our perspectives on why these issues remain largely unsolved, and point out why some of the proposals made so far have not yet been adopted. We hope this can provide some insight on future directions in this complex research area.

Fast handover support in a WLAN environment: challenges and perspectives

Abstract: While handover management has traditionally used radio-technology-specific mechanisms, the need for integration of this diverse network environment has obviated the "push" of the handover functionality to the generic IP layer that serves the rendezvous point of underlying technologies. In this context, we study and analyze the implications of the link-layer agnostic operation of IP handover control on handover performance, having as a reference the fast mobile IPv6 protocol. We show that the behavior of the protocol (i.e., whether a reactive or proactive operation will be executed) is highly dependent on the timely availability of link layer information. A non-exhaustive list of generic link-layer triggers used for this purpose, as identified by the IEEE 802.21 WG, is also presented. Last, we apply this generic framework to a WLAN environment running fast mobile IPv6 and study the improvements in fast handoff support.

Quality of service provisioning in 802.11e networks: challenges, approaches, and future directions

Abstract: In order to support diverse application requirements, a new standard called IEEE 802.11e is being proposed to improve quality of service in wireless LAN networks. There are, however, a few remaining challenges that need to be addressed in order to enable comprehensive QoS support using 802.11e. In this article we provide an overview of a few of these challenges, describe their possible impact on QoS, and provide a survey of techniques that potentially could be used to address the identified challenges. Specifically, we focus on three challenges: handling time-varying network conditions, adapting to varying application profiles, and managing link layer resources. Additionally, we present several potential future directions toward improved QoS in wireless networks.

Applications and challenges of the 802.11e EDCA mechanism: an experimental study

Abstract: In this article we conduct an experimental study of the enhanced distributed channel access mechanism of the upcoming 802.11e standard. The main focus of the study is on two applications of EDCA: traffic engineering and service guarantees. With traffic engineering we aim at distributing the bandwidth in the WLAN according to a given throughput allocation criterion. With service guarantees the objective is to ensure that the performance metrics (throughput and delay) experienced by a station meet a given quality criterion. We build a testbed with wireless cards that support a substantial subset of the EDCA functionality and analyze performance against different sets of requirements. Experimental results show that EDCA can effectively be used for traffic engineering purposes. The goal of providing service guarantees with EDCA is shown to be more challenging; we identify future research directions that need to be addressed in order to achieve this goal.

Size-based scheduling to improve the performance of short TCP flows

Abstract: The Internet today carries different types of traffic that have different service requirements. A large fraction of the traffic is either Web traffic requiring low response time or peer-to-peer traffic requiring high throughput. Meeting both performance requirements in a network where routers use droptail or RED for buffer management and FIFO as the service policy is an elusive goal. It is therefore worthwhile to investigate alternative scheduling and buffer management policies for bottleneck links. We propose to use the least attained service (LAS) policy to improve the response time of Web traffic. Under LAS, the next packet to be served is the one belonging to the flow that has received the least amount of service. When the buffer is full, the packet dropped belongs to the flow that has received the most service. We show that under LAS, as compared to FIFO with droptail, the transmission time and loss rate for short TCP flows are significantly reduced, with only a negligible increase in transmission time for the largest flows. The improvement seen by short TCP flows under LAS is mainly due to the way LAS interacts with the TCP protocol in the slow start phase, which results in shorter round-trip times and zero loss rates for short flows.

DTRA: directional transmission and reception algorithms in WLANs with directional antennas for QoS support

Abstract: Recent research results show that there are significant gains in throughput to be realized with directional transmission and directional reception compared to using omnidirectional; however, no specific reservation/scheduling algorithms are presented (Su Yi et al., 2003). In this article we propose a novel directional transmit and receive algorithm (DTRA) in wireless local area networks with directional antennas for quality of service support. To the best of our knowledge, all the previous work assumes omnidirectional reception at certain stages of the algorithms. However, the omnireceive requirement makes the protocol vulnerable to jamming. In this article no omniantennas or omnidirectional reception capability is assumed at all. The proposed algorithm exploits the beamforming capabilities of smart antennas to tailor resource access according to the services desired for individual traffic flows while limiting interference, probability of detection, and jamming in the network. Specifically, we present a TDMA-based MAC algorithm for load-dependent negotiation of slot reservations. Our new protocol offers four significant advantages: it assumes directional transmission/reception, it is distributed (i.e., it relies on local information only), it allocates slots to different links dynamically based on demand, and power control is easily carried out during neighbor discovery, reservation, and data transmission with very little overhead. We believe this is the first work on pure directional transmission and reception in wireless ad hoc networks. The algorithm can be used in many commercial and military applications. Preliminary simulation results indicate that DTRA performs much better than IEEE 802.11 for the network considered.

