Applying Coordination for Service Adaptation in Mobile Computing

Mobile computing devices vary in terms of display, memory, and battery life, and current network protocols aren’t necessarily suited to the mobile computing environment. As computer networks' complexity increases, communication-related software must be able to adapt to mobile computing’s constraints. This study aims to develop a software system that adapts data flows over dynamic wireless network conditions and various mobile devices. With their MobiGATE system, the authors adopt the principle of separation of concerns to support the system's service composition and reconfiguration. This approach can support ease of dynamic reconfiguration and the reusability of adaptation services across applications.     

Active Service for Mobile Middleware

This paper describes a dynamic service reconfiguration model where the proxy is composed of a chain of service objects called mobilets (pronounced as mo-be-lets), which can be actively deployed onto a network. This model offers flexibility because the chain of mobilets can be dynamically reconfigured to adapt to dynamic changes in the wireless environment, without interrupting service provision for other mobile nodes. We have realized the dynamic service reconfiguration model by crafting its design into a programmable infrastructure that forms the baseline architecture of the WebPADS (short for Web Proxy for Actively Deployable Services) system.     

TCP in a wireless world

Mobile wireless is one of the more challenging environments for the Internet protocols, and for TCP in particular. One approach to supporting the wireless environment is the so-called “walled garden”. Here the transport protocol used within the mobile wireless environment is not TCP, but is instead a transport protocol that has been specifically adapted to mobile wireless. In this model, Internet applications interact with an application gateway to reach the wireless world, and the application gateway uses a wireless transport protocol and potentially a modified version of the application data to interact with the wireless device. The most common implementation of this approach is to extend a Web client into the mobile wireless device, using some form of proxy server at the boundary of the wireless network and the Internet. This is the approach adopted by the Wireless Access Protocol (WAP) Forum. An alternative is to allow mobile wireless devices to function as any other Internet-connected device. This approach requires some form of end-to-end direct IP continuity and an associated end-to-end TCP functionality, where the TCP path straddles both wired and wireless segments. Ensuring the efficient operation of TCP in this environment becomes integral to the development of the environment itself; the problem is no longer one of adjusting TCP to match the requirements of the wireless environment, but one of providing seamless interworking between the wired and wireless worlds     

MobiPADS: a reflective middleware for context-aware mobile computing

Traditionally, middleware technologies, such as CORBA, Java RMI, and Microsoft's DCOM, have provided a set of distributed computing services that essentially abstract the underlying network services to a monolithic "black box." In a mobile operating environment, the fundamental assumption of middleware abstracting a unified distributed service for all types of applications operating over a static network infrastructure is no longer valid. In particular, mobile applications are not able to leverage the benefits of adaptive computing to optimize its computation based on current contextual situations. In this paper, we introduce the Mobile Platform for Actively Deployable Service (MobiPADS) system. MobiPADS is designed to support context-aware processing by providing an executing platform to enable active service deployment and reconfiguration of the service composition in response to environments of varying contexts. Unlike most mobile middleware, MobiPADS supports dynamic adaptation at both the middleware and application layers to provide flexible configuration of resources to optimize the operations of mobile applications. Within the MobiPADS system, services (known as mobilets) are configured as chained service objects to provide augmented services to the underlying mobile applications so as to alleviate the adverse conditions of a wireless environment.     

Interworking wireless mesh networks: Problems,performance characterization,and perspectives

Wireless broadband networks based on the IEEE 802.11 technology are being increasingly deployed as mesh networks to provide users with extended coverage for wireless Internet access. These wireless mesh networks, however, may be deployed by different authorities without any coordination a priori, and hence it is possible that they overlap partially or even entirely in service area, resulting in contention of radio resources among them. In this paper, we investigate the artifacts that result from the uncoordinated deployment of wireless mesh networks. We use a network optimization approach to model the problem as resource sharing among nodes belonging to one or different networks. Based on the proposed LP formulation, we then conduct simulations to characterize the performance of overlaying wireless mesh networks, with the goal to provide perspectives for addressing the problems. We find that in a system with multiple overlaying wireless mesh networks, if no form of inter-domain coordination is present, individual mesh networks could suffer from capacity degradation due to increased network contention. One solution toward addressing the performance degradation is to “interwork” these wireless mesh networks by allowing inter-domain traffic relay through provisioning of “bridge” nodes. However, if such bridge nodes are chosen arbitrarily, the problems of throughput sub-optimality and unfairness may arise. We profile the impact of bridge node selection and show the importance in controlling network unfairness for wireless mesh network interworking. We conclude that mesh network interworking is a promising direction to address the artifacts due to uncoordinated deployment of wireless mesh networks if it is supplemented with appropriate mechanisms.     

