Quality of Service Management in GPRS-Based Radio Access Networks

In this article, the performance and capacity gain achievable with quality of service (QoS) management in packet switched radio networks based on the General Packet Radio Service (GPRS) are examined. Both the functions defined in the GPRS specification for QoS support and implementation-specific strategies for subscriber- and application-based Connection Admission Control (CAC) and scheduling are introduced. The feasibility of QoS provisioning in mobile core networks with use of DiffServ compared to present IP technology realizing a pure Best-effort service is examined in addition. To achieve this, simulation results of GPRS performance and system measures for different load situations are produced with the simulation tool GPRSim that models the realistic traffic behavior of a GPRS network.     

Enhancing Fairness and Throughput of TCP in Heterogeneous Wireless Access Networks

Most of the recent research on TCP over heterogeneous wireless networks has concentrated on differentiating between packet drops caused by congestion and link errors, to avoid significant throughput degradations due to the TCP sending window being frequently shut down, in response to packet losses caused not by congestion but by transmission errors over wireless links. However, TCP also exhibits inherent unfairness toward connections with long round-trip times or traversing multiple congested routers. This problem is aggravated by the difference of bit-error rates between wired and wireless links in heterogeneous wireless networks. In this paper, we apply the TCP Bandwidth Allocation (TBA) algorithm, which we have proposed previously, to improve TCP fairness over heterogeneous wireless networks with combined wireless and wireline links. To inform the sender when congestion occurs, we propose to apply Wireless Explicit Congestion Notification (WECN). By controlling the TCP window behavior with TBA and WECN, congestion control and error-loss recovery are effectively separated. Further enhancement is also incorporated to smooth traffic bursts. Simulation results show that not only can the combined TBA and WECN mechanism improve TCP fairness, but it can maintain good throughput performance in the presence of wireless losses as well. A salient feature of TBA is that its main functions are implemented in the access node, thus simplifying the sender-side implementation.     

面向WLAN的无线传感器网络网关设备及其接入机制

网关是实现无线传感器网络与其他基础网络（如移动通信网、电信网等）互联互通的重要设备。文章设计并实现了一种基于CC2420芯片的网关,实现了与传感器网络的通信,并利用无线网卡模块实现了网关设备与无线局域网的连接,克服了网关硬件设备布置的局限性,扩大了网关设备和无线传感器网络的应用范围。     

宽带无线接入系统中抑制多径效应的关键技术

主要介绍宽带无线接入系统中的多径效应，以及采用VOFDM技术抑制我径效应的机理，分析基于VOFDM和DOCSIS MAC的无线调制解调器工作原理和提高通信质量的关键技术。     

Improving Web Performance in Home Broadband Access Networks

Web caching is a significantly important strategy for improving Web performance. In this paper, we design SmartCache, a router-based system of Web page load time reduction in home broadband access networks, which is composed of cache, SVM trainer and classifier, and browser extension. More specifically, the browser interacts with users to collect their experience satisfaction and prepare training dataset for SVM trainer. With the desired features extracted from training dataset, the SVM classifier predicts the classes of the Web objects. Then, integrated with LFU, the cache makes a cache replacement based on SVM-LFU policy. Finally, by implementing SmartCache on a Netgear router and Chrome browsers, we evaluate our SVM-LFU algorithm in terms of Web page load time, SVM accuracy, and cache performance, and the experimental results illustrate that SmartCache can greatly improve Web performance in Web page load time.     

