Simulation-based comparisons of Tahoe, Reno and SACK TCP

ABSTRACT

This paper uses simulations to explore the benefits of adding selective acknowledgments (SACK) and selective repeat to TCP. We compare Tahoe and Reno TCP, the two most common reference implementations for TCP, with two modified versions of Reno TCP. The first version is New-Reno TCP, a modified version of TCP without SACK that avoids some of Reno TCP's performance problems when multiple packets are dropped from a window of data. The second version is SACK TCP, a conservative extension of Reno TCP modified to use the SACK option being proposed in the Internet Engineering Task Force (IETF). We describe the congestion control algorithms in our simulated implementation of SACK TCP and show that while selective acknowledgments are not required to solve Reno TCP's performance problems when multiple packets are dropped, the absence of selective acknowledgments does impose limits to TCP's ultimate performance. In particular, we show that without selective acknowledgments, TCP implementations are constrained to either retransmit at most one dropped packet per round-trip time, or to retransmit packets that might have already been successfully delivered.

REFERENCES

• 1: [BBJ92] D. Borman, R. Braden, and V. Jacobson. "TCP Extensions for High Performance,". Request for Comments (Proposed Standard) RFC 1323, Internet Engineering Task Force, May 1992. (Obsoletes RFC1185).
• 2: [BJ88] R. Braden and V. Jacobson. "TCP extensions for long-delay paths,". Request for Comments (Experimental) RFC 1072, Internet Engineering Task Force, October 1988.
• 3: [BJZ90] R. Braden, V. Jacobson, and L. Zhang. "TCP Extension for High-Speed Paths,". Request for Comments (Experimental) RFC 1185, Internet Engineering Task Force, October 1990. (Obsoleted by RFC1323).
• 4: Hari Balakrishnan , Venkata N. Padmanabhan , Srinivasan Seshan , Randy H. Katz, A comparison of mechanisms for improving TCP performance over wireless links, Conference proceedings on Applications, technologies, architectures, and protocols for computer communications, p.256-269, August 28-30, 1996, Palo Alto, California, United States
• 5: R. Braden, T/TCP -- TCP Extensions for Transactions Functional Specification, RFC Editor, 1994
• 6: [CH95] D.D. Clark and J. Hoe. "Start-up Dynamics of TCP's Congestion Control and Avoidance Schemes,". Technical report, Jun. 1995. Presentation to the Internet End-to-End Research Group, cited for acknowledgement purposes only.
• 7: D. R. Cheriton, VMTP: Versatile Message Transaction Protocol, RFC Editor, 1988
• 8: D. D. Clark , M. L. Lambert , L. Zhang, NETBLT: A bulk data transfer protocol, RFC Editor, 1987
• 9: Sally Floyd , Van Jacobson, Random early detection gateways for congestion avoidance, IEEE/ACM Transactions on Networking (TON), v.1 n.4, p.397-413, Aug. 1993 [doi>10.1109/90.251892]
• 10: [Flo95] Sally Floyd. "Simulator Tests". Technical report, Jul. 1995. URL http://www-nrg.ee.lbl.gov/nrg-papers.html.
• 11: [Flo96a] S. Floyd. "Issues of TCP with SACK,". Technical report, Mar. 1996. URL ftp://ftp.ee.lbl.gov/papers/issues_sa.ps.Z.
• 12: [Flo96b] S. Floyd. "SACK TCP: The sender's congestion control algorithms for the implementation "sack1" in LBNL's "ns" simulator (viewgraphs).,". Technical report, Mar. 1996. Presentation to the TCP Large Windows Working Group of the IETF, March 7, 1996. URL ftp://ftp.ee.lbl.gov/talks/sacks.ps.
• 13: [Hoe95] J. Hoe. "Start-up Dynamics of TCP's Congestion Control and Avoidance Schemes,". Jun. 1995. Master's thesis, MIT.
• 14: Janey C. Hoe, Improving the start-up behavior of a congestion control scheme for TCP, Conference proceedings on Applications, technologies, architectures, and protocols for computer communications, p.270-280, August 28-30, 1996, Palo Alto, California, United States
• 15: [HSV84] R. Hinden, J. Sax, and D. Velten. "Reliable Data Protocol,". Request for Comments (Experimental) RFC 908, Internet Engineering Task Force, July 1984. (Updated by RFC1151).
• 16: V. Jacobson, Congestion avoidance and control, Symposium proceedings on Communications architectures and protocols, p.314-329, August 16-18, 1988, Stanford, California, United States
• 17: [Jac90] V. Jacobson. "Modified TCP Congestion Avoidance Algorithm,". Technical report, 30 Apr. 1990. Email to the end2end-interest Mailing List, URL ftp://ftp.ee.lbl.gov/email/vanj.90apr30.txt.
• 18: Srinivasan Keshav, REAL: A Network Simulator, University of California at Berkeley, Berkeley, CA, 1988
• 19: [Kes94] S. Keshav. "Packet-Pair Flow Control,". Technical report, Nov. 1994. Presentation to the Internet End-to-End Research Group, cited for acknowledgement purposes only.
• 20: [MF95] Steven McCanne and Sally Floyd. "NS (Network Simulator),". 1995. URL http://www-nrg.ee.lbl.gov/ns.
• 21: Matthew Mathis , Jamshid Mahdavi, Forward acknowledgement: refining TCP congestion control, Conference proceedings on Applications, technologies, architectures, and protocols for computer communications, p.281-291, August 28-30, 1996, Palo Alto, California, United States
• 22: [MMFR96] Matthew Mathis, Jamshid Mahdavi, Sally Floyd, and Allyn Romanow. "TCP Selective Acknowledgment Options,". (Internet draft, work in progress), 1996.
• 23: W. Timothy Strayer , Bert J. Dempsey , Alfred C. Weaver, XTP: the Xpress Transfer Protocol, Addison Wesley Longman Publishing Co., Inc., Redwood City, CA, 1992
• 24: [Ste94] W. Richard Stevens. TCP/IP Illustrated, Volume I: The Protocols. Addison Wesley, 1994.

INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS

Additional Classification:
  I. Computing Methodologies
  I.6 SIMULATION AND MODELING

General Terms:
Management, Theory