一种新的基于移动IPv6的快速切换方案

基本的移动IPv6（MIPv6）切换延迟非常大，不能满足实时业务的要求。本文基于对MIPv6的切换时延的分析，提出了一种IEEE802．11无线局域网环境下MIPv6的低时延切换方法，该方法通过结合使用连接触发器和快速路由器公告，并通过IP地址与MAC地址的映射机制来优化切换过程。仿真结果表明，该方法能够有效降低节点切换过程的时延，同时其性能优于以往相关的工作。     

一种新的WLAN环境下移动IPv6的低时延切换方法

提出了一种IEEE 802.11无线局域网环境下移动IPv6的低时延切换方法NDPR.在不依靠链路层触发的条件下,NDPR使用非均匀检测模型来减小切换检测产生的时延,降低了切换检测过程的开销.通过IP地址与MAC地址的映射机制和转交地址的预注册机制,NDPR减小了移动IPv6的移动检测和转交地址配置过程的时延.仿真结果表明,该方法不但能够有效降低节点切换过程的时延,而且其性能优于以往相关的工作.     

A conflict-insensitive NATed roaming framework using NAToD for proxy mobile IPv4 in WLANs

Providing efficient mobility management in the current Internet is increasingly important due to the quick growth of wireless mobile users. The emerging Proxy Mobile IPv4 (PMIPv4) technique brings a possible solution for that purpose. Since NAT function is widely adopted in IPv4 environment nowadays because of lacking IPv4 addresses, the PMIPv4 interoperating with NAT must be considered. Unfortunately, owing to the possible conflict of private IP address, we encounter a problem in broadcasted point-to-multipoint wireless networks such as IEEE 802.11 networks. To address this issue, we proposed a novel Network Address Translation on Demand (NAToD) scheme, which can well interoperate with the PMIPv4 solution. With our scheme, single public IPv4 addresses can be shared by multiple mobile nodes in both home and foreign networks, low-latency handoff can be achieved, deployment cost can be reduced, and software upgrade can be avoided for mobile nodes in wireless LANs. Our work allows mobile users in WLAN to access Internet based on the advantages of both PMIPv4 and NAT.     

High-performance architectures for IP-based multihop 802.11 networks

The concept of a forwarding node, which receives packets from upstream nodes and then transmits these packets to downstream nodes, is a key element of any multihop network, wired or wireless. While high-speed IP router architectures have been extensively studied for wired networks, the concept of a "wireless IP router" has not been addressed so far. We examine the limitations of the IEEE 802.11 MAC protocol in supporting a low-latency and high-throughput IP datapath comprising multiple wireless LAN hops. We first propose a wireless IP forwarding architecture that uses MPLS with modifications to 802.11 MAC to significantly improve packet forwarding efficiency. We then study further enhancements to 802.11 MAC that improve system throughput by allowing a larger number of concurrent packet transmissions in multihop 802.11-based IP networks. With 802.11 poised to be the dominant technology for wireless LANs, we believe a combined approach to MAC, packet forwarding, and transport layer protocols is needed to make high-performance multihop 802.11 networks practically viable.     

A Seamless Handoff Mechanism for DHCP-Based IEEE 802.11 WLANs

IEEE 802.11 wireless networks have gained great popularity. However, handoff is always a critical issue in this area. In this paper, we propose a novel seamless handoff mechanism for IEEE 802.11 wireless networks which support IEEE 802.11i security standard. Our approach consists of a dynamic tunnel establishing procedure and a seamless handoff mechanism. Both intra- and inter-subnet handoff cases are considered in our seamless handoff approach. Our work focuses on handoffs in DHCP-based IP networks rather than mobile IP-supported networks, but the proposed scheme can be easily tailored to mobile IP-supported networks.     

