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6TiSCH                                                      Q. Wang, Ed.
Internet-Draft                           Univ. of Sci. and Tech. Beijing
Intended status: Informational                             X. Vilajosana
Expires: April 11, 2016                  Universitat Oberta de Catalunya
                                                         October 9, 2015


                    6TiSCH Operation Sublayer (6top)
                   draft-wang-6tisch-6top-sublayer-02

Abstract

   This document defines the 6TiSCH Operation Sublayer (6top), which
   offers mechanisms for distributed scheduling in 6TiSCH networks.  The
   6top sublayer is the next higher layer of the IEEE802.15.4e TSCH
   medium access control layer.  The 6top Protocol (6P) defined in this
   document allows neighbor nodes to add/delete TSCH cells to one
   another.  To be able to match different application requirements, the
   algorithm of when to add/delete cells, called the 6top Objective
   Function (6OF), is left out of scope, and will be specified in one of
   more companion documents.

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 April 11, 2016.






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Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  6TiSCH Operation Sublayer (6top)  . . . . . . . . . . . . . .   4
     2.1.  Hard/Soft Cells . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  6top and minimal  . . . . . . . . . . . . . . . . . . . .   4
   3.  6top Protocol (6P)  . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Message Format  . . . . . . . . . . . . . . . . . . . . .   6
       3.1.1.  6top Information Element  . . . . . . . . . . . . . .   6
       3.1.2.  General Message Format  . . . . . . . . . . . . . . .   6
       3.1.3.  6P OpCode . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.4.  6P Cell Format  . . . . . . . . . . . . . . . . . . .   7
       3.1.5.  6P ADD Request Format . . . . . . . . . . . . . . . .   7
       3.1.6.  6P DELETE Request Format  . . . . . . . . . . . . . .   8
       3.1.7.  6P Response Format  . . . . . . . . . . . . . . . . .   8
     3.2.  Protocol Behavior . . . . . . . . . . . . . . . . . . . .   8
       3.2.1.  Version Checking  . . . . . . . . . . . . . . . . . .   8
       3.2.2.  6OFID Checking  . . . . . . . . . . . . . . . . . . .   9
       3.2.3.  Concurrent Atomic Transactions  . . . . . . . . . . .   9
       3.2.4.  Timeout . . . . . . . . . . . . . . . . . . . . . . .   9
       3.2.5.  Adding cells  . . . . . . . . . . . . . . . . . . . .   9
       3.2.6.  Deleting cells  . . . . . . . . . . . . . . . . . . .  10
       3.2.7.  Handling error responses  . . . . . . . . . . . . . .  10
     3.3.  Security  . . . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Guidelines for 6top Objective Functions (6OF) . . . . . . . .  11
     4.1.  6OF Identifier (6OFID)  . . . . . . . . . . . . . . . . .  11
     4.2.  Requirements for a 6OF  . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  [TEMPORARY] IEEE Liaison Considerations  . . . . . .  13



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   Appendix B.  [TEMPORARY] Terms for the Terminology Draft  . . . .  13
   Appendix C.  [TEMPORARY] Changelog  . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   All communication in a 6TiSCH network is orchestrated by a schedule.
   This specification defines the mechanisms offered by the 6TiSCH
   Operation Sublayer (6top) sublayer.  These mechanisms allow a node to
   communicate with its neighbor node(s) to agree on a TSCH schedule in
   a distributed manner.

                                    (A)
                                    / \
                                   /   \
                                (B)-----(C)
                                 |       |
                                 |       |
                                (D)     (E)

                    Figure 1: A simple 6TiSCH network.

   For example, node C in Figure 1 monitors the communication cells to
   node A it has in its schedule.

   o  If node C determines the number of frames it is sending to A per
      unit of time is larger than the capacity offered by the TSCH cells
      it has scheduled to A, it communicates with node A to add one or
      more cells.
   o  If node C determines collisions are happening on a particular cell
      to node A, it communicates with node A to add a new cell and
      delete the cell which suffered from collisions.  This results,
      conceptually, in "relocating" the cell which suffered from
      collisions to a different slotOffset/channelOffset location in the
      TSCH schedule.
   o  If the traffic is lower than the capacity, node C communicates
      with node A to delete one or more cells to A.

   This results in a distributed schedule management solution.

   The mechanisms needed to enable this interaction are defined by the
   6TiSCH Operation Sublayer (6top) sublayer, described in Section 2.
   The 6top Protocol (6P), specified in Section 3, defines the
   communication between neighbor nodes in this context.  The 6top
   sublayer includes a 6top Objective Function (6OF) which defines
   policy of when to add/delete a cell to a neighbor.  Different
   applications require different 6OFs, so the 6OF is left out of scope
   of this document.  One of more 6OFs will be defined in one of more



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   companion documents.  Section 4 provides some guidelines on how to
   design a 6OF.

2.  6TiSCH Operation Sublayer (6top)

   As depicted in Figure 2, the 6TiSCH Operation Sublayer (6top) sits
   directly above the IEEE802.15.4e TSCH medium access control layer
   [IEEE802154e].

                                   .
               |                   .                      |
               |            next higher layer             |
               +------------------------------------------+
               |                 6top                     |
               +------------------------------------------+
               |          IEEE802.15.4e TSCH              |
               |                   .                      |
                                   .

            Figure 2: The 6top sublayer in the protocol stack.

