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Versions: (draft-pkm-roll-nsa-extension) 00 01 02 03 04 draft-ietf-roll-nsa-extension

ROLL                                                R. Koutsiamanis, Ed.
Internet-Draft                                           G. Papadopoulos
Intended status: Standards Track                            N. Montavont
Expires: April 25, 2019                                   IMT Atlantique
                                                              P. Thubert
                                                                   Cisco
                                                        October 22, 2018


RPL DAG Metric Container Node State and Attribute object type extension
                draft-koutsiamanis-roll-nsa-extension-03

Abstract

   Implementing 6TiSCH Packet Replication and Elimination from / to the
   RPL root requires the ability to forward copies of packets over
   different paths via different RPL parents.  Selecting the appropriate
   parents to achieve ultra-low latency and jitter requires information
   about a node's parents.  This document details what information needs
   to be transmitted and how it is encoded within a packet to enable
   this functionality.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 25, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Node State and Attribute (NSA) object type extension  . . . .   4
     3.1.  Usage . . . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  DAG Metric Container fields . . . . . . . . . . . . .   6
       3.1.2.  Node State and Attribute fields . . . . . . . . . . .   6
     3.2.  Compression . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Informative references  . . . . . . . . . . . . . . . . .   7
     6.2.  Other Informative References  . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Industrial network applications have stringent requirements on
   reliability and predictability, and typically leverage 1+1
   redundancy, aka Packet Replication and Elimination (PRE)
   [I-D.papadopoulos-6tisch-pre-reqs] to achieve their goal.  In order
   for wireless networks to be able to be used in such applications, the
   principles of Deterministic Networking [I-D.ietf-detnet-architecture]
   lead to designs that aim at maximizing packet delivery rate and
   minimizing latency and jitter.  Additionally, given that the network
   nodes often do not have an unlimited power supply, energy consumption
   needs to be minimized as well.

   To meet this goal, IEEE Std. 802.15.4 [IEEE802154-2015] provides
   Time-Slotted Channel Hopping (TSCH), a mode of operation which uses a
   fixed communication schedule to allow deterministic medium access as
   well as channel hopping to work around radio interference.  However,
   since TSCH uses retransmissions in the event of a failed
   transmission, end-to-end delay and jitter performance can
   deteriorate.

   The 6TiSCH working group, focusing on IPv6 over IEEE Std.
   802.15.4-TSCH, has worked on the issues previously highlighted and
   produced the "6TiSCH Architecture" [I-D.ietf-6tisch-architecture] to
   address that case.  Building on this architecture, "Exploiting Packet
   Replication and Elimination in Complex Tracks in 6TiSCH LLNs"



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   [I-D.papadopoulos-6tisch-pre-reqs] leverages PRE to improve the
   Packet Delivery Ratio (PDR), provide a hard bound to the end-to-end
   latency, and limit jitter.

   PRE achieves a controlled redundancy by laying multiple forwarding
   paths through the network and using them in parallel for different
   copies of a same packet.  PRE can follow the Destination-Oriented
   Directed Acyclic Graph (DODAG) formed by RPL from a node to the root.
   Building a multi-path DODAG can be achieved based on the RPL
   capability of having multiple parents for each node in a network, a
   subset of which is used to forward packets.  In order for this subset
   to be defined, a RPL parent subset selection mechanism, which falls
   within the remit of the RPL Objective Function (OF), needs to have
   specific path information.  The specification of the transmission of
   this information is the focus of this document.

   More concretely, this specification focuses on the extensions to the
   DAG Metric Container [RFC6551] required for providing the PRE
   mechanism a part of the information it needs to operate.  This
   information is the RPL [RFC6550] parent address set of a node and it
   must be sent to potential children nodes of the node.  The RPL DIO
   Control Message is the canonical way of broadcasting this kind of
   information and therefore its DAG Metric Container [RFC6551] field is
   used to append a Node State and Attribute (NSA) object.  The node's
   parent address set is stored as an optional TLV within the NSA
   object.  This specification defines the type value and structure for
   this TLV.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The draft uses the following Terminology:

   Track  A sequence of 6TiSCH schedule resources to support a single-
      path multi-hop transmission of a packet.  See "6TiSCH
      Architecture" [I-D.ietf-6tisch-architecture] for more.

