在無線環境裡，行動用戶可能會想要獲得或分享某些資訊，這些資訊可能包括了網路服務的相關資訊，像是印表機、顯示器、資料庫、檔案傳輸，或是關於網路拓樸的各種伺服器位址等等，而為了能夠有效率的得知儲存這些網路服務資訊的網路節點位置，我們使用了Chord這樣的一個分散式查詢協定來得到這些資訊。
在Chord協定裡，網路上的每個節點和服務資訊會使用穩定散列函數來被對應並依序指派到一個環狀的架構上，在原始的Chord協定裡，當網路節點要加入這樣的環狀架構時，必須知道一個已知的根節點來作為入口，這樣的根節點，可能是一個已經在Chord環狀架構裡的網路節點，也可能是一個一開始就被指定當作加入點的網路節點，所以，當網路節點使用了不同的根節點來加入時，可能會造成同時有多個Chord ring的形成。另外，由於Chord是一個環狀的類似link list的架構，當有許多的網路節點同時間加入或離開Chord環狀架構，會造成環狀架構的錯誤，進而分裂成數個不相連獨立的Chord環狀架構，像這樣有多個獨立Chord環狀架構存在時，會造成當某些服務資訊存在於某個Chord環狀架構時，另一個環狀架構裡的用戶將無法得知。
為了解決這樣的問題，我們提出了一個利用行動用戶的移動來攜帶和網路節點以及其他Chord環狀架構相關資訊的分散式方法來合併所有的Chord環狀架構來成為一個完整的Chord環狀架構。和傳統使用「super-peer」來轉送服務需求到其他Chord環狀架構的方法比起來，這個方法提供了較高的擴充性及服務可得性，為了驗證我們的推論，我們將使用NS2來模擬這兩種方法，並利用得到的結果進行分析。

In wireless networks, mobile users may want to discover and share information about some services. In order to efficiently locate the node that stores the particular information, we use Chord, a distributed lookup protocol, to find the needed information. Each node and information will be mapped to a ring architecture which is called a
Chord ring. Original Chord protocol requires a known root node to join the Chord ring. When nodes use different root nodes to join, it may cause many Chord rings to be formed simultaneously. When too many nodes join or leave the Chord ring at the same time, it may also cause a Chord ring to split into several independent ones. Information located in one Chord ring may not be discovered by users in other Chord rings. In order to solve this problem, we use the routine of mobile users' movement to let Chord rings be aware of each others. We propose a distributed solution to combine all of the small Chord rings into a big one. It
provides higher scalability and service availability than the traditional solution which assigns a node called "super-peer" to one Chord ring to forward the service request messages to another to get the dedicated service if the mobile user can't find it in his own Chord ring.

[1] T. Zhang, E. V. den Berg, and S. Madhani, “Peer-to-Peer Network and User Information Discovery and Dharing for Mobile Users and Devices,” Vehicular Technology Conference, 2005.
[2] “Jini website.” http://www.sun.com/jini/.
[3] C. Bettstetter and C. Renner, “A Comparison of Service Discovery Protocols and Implementation of the Service Location Protocol,” Proceedings of EUNICE, 2000.
[4] U. Plug and P. D. Architecture, “Microsoft Corporation.” http://www.upnp.org/.
[5] C. Bettstetter and C. Renner, “Protocols for Service Discovery in Dynamic and Mobile Nerwork,” International Journal of Computer Research, Special Issue on Wireless
Systems and Mobile Computing, 2002.
[6] I. Stoica, R. Morris, D. Karger, M. F. Kaashoek, and H. Balakrishnan, “Chord: A scalable peer-to-peer lookup service for internet applications,” ACM SIGCOMM, 2001.
[7] A. Datta and K. Aberer, “The Challenges of Merging Two Similar Structured Overlays: A Tale of Two Networks,” International Workshop on Self-Organizing Systems (IWSOS), 2006.
[8] D. Liben-Nowell, H. Balakrishnan, and D. Karger,“Observations on the Dynamic Evolution of Peer-to-Peer Networks,” In Proceedings of the First International Workshop on Peer-to-Peer Systems (IPTPS), 2002.
[9] D. Liben-Nowell, H. Balakrishnan, and D. Karger,“Analysis of the Evolution of PeertoPeer Systems,” Proceedings of the twenty-first annual symposium on Principles of distributed computing, 2002.
[10] B. Yang and H. Garcia-Molina, “Designing a Super-Peer Network,” 19th International Conference on Data Engineering (ICDE), 2003.
[11] “KaZaA website.” http://www.kazaa.com.
[12] “Gnutella website.” http://www.gnutella.com.
[13] J. Liang, R. Kumar, and K.W. Ross, “Understanding KaZaA,” Proceedings of the Fifth New York Metro Area Networking Workshop (NYMAN), Sept. 2005.
[14] “The Network Simulator 2 (NS2).”http://www.isi.edu/nsnam/ns/.