Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01
Joe Touch <touch@ISI.EDU> Wed, 23 September 2009 15:40 UTC
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Date: Wed, 23 Sep 2009 08:40:36 -0700
From: Joe Touch <touch@ISI.EDU>
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To: Alexander Zimmermann <Alexander.Zimmermann@nets.rwth-aachen.de>
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Cc: "tcpm@ietf.org" <tcpm@ietf.org>, "mallman@icir.org" <mallman@icir.org>
Subject: Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Works for me. Joe Alexander Zimmermann wrote: > Hi Joe, hi Mark, > > may be we can reuse a paragraph from RFC 3517: > > "We define a variable "DupThresh" that holds the number of duplicate > acknowledgments required to trigger a retransmission. Per [RFC2581] this > threshold is defined to be 3 duplicate acknowledgments. However, > implementers should consult any updates to [RFC2581] to determine the > current value for DupThresh (or method for determining its value)." > > First, it's easier to see where the magic *4* comes from, second it's > future-proof when "5681bis" alters the number of duplicate Acks required > for fast retransmit. :-) > > Alex > > Am 23.09.2009 um 16:28 schrieb Joe Touch: > >> ... >>>> In 2.1, do you want to define this in terms a fixed value of 4*SMSS, >>>> or define it as a pointer (i.e., to the initial CWND, so if init CWND >>>> increases, so does this?) same for the part about packet-based (again, >>>> would that be segment-based?) not referring to 4, but the number of >>>> segments in the initial CWND (e.g., as "currently 4" -- PS, should >>>> that be 4, or shouldn't it be "initial_CWND/SMSS", i.e., a max of 4, >>>> but in most current cases it seems like this would still be 3). >>> >>> No, I don't. This doesn't have anything to do with the initial >>> congestion window size. The "4"---which I thought was well motivated, >>> perhaps not---comes from fast retransmit's magic constant of "3". I.e., >>> if there are at least 4 segments outstanding and we lose one then we'll >>> have a shot at getting 3 dupacks. If there are fewer segments >>> outstanding then we will have no chance at getting 3 dupacks. So, this >>> has nothing to do with the initial window. >> >> I didn't get that as clearly. It might be useful to reiterate it when >> the number is introduced (maybe a few times for people like me who >> miss it). > > // > // Dipl.-Inform. Alexander Zimmermann > // Department of Computer Science, Informatik 4 > // RWTH Aachen University > // Ahornstr. 55, 52056 Aachen, Germany > // phone: (49-241) 80-21422, fax: (49-241) 80-22220 > // email: zimmermann@cs.rwth-aachen.de > // web: http://www.umic-mesh.net > // -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (MingW32) iEYEARECAAYFAkq6QXQACgkQE5f5cImnZrvejQCg53uwYJsYZ2S1vVQ1udQT4/LL eFUAn0/WXmKENoHZPHqWX6in8De+V3cw =eLRy -----END PGP SIGNATURE-----
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Mark Allman
- [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Alexander Zimmermann
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Joe Touch
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Mark Allman
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Joe Touch
- [tcpm] delayed ACKs (was Re: Review: draft-ietf-t… Mark Allman
- Re: [tcpm] delayed ACKs (was Re: Review: draft-ie… Joe Touch
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Mark Allman
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Joe Touch
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Alexander Zimmermann
- Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01 Joe Touch