【作者】 李洁；

【导师】 王兴伟；

【作者基本信息】 东北大学 ， 计算机应用技术， 2019， 博士

【摘要】 随着Internet中内容分发型应用的日益增长,当前网络的内容消费呈爆炸增长,且移动通信的流量消耗在网络中的比重逐渐增加。传统Internet这种以主机为中心建立通信的网络架构,势将淹没在日益增长的Gb甚至Tb的数据传输中。因此,内容中心网络(Content Centric Networking,CCN)这种以内容为中心的未来互联网架构孕育而生。CCN采用按名路由方式基于内容的名字而非其地址获取内容,并提供网内缓存以进一步提高内容分发效率,具有组播支持、多源通信等优势。近年来,对CCN的研究主要包括网内缓存、路由决策以及移动支持等方面。然而,不论是网内缓存还是移动支持都与路由技术息息相关。作为CCN网络架构发展的基石,CCN路由技术的研究甚为关键且遭遇到诸多挑战。考虑到内容的命名空间比IP地址空间高好几个数量级,CCN路由面临着比传统网络更为严峻的可扩展性问题。且按名路由中暗含的内容名与内容地址之间的绑定,使得内容的移动支持也是CCN路由面临的一大挑战。此外,如何有效地利用网内缓存提高内容分发效率也是CCN路由需要解决的一个重要问题。面对这些挑战,虽然研究人员提出了众多解决方案,但这些方案或是牺牲了一些CCN特性,或是专注于部分问题。针对此问题,本文设计了基于虚拟域的CCN路由机制,其主要创新和贡献点总结如下:(1)针对FIB面临的巨大的存储压力,设计基于虚拟域的CCN路由模型。提出虚拟域概念,基于分层的内容名字建立分层的虚拟域网络,实现域级名字聚合。创建新的FIB结构,基于分层的虚拟域网络结构建立分层的路由表,减少FIB存储条目。设计基于虚拟域的CCN路由机制,执行兴趣包的转发。实验表明虚拟域网络能够有效地减少FIB存储压力,且随着虚拟域层数的增加,该路由模型在可扩展性上的优势愈加明显。此外,实验结果也显示出虚拟域层数的增加对路由效率的负面影响,反映出路由模型在可扩展性和路由效率间存在权衡问题,为下一步的研究指明方向。(2)为了进一步优化和评估基于虚拟域的CCN路由模型,提出一种基于两层虚拟域的CCN路由机制。考虑到路由模型在可扩展性和路由效率间的权衡问题,在网络中建立一个两层的虚拟域网络,在保证虚拟域网络的分层结构的情况下,最小化虚拟域层数对路由效率的影响。调整虚拟域的数量,评估虚拟域的数量对网络中维护路由条目数的影响。设计简单的缓存管理方案以及兴趣包和数据包的转发处理方案,优化路由模型,提高缓存利用率。实验表明即使是在最少的分层(两层)情况下,虚拟域网络仍有效地改善了 CCN的可扩展性,且与当前经典的方案相比,该机制在可扩展性、缓存利用以及路由效率上具有较好综合性能。此外,实验结果显示了虚拟域的数量对路由可扩展性的影响,为进一步提高路由模型的可扩展性优势指明方向。(3)为了进一步提高基于虚拟域的CCN路由模型的可扩展性,提出一种基于虚拟域的CCN高可扩展性路由机制。针对FIB路由填充的可扩展性,设计一种两阶段路由协议以较低的填充开销完成FIB中路由信息的建立。建模分析虚拟域网络结构对FIB中存储的路由条目数的影响,设计虚拟域网络结构优化方案,最小化网络中维护的路由状态。此外,讨论分析基于虚拟域的CCN路由模型对内容提供者的移动支持。实验表明该机制从FIB填充开销和FIB存储压力两个方面上有效地解决了 CCN的可扩展性问题。(4)针对基于虚拟域的CCN路由模型的域间路由带来的路径伸展性问题,利用CCN的网内缓存特性,提出一种基于虚拟域的CCN高效路由机制,在保证CCN可扩展性的同时提高路由效率,使得用户能获得较近的内容副本。该机制首先计算基于虚拟域的CCN路由模型中各路由器的请求到达率;然后,根据内容流行度和得到的路由器的请求到达率,设计一种贪心缓存策略,解决缓存资源分配和副本放置问题。通过提高缓存命中率减少兴趣包路由长度改善路由效率。实验表明该机制在确保路由可扩展性的同时能有效地通过改善缓存命中率提高路由效率,缓解路径伸展性问题。(5)针对内容提供者的移动带来的路由挑战,提出基于虚拟域的CCN移动支持路由机制。建立异构虚拟域网络区分管理固定内容和移动内容的路由信息,在减少FIB存储条目数的同时解决内容提供者的移动对路由状态的影响,从路由存储及路由更新两方面确保路由的可扩展性。设计移动支持的路由协议和转发机制完成FIB的路由填充及兴趣包转发规则的制定。考虑到内容提供者的迁移对时延敏感型业务的影响,提出一种快速切换机制,以较低的切换开销减少切换时延,使得移动内容的请求者能尽快获取其所需内容。实验表明该机制不仅改善了路由的可扩展性,而且有效地降低了切换时延和切换开销。本文针对CCN路由的可扩展性问题,引入虚拟域概念,提出基于虚拟域的CCN路由模型。为了进一步优化并评估该模型的可行性和有效性、提高路由可扩展性、改善路由效率以及支持内容移动性,在该路由模型的基础上设计了四种路由机制。并通过与当前一些解决方案进行性能对比,证明本文提出的路由机制具有可行性和有效性。更多还原

