CURRENT_MEETING_REPORT_ Reported by David Borman/Cray Minutes of the TCP Large Windows Working Group (TCPLW) The TCP Large Windows Working Group met for the first time in over a year and a half. Since the last time the group met, RFCs 1072 and 1185 had been proposed as Internet Standards, but problems with the specifications were discovered, and a new version, combining the two documents, was drafted and modified to address the problems. This document was circulated for comments and discussion, and the Working Group was scheduled to review the current status of the document, and hopefully come up with something that could be recommended for the standards track. Bob Braden gave an overview of the proposed options. (The overheads that were presented are attached to this report.) One of the assumptions made when the options were being designed was that vendors would not want to change the TCP header. Discussion was then broken up into several segments, to allow discussion of each proposed option, and the merits of each proposed option versus other ways of solving the same problems. It was agreed that the Window Scale options was well defined, and discussion of a window scale option versus a 32 bit window option in each packet was deferred until later in the meeting. The timestamp option was then discussed, just as a timestamp. The PAWS discussion was deffered to later. It was agreed that the definition was sufficient. The next item for discussion was the SACK option. The first item of discussion was whether the offset and length values should be 16 or 32 bits. There was also discussion about if the SACK option needed to have more than one SACK field. The decisions were that the fields would be 32 bit fields; it simplifies the specification and processing of the option, and eliminates any dependencies on the window-scale option. It was also felt that nothing was gained by limiting the number of SACKs in a single SACK option. The other item of discussion on SACK was whether SACK is advisory or a real acknowledgement. It was agreed that it was a real ACK; hence once a piece of data has been SACKed, the receiver of the data has committed to accepting the data, and the sender is free to discard its copy of the data that it was saving for possible re-transmission. Having approved the three options as being adequately defined, with the agreed upon changes, the discussion turned back to window scale option vs. a 32 bit window in each packet, and the PAWS mechanism. With the caveat that the WS option would have no effect on other options (done by expanding the SACK option to 32 bits), and that the initial value for 1 the shift is recommended to be based on the size of the receivers buffer, it was agreed to go with the window scale option. The final discussion was on PAWS, Protection Against Wrapped Sequence. First, the question was, did the PAWS mechanism provided adequate protection, and was it clearly defined? The answer was ``yes''. The final discussion then rested on PAWS vs. expanding the sequence space to 64 bits. Since PAWS works, and 64 bit sequence space eats up option space, and there were some concerns about the extra processing needed to deal with a 64 bit sequence space, it was decided to accept the PAWS method instead of expanding the sequence space. Bob Braden will incorporate the changes into the document, and get it published as an Internet Draft. Editoral comments on the document are to be sent to Bob. Attendees David Borman dab@cray.com Robert Braden braden@isi.edu Randy Butler rbutler@ncsa.uiuc.edu Richard Cherry rcherry@wc.novell.com Jim DeMarco jdemarco@ftp.com Joseph Godsil jgodsil@ncsa.uiuc.edu Olafur Gudmundsson ogud@cs.umd.edu Kenneth Hayward crm57d@bnr.ca Frank Heath heath@cmc.com Jean-Michael Jouanigot jimi@cernvax.cern.ch Darren Kinley kinley@crim.ca Ron Mackey rem@dsiinc.com Donald Merritt don@brl.mil Glenn Michel gym@lanl.gov Sean O'Malley sean@cs.utexas.edu Manoel Rodrigues manoel.rodrigues@att.com Miguel Sasson sasson@xylogics.com Tim Seaver tas@mcnc.org John Seligson johns@ultra.com Mike Spengler mks@msc.edu Kathleen Wilde wilde@decvax.dec.com Johnathan Wilson wilson@ddnuvax.af.mil Nancy Yeager nyeager@ncsa.uiuc.edu 2