新一代位於傳輸層之串流控制傳輸協定STCP(Streaming Control Transmission Protocol, SCTP)在網路傳輸上沿用與TCP(Transmission Control Protocol, TCP)相同的擁塞控制(congestion control)機制，每當傳送端偵測到封包遺失，皆視為網路擁塞發生，傳送端會大幅度減少擁塞視窗(congestion window)大小來避免擁塞的情況。但是在有線/無線網路環境下，封包的遺失並非全然肇因於網路擁塞，例如無線網路發生無線訊號錯誤，此時如果仍大幅度降低擁塞視窗，將無法妥善運用現有的有線/無線網路之頻寬。

為了改善SCTP擁塞控制的效能，特別是在因無線傳輸訊號錯誤致使網路具有一定封包遺失率的情況下，本論文提出一個適應性的擁塞控制方法以增進SCTP的效能。此一利用接收端頻寬估計之串流控制傳輸協定稱為RSCTP(Receiver Bandwidth Estimation SCTP, RSCTP)，其中包含SCTP封包遺失的判別方法是透過接收端回饋的可利用頻寬(available bandwidth estimation)與傳輸流量作比較，決定封包遺失的原因再對擁塞視窗做適當的調整。在多重定址(Multihoming)的模式下，RSCT因為加入了估計封包遺失率的功能，所以能夠在封包遺失嚴重時進行傳輸路徑的主動的切換。

本論文是以NS2網路模擬工具對所提出之RSCTP進行驗證，模擬網路擁塞與無線訊號錯誤的情形，模擬之結果相較於SCTP證明RSCTP可以對擁塞視窗作出適當調整，能有效提升SCTP擁塞控制在無線網路的效能。

Streaming control transmission protocol (SCTP) is one kind of new generation transport layer protocol, is a little modification form TCP. Like TCP, the congestion control mechanism of current SCTP which rely on packet loss as an indicator of network congestion. When congestion been detected the sender will reduce congestion window size to half to avoid congestion. In wire/wireless network environment, the packet losses are not all ways because of congestion. If SCTP reduces the congestion window inappropriately in an error prone wireless network, it may not use the network resource efficiently. For the purpose to improve the performance of SCTP congestion control, especially in an error prone wireless network, we propose a new enhancement SCTP called RSCTP (Receiver Bandwidth Estimation SCTP) based on receiver-side available bandwidth estimation. RSCTP relies on bandwidth estimation to discriminate wireless loss from congestion loss over error prone wireless link, it also reduces congestion window and slow start threshold appropriately. In multihoming mode, using chunk loss rate estimation, RSCTP can switch path actively over the high loss rate environment. We use NS2 to simulate RSCTP and the simulation results reveal that our scheme improves performance efficiently over error prone wireless network in evidence.