   Complex Track  A Track which supports a multi-path multi-hop
      transmission of a packet.  See "6TiSCH Architecture"
      [I-D.ietf-6tisch-architecture] for more.

   Packet Replication and Elimination (PRE)  The sending of multiple
      copies of a packet using multi-path forwarding over a multi-hop
      network and the consolidation of multiple received packet copies
      to control flooding.  See "Exploiting Packet Replication and



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      Elimination in Complex Tracks in 6TiSCH LLNs"
      [I-D.papadopoulos-6tisch-pre-reqs] for more.

   Alternative Parent (AP) Selection  The problem of how to select the
      next hop target node for a packet copy to be forwarded to when
      performing packet replication.  See "Exploiting Packet Replication
      and Elimination in Complex Tracks in 6TiSCH LLNs"
      [I-D.papadopoulos-6tisch-pre-reqs] for more.

3.  Node State and Attribute (NSA) object type extension

   For supporting PRE, nodes need to report their parent set to their
   potential children.  DIO messages can carry multiple options, out of
   which the DAG Metric Container option [RFC6551] is the most suitable
   structurally and semantically for the purpose of carrying the parent
   set.  The DAG Metric Container option itself can carry different
   nested objects, out of which the Node State and Attribute (NSA)
   [RFC6551] is appropriate for transferring generic node state data.
   Within the Node State and Attribute it is possible to store optional
   TLVs representing various node characteristics.  As per the Node
   State and Attribute (NSA) [RFC6551] description, no TLV has been
   defined for use.  This document defines one TLV for the purpose of
   transmitting a node's parent set.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RPLInstanceID |Version Number |             Rank              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |G|0| MOP | Prf |     DTSN      |     Flags     |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                            DODAGID                            +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | DAGMC Type (2)| DAGMC Length  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   //                   DAG Metric Container data                 //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     Figure 1: Example DIO Message with a DAG Metric Container option



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   Figure 1 shows the structure of the DIO Control Message when a DAG
   Metric Container option is included.  The DAG Metric Container option
   type (DAGMC Type in Figure 1) has the value 0x02 as per the IANA
   registry for the RPL Control Message Options, and is defined in
   [RFC6550].  The DAG Metric Container option length (DAGMC Length in
   Figure 1) expresses the DAG Metric Container length in bytes.  DAG
   Metric Container data holds the actual data and is shown expanded in
   Figure 2.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Routing-MC-Type|Res Flags|P|C|O|R| A   |  Prec | Length (bytes)| |=>MC
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Res       |  Flags    |A|O|    PS  type   |   PS  Length  | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |=>NSA
| PS IPv6 address(es) ...                                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       Figure 2: DAG Metric Container (MC) data with Node State and
                   Attribute (NSA) object body and a TLV

   The structure of the DAG Metric Container data in the form of a Node
   State and Attribute (NSA) object with a TLV in the NSA Optional TLVs
   field is shown in Figure 2.  The first 32 bits comprise the DAG
   Metric Container header and all the following bits are part of the
   Node State and Attribute object body, as defined in [RFC6551].  This
   document defines a new TLV, which CAN be carried in the Node State
   and Attribute (NSA) object Optional TLVs field.  The TLV is named
   Parent Set and is abbreviated as PS in Figure 2.

   PS type:  The type of the Parent Set TLV.  The value is TBD1.

   PS Length:  The total length of the TLV value field (PS IPv6
         address(es)) in bytes.

   PS IPv6 address(es):  A sequence of zero or more IPv6 addresses
         belonging to a node's parent set.  Each address requires 16
         bytes.  The order of the parents in the parent set is in
         decreasing preference based on the Objective Function [RFC6550]
         used by the node.