【Abstract】 Accompanied with the increasing content distribution applications on the Internet,the consumption of content in current network is exploding,and the proportion of mobile traffic consumption in the network is increasing gradually as well.The traditional network,which is set up based on host to host communication mode,will be overwhelmed in all these growing gigabytes and even terabytes of data transmission.Therefore,Content Centric Networking(CCN),this kind of future Internet architecture,has been born.CCN adopts a name-based routing to fetch the content with its name instead of its location.In addition,it further improves content distribution efficiency with in-network caching,and provides benefits like multi-source content retrieval,multicast,etc.In recent years,the research on CCN mainly includes the following aspects:cache management,routing decision and mobility support.However,routing technologies are involved in the other aspects.With the cornerstone of CCN development,the research of CCN routing technology is crucial and suffers from several problems.Given that the namespace is several orders of magnitude higher than the IP address space,CCN routing suffers more severe scalability issue than traditional Internet does.Meanwhile,the content mobility is remained as one challenge due to the binding between content name and locator that underlies the name-based routing.Furthermore,how to effectively use in-network caching to improve the distribution efficiency is also a challenge.Facing these challenges,researchers have proposed many solutions,but they either sacrifice some features of CCN or focus on part of these problems.Based on this,this dissertation mainly designs virtual domain based routing mechanism for CCN,and major innovations and contributions are summarized as follows.(1)Aiming at the scalability issue brought by the huge storage pressure of CCN FIB,this dissertation proposes a virtual domain-based routing model for CCN.At first,for the sake of facilitating name aggregation,we propose the concept of virtual domain and build hierarchical virtual domain network according to the hierarchical content names to realize domainlevel aggregation.Then,to decrease FIB entries further,we design a new FIB structure which maintains routes to names in hierarchical routing tables built based on the hierarchical virtual domain network.Finally,we present the virtual domain based routing scheme for CCN to direct the forwarding of content requirements.The experimental results demonstrate that the proposed hierarchical virtual domain network can reduce the route states maintained in FIB effectively.And as the number of virtual domain layers increases,the advantage of routing model in scalability increases.In addition,the experimental results also reflect the negative impact of the increase of domain layers on the routing efficiency,which shows that the tradeoff between scalability and routing efficiency,and points out the direction for further research.(2)To further improve and vertify the performance of the virtual domain based routing model for CCN,we propose a two-level virtual domain-based routing scheme for CCN.Considering the tradeoff between scalability and routing efficiency in the routing model,a twolayer virtual domain network is established to minimize the influence of the number of domain layers on routing efficiency while ensuring the hierarchical structure of the virtual domain network.The number of virtual domains is adjusted to assess the impact of the number of virtual domains on the number of route states maintained in FIB.A simple cache management scheme and the corresponding forwarding processing are presented to optimize routing model with improved cache hit.The experimental results demonstrate that the virtual domain network can improve scalability effectively even with the least layering(two layers).And comparing to the state of art,the proposed mechanism has better comprehensive performance on scalability,cache utilization and routing efficiency.In addition,the experimental results show the influence of the number of virtual domains on scalability,which points out the direction to improve the scalability of the routing model further.(3)To improve scalability of virtual domain based routing model further,we present an enhanced scalable virtual domain-based routing scheme for CCN.Aiming at the scalability of FIB population,we propose a two-stage routing protocol to mitigate the huge populating overhead to build FIB in CCN.For the FIB storage pressure,we study the influence of virtual domain structure on the number of routing entries,and present improved methods to shrink FIB by optimizing virtual domain structure.In addition,we discuss and analyze the mobile support of content providers in the virtual domain based routing model.The experimental results demonstrate that the proposed mechanism reduces the FIB entries in a router significantly,and at the same time decreases the populating overhead for creating FIB.(4)For the path stretch arose by inter(virtual)domain routing,leveraging the in-network caching,we propose an efficient virtual domain-based routing scheme for CCN to address scalability and improve routing efficiency with fetching closer replica for consumer.It analysises and calculates the request arrival rate of router in inter-domain routing,and designs a greedy cache management strategy to enhance routing efficiency.The greedy cache management strategy solves cache allocation and replica placement based on content popularity and router’s request arrival rate,and decreases path length by increasing cache hit.Performance evaluation shows that the proposed mechanism significantly shortens path length by improving cache hit ratio without compromising the FIB scalability.(5)To overcome the routing challenges arose by the movement of content producer,we propose a mobility support virtual domain-based routing scheme for CCN.For sake of scalability in terms of FIB storage and FIB update,we establish a heterogeneous virtual domain network to manage routes to stable content and routes to mobile content,to cut down FIB entries and remove the influence of mobile content on route state.Meanwhile,we present the corresponding mobile support routing protocol and forwarding mechanism to perform FIB population and interest forwarding.In addition,considering the impact of content producer migration on time-delay sensitive services,a fast handover mechanism is proposed to reduce the handover latency with a lower handover overhead.The experimental results demonstrate that the proposed mechanism can not only improve scalability,but also effectively cut down the handover latency and overhead.In summary,this dissertation introduces the concept of virtual domain and designs the virtual domain-based routing model for CCN to address scalability issue firstly.Then,four routing mechanisms are proposed on the basis of the virtual domain-based routing model to further optimize and verify the feasibility and effectiveness of the routing model,enhance routing scalability,improve routing efficiency and support content mobility.And the feasibility and effectiveness of these routing mechanisms are demonstrated by comparing with some current solutions.更多还原