[1] G. Xylomenos, G.C. Polyzos, P. Mahonen and M. Saaranen, TCP performance issues over wireless links, IEEE Communications Magazine 39, pp. 52-58., 2001.
[2] Y. Tian, K. Xu, and N. Ansari, “TCP in Wireless Environments: Problems and Solutions,” IEEE Commun. Mag., vol. 43, no. 3, pp. S27-S32. , 2005.
[3] M. Allman, V. Paxson, and W. Stevens. TCP Congesfion Control, RFC 2581, April 1999.
[4] H. C. Lee and Fongray Frank Young, "Congestion Scheme Investigations on TCP/IP Network," 2003 Symposium on Century Digital Life and Internet Technologies, Taiwan., P0317 Page 1-8, 2003.
[5] S. Floyd, "HighSpeed TCP for Large Congestion Windows" , IETF Internet Draft, Feb 2003.
[6] Balakrishnan, H., et al., "Improving TCP/IP Performance over Wireless Networks. in Int. Conf. on Mobile Computing and Networking. Berkeley, CA 1995.
[7] K. Xu, Y. Tian, and N. Ansari, “Improving TCP performance in integrated wireless communication networks,” vol. 47, pp. 219-237, February 2005.
[8] C. Liu and R. Jain, “Approaches of Wireless TCP enhancement and a new proposal based on congestion coherence,” in Proc. 36th Annu. Hawaii Int. Conf., pp. 307-316. , Jan. 2003.
[9] Lawrence S. Brakmo, and Larry L. Peterson., "TCP Vegas: End to End Congestion Avoidance on a Global Internet", IEEE J. Select. Areas. Commun , vol. 13, pp. 1465-1480, Oct. 1995.
[10] Cheng Peng Fu, and Soung C. Liew, "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks", IEEE J. Select. Areas. Commun, vol. 21 , pp. 216-228, Feb. 2003.
[11] A. Jayananthan, and H.R. Sirisena, "TCP Performance Enhancement over WLAN with Wireless Loss Detection Proxy", Information, Communications and Signal Processing, 2005 Fifth International Conference, Page(s):654-658, 06-09 Dec. 2005.
[12] D. Bansal and H. Balakrishnan, "TCP-friendly congestion control for real-time streaming applications," Technical Report MIT-LCS-TR-806, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A., May 2000.
[13] D. Bansal and H. Balakrishnan, "Binomial Congestion Control Algorithms," In Proceedings INFOCOM 2001, April 2001.
[14] CHIU, D.-M., AND JAIN, R. Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks. Computer Networks and ISDN Systems 17 , pp.1-14. , 1989.
[15] C. Casetti, M. Gerla, S. Mascolo, M. Y. Sanadidi, and R. Wang, “TCP Westwood: Bandwidth estimation for enhanced transport over wireless links,” in Proc. ACM Mobicom, Rome, Italy, pp. 287-297. , July 2001.
[16] Grieco, L. A. , and Mascolo, S., End-to-End Bandwidth Estimation for Congestion Control in Packet Networks. Second International Workshop, QoS-IP 2003, Milano, Italy, February 2003.
[17] 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.
[18] A. L. Caro et al., "SCTP: A Proposed Standard for Robust Internet Data Transport," IEEE Comp., vol. 36, no. 11, pp. 56-63. , Nov. 2003.
[19] Shaojian Fu; Atiquzzaman, M.; "SCTP: state of the art in research, products, and technical challenges," Computer Communications, pp. 85-91, Oct. 2003.
[20] R. Stewart et al., Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration, Internet Draft, draft-ietf-tsvwg-addip-sctp-08.txt, Sept. 2003.
[21] J. Shi, Y. Jin, H. Huang, D. Zhang, "Experimental performance studies of SCTP in wireless access networks," in Proc. Of ICCT’03, vol. 1, pp. 392-395. , Apr. 2003.
[22] I Ahmed, O Yasuo, K Masanori, "Improving Performance of SCTP over Broadband High Latency Networks," Proceedings of the 28th Annual IEEE International Conference on Local Computer Networks , 2003.
[23] G. Camarillo, R. Kantola, and H. Schulzrinne, “Evaluation of Transport Protocols for the Session Initiation Protocol”, IEEE Network , Volume 17, Issue 5, Page 40-46, Sept.-Oct. 2003.
[24] Stewart,R., M. Ramalho, Q. Xie, M. Tuexen and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, IETF, May 2004.
[25] H. Huang, J. Ou, and D. Zhang, "Efficient Multimedia Transmission in Mobile Network by using PR-SCTP", Communications and Computer Networks, Marina del Rey, USA, 2005.
[26] S. Kashihara, K. Iida, H. Koga, Y. Kadobayashi, and S. Yamaguchi. "End-to-End Seamless Handover using Multi-path Transmission Algorithm", In IC, Tokyo, Japan, 2003.
[27] Dapeng Wang, Shoubao Yang, Weifeng Sun, “A Mac-Error-Warning Method for SCTPCongestion Control over High BER Wireless Network”, Proceedings 2005 International Conference on Wireless Communications, Networking and Mobile Computing, pp.513-516, 2005.
[28] Tomohiko Ogishi, Akira Idoue, Toru Hasegawa, and Toshihiko Kato,“Design of Performance Monitor Collecting TCP Level Statistics from Unidirectional IP Traffic,” IEICE General Conference, B-7-3, March 2000.
[29] The Network Simulator - ns-2: http://www.isi.edu/nsnam/ns/
[30] SCTP module of ns2 simulator: http://pel.cis.udel.edu
[31] NS2使用說明手冊：http://hpds.ee.ncku.edu.tw/~smallko/ns2/ns2.htm