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6TiSCH                                               MR. Palattella, Ed.
Internet-Draft                                   SnT/Univ. of Luxembourg
Intended status: Informational                                P. Thubert
Expires: August 17, 2014                                           cisco
                                                             T. Watteyne
                                       Linear Technology / Dust Networks
                                                                 Q. Wang
                                         Univ. of Sci. and Tech. Beijing
                                                       February 13, 2014

        Terminology in IPv6 over the TSCH mode of IEEE 802.15.4e


   6TiSCH proposes an architecture for an IPv6 multilink subnet that is
   composed of a high speed powered backbone and a number of
   IEEE802.15.4e TSCH wireless networks attached and synchronized by
   backbone routers.  This document extends existing terminology
   documents available for Low-power and Lossy Networks to provide
   additional terminology elements.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

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 http://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 August 17, 2014.

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Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
     6.3.  External Informative References . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   A new breed of Time Sensitive Networks is being developed to enable
   traffic that is highly sensitive to jitter and quite sensitive to
   latency.  Such traffic is not limited to voice and video, but also
   includes command and control operations such as in industrial
   automation or in-vehicle sensors and actuators.

   At IEEE802.1, the "Audio/Video Task Group", was renamed TSN for Time
   Sensitive Networking.  The IEEE802.15.4 Medium Access Control (MAC)
   has evolved with IEEE802.15.4e which provides in particular the Time
   Slotted Channel Hopping (TSCH) mode for industrial-type applications.
   Both provide deterministic capabilities to the point that a packet
   that pertains to a certain flow crosses the network from node to node
   following a very precise schedule, like a train leaves intermediate
   stations at precise times along its path.

   This document provides additional terminology elements to cover terms
   that are new to the context of TSCH wireless networks and other
   deterministic networks.

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2.  Terminology

   The draft extends [I-D.ietf-roll-terminology] and use terms from RFC
   6550 [RFC6550] and RFC 6552 [RFC6552], which are all included here by

   The draft does not reuse terms from IEEE802.15.4e such as "path" or
   "link" which bear a meaning that is quite different from classical
   IETF parlance.

   This document adds the following terms:

   6TiSCH:     IPv6 over the Timeslotted Channel Hopping (TSCH) mode of
               IEEE 802.15.4e. It defines a set of IETF sublayers and
               protocols (in particular, for setting up a schedule with
               a centralized or distributed approach, managing the
               resource allocation), as well as the architecture to bind
               them together, for use in IPv6 TSCH based networks.

   6F:         IPv6 Forwarding.  One of the three forwarding model
               supported by 6TiSCH.  Packets are routed at layer 3,
               where QoS and RED operations are expected to prioritize
               flows with differentiated services.

   6top:       6top is the adaptation layer between TSCH and upper
               layers like 6LoWPAN and RPL.  It is defined in

   6top Data Convey Model:  Model describing how the 6top adaptation
               layer feeds the data flow coming from upper layers into
               TSCH.  It is composed by an I-MUX module, a MUX module, a
               set of priority queues, and a PDU (Payload Data Unit).

   ASN:        Absolute Slot Number, the timeslot counter, incremented
               by one at each timeslot.  It is wide enough to not roll
               over in practice.  See

   Blacklist:  Set of frequencies which should not be used for

   BBR:        Backbone Router.  In the 6TiSCH architecture, it is an
               LBR and also a NEAR.  It performs ND proxy operations
               between registered devices and classical ND devices that
               are located over the backbone.

   Broadcast cell:  A scheduled cell whose neighbor MAC address is set
               to the broadcast address.

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   Bundle:     A group of equivalent scheduled cells, i.e. cells
               identified by different [slotOffset, channelOffset],
               which are scheduled for a same purpose, with the same
               neighbor, with the same flags, and the same slotframe.
               The size of the bundle refers to the number of cells it
               contains.  Given the length of the slotframe, the size of
               the bundle translates directly into bandwidth, either
               logical, or physical.

   Cell:       A single element in the TSCH schedule, identified by a
               slotOffset, a channelOffset, a slotframeHandle.  A cell
               can be scheduled or unscheduled.