Sliding contention window (SCW): towards backoff range-based service differentiation over IEEE 802.11 wireless LAN networks

Abstract: A number of works have tried to adjust the contention window in order to provide differentiated quality of service in IEEE 802.11-based wireless networks. By giving different service classes different CWs, the distribution of backoff intervals (chosen randomly, on the interval [O, CW]) will reflect the desired service classes. However, these protocols cannot deliver firm service guarantees while maintaining high network utilization, particularly under congested network conditions. In this article we propose a new MAC protocol featuring a sliding CW (SCW) for each network flow. The SCW dynamically adjusts to changing network conditions, but remains within a per-class predefined range in order to maintain a separation between different service classes. Each flow's SCW reacts based on the degree to which class-defined QoS metrics are satisfied. Simulation results show that compared to the enhanced distributed coordination function (EDCF) scheme of 802.11e, SCW consistently excels, in terms of network utilization, strict service separation, and service-level fairness.

An architecture for next-generation radio access networks

Abstract: With fourth-generation wireless technologies envisioned to provide high bandwidth for content-rich multimedia applications, next-generation mobile communication systems are well poised to lead the technology march. Incumbent with the new technology is the challenge of providing flexible, reconfigurable architectures capable of catering to the dynamics of the network, while providing cost-effective solutions for service providers. In this article we focus on IP-based radio access network architectures for next-generation mobile systems. We provide an insight into wireless mesh-based connectivity for the RAN network elements - using short high-bandwidth links to interconnect the network entities in a multihop mesh network for backhauling traffic to the core. A generic self-similar fractal topology, using optical wireless transmission technology, is described. We study the performance of the architecture and conclude that mesh-based architectures are well suited to provide highly scalable, dynamic radio access networks with carrier-class features at significantly low system costs.

Traffic engineering in metro Ethernet

Abstract: Traffic engineering is a critical issue that has to be addressed in metro Ethernet networks for proper and efficient resource utilization as well as facilitating quality of service. This article aims at understanding the relevant issues and outlines novel algorithms for multipoint-TE in the metro Ethernet. We first propose a grouping scheme that extends the current label space in the provider domain and allows for a large number of VLANs to be provisioned efficiently. Next, the issues of load balancing, multiple spanning trees, and interaction between grouping and bandwidth provisioning are discussed, and solutions are provided. Finally, we address differentiated survivability in next-generation Ethernet and provide a novel scheme based on multiple spanning trees. The schemes proposed in this article are shown to be scalable, bandwidth-efficient, and practical for both the customer and the provider.

The performance impact of BGP security

Abstract: The border gateway protocol possesses security vulnerabilities, because speakers can lie. Proposed security protocols can address the vulnerabilities, but can significantly increase the performance overheads, which prevent their real-world deployment. Public key cryptography can address these vulnerabilities. We report our research into analyzing recently proposed security protocols and building simulation frameworks to evaluate their costs, and designing and validating techniques to reduce them.

Instant messaging and presence technologies for college campuses

Abstract: Instant messaging is an application that enables networked users to send and receive short messages. Presence provides information about users' reachability and willingness to accept/reject a brief chat session. Various proprietary IM and presence (IMP as a result, this important application is finding difficulty in widespread deployment within college campuses and businesses. We describe a brief history of the development of IM&P technology discuss the current standardization work being done within IETF, and present an overall architecture of emerging standards. We provide a comparison between the SIP/SIMPLE and Jabber/XMPP standards. We also present data and its analysis from a survey of campus organizations that sheds light into the main issues of deploying, managing and provisioning of IM&P services on college campus.

Radio resource sharing games: enabling QoS support in unlicensed bands

Abstract: Distributed quality of service support in wireless networks that are sharing unlicensed frequency bands is an increasingly significant research problem. The spectral coexistence of dissimilar radio systems has to be addressed in the near future in concerning the widely deployed IEEE 802.11 wireless local area networks and other future radio systems operating in unlicensed or opportunistically used frequency bands. The competition between independent wireless networks for allocating a common shared radio channel is modeled in this article as a stage-based game model: players, representing wireless networks, interact repeatedly in radio resource sharing games, without direct coordination or information exchange. Solution concepts derived from game theory allow the analysis of such models under the microeconomic aspects of welfare. Decisions players repeatedly have to make are about when and how often to attempt medium access. In multistage games the players apply strategies in order to maximize their observed utility as a summarizing value for successfully supported quality of service. Strategies determine whether competing radio networks cooperate or ignore the presence of other radio networks. The traffic requirements of a player thereby decide which strategy is adequate to guarantee quality of service.

On route selection for interdomain traffic engineering

Abstract: In this article we investigate a model of route selection for interdomain traffic engineering where routing to multiple destinations can be coordinated. We identify potential routing instability and inefficiency problems, and derive a set of practical guidelines to guarantee stability without global coordination. Using a realistic Internet topology, we show that route oscillations can happen even when a small number of ASes coordinate route selection for just a small number of destinations if the coordination does not follow our guidelines. Wc further extend our model so that ASes can adopt any route selection algorithms in a class of algorithms we call rational route selection algorithms; and the local ranking of routes of an AS can depend on ingress traffic patterns. We show that persistent route oscillations can happen in certain network settings even if the ASes strictly follow the constraints imposed by business considerations, and adopt any rational route selection algorithms.

