電腦輔助設計(CAD)的發明，改善了費時且精度低的手工製圖方式，設計的工作變得迅速、精確且易於修正；近年來，網際網路(Internet)相關技術的發展革命性地改變了程式系統的運作方式，程式系統間透過網路連線互動與合作已成為趨勢，將網路技術應用於電腦輔助設計，讓多位設計人員同時使用互相連線的電腦輔助設計系統成為合作式的設計環境，亦成為近年來新的研究的課題，然而現有的研究大多使用主從式(Client-Server)架構來開發合作式的設計系統，主從式架構無論在系統之運作與用戶間之溝通均仰賴中央伺服器，於系統的硬體要求上或使用的便利性上，都無法滿足合作設計組成團隊所需之機動性與彈性，以致無法普及。
本研究引進了同儕式架構(Peer to Peer based, P2P)的概念開發原型系統－ROCCAD，讓設計人員間不需如主從式架構需透過與中央伺服器的連線來達成共同設計，而是設計人員間能夠機動地自行相互連線來形成合作設計團隊，且設計人員可彈性地隨時加入或退出團隊，本系統並配合應用層群播(Application Level Multicast, ALM)中樹狀結構式(Tree First)疊加網路(overlay network)的方式來有效地降低連線程式間的訊息傳輸量，此原型系統不但改善了主從式架構中中央伺服器在網路傳輸上的極大負擔，亦避免了IP群播的低延展性與低可靠度，且本研究亦考量實際應用之需要提出搜尋使用者、連線修復、模型傳遞及模型使用權等機制，以提昇系統之使用性與穩定性，以期能對網路合作式電腦輔助設計之實際應用與普及有所貢獻。

The Internet has revolutionized the way software systems work. Recently, some researchers have utilized the web-related technologies in Computer–Aided Design to fulfill real-time collaboration between users over the web. All these systems are based on the client-server model. In this kind of distributed design environment, the system grouping, operation and communication all have to rely on the central server. In order to improve the accessibility and flexibility in collaborative design and provide a more load-balancing environment, this paper presents a prototype implementation on collaborative design based on the Peer-to-peer (P2P) model. The users can conveniently form the design group by connecting directly to each other without the presence of the central server. All peers are equal in functionality and computing load. In addition, the Application Level Multicast (ALM) technology is adopted in the proposed system to improve the efficiency in Internet communication. Based on the P2P network model and ALM communication scheme, several mechanisms are proposed in this research to form the working model of this system. Then the object model design and implementation of this P2P system is presented.

[1] www.acm.org/cscw2004/index.html
[2] Kao, Y.C. and Lin, G.C.I. (1996), “CAD/CAM collaboration and remote machining”, The Journal of Computer-Integrated Manufacturing Systems 9 (3), p.149–160.
[3] Abdel-Wahab, H.M., Guan, Sheng-Uei and Nievergelt, J. (1988), “Shared workspaces for group collaboration: an experiment using Internet and UNIX interprocess communications”, IEEE Co&m Magazine, Vol 26 No 11 November, p.10–16.
[4] Mitchell, W.J. (1997), “CAD as a social process, CAD futures 1997”, Proceedings of the 7th International Conference on Computer-Aided Architectural Design Futures, Munich, Germany, p.7–9.
[5] Pang, A. and Wittenbrink, C. (1997), “Collaborative 3D visualization with CSpray”, IEEE Computer Graphics and Applications, v 17, n 2, Mar-Apr, p.32–41.
[6] Nam, T.-J. and Wright, D. (2001), “The development and evaluation of Syco3D: A real-time collaborative 3D CAD system”, Design Studies, v 22, n 6, November, p.57–582.
[7] dlab.nus.edu.sg/cybercad/index.html
[8] Roy, A. (2000), “CyberCAD—a JavaTM-based synchronized collaborative CAD system”, Master of Engineering thesis, National University of Singapore
[9] Tay, F.E.H. and Roy, A. (2000), “3D solid modeling techniques using CyberCAD for Web-based CAD application”, Proceedings of the 5th International Conference on Computer Integrated Manufacturing, Singapore, p.1072–1083.
[10] Tay, F.E.H. and Roy, A. (2003), “CyberCAD: A collaborative approach in 3D-CAD technology in a multimedia-supported environment”, Computers in Industry, v 52, n 2, October, p.127–145.
[11] Chu, Y., Rao, S.G., Seshan, S. and Zhang, H. (2001), “A case for end system multicast”, IEEE Journal on Selected Areas in Communication
[12] Pendarakis, D., Shi, S., Verma, D. and Waldvogel, M. (2001),“Almi: An application level multicast infrastructure”, USITS.
[13] www.GameTutorials.com