From nobody Fri Sep 25 10:52:24 2020 Return-Path: X-Original-To: lwip@ietfa.amsl.com Delivered-To: lwip@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 783563A13D3 for ; Fri, 25 Sep 2020 10:52:19 -0700 (PDT) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -1.899 X-Spam-Level: X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=unavailable autolearn_force=no Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=fugue-com.20150623.gappssmtp.com Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id c7pTVzgtmn2S for ; Fri, 25 Sep 2020 10:52:17 -0700 (PDT) Received: from mail-qt1-x82a.google.com (mail-qt1-x82a.google.com [IPv6:2607:f8b0:4864:20::82a]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 8698D3A13CD for ; Fri, 25 Sep 2020 10:52:17 -0700 (PDT) Received: by mail-qt1-x82a.google.com with SMTP id o21so2119421qtp.2 for ; Fri, 25 Sep 2020 10:52:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fugue-com.20150623.gappssmtp.com; s=20150623; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=4kx8DhaHFR7RbBa7yht6/yrLbLwhN+MQwP9SNMK/Yok=; b=OxXATGT9jTA1FlMDeN39rDin+kFQZwdVAujnn0ekpdWp3KBdpNt5jb9xQF+Xb7pAuQ kYQB1T4t02y4yNN9vuiS63N/lSSuFPBxKfzPujLWeTFaoceB/vuHLKVFjyQjF4YbLGVQ 228mh1b2AAc+dyWsTG6MC+1CkMIFS9oLf8fgQfrZSfDOylvcOS0zgj75udKLolyCEUVO AtOx4c1QkPxPFxAy4HHSOvKj3uBmD8eIO6t6iQ63G/lhfj3b9KJoAwybQ0Tf527t436U 1jRudoohrg3nOEqUPVzYJujcqprpnXOrCUbrfBWLbWi2HbnDy+IU9QcPgbeopWbcD4JB qseg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=4kx8DhaHFR7RbBa7yht6/yrLbLwhN+MQwP9SNMK/Yok=; b=eaioWpakJhNOAuieuoPm3QdkwDcYPH1CNYhjf7t3hgm3WKpNYcSgBBHbLuuIhG8DUE +3H2SCyhavOvIWsqs742cZTJswZSUA2IUdhYjf9WrIqp87jeRpHYmJs5GyXqs7ebmGc6 kfu0HNCV+kHitt4HGeD50wVNLknFLpW3GyXP/QspwK+yiLDkas7y3AxHiiAVJJPUQIyG F3VWvr+LJubAeJOGBWqkMrNmBK2ZSOkbKO5gnOKXbxEeKHyS4crgtmzK/VRKvazTK/gk hrj58SC45WWtlQlghIoWl58WnT+AuitykvxCZiaRhRZTb6hmwlxPurBCpgPuM1il5c16 P7OQ== X-Gm-Message-State: AOAM530waoSzmTGrYXMHBmqAjZKynipj61/K4WxSaBtDcjvV0rxWheG8 XyJnfILxT59eMKwdXy4GI0XU8g== X-Google-Smtp-Source: ABdhPJzQF9SAY4VZ8NdElzyWvQOgz8jnezgnQb+8wpQlqVFPFvd3+U1NvXpI8H2E68y8OrOlIBlcuQ== X-Received: by 2002:ac8:5650:: with SMTP id 16mr837844qtt.120.1601056336235; Fri, 25 Sep 2020 10:52:16 -0700 (PDT) Received: from localhost.localdomain (c-24-91-177-160.hsd1.ma.comcast.net. [24.91.177.160]) by smtp.gmail.com with ESMTPSA id 10sm2134888qkk.88.2020.09.25.10.52.15 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 25 Sep 2020 10:52:15 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.0.3.2.33\)) From: Ted Lemon X-Priority: 3 (Normal) In-Reply-To: Date: Fri, 25 Sep 2020 13:52:14 -0400 Cc: last-call@ietf.org, draft-ietf-lwig-tcp-constrained-node-networks@ietf.org, lwig-chairs@ietf.org, lwip@ietf.org Content-Transfer-Encoding: quoted-printable Message-Id: <987B05DB-BF9C-4D50-84CD-A704ECB1F9F3@fugue.com> References: <160026450341.4741.15386274889650653489@ietfa.amsl.com> <157F51F5-28D9-46BE-A408-D79D647AE495@fugue.com> <8BDF59D7-8451-46DA-A0AD-2AA1EDB59943@fugue.com> To: Carles Gomez Montenegro X-Mailer: Apple Mail (2.3654.0.3.2.33) Archived-At: Subject: Re: [Lwip] Last Call: (TCP Usage Guidance in the Internet of Things (IoT)) to Informational RFC X-BeenThere: lwip@ietf.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Lightweight IP stack. Official mailing list for IETF LWIG Working Group." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 25 Sep 2020 17:52:20 -0000 On Sep 20, 2020, at 2:28 AM, Carles Gomez Montenegro = wrote: > Thanks for the insight on the paper you mention. It offers interesting > details, and also experimental results consistent with our text, at = least > for some MSS range. It would have been great to see results for even > greater MSS than the ones considered in the paper. I agree. My intuition is that there is likely a peak number of segments = past which adding more segments reduces performance; I suspect that this = is probably close to the numbers the Berkeley paper arrived at, but we = have no data. It would be good to have more data before making general = assertions about what mss IoT devices should use, particularly given = that some IoT transports may do per-fragment retransmission, while = others won=E2=80=99t, and as you say, some IoT transports have = reasonably large MTUs, while others don=E2=80=99t. >=20 > Would the following proposed new text (that would replace the last > paragraph of 4.1.1) address your concern? >=20 > PROPOSED: >=20 > Using larger MSS (to a suitable extent) may be beneficial in some > scenarios, especially when transferring large payloads, as it = reduces the > number of packets (and packet headers) required for a given payload. > However, the characteristics of the constrained network need to be > considered. In particular, in a network where unreliable fragment > delivery is used, the amount of data that TCP unnecessarily > retransmits due to fragment loss increases with the MSS. This = happens > because the loss of a fragment leads to the loss of the whole = fragmented > packet being transmitted. Unnecessary data retransmission is = particularly > harmful in CNNs due to the resource constraints of such = environments. > Note that, while the original 6LoWPAN fragmentation mechanism [RFC = 4944] > does not offer reliable fragment delivery, fragment recovery > functionality for 6LoWPAN or 6Lo environments is being standardized = as of > the writing [draft-ietf-6lo-fragment-recovery]. I think this is okay, although you don=E2=80=99t mention that given a = constant per-frame error rate, the more frames you send, the higher the = actual error rate will be, that this increases exponentially as the = number of fragments increases, and further that, as you mention, in = CNNs, retransmission traffic can swamp successful transmissions leading = to worse and worse throughput as MSS increases. I don=E2=80=99t think it=E2=80=99s sufficient to mention this in a few = sentences in a single paragraph. This needs to be part of a more = detailed analysis. > Thanks for your words. Yes, breaking the myth that 'TCP is not = suitable > for IoT' is one of the main objectives of this document. Let's hope we = can > contribute to that! 100% agree. Thanks!