Re: [6lo] [6tisch] comments on draft-watteyne-6lo-minimal-fragment-00.txt
Thomas Watteyne <thomas.watteyne@inria.fr> Sat, 03 March 2018 22:08 UTC
Return-Path: <thomas.watteyne@inria.fr>
X-Original-To: 6lo@ietfa.amsl.com
Delivered-To: 6lo@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C0A261272E1; Sat, 3 Mar 2018 14:08:49 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.908
X-Spam-Level:
X-Spam-Status: No, score=-6.908 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_HI=-5, T_RP_MATCHES_RCVD=-0.01, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
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 07v0VWNLU1ow; Sat, 3 Mar 2018 14:08:47 -0800 (PST)
Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 41119127333; Sat, 3 Mar 2018 14:08:46 -0800 (PST)
X-IronPort-AV: E=Sophos;i="5.47,419,1515452400"; d="scan'208,217";a="256854509"
Received: from mail-vk0-f45.google.com ([209.85.213.45]) by mail3-relais-sop.national.inria.fr with ESMTP/TLS/AES128-GCM-SHA256; 03 Mar 2018 23:08:43 +0100
Received: by mail-vk0-f45.google.com with SMTP id p189so7714714vkd.10; Sat, 03 Mar 2018 14:08:43 -0800 (PST)
X-Gm-Message-State: APf1xPCzix9YYhGnBOcn0NrF7cdSWFGtXLs/RqPbmJcxIXFWqqTrBKaJ UU7SPqVVY5w/oaIcJUKvcEAKePBx3fVYm3pCBgs=
X-Google-Smtp-Source: AG47ELv68yG1j3U1qw77CaoEhYzgbDbcJfLWl9Bz86HiQndCER7Q5z3Lv+0eKHTKD/frZEayHoAGm4R1u1tPHAnDgw0=
X-Received: by 10.31.138.72 with SMTP id m69mr6678102vkd.13.1520114922579; Sat, 03 Mar 2018 14:08:42 -0800 (PST)
MIME-Version: 1.0
Received: by 10.176.112.21 with HTTP; Sat, 3 Mar 2018 14:08:22 -0800 (PST)
In-Reply-To: <3BA32A0F-907D-45F1-AC88-C856F877F45B@inria.fr>
References: <3BA32A0F-907D-45F1-AC88-C856F877F45B@inria.fr>
From: Thomas Watteyne <thomas.watteyne@inria.fr>
Date: Sat, 03 Mar 2018 23:08:22 +0100
X-Gmail-Original-Message-ID: <CADJ9OA_GJXCxML=tNaskuz7Z=2h3AGMUNifAdXxRUg7Fs4Bk8g@mail.gmail.com>
Message-ID: <CADJ9OA_GJXCxML=tNaskuz7Z=2h3AGMUNifAdXxRUg7Fs4Bk8g@mail.gmail.com>
To: Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr>
Cc: 6lo@ietf.org, tisch <6tisch@ietf.org>
Content-Type: multipart/alternative; boundary="001a11456322fa6eed05668955b9"
Archived-At: <https://mailarchive.ietf.org/arch/msg/6lo/ncgs3xRdWK85GpFJlgp0Sg5O4a8>
Subject: Re: [6lo] [6tisch] comments on draft-watteyne-6lo-minimal-fragment-00.txt
X-BeenThere: 6lo@ietf.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: "Mailing list for the 6lo WG for Internet Area issues in IPv6 over constrained node networks." <6lo.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/6lo>, <mailto:6lo-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/6lo/>
List-Post: <mailto:6lo@ietf.org>
List-Help: <mailto:6lo-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/6lo>, <mailto:6lo-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sat, 03 Mar 2018 22:08:50 -0000
Yatch, Thanks for your review. I have taken all of your suggestions into account, and plan to publish -01 by the cut-off date. The plan is to have a "fragmentation DT" section at the 6lo meeting where this draft will be presented. Thomas On Tue, Feb 27, 2018 at 7:20 PM, Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr> wrote: > Hi all, > > I'd like to share my comments on draft-watteyne-6lo-minimal- > fragment-00.txt. > > LLN Minimal Fragment Forwarding > https://www.ietf.org/id/draft-watteyne-6lo-minimal-fragment-00.txt > > I have four comments: > > [1] > > 1. Overview of 6LoWPAN Fragmentation > > (snip) > > In Figure 1, node A has sent fragments 1, 2, 3, 5, 6 to node B, node > > B has received fragments 1, 2, 3, 6 from node A, fragment 5 is still > > being transmitted at the link layer from node A to node B. > > It'd be nice to explain the figure a little bit more, the symbol of '#' and > numbers above the boxes, like this: > > In Figure 1, a packet forwarded by node A to node B is cut into > nine fragments, from fragment 1 to fragment 9. Each of them is > represented with '#' symbol. Node A has sent fragments 1, 2, 3, 5, > 6 to node B, node B has received