ECN (Explicit Congestion Notification) in TCP/IP

• The ECN BOF at the L.A. IETF.
• To subscribe to the ECN mailing list, send a message to "ecn-interest-request@research.att.com" with the line "subscribe" in the body of the message. The archives for the mailing list are at http://www-nrg.ee.lbl.gov/ecn-arch/.
• Ramakrishnan, K.K., and Floyd, S., A Proposal to add Explicit Congestion Notification (ECN) to IP. RFC 2481, January 1999. (or get the local copy, in text or postscript).
• Floyd, Black, and Ramakrishnan, IPsec Interactions with ECN ( text, postscript), soon to be submitted as internet-draft draft-ipsec-ecn-00.txt. (I missed the submission deadline for the Minneapolis IETF by one hour...)
• Floyd, S., TCP and Explicit Congestion Notification (compressed postscript, pdf). ACM Computer Communication Review, V. 24 N. 5, October 1994, p. 10-23. [This issue of CCR incorrectly has "1995" on the cover instead of "1994".] Abstract.

Experimental Implementations of ECN:

• Chris Chen, Hariharan Krishnan, Steven Leung, Nelson Tang, UCLA-ECN is a early research prototype implementation of Explicit Congestion Notification for TCP over IPv6.,
• Kenjiro Cho has added ECN support to ALTQ/RED, and has modified TCP to support ECN. Preliminary test results of ALTQ/RED Performance compare performance without RED, with RED but without ECN, and with both RED and ECN.
• J. Hadi Salim, B. Nandy and N. Seddigh at the Computing Technology Labs (CTL), Nortel, have implemented ECN on Linux IPv4. This README describes the contents of the gzipped tar file (large!).
• Vishnu Priya Natchu, vishnu@cs.ucr.edu, is implementing ECN in IPv4 and in Reno TCP. Development on linux.
• Floyd, S., Experiments using ECN bits in the IPv6 and IPv4 headers, January 1998.
• Floyd, S., Implementing ECN in TCP, January 29, 1998.
• Jamal Hadi Salim, Tcpdump patch to print ECN info, May 8, 1998, Message-ID to the ecn-interest mailing list.

ECN in Simulators:

• The ns-2 simulator implements ECN with TCP. There are two validation test suites for the ECN implementation in ns, "test-all-ecn" and "test-all-ecn-ack". The validation test suite is described in the note ECN Implementations in the NS Simulator (postscript, PDF), and in the file "test-suite-ecn.txt" in the ns directory tcl/test.
• The note on Ns Simulator Tests for Random Early Detection (RED) Gateways, October 1996, shows a simple simulation using ECN with RED queue management and Reno TCP. This test can be run in ns-2 with the command "ns test-suite-red.tcl ecn" in the directory tcl/test.
• In ns-2, a simple simulation with one Tahoe TCP connection that is ECN-Capable and a second Tahoe TCP connection that is not ECN-Capable can be run with the command "ns test-suite-tcp.tcl ecn" in the directory tcl/test.
• A brief discussion about the model of ECN in the ns-2 simulator.

Notes and Email:

• Email on current status, Sally Floyd and K. K. Ramakrishnan, November 19, 1997.
• Floyd, S., ECN - one bit or two?, November 19, 1997.
• Floyd, S., ECN vs. Source Quench, November 20, 1997. Addendum on Source Quench, May 7, 1998.
• Floyd, S., ECN and defenses against evil applications, December 1, 1997. Addendum, Sally Floyd, January 1998.
• Floyd, S., ECN, TCP, and congestion on the ACK-path , December 16, 1997.
• Blake, S., ECN and IPv4 Header Checksum Recalculation, February 12, 1998.
• Floyd, S., ECN and Security Concerns, March 18, 1998.

Research on ECN and Related Work:

• Hari Balakrishnan, Venkata Padmanabhan, and Randy H. Katz, The Effects of Asymmetry on TCP Performance, Proc. Third ACM/IEEE MobiCom Conference, Budapest, Hungary, Sep 1997.
  This paper includes a proposal for Ack Congestion Control, for responding to ACK packets that have had the ECN bit set.
• K. K. Ramakrishnan and Raj Jain, A Binary Feedback Scheme for Congestion Avoidance in Computer Networks, ACM Transactions on Computer Systems, Vol.8, No.2, pp. 158-181, May 1990.

Talks:

• Talk on A Proposal to add Explicit Congestion Notification (ECN) to IPv6 and to TCP (viewgraphs). Munich IETF, Sally floyd, joint work with K. K. Ramakrishnan, August 11-15, 1997.
• Second talk on A Proposal to add Explicit Congestion Notification (ECN) to IPv6 and to TCP ( viewgraphs). TCP Implementors Working Group, Washington IETF, December 8, 1997.

Open issues for ECN:

• What are the quantitative benefits of ECN for TCP? What new dynamics does ECN add to TCP, in terms of competition between ECN-capable and non-ECN-capable traffic, the robustness of ECN in the presence of dropped ACK packets, performance with multiple congested gateways, etc.?
• What are the benefits of ECN for rate-adaptive realtime traffic with fixed or adaptive playback times? What would be the risks in adding ECN to the UDP API, for ECN-capable traffic applications that use end-to-end congestion control? Would "lying about ECN-capability" be significantly more attractive to misbehaving users than simply adding another layer of FEC to an application without end-to-end congestion control?
• What are the benefits of ECN in reliable multicast, for sessions using end-to-end congestion control? What are the relative benefits and costs of ECN relative to simply using more FEC?

Other approaches: FECN, BECN, and EFCI

• Hadi Salim, J., Nandy, B., and Seddigh, N., A proposal for Backward ECN for the Internet Protocol (IPv4/IPv6), internet draft draft-salim-jhsbnns-ecn-00.txt, work-in-progress, June 1998.
  This draft proposes a backward-ECN mechanism based on ICMP Source Quench messages. My understanding is that this proposal is intended to apply only for unicast traffic.
• FECN and BECN are Explicit Congestion Notification mechanisms for Frame Relay, based on the instantaneous queue size (as opposed to the average queue size).
• ATM's Explicit Forward Congestion Indication (EFCI). Some of the ATM documents are available from the Inside ATM: Bibliography.

Return to [ Sally Floyd] [ K. K. Ramakrishnan].