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6TSCH                                                    P. Thubert, Ed.
Internet-Draft                                                     cisco
Intended status: Standards Track                            RA. Assimiti
Expires: September 12, 2013                                        Nivis
                                                             T. Watteyne
                                       Linear Technology / Dust Networks
                                                          March 11, 2013


    An Architecture for IPv6 over Time Synchronized Channel Hopping
                  draft-thubert-6tsch-architecture-00

Abstract

   This document presents 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.  Route Computation may be achieved in a centralized
   fashion by a Path Computation Element, in a distributed fashion using
   the Routing Protocol for Low Power and Lossy Networks, or in a mixed
   mode.  The Backbone Routers perform proxy Neighbor discovery
   operations over the backbone on behalf of the wireless device, so
   they can share a same subnet and appear to be connected to the same
   backbone as classical devices.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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 September 12, 2013.



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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
   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
   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.  Overview and Scope  . . . . . . . . . . . . . . . . . . . . .   3
   4.  Centralized vs. Distributed Routing . . . . . . . . . . . . .   6
   5.  Functional Flows  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Network Synchronization . . . . . . . . . . . . . . . . . . .   6
   7.  TSCH and 6TUS . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  6tus  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.2.  Slotframes and Priorities . . . . . . . . . . . . . . . .   7
     7.3.  Centralized Flow Reservation  . . . . . . . . . . . . . .   7
     7.4.  Distributed Flow Reservation  . . . . . . . . . . . . . .   7
     7.5.  Packet Marking and Handling . . . . . . . . . . . . . . .   8
   8.  Management  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     12.2.  Informative References . . . . . . . . . . . . . . . . .  10
     12.3.  External Informative References  . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   A new breed of Time Sensitive Networks is being developped 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 found in industrial
   automation or in-vehicule sensors and actuators.





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   At IEEE802.1, the "Audio/Video Task Group", was rename 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
   Synchronized Channel Hopping (TSCH) mode for industrial-type
   applications.  Both provide Deterministic capabities to the point
   that a packet that pertains to a certain flow will cross the network
   from node to node following a very precise schedule, like a train
   leaves intermediate stations at precise times along its path.  The
   time slotted aspect reduce collisions, and saves energy.  The channel
   hopping aspect is a simple and efficient technique to get around
   statistical interference by WIFI emitters.

   This document presents 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.  Route Computation may be achieved in a centralized
   fashion by a Path Computation Element (PCE), in a distributed fashion
   using the Routing Protocol for Low Power and Lossy Networks (RPL), or
   in a mixed mode.  The Backbone Routers perform proxy Ipv6 Neighbor
   Discovery (ND) operations over the backbone on behalf of the wireless
   device, so they can share a same IPv6 subnet and appear to be
   connected to the same backbone as classical devices.

2.  Terminology

   The draft uses terminology defined in
   [I-D.palattella-6tsch-terminology],
   [I-D.chakrabarti-nordmark-6man-efficient-nd], [RFC5191] and
   [RFC4080].

   It conforms to the terms and models described for IPv6 in [RFC5889]
   and uses the vocabulary and the concepts defined in [RFC4291] for
   IPv6.

3.  Overview and Scope

   The scope of the present work is a subnet that, in its basic
   configuration, is made of a IEEE802.15.4e Time Synchronized Channel
   Hopping (TSCH) [I-D.watteyne-6tsch-tsch-lln-context] MAC Route-Over
   Low Power Lossy Network (LLN).


               +-----+
               |     | LLN Border
               |     | router
               +-----+
             o    o   o
      o     o   o     o



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         o   o LLN   o    o     o
            o   o   o       o
                    o

                       Figure 1: Basic Configuration

   The LLN devices communicate over IPv6 [RFC2460] using the 6LoWPAN
   Header Compression (6LoWPAN HC) [RFC6282].  Neighbor Devices are
   discovered with 6LoWPAN Neighbor Discovery (6LoWPAN ND) [RFC6775] and
   the Routing Protocol for Low Power and Lossy Networks (RPL) [RFC6550]
   enables routing within the LLN.  RPL forms Destination Oriented
   Directed Acyclic Graphs (DODAGs) within instances of the protocol,
   each instance being associated with an Objective Function (OF) to
   form a routing topology.  A particular LLN device, usually powered,
   acts as RPL root, 6LoWPAN HC terminator, and LLN Border Router (LBR)
   to the outside.

