Ad Hoc几种不同的跨层机制的分析

传统的分层协议栈的设计方法已越来越不适应Ad Hoc网络，而应采用一种新型的跨层协议栈和跨层设计方案，本文阐述了Ad Hoc网络的特点和通用Ad Hoc网络协议栈的构成和缺点，介绍了自适应跨层机制，速率自适应跨层机制，MobileMan跨层机制。     

一种集成ad hoc与蜂窝的4G新型网格（IACG）

在第四代移动通信系统( 4G)中,采用ad hoc网络为核心技术,以满足2 0 1 0年后市场对大容量、高带宽、无缝漫游的需求,是近一两年来全球业界提出的一种崭新的技术思路和发展方向。本文根据4G工程原则和ad hoc网络框架,构建了一种新型的集成ad hoc与蜂窝网格( Integrated Cellular and Ad hoc Grid,IACG)。在此基础上,研究提出了其容量提高方案、移动预测模型、网络动态变化中的容错设计、基于代理的可靠路由协议以及低功耗无线多层优化协议,解决了当前ad hoc网络如何在移动通信领域走向实用化的关键技术     

基于协议栈的移动性技术对比分析

传统的协议栈没有对实现移动性的层次进行准确定位,所以几乎协议栈中的每一层都有实现移动性的方案,但对于移动互联网这种异质网络,分层的协议栈效率很低。根据协议栈和移动互联网移动性的特点,从协议栈的链路层、网络层、传输层和应用层上具体分析了各个层实现移动性的优缺点,通过这些分析可见,要给移动互联网中的移动节点提供良好的移动性支持,跨层实现移动性是未来移动性发展的趋势。     

无线通信中的跨层设计应用

传统的OSI分层结构无法适应无线网络环境,随着越来越多无线应用的出现,人们提出了跨层设计,其主要内容是通过在协议栈的各层之间传递特定的信息,使协议栈能够根据无线环境的变化来实现对资源的自适应优化配置,从而更有效的利用无线网络资源,提高系统的性能.文章举例说明了此设计.     

基于协议栈的移动性技术对比分析

传统的协议栈没有对实现移动性的层次进行准确定位．所以协议栈中的每一层都有实现移动性的方案，但对于移动互联网这种异质网络．分层的协议栈效率很低．本文根据协议栈和移动互联网移动性的特点，从协议栈的链路层、网络层、传输层和应用层上．分析各个层实现移动性的优缺点，提出要给移动互联网中的移动节点提供良好的移动性支持，跨层实现动性是未来移动性发展的趋势。     

基于协议栈的移动性技术对比分析

传统的协议栈没有对实现移动性的层次进行准确定位，所以几乎协议栈中的每一层都有实现移动性的方案，但对于移动互联网这种异质网络。分层的协议栈效率很低。根据协议栈和移动互联网移动性的特点，从协议栈的链路层、网络层、传输层和应用层上具体分析了各个层实现移动性的优缺点，通过这些分析可见，要给移动互联网中的移动节点提供良好的移动性支持，跨层实现动性是未来移动性发展的趋势。     

下一代无线网络中的跨层设计

下一代无线通信系统必须能够与互联网实现信息交互,这就需要利用通信协议来实现系统与其他通信系统间的互连互通。但是,现有通信协议基于OSI标准,其协议栈按照严格的分层方式工作,很难适应快速变化的无线通信环境。通过对现有协议栈进行改进,加入跨层设计方案则有助于改善下一代无线系统性能。文章简要分析了分层协议栈局限性,讨论了跨层设计原理,并系统地阐述了跨层设计时物理层、链路层、网络层、传输层和应用层协议应考虑的因素。     

Ad hoc网络时钟同步研究

由于ad hoc网络应用环境的多样性且不同的应用具有不同的同步要求，没有一种时钟同步协议可以适应各种情况。在分析了网络时钟同步困难的基础上，结合不同的ad hoc网络应用，探讨了不同应用环境下时钟同步协议的特殊性，并介绍了现有典型的ad hoc网络时钟同步协议。最后，针对ad hoc网络时钟同步中值得进一步研究的几个问题做了初步的分析。     