基于平面路由的无线Mesh网切换技术

通过对无线Mesh网络区别于传统无线局域网的特性的分析,以及无线Mesh网的链路层切换机制、网络层切换机制的深入研究,提出了一种基于平面路由和移动IP的无线Mesh网络快速切换机制,并在该机制下给出了2种具体的实现方案。仿真分析表明,上述方案都充分利用了无线Mesh网络的特性,能够有效降低切换时延、减少数据包丢失率,基本可实现无线Mesh网络的无缝切换,并且能够保证与现有的IEEE802.11协议标准兼容。     

IEEE 802.11 roaming and authentication in wireless LAN/cellular mobile networks

A wireless LAN service integration architecture based on current wireless LAN hot spots is proposed so that migration to a new service becomes easier and cost effective. The proposed architecture offers wireless LAN seamless roaming in wireless LAN/cellular mobile networks. In addition, a link-layer-assisted mobile IP handoff mechanism is introduced to improve the network/domain switching quality in terms of handoff delay and packet loss. An application layer end-to-end authentication and key negotiation scheme is proposed to overcome the open-air connection problem existing in wireless LAN deployment. The scheme provides a general solution for Internet applications running on a mobile station under various authentication scenarios and keeps the communications private to other wireless LAN users and foreign network. A functional demonstration of the scheme is given. The research results can contribute to rapid deployment of wireless LANs.     

Design of a lightweight authentication scheme for IEEE 802.11p vehicular networks

With the growing popularity of vehicle-based mobile devices, vehicular networks are becoming an essential part of wireless heterogeneous networks. Therefore, vehicular networks have been widely studied in recent years. Because of limited transmission range of wireless antennas, mobile vehicles should also switch their access points to maintain the connections as conventional mobile nodes. Considering the inherent characteristics of vehicular networks such as dynamic topology and high speed, the question of how to implement handoff protocol under real-time scenarios is very important. IEEE 802.11p protocol is designed for vehicular networks for the long distance transmission. To reduce handoff latency for 802.11p protocol, the authentication phase is waived during the handoff. However, security is also very important for wireless communications, and authentication can forbid access from malicious nodes and prevent wireless communications from potential attacks. Thus, in this paper, a lightweight authentication scheme is introduced to balance the security requirements and the handoff performance for 802.11p vehicular networks. In our scheme, the access points are divided into different trust groups, and the authentication process is completed in a group-based method. Once a vehicle is authenticated by an access point group, during the handoff within the same group, few extra authentication operations are needed. As a result, there is no extra overhead introduced to the authentication servers. Simulation results demonstrate that our authentication scheme only introduces small handoff latency and it is ideal for vehicular networks.     

一种基于无线局域网的移动检测优化方案

无线局域网采用移动IP实现移动性管理.移动IP切换存在切换时延大,数据包易丢失的问题.切换时延由移动检测时延和注册时延组成,而移动检测时延在其中占主要部分.文章提出了一种移动检测优化方案,采用了自适应绑定的算法,同时充分考虑了域内小范围高频度切换的情况,使移动节点在无线局域网环境中进行快速有效的切换.     

Bandwidth Sharing Schemes for Multimedia Traffic in the IEEE 802.11e Contention-Based WLANs

Bandwidth allocation schemes have been well studied for mobile cellular networks. However, there is no study about this aspect reported for IEEE 802.11 contention-based distributed wireless LANs. In cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the contrary, bandwidth allocation in contention- based distributed wireless LANs is extremely challenging due to its contention-based nature, packet-based network, and the most important aspect: only one channel is available, competed for by an unknown number of stations. As a consequence, guaranteeing bandwidth and allocating bandwidth are both challenging issues. In this paper, we address these difficult issues. We propose and study nine bandwidth allocation schemes, called sharing schemes, with guaranteed Quality of Service (QoS) for integrated voice/video/data traffic in IEEE 802.11e contention-based distributed wireless LANs. A guard period is proposed to prevent bandwidth allocation from overprovisioning and is for best-effort data traffic. Our study and analysis show that the guard period is a key concept for QoS guarantees in a contention-based channel. The proposed schemes are compared and evaluated via extensive simulations.     