   An extended configuration of the subnet comprises multiple LLNs.  The
   LLNs are interconnected and synchronized over a backbone, that can be
   wired or wireless.  The backbone can be a classical IPv6 network,
   with Neighbor Discovery operating as defined in [RFC4861] and
   [RFC4862].  The backbone can also support Efficiency aware IPv6
   Neighbor Discovery Optimizations
   [I-D.chakrabarti-nordmark-6man-efficient-nd] in mixed mode as
   described in [I-D.thubert-6lowpan-backbone-router].

   Security is often handled at layer 2 and Layer 4.  Authentication
   during the join process is handled with the Protocol for Carrying
   Authentication for Network Access (PANA) [RFC5191].

   The LLN devices are time-synchronized at MAC level.  The MAC
   coordinator that serves as time source through Enhanced Beacons (EB)
   is loosely coupled with the RPL parent; this way, the time
   synchronization starts at the RPL root and follows the RPL DODAGs
   with no timing loop.

   In the extended configuration, the functionality of the LBR is
   enhanced to that of Backbone Router (BBR).  A BBR is an LBR, but also
   an Energy Aware Default Router (NEAR) as defined in
   [I-D.chakrabarti-nordmark-6man-efficient-nd].  The BBR performs ND
   proxy operations between the registered devices and the classical ND
   devices that are located over the backbone.  6TSCH BBRs synchronize
   with one another over the backbone, so as to ensure that the multiple
   LLNs that form the IPv6 subnet stay tightly synchronized.  If the
   Backbone is Deterministic (such as defined by the Time Sensitive
   Networking WG at IEEE), then the Backbone Router ensures that the
   end-to-end deterministic behavior is maintained between the LLN and
   the backbone.



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               ---+------------------------
                  |      External Network
                  |
               +-----+                  +-----+
               |     | Router           |     | PCE
               |     |                  |     |
               +-----+                  +-----+
                  |                        |
                  |     Subnet Backbone    |
            +--------------------+------------------+
            |                    |                  |
         +-----+             +-----+             +-----+
         |     | Backbone    |     | Backbone    |     | Backbone
    o    |     | router      |     | router      |     | router
         +-----+             +-----+             +-----+
    o                  o                   o                 o   o
        o    o   o         o   o  o   o         o  o   o    o
   o             o        o  LLN      o      o         o      o
      o   o    o      o      o o     o  o   o    o    o     o

                     Figure 2: Extended Configuration

   The main architactural blocks are arranged as follows:

        +-----+-----+-----+-----+-----+--------+
        |PANA | RPL |RSVP | PCE |   IP         |
        |     |     |/NSIS| /CNM|/ FORWARDING  |
        +-----+-----+-----+-----+--------+-----+-------+
        |        6LoWPAN                 | 6LoWPAN ND  |
        |          HC                    +-------------+
        |                                              |
        +----------------------------------------------+
        |            6TUS                              |
        +----------------------------------------------+
        |          802.15.4e   TSCH                    |
        +----------------------------------------------+

                           Figure 3: 6TSCH stack

   RPL is the routing protocol of choice.  TBD whether there is a need
   to define a 6TSCH OF.

   PCE => group needs to work with PCE WG to define flows to PCE, and
   define how to accomodate PCE routes and reservation.

   BBR => group needs to work woth 6MAN to define ND proxy.  Also need
   BBR sync, time sync between deterministic ethernet and 6TSCH net.




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   IEEE802.1TSN => external, maintain liaison.

   IEEE802.15.4 => external, maintain liaison.

   ISA100.20 Common Network Management (CNM) => external, maintain
   liaison.

   IoT6 => external, maintain liaison.

4.  Centralized vs.  Distributed Routing

5.  Functional Flows

6.  Network Synchronization

   The mechanism(s) used for time synchronization is something that we
   might have to reconcile with RPL discovery and maintenance traffic.

