隨著3G 時代的到來，使用者對行動通訊有了更高的期望，不僅要求有穩定的語音通信，而且還要求能夠進行數據和多媒體的多種方式通信。IP 多媒體子系統 (IP Multimedia Subsystem；IMS) 是包含於全球行動通訊系統 (Universal Mobile Telecommunication System；UMTS) 核心網路中一個子系統。IMS 提供並改善了即時性的行動多媒體服務。在IMS 中，訊號(signaling)和資料(media)是分開的。針對每一次資料會話(session)交談的建立，IMS 訊號必須透過一些Call
Session Control Function (CSCF)的集合傳送，其中有Proxy CSCF (P-CSCF)、Interrogating CSCF (I-CSCF)和Serving CSCF (S-CSCF)。當會話建立之後，資料則是透過端點對端點的方式傳送。因此在IMS 中定義了兩個基本的程序，分別為 (i) IMS registration procedure 和 (ii) IMS incoming call setup procedure。然而，
我們觀察到在這些程序中，I-CSCF 都必須透過Home Subscriber Server (HSS)查詢來獲得相對應的S-CSCF 名稱和其位址的資訊。結果造成了HSS 的負載和IMS程序的延遲。在這篇論文中，我們提出結合分散式雜湊表和快取的技術到IMS中並設計了以分散式雜湊表為基礎的I-CSCF 網路系統。根據我們的研究HSS 的負載可以有效的被減輕，而IMS incoming call setup 程序的速度也可以有效的提升。

IP Multimedia Subsystem (IMS) is an overlaid infrastructure above the packet-switched domain of the Universal Mobile Telecommunication System (UMTS) core network. IMS enables and enhances real-time multimedia mobile services. IMS signaling and media are separated in IMS. For media session negotiation, IMS signaling needs to traverse a set of Call Session Control Functions (CSCFs), which are Proxy CSCF (P-CSCF), Interrogating CSCF (I-CSCF), and Serving CSCF (S-CSCF). After media session negotiation, media is sent from end to end. Therefore, two basic procedures in IMS are (i) IMS registration procedure and (ii) IMS incoming call setup procedure. However, we obverse that I-CSCFs need to query the home subscriber server (HSS) to obtain the name of S-CSCF no matter in the IMS registration procedure and the IMS incoming call setup procedure. It results in that a certain load occurs in the HSS and a certain procedure delay also occurs. Therefore, we employ the Distributed Hash Table (DHT) into IMS to form a DHT-based I-CSCF network, in which the Chord is as the base DHT. Each I-CSCF in the DHT-based I-CSCF network can share and relieve the HSS’s load. Furthermore, the incoming call setup procedure can be speeded up.

[1] The 3rd Generation Partnership Project (3GPP). [Online]. Available: http://www.3gpp.org/
[2] Universal Mobile Telecommuncations system. [Online]. Available: http://www.umtsworld.com/
[3] 3GPP, “3G security; Security architecture,” 3rd Generation Parnership Proejct (3GPP), TS 33.102, Dec. 2006. [Online]. Available: http://www.3gpp.org/ftp/Specs/htmlinfo/
33102.htm
[4] 3GPP, “IP Multimedia (IM) Subsystem Cx and Dx interfaces; Signalling flows and
message contents,” 3rd Generation Partnership Project (3GPP), TS 29.228, Dec. 2007.
[Online]. Available: http://www.3gpp.org/ftp/Specs/html-info/29228.htm
[5] 3GPP, “IP Multimedia Subsystem (IMS); Stage 2,” 3rd Generation Parnership Proejct (3GPP), TS 23.228, Dec. 2007. [Online]. Available: http://www.3gpp.org/ftp/Specs/html-info/23228.htm
[6] 3GPP TS23.002 , Technical Specification Group Services and Systems Aspects; Network Archetecture, Release 5.
[7] G. Bolch, S. Greiner, H. de Meer, and K. S. Trivedi, Queueing networks and Markov chains: modeling and performance evaluation with computer science applications. New York, NY, USA: Wiley-Interscience, 1998.
[8] P. Calhoun, G. Zorn, D. Spence, and D. Mitton, “Diameter Network Access Server Application,” RFC 4005 (Proposed Standard), Aug. 2005. [Online]. Available: http://www.ietf.org/rfc/rfc4005.txt
[9] D. Gross and C. M. Harris, Fundamentals of queueing theory (3nd ed.). New York, NY, USA: John Wiley & Sons, Inc., 1998.
[10] M. Handley, V. Jacobson, and C. Perkins, “SDP: Session Description Protocol,” RFC 4566 (Proposed Standard), Jul. 2006. [Online]. Available: http://www.ietf.org/rfc/rfc4566.txt
[11] Y.-B. Lin and M.-H. Tsai, “Caching in i-cscf of umts ip multimedia subsystem,” Wireless Communications, IEEE Transactions on, vol. 5, no. 1, pp. 186–192, Jan. 2006.
[12] S. Ratnasamy, P. Francis, M. Handley, R. Karp, and S. Schenker, “A scalable content addressable network,” in SIGCOMM ’01: Proceedings of the 2001 conference on Applications, technologies, architectures, and protocols for computer communications. New York, NY, USA: ACM, 2001, pp. 161–172.
[13] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, “SIP: Session Initiation Protocol,” RFC 3261 (Proposed Standard), Jun. 2002, updated by RFCs 3265, 3853, 4320, 4916. [Online]. Available: http://www.ietf.org/rfc/rfc3261.txt
[14] S. M. Ross, Introduction to Probability Models, Ninth Edition. Orlando, FL, USA: Academic Press, Inc., 2006.
[15] A. Rowstron and P. Druschel, “Pastry: Scalable, decentralized object location, and routing for large-scale peer-to-peer systems,” Lecture Notes in Computer Science, vol. 2218, pp. 329–350, 2001. [Online]. Available: citeseer.
ist.psu.edu/rowstron01pastry.html
[16] I. Stoica, R. Morris, D. Karger, M. F. Kaashoek, and H. Balakrishnan, “Chord: A scalable peer-to-peer lookup service for internet applications,” in Proceedings of the ACM SIGCOMM ’01 Conference, San Diego, California, August 2001.
[17] B. Y. Zhao, L. Huang, J. Stribling, S. C. Rhea, A. D. Joseph, and J. Kubiatowicz,“Tapestry: A resilient global-scale overlay for service deployment,” IEEE Journal on Selected Areas in Communications, vol. 22, no. 1,, pp. 41–53, 2004.