基于协议栈的移动性技术对比分析

传统的协议栈没有对实现移动性的层次进行准确定位，所以几乎协议栈中的每一层都有实现移动性的方案，但对于移动互联网这种异质网络，分层的协议栈效率很低。根据协议栈和移动互联网移动性的特点，从协议栈的链路层、网络层、传输层和应用层上具体分析了各个层实现移动性的优缺点，通过这些分析可见，要给移动互联网中的移动节点提供良好的移动性支持，跨层实现动性是未来移动性发展的趋势。     

基于无线Mesh网络跨层协议研究

介绍无线Mesh网络的基本概念和特点,基于Mesh网络的相关MAC协议和路由协议,从物理层、MAC层、路由协议层等层面介绍WMN跨层设计的一般原则和方法,对WMN的跨层设计方法和方案进行了阐述,对目前Mesh网络中的传统OSI分层结构参考模型存在的问题进行了分析,提出需要进一步研究的问题。     

A survey of cross-layer design for VANETs

Recently, vehicular communication systems have attracted much attention, fueled largely by the growing interest in Intelligent Transportation Systems (ITS). These systems are aimed at addressing critical issues like passenger safety and traffic congestion, by integrating information and communication technologies into transportation infrastructure and vehicles. They are built on top of self organizing networks, known as a Vehicular Ad hoc Networks (VANET), composed of mobile vehicles connected by wireless links. While the solutions based on the traditional layered communication system architectures such as OSI model are readily applicable, they often fail to address the fundamental problems in ad hoc networks, such as dynamic changes in the network topology. Furthermore, many ITS applications impose stringent QoS requirements, which are not met by existing ad hoc networking solutions. The paradigm of cross-layer design has been introduced as an alternative to pure layered design to develop communication protocols. Cross-layer design allows information to be exchanged and shared across layer boundaries in order to enable efficient and robust protocols. There has been several research efforts that validated the importance of cross-layer design in vehicular networks. In this article, a survey of recent work on cross-layer communication solutions for VANETs is presented. Major approaches to cross-layer protocol design is introduced, followed by an overview of corresponding cross-layer protocols. Finally, open research problems in developing efficient cross-layer protocols for next generation transportation systems are discussed.     

Cross-Layer Design for QoS Support in Multihop Wireless Networks

Due to such features as low cost, ease of deployment, increased coverage, and enhanced capacity, multihop wireless networks such as ad hoc networks, mesh networks, and sensor networks that form the network in a self-organized manner without relying on fixed infrastructure is touted as the new frontier of wireless networking. Providing efficient quality of service (QoS) support is essential for such networks, as they need to deliver real-time services like video, audio, and voice over IP besides the traditional data service. Various solutions have been proposed to provide soft QoS over multihop wireless networks from different layers in the network protocol stack. However, the layered concept was primarily created for wired networks, and multihop wireless networks oppose strict layered design because of their dynamic nature, infrastructureless architecture, and time-varying unstable links and topology. The concept of cross-layer design is based on architecture where different layers can exchange information in order to improve the overall network performance. Promising results achieved by cross-layer optimizations initiated significant research activity in this area. This paper aims to review the present study on the cross-layer paradigm for QoS support in multihop wireless networks. Several examples of evolutionary and revolutionary cross-layer approaches are presented in detail. Realizing the new trends for wireless networking, such as cooperative communication and networking, opportunistic transmission, real system performance evaluation, etc., several open issues related to cross-layer design for QoS support over multihop wireless networks are also discussed in the paper.     

UPS: Universal Protocol Stack for emerging wireless networks

Recent devices developed for emerging wireless networks, such as 4G cellular networks, wireless mesh networks, and mobile ad hoc networks, support multiple communication substrates and require execution of multiple protocols within a layer, which cannot be supported efficiently by traditional, layered protocol stack approaches. While cross-layer approaches can be designed to support these new requirements, the lack of modularity makes cross-layer approaches inflexible and hence difficult to adapt for future devices and protocols. Thus, there is a need for a new protocol architecture to provide universal support for cross-layer interactions between layers, while also supporting multiple communication substrates and multiple protocols within a stack. In this paper, we propose Universal Protocol Stack (UPS), which provides such support in a modular way through packet-switching, information-sharing and memory management. To show that UPS is realizable with very low overhead and that it enables concurrent and independent execution of protocols of the same stack layer, first, we present a wireless sensor network test-bed evaluation, where UPS is implemented in TinyOS and installed on individual sensor motes. Two cross-layer routing protocols are implemented and evaluated with UPS and without UPS. We also implemented UPS in the OPNET simulator, where the IP (e.g., Routing Information Protocol (RIP)) and AODV routing protocols are executed concurrently to support networks with both static and mobile wireless nodes. Our implementation shows that the overhead incurred to implement UPS is very low, and little or no modification is required to adapt existing protocols to the UPS framework. Both studies also show the advantage of enabling concurrent protocol execution within a stack layer, improving the successful packet delivery ratio or the total number of packets sent for the investigated scenarios.     

