Re: [conex] Review of draft-ietf-conex-tcp-modifications-02
Mirja Kuehlewind <mirja.kuehlewind@ikr.uni-stuttgart.de> Mon, 03 June 2013 12:59 UTC
Return-Path: <mirja.kuehlewind@ikr.uni-stuttgart.de>
X-Original-To: conex@ietfa.amsl.com
Delivered-To: conex@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 958B021F96ED for <conex@ietfa.amsl.com>; Mon, 3 Jun 2013 05:59:37 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -0.76
X-Spam-Level:
X-Spam-Status: No, score=-0.76 tagged_above=-999 required=5 tests=[BAYES_05=-1.11, HELO_EQ_DE=0.35]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id iwunWza20Lpw for <conex@ietfa.amsl.com>; Mon, 3 Jun 2013 05:59:33 -0700 (PDT)
Received: from mailsrv.ikr.uni-stuttgart.de (mailsrv.ikr.uni-stuttgart.de [129.69.170.2]) by ietfa.amsl.com (Postfix) with ESMTP id CDEF821F965A for <conex@ietf.org>; Mon, 3 Jun 2013 05:59:32 -0700 (PDT)
Received: from netsrv1.ikr.uni-stuttgart.de (netsrv1-c [10.11.12.12]) by mailsrv.ikr.uni-stuttgart.de (Postfix) with ESMTP id E5D8B601C9; Mon, 3 Jun 2013 14:59:30 +0200 (CEST)
Received: from vpn-2-cl195 (vpn-2-cl195 [10.41.21.195]) by netsrv1.ikr.uni-stuttgart.de (Postfix) with ESMTP id DEDB7601C8; Mon, 3 Jun 2013 14:59:30 +0200 (CEST)
From: Mirja Kuehlewind <mirja.kuehlewind@ikr.uni-stuttgart.de>
Organization: University of Stuttgart (Germany), IKR
To: jiyengar@fandm.edu
Date: Mon, 03 Jun 2013 14:59:30 +0200
User-Agent: KMail/1.9.10 (enterprise35 0.20101217.1207316)
References: <CAGgfs97ETmiODavn8eYfmU1PFqhrKyWnrgD=ULMAH91zWjFYYw@mail.gmail.com>
In-Reply-To: <CAGgfs97ETmiODavn8eYfmU1PFqhrKyWnrgD=ULMAH91zWjFYYw@mail.gmail.com>
X-KMail-QuotePrefix: >
MIME-Version: 1.0
Content-Type: Text/Plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Message-Id: <201306031459.30749.mirja.kuehlewind@ikr.uni-stuttgart.de>
Cc: conex@ietf.org
Subject: Re: [conex] Review of draft-ietf-conex-tcp-modifications-02
X-BeenThere: conex@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Congestion Exposure working group discussion list <conex.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/conex>, <mailto:conex-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/conex>
List-Post: <mailto:conex@ietf.org>
List-Help: <mailto:conex-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/conex>, <mailto:conex-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 03 Jun 2013 12:59:37 -0000
Hi Jana, thank you for your feedback. We just uploaded a new version for addressing quickly the last two ToDo: 1. Sending Credits -> A ConEx sender should maintain flightsize number of packets as credits (in CA) 2. Loss of ConEx infos -> A ConEx sender should detect this case and send further credits But there are actually still some open questions mainly regarding the credits: 1) What's the right reaction if ConEx markings get lost? 2) How to detect false positives of the audit at the sender? 3) How to incentives a sender to send right markings at the right time (e.g. to not send credits instead of L/E markings)? I'm going to send separate emails now to further explain these points and hopefully discuss these questions on the list. Mirja On Friday 31 May 2013 19:55:06 Janardhan Iyengar wrote: > Mirja, Richard, all > > A bit late, I'm sending along my review > of draft-ietf-conex-tcp-modifications-02. I noticed that -03 came along > while I was reading the -02 version; I'm also happy to review later > versions. > > Overall, the text could use some tightening up. Some text may need to be > rewritten (I've suggested some below), and some could be eliminated > altogether. My major feedback at this time would be that the draft should > focus on mechanisms that are clear and are to be specified (such as LEG and > CEG counts, for example). Other mechanisms that are either nascent or are > not yet fully specified ought to be left out from this document (such as > the more accurate ECN marking). More specific details follow. > > 1. Introduction: > - "ConEx is a ...": cite RFC 6789. For someone who hits this draft, it is > not clear where to go to find more about ConEx itself. > - End paragraph after "use ConEx with the Transmission Control Protocol > (TCP)." > > - Suggested restructuring: > + Move last paragraph "ConEx is currently/will be defined as an > destination option for IPv6..." up here to the beginning of the second > paragraph. > + Continue paragraph with "The ConEx