這篇論文中，我們提出一個針對異質性網路VoIP (Voice over Internet Protocol)服務設計之串流控制傳輸協定 (Stream Control Transmission Protocol) 省電換手機制。利用這個串流控制傳輸協定省電換手機制來增進VoIP服務中聲音傳輸的品質，並且降低支援串流控制傳輸協定行動裝置的耗電量。由於串流控制傳輸協定的multi-homing機制可以讓兩個支援串流控制傳輸協定的端點建立一個包含多條傳輸路徑的連線，而每條傳輸路徑可以透過不同的無線擷取網路連上網際網路。利用這個特性，在所提出的串流控制傳輸協定省電換手機制中，實作一個選擇最佳傳輸路徑的機制，從眾多可用的傳輸路徑中，選出一條認為是最佳路徑的來做資料傳輸。在最佳路徑的選擇上，利用兩個選擇的標準，一個是VoIP的品質，另一個是耗電量。經由測量每一條路徑可以提供的VoIP品質以及選擇每一條路徑行動裝置的耗電量，找出一條能提供良好VoIP品質並且擁有最小耗電量的路徑，再利用串流控制傳輸協定多重連線(multi-homing)的機制，換手到該最佳路徑做連線的資料傳輸。在VoIP品質的測量上，是利用ITU-T (International Telecommunication Union Technical standards) 所制定的MOS值　(Mean Opinion Score) 作為判斷VoIP品質的標準。MOS值可以經由測量計算ITU-T E-model所得到的R值來做轉換。由於SCTP是新制定的傳輸層通訊協定，在使用上並不如TCP或UDP來的普及。因此，我們另外設計並且實作一個在串流控制傳輸協定和TCP協定之間做透明化轉換的機制，來增加我們提出的串流控制傳輸協定省電換手機制在使用上的普及率。

In this thesis, we propose an energy-efficient transport layer handoff mechanism for VoIP (Voice over Internet Protocol) service in heterogeneous network environment using SCTP (Stream Control Transmission Protocol). The proposed handoff mechanism is used to improve the transmission quality of VoIP service and reduce the power consumption of mobile hosts. The multi-homing feature of SCTP allows two SCTP endpoints to maintain an association with multiple transmission paths accessed by different types of wireless access networks. The proposed handoff mechanism implements a new path selection mechanism to select the best path from all available paths based on the VoIP quality and power consumption of each path and use SCTP multi-homing feature to handover to that selected path. VoIP quality is measured by the MOS (Mean Opinion Score) calculated from the ITU-T (International Telecommunication Union Technical standards) E-model. SCTP is a newly standardized transport layer protocol, and not widely used as TCP or UDP. In order to increase the generality of our proposed handoff mechanism, we design and implement a new transparent transformation mechanism between SCTP and TCP.

[1] S. Y. Hui and K. H. Yeung. Challenges in the Migration to 4G Mobile Systems. IEEE Commun. Mag., vol. 41, no. 12, pp. 54–59, Dec. 2003.
[2] R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang and V. Paxson. Stream Control Transmission Protocol. RFC2960, October 2000.
[3] ITU-T. The E-Model, A computational Model in Use in Transmission Planning. G.107, March 2003.
[4] J. Funasaka, K. Ishida, H. Obata, and Y. Jutori. A Study on Primary Path Switching Strategy of SCTP. Workshop on Cooperative Computing, Internetworking and Assurance (WCCIA 2005), pp. 536-541, April 2005.
[5] K. Lai and M. Baker. A Tool for Measuring Bottleneck Link Bandwidth. Proc. USENIX symposium on Internet Technology and Systems, March 2001.
[6] S. Kashihara, T. Nishiyama, K. Iida, H. Koga, Y. Kadobayashi, and S. Yamaguchi. Path Selection Using Active Measurement in Multi-Homed Wireless Networks. Proc. the 2004 International Symposium on Applications and the Internet (SAINT2004), pp.273-276, 2004.
[7] R.G. Cole and J.H. Rosenbluth. Voice over IP Performance Monitoring. SIGCOMM Computer Communications Review, 31(2):9.24, 2001.
[8] ITU-T. Mean Opinion Score（MOS）terminology. Recommendation P.800.1, 2003
[9] The Network Simulator –ns2-. http://www.isi.edu/nsnam/ns/.
[10] Protocol Engineering Lab. http://www.pel.cis.undel.edu/.
[11] ITU-T. One-way transmission time. Rec. G.114, May 2000.
[12] T.C. Huang. Design and Implementation of TCP-Compatible SCTP Vertical Handoff Platform for All-IP Heterogeneous Networks. June 2006.
[13] 3G device Option Fusion Quad hardware spec.
http://www.option.com/products/fusionquad.shtml