Robust wireless sharing of internet video streams

The gateways are the performance bottleneck of wireless mesh access networks and thus alleviating stress on them is essential to making such wireless networks robust and scalable. Using proxy servers or wireless peer-to-peer streaming techniques can help reduce the gateway load. However, these techniques, because they are data caching methods, do not save wireless resources. We instead consider a communication-sharing approach in this paper. Traditional stream sharing solutions depend on cooperation with the video server. However, in the wireless access network it is difficult to cooperate with online video sites. To address this problem in wireless mesh access networks, we propose a distributed video sharing technique called Dynamic Stream Merging (DSM). DSM is able to improve the robustness of the access network without cooperation from the online video site or the users and has the intelligence to handle sudden spikes in demand for certain videos due to specific events, thereby preventing adverse effects to other daily wireless traffic. The technique can also leverage the 80:20 data access pattern, common for many video applications, to substantially increase the service throughput. We explain the DSM technique, present the system prototype, and discuss the experimental results.     

基于主动网络技术的战术互联网无线子网的管理

为克服管理战术互联网无线子网的拓扑、设备状态以及流量工程的困难，提出了利用主动网络技术管理战术互联网无线子网的方法。在连接电台的战术互联网网关或互联网控制器上部署主动网管节点服务器，侦听网络相关信息，推测无线子网的拓扑和设备状态；依据报文的业务类型和链路状态，实时控制信息传输的路由和优先级，解决流量控制问题；允许用户动态定制无线子网的管理服务和管理策略。该方法提高了网络管理的实时性，减轻了网管业务对网络的负担，改善了网络服务能力，并与传统的管理体制兼容。     

基于网关的ZigBee网络与Internet互联框架

针对如何将ZigBee网络与Internet紧密融合的问题,提出一种网关设计方案.介绍了工作在传输层的互联网关,在分析此网关不足的基础上,根据面向服务的网络中间件思想,提议网关的体系结构.包括服务注册、服务绑定、服务调用和取消服务4个模块,以实现为用户提供服务的透明性;同时,为了减少ZigBee网络节点占用的IP地址数目,服务调用模块中使用传输层网关的协议转换方式.该网关从网络协议和服务两个角度实现ZigBee网络和Internet网络的互联,通过分析和比较证明具有用户透明性、业务提供方便等特点.     

A proxy-based integrated cache consistency and mobility management scheme for client–server applications in Mobile IP systems

In this paper, we investigate a proxy-based integrated cache consistency and mobility management scheme for supporting client–server applications in Mobile IP systems with the objective to minimize the overall network traffic generated. Our cache consistency management scheme is based on a stateful strategy by which cache invalidation messages are asynchronously sent by the server to a mobile host (MH) whenever data objects cached at the MH have been updated. We use a per-user proxy to buffer invalidation messages to allow the MH to disconnect arbitrarily and to reduce the number of uplink requests when the MH is reconnected. Moreover, the user proxy takes the responsibility of mobility management to further reduce the network traffic. We investigate a design by which the MH’s proxy serves as a gateway foreign agent (GFA) as in the MIP Regional Registration protocol to keep track of the address of the MH in a region, with the proxy migrating with the MH when the MH crosses a regional area. We identify the optimal regional area size under which the overall network traffic cost, due to cache consistency management, mobility management, and query requests/replies, is minimized. The integrated cache consistency and mobility management scheme is demonstrated to outperform MIPv6, no-proxy and/or no-cache schemes, as well as a decoupled scheme that optimally but separately manages mobility and service activities in Mobile IPv6 environments.     

