| 摘要: | Topos計畫探討建構一個以同儕式(Peer-to-Peer, P2P) 運算為基礎，具有高擴展性(Scalability)、低維護成本、且容易使用的個人(personal)網路虛擬環境(networked virtual environment, NVE)架構。Topos源自於希臘字，代表koinos topos，意思為「共同處所(common place)」。在Topos架構中，使用者可以在沒有伺服器的狀態下，透過P2P覆疊網路(overlay network)輕鬆地建立並發布個人專屬的NVE空間，以供其他使用者瀏覽(navigate)。使用者在瀏覽他人NVE空間的同時，也能夠看到其他瀏覽者的化身(avatar)，並能與其進行互動，如互相交談、握手、顯示表情與手勢等。由於Topos的架構是由所有使用者透過P2P網路來共同保存每位使用者的個人空間，因此，如何在P2P環境中分散地、可容錯地儲存個人空間的資料，並能讓瀏覽者確認空間的散佈者身份與快速獲得並顯示最新版本的空間資料是一個重要的議題。另一個重要的議題是如何以同儕式運算的方式，提供個人空間中物件可變狀態(如化身的位置、表情、交談的內容、電燈物件的開與關、可編輯塗鴉區的內容等)的一致性控制(consistency control)，可以讓瀏覽者有更佳的互動經驗。Topos 的研究動機來自於以下網際網路發展趨勢的觀察：多人線上遊戲(Massively Multiplayer Online Games)註冊者的急遽增加、使用者自製內容網站的快速成長(如網誌、影片之線上分享網站)及P2P架構較佳之擴展性等，我們預計以二年的時間進行下列研究： 1. P2P-NVE 場景資料的發佈、更新、傳遞與驗證：我們假設每個使用者都擁有公鑰憑證(certificate)及獨一無二的ID，並可以正確地驗證其他使用者的憑證及簽章(signature)。每個使用者透過P2P儲存系統(P2P storage system)發佈專屬的NVE空間及自己的憑證，而其他使用者則可以利用發佈者ID獲取這個空間的最新版本，並透過憑證及簽章確認發佈者的身份。我們利用Hash-chain 3D 串流(3D streaming)技術以傳遞NVE空間場景資料，瀏覽者只需要下載NVE空間中互動範圍(area of interest, AOI)內所有物件的基礎片斷(base pieces)，即可以驗證並開始瀏覽NVE空間，稍後即可以使用計算成本相對很低的Hash-chain方式驗證下載的精細片斷(refinement pieces)，並以更細緻的方式呈現NVE空間。 2. P2P-NVE 物件可變狀態一致性控制： P2P-NVE 物件可變狀態可以分為二種: 化身狀態(avatar state)與靜止物件狀態(stationary object state)。透過分散式雜湊表(distributed hash table)的機制，使用者可以與入口控制者(portal controller)進行連線，並取得目前在NVE空間中的瀏覽者清單(內含瀏覽者ID及其IP address)。使用者可以透過瀏覽者清單中之任意瀏覽者取得所有AOI內的瀏覽者資訊並建立連線，然後就可以透過不斷與AOI內瀏覽者交換化身狀態的方式進行化身狀態一致性控制。入口控制者並利用范諾圖(Voronoi diagram)來切割NVE空間，並挑選資源較豐富的超級同儕節點(super peer)管理空間中的物件狀態以進行靜止物件狀態一致性控制。超級同儕節點並可利用Delaunay Triangulation 將物件狀態備份於其他的超級同儕節點，以達到容錯的目的。另外，特過范諾圖細微且可彈性改變空間切割的特性，可以提升整體系統的負載平衡能力。 ; Topos aims to create a framework of scalable, affordable, and easy-to-use peer-to-peer (P2P) personal networked virtual environments (NVEs). Topos is a word originating from Greek, which stands for a “common place.” In Topos, users can easily build and publish personal NVE spaces for others to navigate as avatars, and interact with other avatars by chatting, handshaking, displaying emotions or gestures. As the spaces are stored on P2P networks, providing such storage in a distributed, fault-tolerant way, while allowing users to authenticate publishers and obtain updates efficiently becomes an important issue. Another issue is the consistency control for mutable objects within such personal spaces (e.g., switching lights on/off, or drawing on a collaborative whiteboard), to provide better navigation experiences. Topos is based on the observations of the following trends: the rapid increase of Massively Multiplayer Online Game (MMOG) subscribers, the rapid growth of user-generated content in popular sites (e.g., blogs, photo and file sharing sites), and the better scalability of peer-to-peer networks. We plan to conduct the following research in 2 years: 1. The publication, update, delivery, and authentication of P2P-NVE scenes: Assume that each user has a public key certificate and a unique ID, and can authenticate any other’s certificate and digital signature. Each user can publish and modify a personal NVE space along with personal certificate in a P2P storage system. Other users obtain the up-to-date version of the space based on the publisher’s ID, authenticate publisher of the space, and check the integrity of the space. We will propose a hash-chain-based 3D streaming technique to lower the costs associated with data publication and authentication. Users only need to download all base pieces of objects within AOI (area of interest) to start authenticating and navigating the space. They then can authenticate refinement pieces, which are downloaded later to render higher-quality scenes, by a low-cost hash-chain method. 2. State consistency control for P2P-NVE objects: There are two types of P2P-NVE object states: avatar state and stationary object state. By way of distributed hash tables (DHTs), a user can connect with portal controller to obtain a navigator list, each item of which includes a navigator ID and an IP address. The user can then connect to one of online active navigator to acquire all AOI neighbors to connect. Avatar state consistency control is carried out by performing neighbor discovery and by users’ sending avatar states to all AOI neighbors periodically. Portal controller also utilizes Voronoi diagram to split an NVE space into regions, and chooses a resource-rich super peer to manage states of objects in a region to achieve stationary object state consistency control. Delaunay Triangulation is also utilized for super peers to replicate object states in other super peers to achieve the goal of fault-tolerance. Since Voronoi diagram is easy to split space in a flexible and subtle way, load-balancing among super peers can be easily achieved. ; 研究期間 9708 ~ 9807 |