ADSL宽带接入网业务分析

认为ADSL是一种全新、快捷和高效的接入方式。介绍了ADSL的发展过程、结构和所承载的业务,将ADSL与N-ISDN、DDN和CABLEModem进行了比较,提出了拓展ADSL市场的策略和要解决的问题等等。     

Improving Radio Resource Utilization and User Level Fairness in OFDMA Femtocell Networks

Poor indoor coverage and high cost of cellular network operators are among the main motivations for the employment of femtocell networks. Since femto access points (FAPs) and macrocells share same spectrum resources, radio resource allocation is an important challenge in OFDMA femtocell networks. Mitigating interference and improving fairness among FAPs are the main objectives in previous resource allocation methods. However, the main drawback is that user level fairness has not been adequately addressed in the previous methods, and moreover, most of them suffer from inefficient utilization of radio resources. In this paper, modeling the problem as a graph multi-coloring, a centralized algorithm is proposed to obtain both user level fairness and spectrum efficiency. This method employs a priority-based greedy coloring algorithm in order to increase the reuse factor and consequently the spectrum efficiency. Moreover, in situations where the number of available OFDM resources is not sufficient, the proposed method employs a novel fairness index to fairly share those remaining resources among users of FAPs. The performance comparison between the proposed and previous methods shows that the proposed method improves the balance between user-level fairness and resource utilization. In addition, the presented analyses show that the time complexity of the proposed method is less than that of conventional methods.     

A Directory Service for Perspective Access Networks

Network fragmentation occurs when the accessibility of a network-based resource to an observer is a function of how the observer is connected to the network. In the context of the Internet, network fragmentation is well known and occurs in many situations, including an increasing preponderance of network address translation, firewalls, and virtual private networks. Recently, however, new threats to Internet consistency have received media attention. Alternative namespaces have emerged as the result of formal objections to the process by which Internet names and addresses are provisioned. In addition, various governments and service providers around the world have deployed network technology that (accidentally or intentionally) restricts access to certain Internet content. Combined with the aforementioned sources of fragmentation, these new concerns provide ample motivation for a network that allows users the ability to specify not only the network location of Internet resources they want to view but also the perspectives from which they want to view them. Our vision of a perspective access network (PAN) is a peer-to-peer overlay network that incorporates routing and directory services that allow network perspective-sharing and nonhierarchical organization of the Internet. In this paper, we present the design, implementation, and evaluation of a directory service for such networks. We demonstrate its feasibility and efficacy using measurements from a test deployment on PlanetLab.     

Improving Throughput and Fairness by Reducing Exposed and Hidden Nodes in 802.11 Networks

Two well-known problems that can cause performance degradations in IEEE 802.11 wireless networks are the exposed-node (EN) and hidden-node (HN) problems. Although there have been isolated and incidental studies of EN and HN, a comprehensive treatment has not been attempted. The contributions of this paper are threefold: First, we provide rigorous mathematical definitions for EN and HN in wireless networks (including wireless local area networks (WLANs) with multiple access points (APs) and ad hoc networks). Second, we relate EN to the nonscalability of network throughput and HN to unfair throughput distributions. Third, we provide schemes to eliminate EN and HN, respectively. We show that the standard 802.11 technology is not scalable because, due to EN, more APs do not yield higher total throughput. By removing EN, our schemes make it possible to achieve scalable throughput commensurate with the seminal theoretical results in [1] and [2]. In addition, by removing HN, our schemes solve the performance problems triggered by HN, including throughput unfairness/starvation and rerouting instability.     

Cross-Layer Rate Optimization for Proportional Fairness in Multihop Wireless Networks With Random Access

In this paper, we address the rate control problem in a multihop random access wireless network, with the objective of achieving proportional fairness amongst the end-to-end sessions. The problem is considered in the framework of nonlinear optimization. Compared with its counterpart in a wired network where link capacities are fixed, rate control in a multihop random access network is much more complex and requires joint optimization at both the transport and link layers. This is due to the fact that the attainable throughput on each link in the network is “elastic” and is typically a nonconvex and nonseparable function of the transmission attempt rates. Two cross-layer algorithms, a dual-based algorithm and a penalty-based algorithm, are proposed in this paper to solve the rate control problem in a multihop random access network. Both algorithms can be implemented in a distributed manner, and work at the link layer to adjust link attempt probabilities and at the transport layer to adjust session rates. We prove rigorously that the two proposed algorithms converge to the globally optimal solutions. Simulation results are provided in support of our conclusions.     