Intelligent Handoff for Mobile Wireless Internet

This paper presents an intelligent mobility management scheme for Mobile Wireless InterNet – MWIN. MWIN is a wireless service networks wherein its core network consisting of Internet routers and its access network can be built from any Internet-capable radio network. Two major standards are currently available for MWIN, i.e., the mobile IP and wireless LAN. Mobile IP solves address mobility problem with the Internet protocol while wireless LAN provides a wireless Internet access in the local area. However, both schemes solve problems independently at different layers, thereby some additional problems occur, e.g., delayed handoff, packet loss, and inefficient routing. This paper identifies these new problems and performs analyses and some real measurements on the handoff within MWIN. Then, a new handoff architecture that extends the features of both mobile IP and wireless LAN handoff mechanism was proposed. This new architecture consists of mobile IP extensions and a modified wireless LAN handoff algorithm. The effect of this enhancement provides a linkage between different layers for preventing packet loss and reducing handoff latency. Finally, some optimization issues regarding network planning and routing are addressed.     

FastScan: a handoff scheme for voice over IEEE 802.11 WLANs

IEEE 802.11 Wireless LANs are increasingly being used in enterprise environments for broadband access. Such large scale IEEE 802.11 WLAN deployments implies the need for client mobility support; a mobile station has to be “handed off” from one Access Point to another. Seamless handoff is possible for data traffic, which is not affected much by the handoff delay. However, voice traffic has stringent QoS requirements and cannot tolerate more than 50ms net handoff delay. The basic IEEE 802.11 handoff scheme (implemented in Layers 1 & 2) only achieves a handoff delay of 300ms at best, leading to disrupted connectivity and call dropping. The delay incurred in scanning for APs across channels contributes to 90% of the total handoff delay. In this paper, the FastScan scheme is proposed which reduces the scanning delay by using a client-based database. The net handoff delay is reduced to as low as 20 ms for IEEE 802.11b networks. We next suggest “Enhanced FastScan” that uses the direction and relative position of the client with respect to the current AP to satisfy the latency constraint in IEEE 802.11a scenarios, which have significantly higher scanning delays due to the larger number of channels. The proposed schemes do not need any changes in the infrastructure (access points) and require only a single radio and a small cache memory at the client side.     

Design and implementation of CLASS: A Cross-Layer ASSociation scheme for wireless mesh networks

This paper focuses on the design and implementation of CLASS, a Cross-Layer Association scheme for IEEE 802.11-based multi-hop wireless mesh networks. The widely-used association strategy in traditional IEEE 802.11 wireless LANs allows a Mobile Station (MS) to scan wireless access links and then associate with the Access Point (AP) that has the best Received Signal Strength Indication (RSSI) value. Unlike traditional wireless LANs, IEEE 802.11-based wireless mesh networks consist of a multi-hop wireless backhaul. As such, the performance experienced by an MS after association with a specific Mesh Access Point (MAP) depends heavily on the conditions of both the access link (e.g., traffic load of associated stations, the frame error rate between an MS and an MAP) and the mesh backhaul (e.g., end-to-end latency and asymmetric uplink/downlink transportation costs). That is, selecting the MAP that yields the “best” performance depends on several factors and cannot be determined solely on the RSSI of the MS-MAP access link. CLASS uses an end-to-end airtime cost metric to determine the MAP to which an MS should associate. The airtime cost metric is based on the IEEE 802.11s, and comprises the access link airtime cost and the backhaul airtime cost. The proposed association scheme considers the frame error rate for various packet sizes, the available bandwidth on the access link after the association of the new MS, and the asymmetric uplink and downlink transportation costs on the backhaul. All experimental results are based on actual Linux-base testbed implementation. We also implement a general Cross-Layer Service Middleware (CLSM) module that is used to monitor network conditions and gather relevant metrics and factor values. Experimental results show that the proposed association scheme is able to identify the MAP which yields the highest end-to-end network performance for the mobile stations after their associations.     