3.1.  Usage

   The PS SHOULD be used in the process of parent selection, and
   especially in alternative parent selection, since it can help the
   alternative path from significantly deviating from the preferred



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   path.  The Parent Set is information local to the node that
   broadcasts it.

3.1.1.  DAG Metric Container fields

   Given the intended usage, when using the PS, the NSA object it is
   contained in MUST be used as a constraint in the DAG Metric
   Container.  More specifically, using the PS places the following
   requirements on the DAG Metric Container header fields:

   o  'P' flag: MUST be cleared, since PS is used only with constraints.

   o  'C' flag: MUST be set, since PS is used only with constraints.

   o  'O' flag: Used as per [RFC6550], to indicated optionality.

   o  'R' flag: MUST be cleared, since PS is used only with constraints.

   o  'A' Field: MUST be set to 0 and ignored, since PS is used only
      with constraints.

   o  'Prec' Field: Used as per [RFC6550].

3.1.2.  Node State and Attribute fields

   For clarity reasons, the usage of the PS places no additional
   restrictions on the NSA flags ('A' and 'O'), which can be used as
   normally defined in [RFC6550].

3.2.  Compression

   The PS IPv6 address(es) field in the Parent Set TLV add overhead due
   to their size.  Therefore, compression is highly desirable in order
   for this extension to be usable.  To meet this goal, a good
   compression method candidate is [RFC8138] 6LoWPAN Routing Header
   (6LoRH).  Furthermore, the PS IPv6 address(es) belong by definition
   to nodes in the same RPL DODAG and are stored in the form of a list
   of addresses.  This makes this field a good candidate for the use of
   the same compression as in Source Routing Header 6LoRH (SRH-6LoRH),
   achieving efficiency and implementation reuse.  Therefore, the PS
   IPv6 address(es) field SHOULD be compressed using the compression
   method for Source Routing Header 6LoRH (SRH-6LoRH) [RFC8138].

4.  Security Considerations

   The structure of the DIO control message is extended, within the pre-
   defined DIO options.  Therefore, the security mechanisms defined in
   RPL [RFC6550] apply to this proposed extension.



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5.  IANA Considerations

   This proposal requests the allocation of a new value TBD1 for the
   "Parent Set" TLV in the Routing Metric/Constraint TLVs sub-registry
   from IANA.

6.  References

6.1.  Informative references

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-15 (work
              in progress), October 2018.

   [I-D.ietf-detnet-architecture]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-08 (work in progress), September 2018.

   [I-D.papadopoulos-6tisch-pre-reqs]
              Papadopoulos, G., Montavont, N., and P. Thubert,
              "Exploiting Packet Replication and Elimination in Complex
              Tracks in 6TiSCH LLNs", draft-papadopoulos-6tisch-pre-
              reqs-02 (work in progress), July 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.

   [RFC6551]  Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
              and D. Barthel, "Routing Metrics Used for Path Calculation
              in Low-Power and Lossy Networks", RFC 6551,
              DOI 10.17487/RFC6551, March 2012,
              <https://www.rfc-editor.org/info/rfc6551>.

   [RFC8138]  Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
              "IPv6 over Low-Power Wireless Personal Area Network
              (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
              April 2017, <https://www.rfc-editor.org/info/rfc8138>.



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6.2.  Other Informative References

   [IEEE802154-2015]
              IEEE standard for Information Technology, "IEEE Std
              802.15.4-2015 Standard for Low-Rate Wireless Personal Area
              Networks (WPANs)", December 2015.

Authors' Addresses

   Remous-Aris Koutsiamanis (editor)
   IMT Atlantique
   Office B00 - 126A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 49
   Email: aris@ariskou.com


   Georgios Papadopoulos
   IMT Atlantique
   Office B00 - 114A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 04
   Email: georgios.papadopoulos@imt-atlantique.fr


   Nicolas Montavont
   IMT Atlantique
   Office B00 - 106A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 23
   Email: nicolas.montavont@imt-atlantique.fr











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   Pascal Thubert
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   MOUGINS - Sophia Antipolis  06254
   FRANCE

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com










































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