本文選題：內(nèi)容分發(fā) + 鏡像服務(wù)器�。� 參考：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文

【摘要】：內(nèi)容分發(fā)網(wǎng)絡(luò)(Content Delivery Network, CDN)作為網(wǎng)絡(luò)中緩解大量并發(fā)訪問引起的擁塞問題的有效技術(shù),得到了國內(nèi)外學(xué)術(shù)界和產(chǎn)業(yè)界的廣泛關(guān)注。在內(nèi)容分發(fā)網(wǎng)絡(luò)中,內(nèi)容被復(fù)制并存儲在多個(gè)鏡像服務(wù)器中,這使得內(nèi)容可以快速地被終端用戶訪問,大大降低了終端用戶的平均請求延遲。由于更多的鏡像服務(wù)器會帶來更大的部署和維護(hù)成本,合理地部署鏡像服務(wù)器對于內(nèi)容分發(fā)網(wǎng)絡(luò)至關(guān)重要。另外,鏡像服務(wù)器的容量是有限的,如何選擇鏡像內(nèi)容分發(fā)到各鏡像服務(wù)器中,直接決定了內(nèi)容分發(fā)網(wǎng)絡(luò)的網(wǎng)絡(luò)性能�；趦�(nèi)容分發(fā)網(wǎng)絡(luò)中現(xiàn)有的研究成果,本文分別從鏡像服務(wù)器部署和鏡像內(nèi)容分發(fā)兩個(gè)方向研究了內(nèi)容分發(fā)網(wǎng)絡(luò)中的相關(guān)問題,以降低網(wǎng)絡(luò)中的平均請求延遲。在鏡像內(nèi)容分發(fā)問題中,從靜態(tài)內(nèi)容分發(fā)方法和動(dòng)態(tài)內(nèi)容分發(fā)方法兩方面進(jìn)行了研究。其中,對于動(dòng)態(tài)內(nèi)容分發(fā)方法,本文結(jié)合無線Mesh網(wǎng)絡(luò)和無線融合網(wǎng)絡(luò)的特征,分別設(shè)計(jì)了相應(yīng)的內(nèi)容分發(fā)機(jī)制。本文的主要研究內(nèi)容及貢獻(xiàn)如下四個(gè)方面。一、基于網(wǎng)絡(luò)中請求的統(tǒng)計(jì)特性與鏡像服務(wù)器的服務(wù)模型,研究了內(nèi)容分發(fā)網(wǎng)絡(luò)中的鏡像服務(wù)器部署方法,以降低網(wǎng)絡(luò)中的平均請求延遲,提高CDNs應(yīng)用的網(wǎng)絡(luò)性能。每個(gè)的用戶請求被模擬為獨(dú)立泊松分布,而鏡像服務(wù)器被作為M/M/1排隊(duì)模型。在給定請求率、鏡像服務(wù)器的服務(wù)率、最大可部署的鏡像服務(wù)器數(shù)量和服務(wù)器的請求等待時(shí)間期望值上界的條件下,我們所研究的問題是從待選位置中選出一個(gè)子集來部署鏡像服務(wù)器,通過最小化網(wǎng)絡(luò)中正在傳輸?shù)恼埱髷?shù)與鏡像服務(wù)器隊(duì)列中等待的請求數(shù)之和,達(dá)到網(wǎng)絡(luò)中平均請求延遲的最優(yōu)化。我們對該問題進(jìn)行了形式化定義,并證明了其NP困難性。禁忌搜索算法和拉格朗日松弛算法被用于解決該問題,其中禁忌搜索算法引入禁忌列表來避免重復(fù)搜索,拉格朗日松弛算法可以獲得較好的近似比。實(shí)驗(yàn)證明,我們所提出的算法均能獲得較低的平均網(wǎng)絡(luò)時(shí)延,并有效地用于實(shí)際CDNs的鏡像服務(wù)器部署。二、內(nèi)容被劃分為多個(gè)內(nèi)容對象,對于每個(gè)內(nèi)容對象,將其熱度定義為該內(nèi)容對象的請求在所有請求中所占的百分比。根據(jù)內(nèi)容對象的熱度信息,我們可以將內(nèi)容預(yù)分配到各個(gè)鏡像服務(wù)器上,用戶請求便可被定向至最近的緩存有所需內(nèi)容對象的鏡像服務(wù)器。我們既考慮了內(nèi)容的熱度,也考慮了鏡像服務(wù)器的服務(wù)能力,通過合理的模型構(gòu)建,對基于內(nèi)容熱度的靜態(tài)鏡像內(nèi)容分發(fā)問題進(jìn)行了形式化的定義。由于該問題的NP困難性,本文提出了兩個(gè)啟發(fā)式算法：貪心移除算法和禁忌搜索算法,用于得到可行的靜態(tài)鏡像內(nèi)容分發(fā)方案。最后,仿真實(shí)驗(yàn)數(shù)據(jù)顯示,我們的方法能夠以較高的概率得到可行的鏡像內(nèi)容分發(fā)方案,且禁忌搜索算法能夠大大降低CDNs中的平均請求延遲。三、針對無線Mesh網(wǎng)絡(luò)中的內(nèi)容鏡像分發(fā)問題,結(jié)合內(nèi)容對象的分布密度與內(nèi)容熱度之間的最優(yōu)關(guān)系,考慮到Mesh路由器的服務(wù)模型,提出了一個(gè)全新的動(dòng)態(tài)分布式四階段內(nèi)容分發(fā)算法,以適應(yīng)無線Mesh網(wǎng)絡(luò)環(huán)境。首先,依據(jù)無線Mesh網(wǎng)絡(luò)的分布式特點(diǎn),對網(wǎng)絡(luò)拓?fù)涫褂脛澐炙惴ㄟM(jìn)行分布化。然后,根據(jù)內(nèi)容對象的熱度信息,計(jì)算出每個(gè)內(nèi)容對象所需的鏡像數(shù)目。在網(wǎng)絡(luò)拓?fù)鋭澐值幕A(chǔ)上,結(jié)合網(wǎng)絡(luò)中的請求模型和服務(wù)模型,使用分布式的算法生成內(nèi)容鏡像的分發(fā)策略,以降低網(wǎng)絡(luò)中的平均請求時(shí)延。最后,采用協(xié)作式的內(nèi)容分發(fā)方式,將內(nèi)容鏡像分發(fā)到各個(gè)Mesh路由器。仿真實(shí)驗(yàn)證明,該算法可在不明顯增加網(wǎng)絡(luò)負(fù)載的情況下,有效地降低網(wǎng)絡(luò)中的平均請求時(shí)延。四、研究了結(jié)合廣播網(wǎng)絡(luò)和4G/LTE的無線融合網(wǎng)絡(luò)中基于推送的動(dòng)態(tài)內(nèi)容分發(fā),內(nèi)容對象通過廣播和4G/LTE蜂窩網(wǎng)絡(luò)單播兩種方式推送到終端用戶。在這樣的網(wǎng)絡(luò)模型下,熱門內(nèi)容對象通過廣播的方式,推送給網(wǎng)絡(luò)覆蓋范圍內(nèi)的所有終端用戶：其余的內(nèi)容對象通過4G/LTE蜂窩網(wǎng)絡(luò),根據(jù)用戶的需求發(fā)送至終端用戶�；谶@樣的內(nèi)容分發(fā)流程,我們設(shè)計(jì)了高效的基于BCSA算法的無線融合網(wǎng)絡(luò)的內(nèi)容分發(fā)機(jī)制,摒棄了以往優(yōu)先將最熱門的內(nèi)容資源進(jìn)行廣播的方案,使用了近似算法,合理地對廣播的內(nèi)容對象進(jìn)行選擇,優(yōu)化廣播內(nèi)容請求的總帶寬。在蜂窩網(wǎng)絡(luò)部分,我們對緩沖隊(duì)列的長度與網(wǎng)絡(luò)延遲和丟包率的關(guān)系進(jìn)行了研究。最后,通過仿真實(shí)驗(yàn)對基于BCSA算法的無線融合網(wǎng)絡(luò)的效果進(jìn)行了實(shí)驗(yàn)。實(shí)驗(yàn)結(jié)果證明本文所提出的內(nèi)容分發(fā)機(jī)制能夠大大地降低4G/LTE的帶寬消耗,降低網(wǎng)絡(luò)的平均時(shí)延。