   ChannelOffset:  Identifies a row in the TSCH slotframe.  The number
               of available channelOffsets is equal to the number of
               available frequencies.  The channelOffset translates into
               a frequency when the communication takes place, resulting
               in channel hopping, as detailed in

   Channel distribution/usage (CDU) matrix:  : Matrix of height equal to
               the number of available channels (i.e, ChannelOffsets),
               representing the spectrum(channel) distribution among the
               different (RPL parent) nodes in the networks.  Every
               single element of the matrix belongs to a specific chunk.
               It has to be noticed that such matrix, even though it
               includes all the cells grouped in chunks, belonging to
               different slotframes, is different from the TSCH

   Chunk:      A well-known list of cells, well-distributed in time and
               frequency, within a slotframe; a chunk represents a
               portion of a slotframe that is globally known by all the
               nodes in the network, but it can be managed separately by
               a single node.  A node can have multiple chunks, and use
               them according to a specific policy.  Chunks may overlap.
               They can be pre-programmed, or can be computed by an
               external entity at the network bootstrap.

   Chunk ownership appropriation:  The process by which an individual
               node obtains a chunk to manage based on peer-to-peer
               interaction with its neighbors.

   Chunk ownership delegation:  The process by which an individual node
               obtains a chunk to manage based on point-to-point
               interaction with an external entity.

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   Communication Paradigm:  It is Associated with the Information Model
               [RFC3444] of the state that is exchanged, and indicates:
               the location of that state (e.g., centralized vs.
               distributed, RESTful, etc.), the numbers of parties
               (e.g., P2P vs. P2MP) and the relationship between parties
               (e.g., master/slave vs. peers) at a high level of
               protocol abstraction.  Layer 5 client/server REST is a
               typical communication paradigm, but industrial protocols
               also use publish/subscribe which is P2MP and source/sink
               which is MP2MP and primarily used for alarms and alerts
               at the application layer.  At layer 3, basic flooding,
               P2P synchronization and path-marking (RSVP-like) are
               commonly used paradigms, whereas at layer 2, master/slave
               polling and peer-to-peer forwarding are classical

   Dedicated Cell:  A cell that is reserved for a given node to transmit
               to a specific neighbor.

   Distributed cell reservation:  A reservation of a cell done by one or
               more in-network entities (typically a connection

   Distributed track reservation:  A reservation of a track done by one
               or more in-network entities (typically a connection

   EB:         Enhanced Beacon frame used by an advertising node to
               announce the presence of the network.  It contains
               information about the timeslot length, the current ASN
               value, the slotframes and timeslots the beaconing mote is
               listening on, and a 1-byte join priority (i.e., number of
               hops separating the node sending the EB, and the PAN

   FF:         6LoWPAN Fragment Forwarding.  It is one of the three
               forwarding model supported by 6TiSCH.  The 6LoWPAN
               Fragment is used as a label for switching at the 6LoWPAN
               sublayer, as defined in

   GMPLS:      Generalized Multi-Protocol Label Switching, a 2.5 layer
               service that is used to forward packets based on the
               concept of generalized labels.

   Hard Cell:  A scheduled cell which the 6top sublayer cannot
               reallocate.  See [I-D.draft-wang-6tsch-6top].

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   Hopping Sequence:  Sequence of frequencies, identified by a
               Hopping_Sequence_ID, used for channel hopping, when
               translating the channel offset value into a frequency
               (i.e., PHY channel).  See

   IE:         Information Elements, a list of Type-Length-Value
               containers placed at the end of the MAC header, used to
               pass data between layers or devices.  A small number of
               types are defined by TSCH, but a range of types is
               available for extensions, and thus, is exploitable by
               6TiSCH.  See [I-D.watteyne-6tsch-tsch-lln-context].

   I-MUX module:  Inverse-Multiplexer, a classifier that receives
               6LoWPAN frames and places them into priority queues.

   Interaction Model:  It is a particular way of implementing a
               communication paradigm.  Defined at a lower level of
               abstraction, it includes protocol-specific details such
               as a particular method (e.g., a REST GET) and a Data
               Model for the state to be exchanged.

   KMP:        Key Managment Protocol.

   LBR:        LLN Border Router.  It is an LLN device, usually powered,
               that acts as a Border Router to the outside within the
               6TiSCH architecture.