Improving QoS and throughput in single- and multihop WLANs through dynamic traffic prioritization

Abstract: Nowadays, research efforts are being put into the design of effective mechanisms to provide service quality differentiation in IEEE 802.11-based wireless LANs. In this article we analyze the effects of augmenting the contention-based channel access mechanism of IEEE 802.11e through the assignment of dynamic traffic priorities, that adapt to either the application's quality requirements or the network congestion status. The aim is to show the effectiveness and robustness of the proposed dynamic mechanism in a wireless ad hoc network, in both single-hop and multihop scenarios, under variable traffic and network load conditions.

The Network Processing Forum switch fabric benchmark specifications: an overview

Abstract: The Network Processing Forum chartered a fabric benchmarking task group to establish a set of switch fabric benchmark specifications that allows the characterization of a wide range of switch fabrics for diverse networking applications. A unique characteristic of the benchmarks is their ability to produce comparable performance results for different switch fabrics, regardless of their underlying architecture and technology. This article provides an overview of the NPF fabric benchmark specifications by describing the various topics addressed by the standard as well as their potential impact.

End-to-end QoS provisioning in 4G with mobile hotspots

Abstract: The novel concept of mobile hotspots, characterized by a group of wireless users equipped with wireless LAN cards, moving as a whole and requiring Internet connectivity, is gaining the interest of the telecommunications research community. This article intends to contribute to this research topic by proposing alternative solutions for the deployment of a mobile gateway device offering 3G connectivity to the group of WLAN users while they are moving. This is a decisive aspect of the 3G migration to 4G networks. The proposed solutions allow for two-hop wireless paths between WLAN and 3G systems, and performing control over-high layer issues, specifically focusing on end-to-end QoS provisioning. The pros and cons of envisaged design solutions are addressed and their relevance justified considering purposes, target users, and applications.

UMTS-to-IP QoS mapping for voice and video telephony services

Abstract: Quality of service mapping between UMTS services and IP transport is crucial for maintaining a suitable end-to-end delay for emerging UMTS multimedia telephony. However, due to incompatibilities in QoS classifications within these two technologies, straightforward mapping is impossible and current proposals within the 3GPP could lead to unpredictable and undesirable behavior for certain services. In this article we focus on two very important UMTS services, voice and video telephony, and establish the QoS issues that exist for these services. We then propose a refined QoS mapping that differentiates between the transmission of voice and video-telephony and a weighted fair queuing scheduler to schedule the transmissions. Through a simulation study, we show the effect on the queuing delays of both traffic types when their WFQ weights vary and then derive an optimal weight that provides the best overall delays for multimedia telephony services.

Inbound traffic engineering for multihomed ASs using AS path prepending

Abstract: This article considers the AS path prepending approach to engineer inbound traffic for multihomed ASs. The AS path prepending approach artificially inflates the length of the AS path attribute on one of the links in hopes of diverting some of the traffic to other links. Unlike the current practice that determines the prepending length in a trial-and-error way, we propose AutoPrepend, a systematic and automated procedure for conducting prepending. The entire process consists of four components: passive measurement, active measurement, traffic change prediction, and AS path update. The main idea is to predict the traffic change due to a new prepending value before effecting the change. We have also employed a number of mechanisms to minimize intrusion into the normal operation of the Internet. We have deployed AutoPrepend on a noncommercial site and evaluated its effectiveness based on the measurements collected over six months.

Interoperability criteria, mechanisms, and evaluation of system performance for transparently interoperating WLAN and UMTS-HSDPA networks

Abstract: The main challenge in the development of future wireless communication systems is to provide users with a wide range of services across different radio access technologies through a single mobile terminal, while maintaining the minimum QoS requirements, and ideally with no limits on the coverage area, mobility or radio conditions. Thus, the need for seamless interworking between heterogeneous wireless communication systems consisting of multiple radio access technologies and overlapping networks emerges. In this article we address the main issues that arise while implementing the interoperability mechanisms between two different radio access networks, with emphasis on UMTS-HSDPA and WLAN (HIPERLAN/2). Two interoperability mechanisms are introduced and described in detail: initial user assignment (optimal network selection) and intersystem handover. Both mechanisms are activated via the optimization of a suitably defined cost function which takes into account all the appropriate system level parameters that trigger the interoperability process. Finally, we investigate the overall performance of the proposed mechanisms by means of a software simulation platform. A number of simulations have been carried out in order to demonstrate the performance enhancements achieved by the proposed mechanisms in terms of unsatisfied users, dropped handovers, and system throughput.

Toward the design of robust interdomain routing protocols

Abstract: The border gateway protocol, the interdomain routing protocol for the Internet, allows for a wide variety of routing policies that may interact in unintended and unstable ways. Recent work on BGP and related protocols has begun to incorporate formal protocol models, which have enabled rigorous descriptive analyses of BGP. More recently, such models have been used to give prescriptive guidelines for the design of new protocols. These guidelines include both sufficient conditions for good routing behavior and limitations on what can be achieved without coordination between routers. Here we review potential routing problems, various formal protocol models, and the design guidelines they have been used to prove.