[Abstract]:Content distribution network (Content Delivery Network, CDN) effective technology as to relieve the congestion problem caused by a large number of concurrent access, has been widespread concern in academia and industry. In the content distribution network, the content is copied and stored in a mirror server, which makes the content can quickly be terminal user access, greatly reducing the average request terminal user delay. Because more mirror server will bring greater deployment and maintenance costs, reasonable deployment of the mirror server for content distribution network is vital. In addition, the mirror server capacity is limited, how to select the image content distributed to the mirror server, directly determine the performance of the network content distribution network. Content distribution network based on the existing research results, this paper from the mirror server deployment and image content distribution Two directions on issues related to content distribution network, in order to reduce the network delay. The average request distribution problem in the mirror in the content distribution method and dynamic content from the static content distribution method two aspects were studied. Among them, the dynamic content distribution method, combining with the characteristics of wireless Mesh networks and wireless network integration and designed the corresponding content distribution mechanism in four aspects. The main contents and contributions of this paper are as follows. First, the statistical characteristics of network service model in the request from the mirror server based on the research content distribution network in the mirror server deployment method, to reduce the average request in the network delay, improve the network performance of CDNs application. Each user request is modeled as independent Poisson distribution, and the mirror server as M/M/1 queuing model. The request rate in a given, the mirror server. The service rate, the mirror server number and server maximum deployment request waiting time upper bound for the conditional expectation, we study the problem is to select a sub set from the candidate position to deploy the image server by being transmitted in the network is minimized the number of requests and mirror like waiting for the server requests in a queue and the number of the average request latency, network optimization. We reached a formal definition of the problem, and prove its NP problem. The tabu search algorithm and Lagrange relaxation algorithm is used to solve this problem, the tabu search algorithm is introduced to avoid repeated search of tabu list, Lagrange relaxation algorithm can obtain better approximation ratio. Experiments show that our proposed algorithm can obtain the average network delay is low, and effectively used in CDNs image server deployment. Two, the content is divided As a content object for each content object, will define the heat as a percentage of the content object request for all requests. According to the contents of the object heat information, we can be content pre assigned to each image on the server, the user requests can be set to have the