fragments 1, 2, 3, 6 from node A, > fragment 5 is still being transmitted at the link layer from node A > to node B. > > [2] > > 3. Virtual Reassembly Buffer (VRB) Implementation > > (snip) > > next hop to send this fragment to. It then creates an entry in the > > VRB table which contains 4 fields: (1) the link-layer address of the > > sender of the fragment it received, (2) the datagram_tag of the > > fragment it received, (3) the link-layer address of the next hop, (4) > > a datagram_tag for the fragments it will send. The latter > > datagram_tag must be locally unique. > > This would also need another explanatory note after this paragraph; > for instance, "note that if node E has multiple network interfaces, > the VRB would have (5) the link-layer address of the sender of the > fragment it received, and (6) the link-layer address of the sender of > the fragment it will use." > > Technically, each fragment is identified by the combination of the > source link-layer address, the destination link-layer address, and the > datagram_tag as explained in Section 1. > > (excerpt from Section 1) > >> to. Each fragment can be uniquely identified by the source and > >> destination link-layer addresses of the frame that carries it, and > >> the datagram_tag. The value of the datagram_tag only needs to be > >> locally unique to nodes A and B. > > I guess the reason to use the destination link-layer address is > that the text shown above and RFC 4944 take into account cases > when a node has multiple network interfaces. > > Then, E's VRB Table in Fugure 3 should have "L2 dest" as a the > "incoming" column and "L2 src" as a the "outgoing" column. But, > putting them into Figure 3 seems too much. Just adding note would > be enough, I think. > > [3] > > Upon forwarding the last fragment of a packet, the VRB table entry > > can be cleared, and reused for a future packet. If the last fragment > > of a packet is dropped, the VRB table entry can be invalidated by > > timeout. Its timeout value is set to a maximum of 60 seconds as the > > reassembly timeout defined in [RFC4944]. > > For the explanation about the basic mechanism of VRB, can we assume > fragments of an IPv6 packet are always received in order? > > In general, fragments could be received out of order. Because of that, > an intermediate node cannot determine which fragment is the last one > for the correspondent packet without any state on received fragments > in the VRB Table. Every active VRB entry is valid until its > expiration. > > However, I believe reordering of fragments rarely happens in reality > with networks which 6tisch WG or 6lo WG deal with. If this is the > case, I'd suggest to keep the paragraph as it is since it's simple and > easy to understand. We may add some text clarifying that this > optimization works under a certain condition, that is, fragments are > received in order. > > > A simple implementation may do away with any attempt to keep packet > > data in the virtual reassembly buffer. It then has to discard all > > non-first fragments for which a reassembly buffer is not already > > available (penalizing reordering, which however may be rare). > > I agree. > > [4] > > 4. Critique of VRB > > (snip) > > It is possible for a network to be composed of some nodes that > > implement VRB, and others that don't. Nodes that do not implement > > VRB reassemble the packet. > > The last sentence is forgotten to be removed...? > > Best, > Yatch > > _______________________________________________ > 6tisch mailing list > 6tisch@ietf.org > https://www.ietf.org/mailman/listinfo/6tisch > -- ________________________________________ Thomas Watteyne, PhD Research Scientist & Innovator, Inria Sr Networking Design Eng, Analog Devices Founder & co-lead, UC Berkeley OpenWSN Co-chair, IETF 6TiSCH www.thomaswatteyne.com ________________________________________
- [6lo] comments on draft-watteyne-6lo-minimal-frag… Yasuyuki Tanaka
- Re: [6lo] [6tisch] comments on draft-watteyne-6lo… Thomas Watteyne