延迟容忍网络自适应差错控制方法

根据延迟容忍网络的时延较大、误码率较高等特点,在现有的传输控制层和MAC层差错控制的基础上改进,结合IEEE 802.11 DCF机制的特点,提出一种基于MAC层丢包率的自适应差错控制方案.该方案能有效改善延迟容忍网络的传输时延,满足对时延要求比较敏感的业务的要求.     

延迟容忍网络中一种多信息融合的改进概率路由算法

综合利用节点物理状态信息(位置和速度矢量信息)和社会关系信息(历史相遇信息),提出一种多信息融合的概率路由算法(PRMF)。该算法依据节点间距离的远近程度动态调整两类信息在预测相遇关系中的权重,以选择合适的信息来计算传输概率,并依据传输概率的大小选择转发节点。另外,还引入有效的分组副本控制和分组散播策略,并结合预测信息改进了节点缓存管理方法。仿真结果表明:与现有的几种路由算法相比,PRMF保持了较低的平均开销,同时具有最高的投递率和最小的平均延迟。     

容迟网络中基于节点间亲密度的分组路由方法

借鉴MANET中通过分簇来减少冗余副本和社交网络中有关挖掘社交圈的思想,通过分析节点的移动规律,定义了基于节点间亲密度的拓扑结构,并将该亲密度在拓扑图中量化为可以比较的边的权值,依据边的权值大小进行拓扑裁剪,挖掘出相互亲密度较高的节点分组,并且针对源节点和目的节点所在的分组对spray and wait路由方法进行改进,来决定本身的报文副本的分配情况,进而提出了基于节点间亲密度的分组路由方法(PBI)。实验结果表明,该路由方法能够明显地提高投递成功率并且减小网络时延。     

基于分组的DTN路由协议

在DTN中,节点没有长时间端到端的链接,所以为了在长时间间歇性链接的环境下提供可靠的数据传输,就需要中继节点来进行数据包的存储和转发。充足的缓存空间和能源是保证DTN网络正常运行的关键,而DTN网络节点的分散性使此条件很难实现,因此,提出一种基于分组的路由协议（group based protocol for DTN,GBP）,它只通过本地信息引导数据包副本到达目的节点,旨在传播少量数据包来减少网络开销。先介绍了GBP协议的原理,然后用ONE(opportunistic network environment)仿真软件对Epidemic协议,Spray and Wait协议,PRoPHET协议,MaxProp协议和GBP协议进行仿真对比,在交付成本、成功投递率、网络平均延时3个方面进行对比分析,得出GBP协议具有更好的性能。最后指出了存在的不足并提出改进措施。     

基于稳定闭域的异构无线网络混合路由策略

分析了异构的网络模型,并提出了一种基于MANET稳定闭域的混合路由策略,使得基于该路由策略设计的路由协议能够实时地根据本地拓扑状态进行转换,在稳定闭域内使用AODV提高路由转发的效率。当数据分组转发到闭域边界后,将转换为改进的Prophet路由继续在非连通区域内寻路,以充分利用MANET与DTN路由的优势。仿真实验证明了该路由策略的可行性,通过比较多种路由算法验证了在特定的异构网络环境下该路由策略的高效性。     

HUBCODE: hub‐based forwarding using network coding in delay tolerant networks

This paper presents an efficient hub‐based message forwarding scheme for people‐centric DTN, wherein hubs (i.e. nodes with high degree distribution) are utilized as message relays. This scheme reduces redundant message transmissions without penalizing delivery ratio, since hubs collectively form a virtual data conduit which reaches most of the nodes. Further, in order to utilize bandwidth efficiently, this approach leverages linear network coding for exchanging messages among hubs. Copyright © 2011 John Wiley & Sons, Ltd.     

Transport layer protocols and architectures for satellite networks

Designing efficient transmission mechanisms for advanced satellite networks is a demanding task, requiring the definition and the implementation of protocols and architectures well suited to this challenging environment. In particular, transport protocols performance over satellite networks is impaired by the characteristics of the satellite radio link, specifically by the long propagation delay and the possible presence of segment losses due to physical channel errors. The level of impact on performance depends upon the link design (type of constellation, link margin, coding and modulation) and operational conditions (link obstructions, terminal mobility, weather conditions, etc.). To address these critical aspects a number of possible solutions have been presented in the literature, ranging from limited modifications of standard protocols (e.g. TCP, transmission control protocol) to completely alternative protocol and network architectures. However, despite the great number of different proposals (or perhaps also because of it), the general framework appears quite fragmented and there is a compelling need of an integration of the research competences and efforts. This is actually the intent of the transport protocols research line within the European SatNEx (Satellite Network of Excellence) project. Stemming from the authors' work on this project, this paper aims to provide the reader with an updated overview of all the possible approaches that can be pursued to overcome the limitations of current transport protocols and architectures, when applied to satellite communications. In the paper the possible solutions are classified in the following categories: optimization of TCP interactions with lower layers, TCP enhancements, performance enhancement proxies (PEP) and delay tolerant networks (DTN). Advantages and disadvantages of the different approaches, as well as their interactions, are investigated and discussed, taking into account performance improvement, complexity, and compliance to the standard semantics. From this analysis, it emerges that DTN architectures could integrate some of the most efficient solutions from the other categories, by inserting them in a new rigorous framework. These innovative architectures therefore may represent a promising solution for solving some of the important problems posed at the transport layer by satellite networks, at least in a medium‐to‐long‐term perspective. Copyright © 2006 John Wiley & Sons, Ltd.     

位置关联的延迟容忍网络路由算法

提出一种位置关联的延迟容忍网络路由(LRR)算法。引入位置信息,将动态的节点间路由转化为静止的位置间路由,利用节点访问位置的概率信息计算并选择中继位置,无需获取全局的节点间概率信息。实验结果表明,与现有的延迟容忍网络路由算法相比,LRR算法具有较高的传输成功率和较小的平均传输延迟。     

DTN中基于两跳ACK确认机制的备用副本转发算法

针对容迟容断网络(Delay/Disruption Tolerant Networks,DTN)在遇到路由空洞问题时缺乏有效回避路由空洞区域的方法,导致信息端到端传输时延较大的问题,提出一种基于两跳ACK确认机制的备用副本转发算法。消息在空洞区域无法传播时由上一跳节点寻找其他符合条件的节点,另辟路径转发消息,从而避开路由空洞区域。仿真实验结果表明,该算法在递交率、平均时延和网络开销方面表现优于Spray and Wait等对比算法,在车载自组网中具有很强的应用性。     

Analytical evaluation of average delay and maximum stable throughput along a typical two-way street for vehicular ad hoc networks in sparse situations

Intermittent connectivity is an intrinsic feature of vehicular ad hoc networks (VANETs) in sparse situations. This type of network is in fact an example of delay and disruption tolerant networks (DTNs). In this paper, we focus on a typical two-way street and analytically evaluate the maximum stable throughput and the average delay for packet forwarding along the street. To this end, we map the mobility patterns of the vehicles with different speeds onto suitable parameters of a BCMP queueing network and derive the location density of vehicles. Then, we employ another queueing network in order to model opportunistic multi-hop packet forwarding along the street with respect to the specifications of MAC and routing schemes. We propose a two-mode MAC scheme suitable for DTNs with predictable mobility patterns. We also consider the effect of vehicles’ velocities and opportunistic relaying for routing schemes. In our analysis, we evaluate the average delay and the maximum stable throughput for the proposed MAC and routing schemes. In the last part of the paper, we show the efficiency of the proposed analytical approach by some numerical results and confirm our analysis by simulation.