6TSCH                                                MR. Palattella, Ed.
Internet-Draft                                   SnT/Univ. of Luxembourg
Intended status: Informational                                P. Thubert
Expires: January 16, 2014                                          cisco
                                                             T. Watteyne
                                       Linear Technology / Dust Networks
                                                                 Q. Wang
                                         Univ. of Sci. and Tech. Beijing
                                                           July 15, 2013

          Terminology in IPv6 over Timeslotted Channel Hopping


   6TSCH 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
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   This Internet-Draft will expire on January 16, 2014.

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Copyright Notice

   Copyright (c) 2013 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
     6.3.  External Informative References . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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] which is included here
   by reference.

   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:

   6TSCH:      IPv6 over Time Slotted Channel Hopping (pronounced
               "sixtus").  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 6TSCH.  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 6TSCH 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.

   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

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               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 sloframe, identified by a
               slotOffset value, a channelOffset value, a slotframe_ID
               and Hopping_Sequence_ID.  A cell can be scheduled or
               unscheduled.  During an unscheduled cell, the node does
               not communicate.  When a cell is scheduled, it is
               assigned a MAC-layer slotframe identifier, a neighbor MAC
               address (which can be the broadcast address), and one or
               more of the following flags: TX, RX, shared,
               timeskeeping, hard.  A broadcast cell is an alias for "a
               scheduled cell with neighbor address the broadcast

   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

   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

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   FF:         6LoWPAN Fragment Forwarding.  It is one of the three
               forwarding model supported by 6TSCH.  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 that is locked, i.e., it cannot be moved
               by 6top in the schedule.  See

   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
               6TSCH.  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.

   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
               6TSCH 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 6TSCH
               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

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               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

   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

   PANA:       Protocol for carrying Authentication for Network Access,
               as defined in [RFC5191] . It is the protocol used in the
               6TSCH 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.

   SA:         Security Association.

   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

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               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 that is not locked, i.e., it may be
               moved in the schedule within a same slotframe by 6top, as
               described in [I-D.draft-wang-6tsch-6top].

   TF:         Track Forwarding.  It is the simplest and fastest
               forwarding model supported by 6TSCH.  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
               achieve ultra low-power operation and channel hopping to
               enable high reliability.

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   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.

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.

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

6.2.  Informative References

              Chakrabarti, S., Nordmark, E., and M. Wasserman,
              "Efficiency aware IPv6 Neighbor Discovery Optimizations",
              draft-chakrabarti-nordmark-6man-efficient-nd-01 (work in
              progress), November 2012.

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


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              Vasseur, J., "Terminology in Low power And Lossy
              Networks", draft-ietf-roll-terminology-12 (work in
              progress), March 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., Assimiti, R., and T. Watteyne, "An
              Architecture for IPv6 over Time Slotted Channel Hopping",
              draft-thubert-6tsch-architecture-01 (work in progress),
              April 2013.

              Thubert, P. and J. Hui, "LLN Fragment Forwarding and
              Recovery", draft-thubert-roll-forwarding-frags-01 (work in
              progress), February 2013.

              Vilajosana, X. and K. Pister, "Minimal 6TSCH
              Configuration", draft-vilajosana-6tsch-basic-01 (work in
              progress), July 2013.

              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

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   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

   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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