The IESG has approved the following document: - 'Adding Explicit Congestion Notification (ECN) Capability to TCP's SYN/ACK Packets ' <draft-ietf-tcpm-ecnsyn-10.txt> as an Experimental RFC This document is the product of the TCP Maintenance and Minor Extensions Working Group. The IESG contact persons are Lars Eggert and Magnus Westerlund. A URL of this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-tcpm-ecnsyn-10.txt Technical Summary This draft specifies a modification to RFC 3168 to allow TCP SYN/ACK packets to be ECN-Capable. For TCP, RFC 3168 only specifies setting an ECN-Capable codepoint on data packets, and not on SYN and SYN/ACK packets. However, because of the high cost to the TCP transfer of having a SYN/ACK packet dropped, with the resulting retransmit timeout, this document specifies the use of ECN for the SYN/ACK packet itself, when sent in response to a SYN packet with the two ECN flags set in the TCP header, indicating a willingness to use ECN. Setting the initial TCP SYN/ACK packet as ECN-Capable can be of great benefit to the TCP connection, avoiding the severe penalty of a retransmit timeout for a connection that has not yet started placing a load on the network. The TCP responder (the sender of the SYN/ACK packet) must reply to a report of an ECN-marked SYN/ACK packet by resending a SYN/ACK packet that is not ECN-Capable. If the resent SYN/ACK packet is acknowledged, then the TCP responder reduces its initial congestion window from two, three, or four segments to one segment, thereby reducing the subsequent load from that connection on the network. If instead the SYN/ACK packet is dropped, or for some other reason the TCP responder does not receive an acknowledgement in the specified time, the TCP responder follows TCP standards for a dropped SYN/ACK packet (setting the retransmit timer). This document updates RFC 3168 Working Group Summary The WG process on this document was fairly smooth. The most interesting bump in the road was that after successfully completing the first WG last call, the authors obtained additional simulation results that warranted changes in the document and a 2nd WG last call. Document Quality There are existing implementations. There is (at least) a Linux implementation in addition to the simulation code. No vendors have formally indicated plans to the WG to implement the modifications in the document, but it is a backwards compatible end-host modification, not a full new protocol or one requiring additional infrastructure support. Personnel Wesley Eddy (weddy@grc.nasa.gov) was the document shepherd. Lars Eggert (lars.eggert@nokia.com) reviewed the document for the IESG. _______________________________________________ IETF-Announce@ietf.org https://www.ietf.org/mailman/listinfo/ietf-announce