   Link:       A communication facility or medium over which nodes can
               communicate at the link layer, i.e., the layer
               immediately below IP.  Thus, the IETF parlance for the
               term "Link" is adopted, as opposed to the incompatible
               IEEE802.15.4e terminology.  In the context of the 6TiSCH
               architecture, which applies to Low Power Lossy Networks
               (LLNs), an IPv6 subnet is usually not congruent to a
               single link and techniques such as IPv6 Neighbor
               Discovery Proxying and Routing Over LLNs are required to
               achieve reachability within the multilink subnet.  A link
               is distinct from a track.  In fact, link local addresses
               are not expected to be used over a track for end to end
               communication.  Finally, from the Layer 3 perspective
               (where the inner complexities of TSCH operations are
               hidden to enable classical IP routing and Forwarding), a
               single radio interface may be seen as a number of Links
               with different capabilities for unicast or multicast

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   Logical Cell:  A cell that corresponds to granted bandwidth but is
               only lazily associated to a physical cell, based on

   MAC:        Medium Access Control.

   MUX module: Multiplexer, the entity that dequeues frames from
               priority queues and associates them to a cell for

   NEAR:       Energy Aware Default Router, as defined in

   NME:        Network Management Entity, the entity in the network
               managing cells and other device resources.  It may
               cooperate with the PCE.  It interacts with LLN nodes
               through the backbone router.

   PANA:       Protocol for carrying Authentication for Network Access,
               as defined in [RFC5191] . It is the protocol used in the
               6TiSCH architecture for handling authentication during
               the join process.

   PCE:        Path Computation Element, the entity in the network which
               is responsible for building and maintaining the TSCH
               schedule, when centralized scheduling is used.

   PCE cell reservation:  The reservation of a cell done by the PCE.

   PCE track reservation:  The reservation of a track done by the PCE.

   QoS:        Quality of Service.

   (to) reallocate a cell:  The action operated by the 6top sublayer of
               changing the slotOffset and/or channelOffset of a soft

   SA:         Security Association.

   (to) Schedule a cell:  The action of turning an unscheduled cell into
               a scheduled cell.

   Scheduled cell:  A cell which is assigned a neighbor MAC address
               (broadcast address is also possible), and one or more of
               the following flags: TX, RX, shared, timeskeeping.  A
               scheduled cell can be used by the IEEE802.15.4e TSCH
               implementation to communicate.  A scheduled cell can be a
               hard cell or a soft cell.

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   Shared Cell:  A cell that is used by more than one transmitter nodes
               at the same time and on the same channelOffset.  Only
               cells with TX flag can be marked as "shared".  A backoff
               algorithm is used to resolve contention.

   SlotOffset: Identifies a column in the TSCH schedule, i.e., the
               number of timeslots since the beginning of the current
               iteration of the slotframe.

   Slotframe:  A MAC-level abstraction that is internal to the node and
               contains a series of timeslots of equal length and
               priority.  It is characterized by a slotframe_ID, and a
               slotframe_size.  Multiple slotframes can coexist in a
               node's schedule, i.e., a node can have multiple
               activities scheduled in different slotframes, based on
               the priority of its packets/traffic flows.  The timeslots
               in the Slotframe are indexed by the SlotOffset; the first
               timeslot is at SlotOffset 0.

   Soft Cell:  A scheduled cell which the 6top sublayer can reallocate,
               as described in [I-D.draft-wang-6tsch-6top].

   TF:         Track Forwarding.  It is the simplest and fastest
               forwarding model supported by 6TiSCH.  It is a G-MPLS-
               like forwarding model.  The input cell characterises the
               flow and indicates the output cell.

   Timeslot:   A basic communication unit in TSCH which allows a
               transmitter node to send a frame to a receiver neighbor,
               and that receiver neighbor to optionally send back an
               acknowledgment.  The length of the timeslot determines
               the maximum size of the frame that can be exchanged.

   Time Source Neighbor:  A neighbor a node uses as its time reference,
               and to which it needs to keep its clock synchronized.  A
               node can have one or more time source neighbors.

   Track:      A determined sequence of cells along a multi-hop path.
               It is typically the result of a reservation.  The node
               that initializes the process for establishing a track is
               the owner of the track.  The latter assigns a unique
               identifier to the track, called TrackID.

   TrackID:    Unique identifier of a track, assigned by the owner of
               the track.