A New Systematic Framework for Autonomous Cross-Layer Optimization

Cross-layer optimization solutions have been proposed in recent years to improve the performance of wireless users that operate in a time-varying, error-prone network environment. However, these solutions often rely on centralized cross-layer optimization solutions that violate the layered network architecture of the protocol stack by requiring layers to provide access to their internal protocol parameters to other layers. This paper presents a new systematic framework for cross-layer optimization, which allows each layer to make autonomous decisions to maximize the wireless user's utility by optimally determining what information should be exchanged among layers. Hence, this cross-layer framework preserves the current layered network architecture. Since the user interacts with the wireless environment at various layers of the protocol stack, the cross-layer optimization problem is solved in a layered fashion such that each layer adapts its own protocol parameters and exchanges information (messages) with other layers that cooperatively maximize the performance of the wireless user. Based on the proposed layered framework, we also design a message-exchange mechanism that determines the optimal cross-layer transmission strategies, given the user's experienced environment dynamics.     

Cross-layer feedback architecture for mobile device protocol stacks

Applications using traditional protocol stacks (e.g., TCP/IP) from wired networks do not function efficiently in mobile wireless environments. This is primarily due to the layered architecture and implementation of protocol stacks. One mechanism to improve the efficiency of the stack is cross-layer feedback, that is, making information from within one layer available to another layer of the stack. For example, TCP retransmissions can be reduced by making it aware of network disconnections or handoff events. We highlight the need for a cross-layer feedback architecture and identify key design goals for an architecture. We present our ECLAIR architecture, which satisfies these design goals. We describe a prototype implementation that validates ECLAIR. We also discuss other cross-layer architectures and provide a cross-layer design guide.     

Cross-layer design: a survey and the road ahead

Of late, there has been an avalanche of cross-layer design proposals for wireless networks. A number of researchers have looked at specific aspects of network performance and, approaching cross-layer design via their interpretation of what it implies, have presented several cross-layer design proposals. These proposals involve different layers of the protocol stack, and address both cellular and ad hoc networks. There has also been work relating to the implementation of cross-layer interactions. It is high time that these various individual efforts be put into perspective and a more holistic view be taken. In this article, we take a step in that direction by presenting a survey of the literature in the area of cross-layer design, and by taking stock of the ongoing work. We suggest a definition for cross-layer design, discuss the basic types of cross-layer design with examples drawn from the literature, and categorize the initial proposals on how cross-layer interactions may be implemented. We then highlight some open challenges and new opportunities for cross-layer design. Designers presenting cross-layer design proposals can start addressing these as they move ahead.     

Cross-layer design of ad hoc networks for real-time video streaming

Cross-layer design breaks away from traditional network design where each layer of the protocol stack operates independently. We explore the potential synergies of exchanging information between different layers to support real-time video streaming. In this new approach information is exchanged between different layers of the protocol stack, and end-to-end performance is optimized by adapting to this information at each protocol layer. We discuss key parameters used in the cross-layer information exchange along with the associated cross-layer adaptation. Substantial performance gains through this cross-layer design are demonstrated for video streaming.     

Layering as Optimization Decomposition: A Mathematical Theory of Network Architectures

Network protocols in layered architectures have historically been obtained on an ad hoc basis, and many of the recent cross-layer designs are also conducted through piecemeal approaches. Network protocol stacks may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems. This paper presents a survey of the recent efforts towards a systematic understanding of layering as optimization decomposition, where the overall communication network is modeled by a generalized network utility maximization problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. There can be many alternative decompositions, leading to a choice of different layering architectures. This paper surveys the current status of horizontal decomposition into distributed computation, and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and channel coding. Key messages and methods arising from many recent works are summarized, and open issues discussed. Through case studies, it is illustrated how layering as Optimization Decomposition provides a common language to think about modularization in the face of complex, networked interactions, a unifying, top-down approach to design protocol stacks, and a mathematical theory of network architectures