Improving Voice and Data Services in Cellular/WLAN Integrated Networks by Admission Control

In this paper, we study voice and data service provisioning in an integrated system of cellular and wireless local area networks (WLANs). With the ubiquitous coverage of the cellular network and the disjoint deployment of WLANs in hot-spot areas, the integrated system has a two-tier overlaying structure. As an essential resource allocation aspect, admission control can be used to properly admit voice and data calls to the overlaying cells and WLANs. A simple admission scheme is proposed in this study to analyze the dependence of resource utilization and the impact of user mobility and traffic characteristics on admission parameters. Both admission control and rate control are considered to limit the input traffic to the WLAN, so that the WLAN operates in its most efficient states and effectively complements the cellular network. The call blocking/dropping probabilities and data call throughput are evaluated for effective and accurate derivation of the admission parameters. It is observed that the utilization varies with the configuration of admission parameters, which properly distributes the voice and data traffic load to the cells and WLANs. Mobility and traffic variability have a significant impact on the selection of the admission parameters.     

Analysis of Traffic Access Control Strategies in Integrated Service Networks

A common digital transmission facility provides service to a community of heterogeneous users generating traffic with differing intensity, message length, and bit rate. In order for this type of integrated communication system to handle its traffic demands with high efficiency and flexibility, close control of access and switching at the input node is required. We propose, analyze, and compare two different strategies for managing the access of two types of traffic, a blockable wide-band (WB) type of traffic and a queueable narrow-band (NB) type of traffic, sharing the transmission resource dynamically. The first strategy assigns preemptive priority to the WB traffic over the NB traffic, whereas the second strategy employs a wide-band to narrow-band bit rate compression mechanism. Exact analytic models are developed, and solution methods are presented and implemented. It is shown that the best combined performance is obtained when the two strategies are adaptively combined according to the offered load.     

Quality of Service Drivers in LTE and LTE-A Networks

In the last years, cellular operators have experienced a rapid growth of mobile broadband subscribers and traffic volume per subscriber. At the same time, operators are moving from a single to a multi-service offering by adding new services such as multimedia telephony and mobile-TV. In this challenging scenario, the Quality of Service (QoS) concept provides network and service operators with a set of tools to enable service and subscriber differentiation. This paper presents an overview of the QoS drivers in Long-Term Evolution (LTE) and LTE-Advanced (LTE-A) networks, focusing on their QoS policy control capabilities. Proposals of policy control and management for increasing the QoS in LTE and LTE-A networks are described. This paper also includes a detailed list and analysis of the inputs to the Policy and Charging Rules Function (PCRF) that can be used for policy decision as well as a set of use cases involving the Policy and Charging Control architecture: (1) the analysis of a potential cooperation between the PCRF and a Deep Packet Inspector, and (2) the analysis of a potential interaction between the PCRF and the radio scheduler to provide a consistent end-to-end QoS.     

Quality of Service and Capacity in Constrained Intermittent-Connectivity Networks

In an intermittent-connectivity network, there rarely exists a connected path between a source node and its destination. These networks arise frequently when each node has a limited transmission range, such as a communication network between separated villages or a surveillance network with a large geographical span. One method of addressing the low connectivity of the network uses redundancy. A node generates and stores data; upon reaching the communication range of another node, it replicates the data to it. Multiple copies of the packet decrease the time to offload the data to the destination, but increase the energy and storage used in the system. In this paper, we quantify the resource-delay trade-off and the throughput capacity for intermittent-connectivity networks with quality of service restrictions such as limited communication bandwidth. Many routing protocols have been proposed for these intermittent-connectivity networks. Using the shared wireless infostation model as an example strategy, we mathematically represent the intermittent-connectivity network and adjust the model to include a quality of service constraint. By completely defining a mathematical model, we allow network designers control over system performance through the adjustment of allocated resources such as communication bandwidth, fraction of time a node spends in sleep mode, or required reliability of packet offloading.     

