國立臺灣大學電機工程學系暨研究所張時中2006-07-252018-07-062006-07-252018-07-062003-07-31http://ntur.lib.ntu.edu.tw//handle/246246/7947本計畫兩年的研究工作分為三部分，(一) 虛擬私人網 路之技術研究，(二)計價收費之機制，(三)正交分頻多工 (OFDM)偏移估測。第一年在虛擬私人網路之技術研究 上，我們整合DiffServ 架構中分類、塑流(traffic shaping)、 封包排序與虛擬私人網路架構中網路安全協定對封包加 密、驗證、建立通道的功能，在Linux 環境中設計並實作 了品質服務(QoS)虛擬私人網路路由器和服務代理人 (Service Broker)。進而據以建構品質服務虛擬私人網路實 驗環境，來對每一個網路流(per flow)作資源保留，提供 各虛擬私人網路使用者一個動態的頻寬設定服務，在安 全通道上提供虛擬私人網路與服務品質。第二年是研究 有頻寬保證的虛擬私人網路服務計價之研究與實做，研 究中考慮ISP 提供「有頻寬保證的網路類型虛擬私人網 路」與「以盡力傳送資料的公眾網路」，而營運目標主 要為了獲得最大營業額。「有頻寬保證的網路類型虛擬 私人網路」的服務，以企業為訴求，企業內的個人使用 者並不直接負擔費用。「盡力傳送資料的公眾網路服 務」，是一個沒有頻寬保證的服務，所以服務的費率影 只響訂購服務的總人數，但不直接影響訂購後的使用行 為。我們探討ISP 如何經由有頻寬保證的虛擬私人網路 和盡力傳送的公眾網路服務間的費率來影響購買和使用 服務的機率，進而決定頻寬的分配策略與期望的總營業 額大小。我們針對所設計的虛擬私人網路計價策略，在 第一年品質服務(QoS)虛擬私人網路路由器和服務代理 人外，加入流量量測與記帳收費的模組，成為一個具體 而微的計價實驗平台實作，來驗證其可行性並掌握了基 本技術。此外，我們也研究了正交分頻多工系統時序和 頻率的偏移造成符元(Symbol)與符元、子頻道(Subchannel) 與子頻道間互相干擾的問題。我們提出了一個混合式頻 率偏移估測演算法，該方法在訊雜比(SNR)低以及循環字 首短的時候，估測效能有相大的改善。This two year research included three tasks: (1) research on QoS-based virtual private network (VPN) technology, (2) the design of pricing scheme for VPN service, and (3) research on the synchronization problem of OFDM system In the first year, we adopted differentiated service (DiffServ) architecture to design and implement a QoS VPN experimental environment. We designed a QoS VPN router and a service broker by combining packet classification, traffic shaping and packet scheduling of DiffServ routing with encryption, authentication and tunneling of VPN. They were implemented into a Linux-based experimental network, where a VPN service with per flow-based QoS can then be provided. In the second year, a decision model was developed for ISP pricing between two types of Internet services: bandwidth guaranteed VPN and best effort public network (BEPN). The VPN users are corporates and their employees, where a corporate subscribes and pays for the VPN service while its employees are the actual users. Each VPN user is guaranteed a minimum bandwidth. The BEPN users are the general public and have no QoS guarantee. Under this setting, our study found that the price level affects the number of subscribers. The usage behavior of a VPN user is insensitive to the pricing policy and the probability that a BEPN subscriber will actually use the service depends on the bandwidth level to share among BEPN subscribers. Bandwidth is shared between VPN and BEPN but the ISP puts the bandwidth guarantee to VPN users in a high priority. We also implemented the pricing scheme and added a NTOPTM-based network traffic metering and accounting module to the QoS VPN experiment environment. In addition, we studied the synchronization problem of OFDM system, including carrier offsets caused by both frequency and time. We designed a hybrid frequency offset correction method that significantly improved for the OFDM system with low signal-to-noise ratio and short cyclic prefix.application/pdf158480 bytesapplication/pdfzh-TW國立臺灣大學電機工程學系暨研究所虛擬私人網路差別服務計價品質服務實驗平台實作正交多頻分工偏移估測Virtual Private NetworkDiffServQuality of ServicePricingOFDMoffset estimationreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/7947/1/912219E002033.pdf