required content object to the nearest cache the mirror server. We not only consider the content of the heat, also considered the mirror server service ability, through constructing reasonable model of distribution static image based on heat content are defined formally. Because the NP difficulty of the problem, this paper proposes two heuristic algorithms: greedy algorithm and remove tabu search algorithm for static image content distribution scheme is feasible. Finally, simulation experiments show that our method can be feasible with high probability in the mirror Content distribution scheme, and the tabu search algorithm can greatly reduce the average delay in the CDNs request. Three, according to the image content in wireless Mesh network distribution problems, combined with the optimal relationship between content objects and contents of heat distribution density, taking into account the service model of Mesh router, the paper proposes a new four stage dynamic distributed content distribution algorithm, in order to adapt to the wireless Mesh network. Firstly, based on the distributed characteristics of wireless Mesh networks, the network topology distribution using partitioning algorithm. Then, according to the contents of the object heat information, calculate the number of image content of each desired object. On the basis of the network topology division, combination model and service request in the network model, distribution strategy algorithm to generate the image using the distributed content, in order to reduce the average request in the network delay. Finally, using collaborative content The content of hair, mirror is distributed to all Mesh routers. Simulation results show that the algorithm can be without significantly increasing network load conditions, effectively reduce the average request in the network delay. Four, the distribution of dynamic content push based on wireless integrated network broadcast network and 4G/LTE, through the content object broadcast and unicast 4G/LTE cellular network in two ways to end users. In such a network model, popular content object by means of broadcast, pushed to the network covering all terminal users within the scope of the object: the rest of the content through a 4G/LTE cellular network, according to the needs of users to send to the terminal users. This is based on the contents of flow distribution and we design efficient wireless network fusion algorithm BCSA based content distribution mechanism, instead of priority will be the most popular content resources for broadcast Using the scheme, approximation algorithm, reasonably to broadcast content object selection, optimization of the total bandwidth request. The broadcast content in a cellular network, we on the buffer queue length and network latency and packet loss rate were discussed. Finally, through the simulation experiment of BCSA algorithm of wireless integrated network based on the results. The experimental results show that the proposed content distribution mechanism can greatly reduce 4G/LTE bandwidth consumption, reduce the average delay of the network.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TP393.02

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