【作者】 钱红燕；

【导师】 秦小麟；

【作者基本信息】 南京航空航天大学 ， 计算机应用技术， 2010， 博士

【摘要】 随着Internet服务以及网络技术的不断发展,越来越多的应用系统被迁移到有线网络或者无线网络环境中,人们的生活与工作也越来越依赖网络。高带宽、低延时、灵活接入以及可移动性成为网络发展的新目标。移动网络的终端设备不仅可以是单个节点,更可扩展为一些移动的小网络,即移动子网。移动子网需要提供更高速度、更高带宽的接入方式。因此,移动子网的整体接入机制很有研究价值。移动子网的整体接入首先要解决移动子网在不同接入点之间的快速切换和无缝切换问题,减少因切换时链路中断造成的数据丢失;其次要解决移动子网在不同IP网络间的漫游,使之在不中断数据传输、不改变自身IP地址的条件下仍能接入不同的网络。本文研究的移动子网切换与漫游关键技术可解决上述问题。本文首先全面分析了各种无线和移动网络中的单个移动节点在接入点或基站间的切换机制,然后研究了网络层的移动性解决方案,主要包括可用于网间漫游的移动IP协议以及对它的各种改进。现有技术主要针对单节点的移动漫游通信,无法对移动子网的整体漫游提供支持。本文研究了可支持移动子网整体切换与漫游的关键技术,论文的主要研究成果包括:1)提出了在单无线链路中切换的触发时机决策算法。通过AP的实际分布位置、无线信号衰减规律,以及STA的移动规律和移动位置确定移动和漫游的切换时机进行切换触发,可以减少切换延迟;提出独立于各种应用的数据链路缓存算法,修改节点的无线驱动模块,保存在链路切换期间网络层交付的数据,待切换完成后重新发送,进一步减少切换过程中的丢包,提高无线链路的服务质量。2)提出在遵循IEEE802.11协议的无线网络中基于双链路实现软切换的DSH机制。设计了可支持双链路切换的无线信道分配机制,并针对小尺寸STA的特点确定了应用DSH的无线信道分配方式;通过全局信号量协同双链路的工作,确定两条链路各自的切换触发时机,确保两条链路不同时进入切换状态,在任何时刻均存在一条可以提供稳定数据传输服务的链路,提高移动传输的可靠性。DSH机制只要求对STA进行功能扩展,不需要修改AP的底层通信机制,在DSH中可以使用支持IEEE 802.1 1协议的任何AP产品,使DSH机制有较好的通用性。3)提出IMIP-RS机制,扩展了移动IP协议,使之可以支持移动子网的整体漫游。IMIP-RS可克服移动IP协议仅支持单个节点漫游的限制,通过家乡代理、外区代理和网内选路代理的服务,结合隧道技术、STA/AP网关技术等实现了多跳的移动IP,可实现高速移动子网的宽带接入。在底层硬件采用IEEE 802.11g标准时,采用TCP传输应用的最高数据传输率可达29Mbps;在要求快速响应的低吞吐量应用中,最大响应时间小于10毫秒。4)在自行研制的STA和AP设备上验证了上述关键技术。综合应用上述单链路快速切换与链路缓存算法、基于双链路的软切换DSH机制和基于扩展移动IP的子网整体漫游IMIP-RS机制,设计并实现了基于无线局域网可支持高速移动子网漫游的通信平台MP-RRS的原型系统。MP-RRS可在轨道交通控制系统的数据通信子系统上应用,经实际测试验证了MP-RRS中各项关键技术的可行性。测试结果显示,通过MP-RRS可实现高速移动子网的宽带接入,在军事和民用领域有着广阔的应用前景。基于上述关键技术的可支持高速移动子网漫游的通信平台已在江苏省重大成果转化专项“城市轨道交通列车自动控制系统”项目得到应用。更多还原

【Abstract】 Grown with internet service and network technology, more and more applications have been moved to network (wire network & wireless network). More and more people’s life and work depend on the network environment. Wide bandwidth, low latency, more flexibility and mobility are goals of the network. Roaming network is not only one client terminal, but also a small network, i.e. a mobile subnet. So mobile subnet’s connection strategy should be investigated and smart technical solution is requested.To make the mobile subnet roaming as a whole, two problems should be solved. The first is the fast and seamless handoff among access points, which aims at shortening the handoff latency and decreasing the data lose during handoff. The second is to allow the mobile subnet access network without interrupting data transmission and without changing its IP address. The dissertation researches core techniques of handoff and roam to solve the above problems. It analyzes the handoff scheme of single mobile node in data link layer, and researches the mobility management in network layer.The mobile subnet connects to the network through only one STA. Therefore the existing techniques supporting one node roaming can’t support the subnet roaming as a whole. The main contributions of the dissertation are summarized as follows:1) A novel handoff opportunity decision scheme is proposed. It aims at triggering accurately to decrease the handoff latency and avoid the“Ping-Pang”handoff. It considers several important factors in the subnet roaming environment, including the distributions of access points, the attenuation law of radio signal, the moving speed and direction of the STA and the subnet. It decreases the handoff latency of a wireless link. And a layer2 Handoff-Buff algorithm independent with applications is proposed to avoid data lose during the handoff. It modifies the wireless driver, saves unsuccessfully sent data and resends them after link restoral. It diminishes the packet loss ratio and improves the QoS of the link.2) A novel soft-handoff scheme in WLAN realized by dual link is proposed. Channel allocating manners are designed for soft handoff in WLAN, and one of them is chosen for small STA and DSH. The proposed DSH scheme cooperates the working of dual wireless network adaptors in one STA by a global semaphore. STA maintains two active links to forward and backward APs respectively, and they never do the handoff simultaneously. The DSH ensures at least one data link to remote network at any moment. DSH is realized on the STA side, so AP can use any standard product. It achieves seamless data transmission during STA’s fast motion and enhances the link reliability.3) A novel improved mobile IP (IMIP-RS) is proposed to support subnet’s roaming. IMIP-RS extends the mobile IP to support muliti-hops connection. It allows the mobile network roaming as a whole. IMIP-RS integrates the home agent, foreign agent and intra-domain agent to transfer packets from remote nodes to mobile nodes in the mobile subnet. In IMIP-RS, STA and AP work as gateways at layer 3 to forward packets instead of as layer 2 device. While adopting IEEE 802.11g wireless devices, the mobile subnet applying IMIP-RS can achieve 29Mbps as the maximum application throughput by TCP data transmission.4) A mobile platform for rapid roaming subnet (MP-RRS) is realized in our developed AP and STA based on the infrastructure of WLAN. The discussed technologies are integrated into the platform, including fast handoff and buffer in data link, soft handoff scheme based on dual-link, and the IMIP-RS. The MP-RRS is applied to the data communication sub-system of the automatic train control system in urban subway. Testing results indicate that the core techniques in MP-RRS are feasible, and broad band connection is provided for fast moving subnet.The MP-RRS is applied to an important production transformation project in Jiangsu province.更多还原