Cost-effective approach inter-LMA domain management and distributed mobility control scheme in proxy mobile IPv6 networks

The Proxy Mobile IPv6 (PMIPv6) is designed to provide network-based mobility management support to a mobile node (MN) without any involvement of the MN in mobility related signaling; hence, the proxy mobility entity performs all related signaling on behalf of the MN. The new principal functional entities of PMIPv6 are the local mobility anchor (LMA) and the mobile access gateway (MAG). In PMIPv6, all the data traffic sent from the MN gets routed to the LMA through a tunnel between the LMA and the MAG, but it still has a single point of failure (SPOF) and a bottleneck state of traffic. To solve these problems, various approaches directed towards PMIPv6 performance improvements, such as route optimization, have been proposed. However, these approaches add additional signaling to support the MN׳s mobility, which incurs extra network overhead and still provides difficulty when applied to multiple-LMA networks. In this paper, we propose an improved route optimization in PMIPv6-based multiple-LMA networks. All LMAs were connected to the proxy internetworking gateway (PIG), which performs inter-domain distributed mobility control. Each MAG keeps the information of all LMAs in the PMIPv6 domain, so it is possible to perform fast route optimization. Therefore, this method supported route optimization without any additional signaling because the LMA receives the state information of route optimization from the PIG.     

无线Internet的业务质量及其改进

在移动网络中,移动用户对Internet的访问,具有与通常的外部Internet网络不同的特点。移动用户发出的对信息内容的请求(例如询问前方交通情况和路线),以及无线Internet信息提供商主动向移动用户发出的信息(例如移动用户附近的商品信息广告),与移动用户的位置、移动状态(方向、速度)和个人情况(userprofile)等有关。因此,要建立恰当的无线Internet流量模型和实现QoS(业务质量)控制,需要考虑用户的移动特性和在不同移动状态下访问Internet的概率分布。该文将建立一个新的定量分析模型,用半马尔可夫过程和一般的状态空间来描述移动用户的行为;并基于该移动模型,建立相应的移动用户对信息内容的访问模型、描述移动用户请求的到达过程;进而得到无线Internet业务质量参数的估计,即无线Internet对移动用户请求的平均响应时间、对无线侧和有线侧传输带宽的需求等;利用这些结果,可以实现无线资源的动态分配和允入控制。该文还将分析无线代理网关的性能、缓存容量需求,并给出改善平均响应时间的可行方案。最后用计算机模拟对提出的理论分析进行验证。     

IPv6 based relay gateway protocol in hybrid networks

During the past few years, WMAN (Wireless Metropolitan Area Network) and WLAN (Wireless Local Area Network) provided fast, convenient and reliable solution for all kinds of users. With the development of the communication technology, the future wireless networks will allow mobile users access Internet anywhere, anytime. Therefore, it is a natural trend to combine different wireless networks to provide a seamless roaming for users. It is feasible for mobile terminal which have multiple modes to handoff between different networks. A relay gateway protocol for the WLAN-mode nodes (mono-mode WLAN nodes and dual-mode nodes) in the hybrid network of IEEE 802.16 WMANs and IEEE 802.11 WLANs is proposed to provide wider mobility. Dual-mode mobile nodes with good service can provide WLAN links to nearby WLAN-mode nodes with bad service or out of the WLAN coverage. Simulation results show that the relay gateway scheme can improve network performance of the hybrid networks. Moreover, the relay gateway method can bring additional service coverage and increase the capacity of WMANs and WLANs.     

TCP with gateway adaptive pacing for multihop wireless networks with Internet connectivity

This paper introduces an effective congestion control pacing scheme for TCP over multihop wireless networks with Internet connectivity. The pacing scheme is implemented at the wireless TCP sender as well as at the Internet gateway, and reacts according to the direction of TCP flows running across the wireless network and the Internet. Moreover, we analyze the causes for the unfairness of oncoming TCP flows and propose a scheme to throttle aggressive wired-to-wireless TCP flows at the Internet gateway to achieve nearly optimal fairness. The proposed scheme, which we denote as TCP with Gateway Adaptive Pacing (TCP-GAP), does not impose any control traffic overhead for achieving fairness among active TCP flows and can be incrementally deployed since it does not require any modifications of TCP in the wired part of the network. In an extensive set of experiments using ns-2 we show that TCP-GAP is highly responsive to varying traffic conditions, provides nearly optimal fairness in all scenarios and achieves up to 42% more goodput for FTP-like traffic as well as up to 70% more goodput for HTTP-like traffic than TCP NewReno. We also investigate the sensitivity of the considered TCP variants to different bandwidths of the wired and wireless links with respect to both aggregate goodput and fairness.     