Vertical Handover Over Intermediate Switching Framework: Assuring Service Quality for Mobile Users

Ensuring quality of service (QoS) for the mobile users during vertical handover between IEEE 802.11 wireless local area networks (WLAN) and data network provided by Ultramodern Telecommunication Systems (UMTS) is one of the key requirements for seamless mobility and transfer of existing connections from one network to another. QoS fulfillment is a complex problem and requires participation of both the mobile users as well as the connection networks. The QoS assurance criteria for existing connections can be affected by fluctuations of data rates when a user moves from the high speed WLAN network to the low speed UMTS network, even in the presence of another WLAN network in its vicinity. This can happen if the alternate WLAN network is highly loaded. Therefore handover from a high speed network to a low speed network should be avoided, whenever possible. This paper proposes a QoS based handover procedure that prioritizes the existing connection over the new connections so that rate fluctuations due to handover can be avoided if there exist another WLAN network in the range of the mobile user. Whenever the possibility of handover is detected, a pre-handover bandwidth reservation technique is used to reserve bandwidth at the alternate WLAN networks to avoid QoS degradation. The proposed scheme is implemented in Qualnet network simulator and the performance is analyzed and compared with traditional handover techniques.     

采用MSTP设备接入IP数据业务的组网方案

根据目前IP数据业务接入的现状，浅谈IP数据业务接入的几种方式并分析存在的问题，然后提出利用MSTP设备建设下一代IP数据业务接入的建设步骤以及组网方案，同时提出IP数据业务与TDM业务分层建设概念。     

User-Centric Offloading to WLAN in WLAN/3G Vehicular Networks

In recent years, there has been a growing demand in 3G data services, leading to deteriorating 3G service quality. Noting that Wireless Local Area Networks (WLANs) as well as 3G cellular networks are widely available today, WLANs could be effectively utilized to relieve the overload in the 3G networks. On the other hand, use of IEEE 802.11 WLAN Access Points (APs) has proliferated tremendously, resulting in a communication device inside a mobile vehicle to access the Internet. However, using Internet through APs in moving vehicles is challenging since WLAN APs have a short range and are typically not deployed to cover all roads. Several studies have investigated the performance of using intermittently available WLAN connectivity from moving vehicles for data transfers and predictive offloading in WLAN/3G networks. However, these works have not addressed mobility pattern from the viewpoint that drivers’ mobility is generally known to have a daily routine. Therefore, in this paper, we consider the user’s historical mobility to decide to offload data to WLAN instead of switching to 3G network. The user’s application usage pattern is also considered into predicting available WLANs. To evaluate the performance of our offloading algorithm, we analyze the prediction error and conduct simulations. The simulation results show that the proposed algorithm achieves shorter transmission time than the existing schemes that do not consider user’s mobility pattern by delivering more data to the WLANs.     

广电宽带小区接入的WLAN解决方案

小区宽带接入方式是各运营商必须面对的问题。从有线网络与无线局域网（WLAN）的比较入手，分析了无线局域网网络组建、网络安全和系统设计优化问题。由于采用成熟的以太网技术，并得到网络设备、手持设备等厂商支持，因此认为在居民小区网络建设中，WLAN不失为一种方便快捷切实可行的接入方法，并给出了解决方案。     

QUORUM—Quality of Service in Wireless Mesh Networks

Wireless mesh networks (WMNs) can provide seamless broadband connectivity to network users with low setup and maintenance costs. To support next-generation applications with real-time requirements, however, these networks must provide improved quality of service guarantees. Current mesh protocols use techniques that fail to accurately predict the performance of end-to-end paths, and do not optimize performance based on knowledge of mesh network structures. In this paper, we propose QUORUM, a routing protocol optimized for WMNs that provides accurate QoS properties by correctly predicting delay and loss characteristics of data traffic. QUORUM integrates a novel end-to-end packet delay estimation mechanism with stability-aware routing policies, allowing it to more accurately follow QoS requirements while minimizing misbehavior of selfish nodes.