   Time synchronization in TSCH is based on three mechanisms:

      Enhanced Beacons

      Enhanced ACKs

      Frame based synchronization

   If a node communicates intermittently (sleepy, battery operated) it
   can also proactively ping its time source and receive time stamps.
   In order to maximize battery life and network throughput, it is
   advisable that RPL ICMP discovery and maintenance traffic (governed
   by the trickle timer) be somehow coordinated with the transmission of
   time synch packets (especially with enhanced beacons).  This could be
   a function of the shim layer or it could be deferred to the device
   management entity.  Any suggestions, ideas on this topic?

7.  TSCH and 6TUS

7.1.  6tus

   6tus is an adaptation layer which is the next higher layer to TSCH
   and which offers a set of commands defining a data and management
   interface.  6tus is defines in [I-D.draft-wang-6tsch-6tus]

   The management interface of 6tus enables an upper layer to schedule
   cells and slotframes in the TSCH schedule.

   If the scheduling entity explicitly specifies the slotOffset/
   channelOffset of the cells to be added/deleted, those cells are



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   marked as "hard".  6tus can not move hard cells in the TSCH schedule.
   Hard cells are typically used by an central PCE.

   6tus contains a monitoring process which monitors the performance of
   cells, and can move a cell in the TSCH schedule when it performs bad.
   This is only applicable to cells which are marked as "soft".  To
   reserve a soft cell, the higher layer does not indicate the
   slotOffset/channelOffset of the cell to add, but rather the resulting
   bandwidth and QoS requirements.  When the monitoring process triggers
   an cell reallocation, the two neighbor motes communication over this
   cells negociate the new position in the TSCH schedule of this cell.

7.2.  Slotframes and Priorities

   6tus uses priority queues to manage concurrent data flows of
   different prioroties.  When a packet is received from an higher layer
   for transmission, the I-MUX module of 6tus inserts that packet in the
   outgoing queue which matches the packet best (DSCP can therefore be
   used).  At each schedule transmit slot, the MUX module looks for the
   frame in all the outgoing queues that best matches the cells.  If a
   frame is found, it is given to TSCH for transmission.

7.3.  Centralized Flow Reservation

   In a centralized setting, a PCE computes the TSCH schedule, and
   communicates with the different nodes in the network to configure
   their TSCH schedule.  Since it has full knowledge of the network's
   topology, the PCE can compute a collision-free schedule, which result
   in a high degree of communication determinism.

   The protocol for the PCE to communicate with the motes is not yet
   defined.  This protocol typically reserves hard cells on the
   transmitter side of a dedicated cell, and the negociation protocol of
   6tus takes care of reserving the same cell on the receiver node.

7.4.  Distributed Flow Reservation

   In a distributed setting, no central PCE in present in the network.
   Nodes use 6tus to reserve soft cells with their neighbors.  Since no
   node has full knowledge of the network's topology and the traffic
   requirements, scheduling collisions are possible, for example because
   of a hidden terminal problem.









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   A schedule collision can be detected if two motes have multiple
   dedicated cells schedule to one another.  The statistics process of
   6tus can be configure to continuously compute the packet delivery
   ratio of those cells, and the monitoring process of 6tus can declare
   a soft cell to perform bad when that statistics for that cell is
   significantly worse than for the other cell to the same neighbor.

   When this happens, the monitoring process of 6tus moves the cell to
   another location in the 6TSCH schedule, through a re-negociation
   procedure with the neighbor.

   The entity that builds and maintains the schedule in a distributed
   fashion is not yet defined.