signal is based on loss or ECN marks > ..." > + Modify "loss or ECN marks" in the above sentence to "Explicit > Congestion Notification (ECN) marks". > > - Suggested rewording for paragraph "With standard TCP ...": > "This document describes mechanisms for TCP both with and without the > Selective Acknowledgment (SACK) extension [RFC2018]. However, ConEx > benefits from more accurate information about the number of packets dropped > in the network. We therefore recommend using the SACK extension when using > TCP with ConEx." > > - Modify: "Explicit Congestion Notification (ECN) is defined in such a way > ..." to "ECN is defined in such a way ..." > > - This paragraph about more information than ECN seems unnecessarily > detailed. One sentence ought to be enough. Something like: "In addition to > standard ECN and SACK feedback, an extension described in [ > draft-kuehlewind-conex-accurate-ecn] shows how more accurate ECN feedback, > especially useful in the case of multiple markings within the same > roundtrip time (RTT), can be obtained." > > > 2: Sender-side Modifications: > - "MUST negotiate for both SACK and ECN or the more accurate ECN feedback > ..." : This strikes me as an odd MUST. SHOULD seems adequate. > - Using "SACK-accECN-Conex" instead of "Full-Conex" seems better > descriptive. > - "A ConEx sender MUST expose congestion to the network...": A compliant > Conex sender has to follow a Conex spec for exposing congestion; that can > be assumed here, without having a MUST in this document. Perhaps cite the > v6 options draft here without specifying here what a Conex sender MUST do. > - "A TCP sender SHOULD account congestion byte-wise (and not packet-wise)": > Cite draft-ietf-tsvwg-byte-pkt-congest or justify otherwise. > - "As network congestion is usually byte-congestion ...": Is this really > the case? Cite. > > > 3: Accounting Congestion: > - The writing in this section can be cleaned up. For instance, "... is > explained in the next section." should specify the section number. > - "A TCP sender SHOULD account congestion byte-wise (and not packet-wise) > ...": Cite draft-ietf-tsvwg-byte-pkt-congest. > - "The subtraction of bytes which have been ConEx marked from both counters > is explained in the next section.": What does "subtraction of bytes" mean? > - "If equal sized packets ...": This sentence needs to be rewritten. > Difficult to read and follow. > - "If a sender sends different sized packets ...": difficult to follow as > well. I understand what it says, but it needs to be rewritten to be clear. > - "ECN is an IP/TCP mechanism ...": cite RFC3168. > - "A receiver can support the accurate ECN feedback scheme ...": cite. It > may be better to structure > - "Note the change in in the SACK information can also be negative if the > number of acknowledged bytes increases.": Not clear. Do you mean to say if > the number of acked bytes decreases? > - What are the variables is_after_dup and num_dup in the DeliveredData > expression? Please describe them before the equation or immediately after. > > 3.1.2: Classic ECN Support: > - It is non-trivial for a sender to determine when delayed acks will be > sent by the receiver, in particular with bidirectional data transfer. I > would be careful about suggesting such heuristics without getting into > details. Is this "Advanced Compatibility" really practical or necessary? > > 3.2: Loss detection with/without SACK: > - "assuming equal sized segments such that the retransmitted packet will > have the same number of header as the original ones." You cannot make this > assumption. There are commonly used stacks that will retransmit differently > sized segments, and even combine retransmitted bytes with new bytes within > a segment. This assumption is not critical, and so I would suggest dropping > it from the text. > > - jana -- ------------------------------------------------------------------- Dipl.-Ing. Mirja Kühlewind Institute of Communication Networks and Computer Engineering (IKR) University of Stuttgart, Germany Pfaffenwaldring 47, D-70569 Stuttgart tel: +49(0)711/685-67973 email: mirja.kuehlewind@ikr.uni-stuttgart.de web: www.ikr.uni-stuttgart.de -------------------------------------------------------------------
- Re: [conex] Review of draft-ietf-conex-tcp-modifi… Mirja Kuehlewind
- Re: [conex] Review of draft-ietf-conex-tcp-modifi… Mirja Kühlewind