   TSCH:       Time Slotted Channel Hopping, a medium access mode of the
               [IEEE802154e] standard which uses time synchronization to

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               achieve ultra low-power operation and channel hopping to
               enable high reliability.

   TSCH Schedule:  A matrix of cells, each cell indexed by a slotOffset
               and a channelOffset.  The slotframe size (the "width" of
               the matrix) is the number of timeslots it contains.  The
               number of channelOffset values (the "height" of the
               matrix) is equal to the number of available frequencies.
               The TSCH schedule contains all the scheduled cells from
               all slotframes and is sufficient to qualify the
               communication in the TSCH network.

   unscheduled cell:  A cell which is not used by the IEEE802.15.4e TSCH

3.  IANA Considerations

   This specification does not require IANA action.

4.  Security Considerations

   This specification is not found to introduce new security threat.

5.  Acknowledgements

   Thanks to the IoT6 European Project (STREP) of the 7th Framework
   Program (Grant 288445).

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3444]  Pras, A. and J. Schoenwaelder, "On the Difference between
              Information Models and Data Models", RFC 3444, January

   [RFC5191]  Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
              Yegin, "Protocol for Carrying Authentication for Network
              Access (PANA)", RFC 5191, May 2008.

   [RFC6550]  Winter, T., Thubert, P., 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, March 2012.

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   [RFC6552]  Thubert, P., "Objective Function Zero for the Routing
              Protocol for Low-Power and Lossy Networks (RPL)", RFC
              6552, March 2012.

6.2.  Informative References

              Chakrabarti, S., Nordmark, E., Thubert, P., and M.
              Wasserman, "Wired and Wireless IPv6 Neighbor Discovery
              Optimizations", draft-chakrabarti-nordmark-6man-efficient-
              nd-04 (work in progress), October 2013.

              Sudhaakar, R., Ed. and P. Zand, "6TiSCH Data Model for
              CoAP-00 (work in progress)", October 2013.

              Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH
              Operation Sublayer (6top). draft-wang-6tisch-6top-00 (work
              in progress)", October 2013.

              Vasseur, J., "Terms used in Routing for Low power And
              Lossy Networks", draft-ietf-roll-terminology-13 (work in
              progress), October 2013.

              Chasko, S., Das, S., Lopez, R., Ohba, Y., Thubert, P., and
              A. Yegin, "Security Framework and Key Management Protocol
              Requirements for 6TSCH", draft-ohba-6tsch-security-01
              (work in progress), July 2013.

              Thubert, P., Watteyne, T., and R. Assimiti, "An
              Architecture for IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-thubert-6tisch-architecture-01 (work in
              progress), October 2013.

              Thubert, P. and J. Hui, "LLN Fragment Forwarding and
              Recovery", draft-thubert-roll-forwarding-frags-02 (work in
              progress), September 2013.

              Vilajosana, X. and K. Pister, "Minimal 6TiSCH
              Configuration", draft-vilajosana-6tisch-minimal-00 (work
              in progress), October 2013.

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              Watteyne, T., Palattella, M., and L. Grieco, "Using
              IEEE802.15.4e TSCH in an LLN context: Overview, Problem
              Statement and Goals", draft-watteyne-6tsch-tsch-lln-
              context-02 (work in progress), May 2013.

6.3.  External Informative References

              IEEE standard for Information Technology, "IEEE std.
              802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
              Networks (LR-WPANs) Amendament 1: MAC sublayer", April

Authors' Addresses

   Maria Rita Palattella (editor)
   University of Luxembourg
   Interdisciplinary Centre for Security, Reliability and Trust
   4, rue Alphonse Weicker
   Luxembourg  L-2721

   Phone: (+352) 46 66 44 5841
   Email: maria-rita.palattella@uni.lu

   Pascal Thubert
   Cisco Systems, Inc
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410

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

   Thomas Watteyne
   Linear Technology / Dust Networks
   30695 Huntwood Avenue
   Hayward, CA  94544

   Phone: +1 (510) 400-2978
   Email: twatteyne@linear.com

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   Qin Wang
   Univ. of Sci. and Tech. Beijing
   30 Xueyuan Road
   Beijing, Hebei  100083

   Phone: +86 (10) 6233 4781
   Email: wangqin@ies.ustb.edu.cn

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