MANET与Internet互联时的广播风暴抑制策略

Mobile Ad Hoc网络(MANET)与Internet互联时，如何使Internet网关适应MANET高度动态变化的网络条件与实际连接需求，以合理的开销向MANET通告可用网关信息是获取良好互联性能的关键。该文根据那些欲访问Internet的MANET节点距离Internet网关的实时位置及其访问需求自适应地设置网关通告报文之TTL值以实现最佳覆盖，同时采用基于计数的广播风暴抑制策略有效地抑制了洪泛网关通告报文所形成的广播风暴。用NS2进行的仿真说明该文提出的方法在将节点密度及规模变化的MANET接入Internet时能获取良好的连接性能而开销合理。     

Adaptive reconfiguration of data networks using genetic algorithms

Genetic algorithms are applied to an important, but little investigated, network design problem, that of reconfiguring the topology and link capacities of an operational network to adapt to changes in its operating conditions. These conditions include: which nodes and links are unavailable; the traffic patterns; and the quality of service (QoS) requirements and priorities of different users and applications. Dynamic reconfiguration is possible in networks that contain links whose endpoints can be easily changed, such as satellite channels, terrestrial wireless connections, and certain types of optical connections. We report preliminary results that demonstrate the feasibility of performing genetic search quickly enough for online adaptation.     

Ethersim: a simulator for application-level performance modeling of wireless and mobile ATM networks

The paper describes Ethersim, a simulation tool to model and study the performance of multimedia-oriented integrated service ATM networks with mobile hosts and wireless links. The key motivation behind Ethersim is to study the application-level impact of host mobility and wireless channels. Ethersim has a discrete event based simulator core and incorporates models of user applications and transport, network and MAC layer protocols. It provides the capability to specify a cellular wireless ATM network topology and host mobility patterns. The software architecture of Ethersim employs five special entities: an air module, a map, a mover, mobile hosts, and basestations. We also present case-studies of using Ethersim to model and study the interaction of transport layer, connection rerouting protocol, and radio characteristics in the SWAN [P. Agrawal, A. Asthana, M. Cravatts, E. Hyden, P. Krzyzanowski, P. Mishra, B. Narendran, M. Srivastava, J. Trotter, SWAN: A Mobile Multimedia Wireless Network, in: IEEE Personal Commun. Mag., April 1996] mobile and wireless ATM based multimedia network.     

基于PMIPv6的域间切换管理方法及性能分析*

针对代理移动IPv6（PMIPv6）中域间切换时延较大的问题,提出了一种基于PMIPv6的域间切换管理方案。新方案通过在PMIPv6域间发送PBU绑定更新消息,使得切换目标PMIPv6域提前知道移动节点（MN）的家乡网络前缀,避免了移动节点参与移动性管理及重新配置转交地址,从而有效减小了切换时延。分析和仿真结果表明,与现有的全局移动性管理方案移动IPv6和快速移动IPv6相比较,新方案更加适应移动性管理中低时延、低复杂度、易于操作的要求。     

无线传感器网络与TCP/IP网络互联通信技术研究

提出了无线传感器网络与Intemet互联通信技术的代理服务器系统结构.设计了具有网络接口功能的代理网关节点.该节点作为无线传感器网络与Internet互联通信的代理网关,实现了远程访问和获取传感器网络监测的信息.给出了精简化的TCP/IP互联协议,以及代理网关主处理程序的软件实现.     

无线Mesh网络中基于奖励机制的均衡传输方案

针对无线Mesh网络存在自私节点而造成的双向流量的均衡问题,提出了一种基于奖励机制的均衡传输方案。首先,推导出了每个传输访问点(TAP)的双向目标吞吐量。然后,提出一种奖励机制,通过信用币和代币支付策略来鼓励闲置TAP转发数据,同时使网关尽可能均衡地向TAP传输下行数据。在一个具有3个TAP的无线Mesh网络上仿真结果表明,该方法能够在存在自私节点情况下确保双向流量的均衡。     

A multi-layer experimental study of multimedia and QoS communication in wireless mesh networks

A significant issue in Mesh networks is to support multimedia transmissions while providing Quality of Service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for a wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We design and implement a campus test-bed for supporting multimedia traffic in mobile wireless mesh networks, and investigate in detail some possible improvements on a number of layers to enable multimedia transmission over wireless networks with QoS support. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoder’s output bit rate based on the available network bandwidth to improve the quality of the received video. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.