Topology-aided cross-layer fast handoff designs for IEEE 802.11/mobile IP environments

This study first reviews state-of-the-art fast handoff techniques for IEEE 802.11 or Mobile IP networks. Based on that review, topology-aided cross-layer fast handoff designs are proposed for Mobile IP over IEEE 802.1.1 networks. Time-sensitive applications, such as voice over IP (VoIP), cannot tolerate the long layer-2 plus layer-3 handoff delays that arise in IEEE 802.11/Mobile IP environments. Cross-layer designs are increasingly adopted to shorten the handoff latency time. Handoff-related layer-2 triggers may reduce the delay between layer-2 handoff completion and the associated layer-3 handoff activation. Cross-layer topology information, such as the association between 802.11 access points and Mobile IP mobility agents, together with layer-2 triggers, can be utilized by a mobile node to start layer-3 handoff-related activities, such as agent discovery, address configuration, and registration, in parallel with or prior to those of layer-2 handoff. Experimental results indicate that the whole handoff. delay can meet the delay requirement of VoIP applications when layer-3 handoff activities occur prior to layer-2 handoffs.     

Dynamic bandwidth partition schemes for integrated voice,video, and data traffic in the IEEE 802.11e distributed wireless LANs

In mobile cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the other hand, bandwidth partition schemes in the contention‐based medium access control (MAC) in distributed wireless LANs are extremely challenging due to the contention‐based nature, packet‐based network, and the most important aspect: only one channel available, competed by an unknown number of stations. In this paper, we study this challenging issue. We propose and study four different bandwidth partition schemes for integrated voice/video/data traffic in the IEEE 802.11e wireless LANs: a Static bandwidth Partition (SP) scheme, a Dynamic budget Partition (DP) scheme, a Dynamic bandwidth Partition with Finer‐Tune (DP‐FT) scheme, and a Dynamic bandwidth Partition with Reserved Region (DP‐RR). The proposed schemes are compared and evaluated via extensive simulations. Results show that the DP‐FT scheme is the best scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis and Evaluation of Mobile IPv6 Handovers over Wireless LAN

In this paper, we analyze the IPv6 handover over wireless LANs. Mobile IPv6 is designed to manage mobile nodes movements between wireless IPv6 networks. Nevertheless, a mobile node cannot receive IP packets on its new point of attachment until the handover completes. Therefore, a number of extensions to Mobile IPv6 have been proposed to reduce the handover latency and the number of lost packets. We focus on Fast Mobile IPv6 which is an extension of Mobile IPv6 that allows the use of L2 triggers to anticipate the handover. We compare the handover latency in four specific cases: basic Mobile IPv6, the forwarding method of Mobile IPv6, the Anticipated method, and the Tunnel-Based Handover. The results of the handover latency are calculated with the L2 properties of IEEE 802.11b. In particular, we take into account the L2 handover for different configurations of the wireless network.     

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs

IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard.     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Performance Evaluation of Layer 3 Low Latency Handoff Mechanisms

This paper investigates the performance of two Layer 3 low latency handoff mechanisms proposed by the IETF, namely Pre- and Post-Registration. These protocols use Layer 2 triggers to reduce the built-in delay components of Mobile IP. We propose a simple analytical model that allows assessing the packet loss and the delay characteristics of these mechanisms. We describe several handoff implementations over a wireless access based on the IEEE 802.11 standard and analyze several implementation issues. Finally we study the scalability of the protocols using an OPNET simulation.     

移动IP在无线局域网下的一种快速切换方法

针对移动IP在无线局域网下的应用,提出了一种新的基于链路层的移动IP快速切换方法,通过在无线局域网的无线接入点间加入特定的MAC网桥来减少移动节点在切换时产生的切换时延,进而减少移动节点上行和下行方向上的数据包的丢失,达到对移动IP切换进行优化的目的。此方法在无线局域网实际环境中进行了性能测试,结果证明优化后的时延较之原来普通移动IP切换时延有明显降低。