7.5.  Packet Marking and Handling

                  ---+----------------
          Sender                                              Receiver
      +-----------+     +----+     +----+      +----+      +-----------+
      |Application|---->| R1 |---->| R2 |----->|BBR |----->|Application|
      |   +--+    |     |+--+|     |+--+|      |+--+|      |   +--+    |
      |   |NE|====|=====||NE||=====||NE||======||NE||======|===|NE|    |
      |   +--+    |     |+--+|     |+--+|      |+--+|      |   +--+    |
      |    |^     |     | |^ |     | |^ |      | |^ |      |    |^     |
      |    v|     |     | v| |     | v| |      | v| |      |    v|     |
      |   +--+    |     |+--+|     |+--+|      |+--+|      |   +--+    |
      |   |6T|    |     ||6T||     ||6T||      ||6T||      |   |6T|    |
      |   |us|    |     ||us||     ||us||      ||us||      |   |us|    |
      |   +--+    |     |+--+|     |+--+|      |+--+|      |   +--+    |
      +-----------+     +----+     +----+      +----+      +-----------+

         +--+
         |NE| = NSIS      ==== = Signaling    ---> = Data flow messages
         +--+   Entity           Messages            (unidirectional)

         +--+
         |6T|   6TUS layer
         |us| (and IEEE802.15.4e TSCH MAC below)
         +--+


                            Figure 4: NSIS flow

   reservation Deterministic flow allocation (hard reservation of time
   slots) eg centralized RSVP?  metrics?  Hop-by-hop interaction with
   6TUS.  Lazy reservation (use shared slots to transport extra burst
   and then dynamically (de)allocate) Classical QoS (dynamic based on
   observation)



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8.  Management

9.  IANA Considerations

   This specification does not require IANA action.

10.  Security Considerations

   This specification is not found to introduce new security threat.

11.  Acknowledgements

12.  References

12.1.  Normative References

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

   [RFC2460]  Deering, S.E. and R.M. Hinden, "Internet Protocol, Version
              6 (IPv6) Specification", RFC 2460, December 1998.

   [RFC4080]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
              Bosch, "Next Steps in Signaling (NSIS): Framework", RFC
              4080, June 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

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

   [RFC5889]  Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
              Hoc Networks", RFC 5889, September 2010.

   [RFC5974]  Manner, J., Karagiannis, G., and A. McDonald, "NSIS
              Signaling Layer Protocol (NSLP) for Quality-of-Service
              Signaling", RFC 5974, October 2010.





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   [RFC6282]  Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              September 2011.

   [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.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.

12.2.  Informative References

   [I-D.chakrabarti-nordmark-6man-efficient-nd]
              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.

   [I-D.draft-wang-6tsch-6tus]
              Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6tus
              Adaptation Layer Specification. draft-wang-6tsch-6tus-00
              (work in progress) ", March 2013.

   [I-D.palattella-6tsch-terminology]
              Palattella, MR., Ed., Thubert, P., Watteyne, T., and Q.
              Wang, "Terminology in IPv6 over Time Slotted Channel
              Hopping. draft-palattella-6tsch-terminology-00 (work in
              progress) ", March 2013.

   [I-D.svshah-tsvwg-lln-diffserv-recommendations]
              Shah, S. and P. Thubert, "Differentiated Service Class
              Recommendations for LLN Traffic", draft-svshah-tsvwg-lln-
              diffserv-recommendations-00 (work in progress), February
              2013.

   [I-D.thubert-6lowpan-backbone-router]
              Thubert, P., "6LoWPAN Backbone Router", draft-thubert-
              6lowpan-backbone-router-03 (work in progress), February
              2013.

   [I-D.watteyne-6tsch-tsch-lln-context]






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              Watteyne, T., "Using IEEE802.15.4e TSCH in an LLN context:
              Overview, Problem Statement and Goals", draft-watteyne-
              6tsch-tsch-lln-context-01 (work in progress), February
              2013.

12.3.  External Informative References

   [HART]     www.hartcomm.org, "Highway Addressable Remote Transducer,
              a group of specifications for industrial process and
              control devices administered by the HART Foundation", .

   [IEEE802.1TSNTG]
              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networks Task Group", March 2013, <
              http://www.ieee802.org/1/pages/avbridges.html>.

   [ISA100.11a]
              ISA, "ISA100, Wireless Systems for Automation", May 2008,
              < http://www.isa.org/Community/
              SP100WirelessSystemsforAutomation>.

Authors' Addresses

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

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


   Robert Assimiti
   Nivis
   1000 Circle 75 Parkway SE, Ste 300
   Atlanta, GA  30339
   USA

   Phone: +1 678 202 6859
   Email: robert.assimiti@nivis.com








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

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










































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