   The roles of the 6top sublayer are:

   o  Implement and terminate the 6top Protocol (6P), which allows
      neighbor nodes to communicate to add/delete cells to one another.
   o  Run a 6top Objective Function (6OF) which defines the algorithm to
      decide when to add/delete cells.
   o  Offer a way for a neighbor node to discover which 6OF is being
      used.

2.1.  Hard/Soft Cells

   6top qualifies each cell in the schedule as either "hard" or "soft":

   o  Soft Cell: can be read, added, deleted or updated by 6top.
   o  Hard Cell: is read-only by 6top.

   In the context of this specification, all cells are soft.  Hard cells
   can be used for example when "hard-coding" a cell (e.g. the 6TiSCH
   Configuration [I-D.ietf-6tisch-minimal]).

2.2.  6top and minimal

   6top MAY be used alongside the Minimal 6TiSCH Configuration
   [I-D.ietf-6tisch-minimal].  In this case, it is RECOMMENDED to use 2
   slotframes, as depicted in Figure 3:





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   o  Slotframe 0 (SF0) is used for traffic defined in the Minimal
      6TiSCH Configuration.  In Figure 3, this slotframe is 5 slots
      long, but it can be of any length.
   o  Slotframe 1 (SF1) is used by 6top to allocate cells from.  In
      Figure 3, this slotframe is 10 slots long, but it can be of any
      length.

   .

   SF0 SHOULD be of higher priority than SF1.  6top MAY support further
   slotframes; how to use more slotframes is out of the scope for this
   document.

           | 0    1    2    3    4  | 0    1    2    3    4  |
           +------------------------+------------------------+
       SF0 | EB |    |    |    |    | EB |    |    |    |    |
           |    |    |    |    |    |    |    |    |    |    |
           ---------------------------------------------------
       SF1 |    |A->B|    |    |    |    |    |    |B->A|    |
           |    |    |    |    |    |    |    |    |    |    |
           +-------------------------------------------------+
           | 0    1    2    3    4    5    6    7    8    9  |

   Figure 3: 2-slotframe structure when using 6top alongside the Minimal
                           6TiSCH Configuration.

3.  6top Protocol (6P)

   The 6top Protocol (6P) allows two neighbor nodes to pass information
   to add/delete cells to their TSCH schedule.  This information is
   carried as IEEE802.15.4 Information Elements (IE) [IEEE802154e] and
   travels only a single hop.

   Conceptually, two neighbor nodes "negotiate" the location of the
   cells to add/delete.  We reuse the topology in Figure 1 to illustrate
   how the protocol works.

   When node A wants to add (resp. delete) 2 cells to/from node B:

   1.  Node A sends a message to node B indicating it wants to add
       (resp. delete) 2 cells to/from node B to its schedule, and
       listing 2 or more candidate cells.
   2.  Node B responds with a message indicating that the operation
       succeeded, and specifying which cells from the candidate list it
       added (resp. deleted).  This allows node A to add (resp. delte)
       the same cells to/from its schedule.





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   We call "6top Atomic Transaction" the action of two neighbor nodes
   exchanging a 6P Request Message and the corresponding 6P Reply
   message.

3.1.  Message Format

3.1.1.  6top Information Element

   The messages exchanges as part of the 6P protocol are carried in a
   6top Information Element.  The 6top Information Element is Payload IE
   with Group ID IANA_6TOP_IE_GROUP_ID.  The length of the 6top
   Information Element is Variable.  The content of the 6top Information
   Element is specified in Section 3.1.

3.1.2.  General Message Format

   All 6P messages have the following format:

                          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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Ver   |OpCode |    6OFID      | Other Fields
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Ver (6P Version):  The version of the 6P protocol.  Only version
         IANA_6P_VERSION is defined in this document.  Future
         specification might define further version of the 6P protocol.
   OpCode (6P OpCode):  Operation to carry out, or the response code.
         The list of OpCode values is defined only for version
         IANA_6P_VERSION in this document.
   6OFID (6top Objective Function Identifier):  The identifier of the
         6OF to use to handle this message.  The 6OFID is defined in
         Section 4.1.
   Other Fields:  The list of other fields depends on the value of the
         OpCode, as detailed below.

3.1.3.  6P OpCode

   Figure 4 lists the possible OpCode values.












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    Value               OpCode         RC  Description
   +-------------------+--------------+---+----------------------------+
   | IANA_ADD          | ADD          | N | add one or more cells      |
   +-------------------+-----------------------------------------------+
   | IANA_DELETE       | DELETE       | N | delete one or more cells   |
   +-------------------+-----------------------------------------------+
   | IANA_RC_SUCCESS   | RC_SUCCESS   | Y | operation succeeded        |
   +-------------------+-----------------------------------------------+
   | IANA_RC_ERR_VER   | RC_ERR_VER   | Y | unsupported 6P version     |
   +-------------------+-----------------------------------------------+
   | IANA_RC_ERR_6OFID | RC_ERR_6OFID | Y | unsupported 6OFID          |
   +-------------------+-----------------------------------------------+
   | IANA_RC_ERR_BUSY  | RC_ERR_BUSY  | Y | the node is busy           |
   +-------------------+-----------------------------------------------+
   | IANA_RC_ERR       | RC_ERR       | Y | operation failed           |
   +-------------------+-----------------------------------------------+
   | TODO-0xf          | reserved                                      |
   +-------------------+-----------------------------------------------+

                Figure 4: 6P OpCodes.  (RC is return code)

3.1.4.  6P Cell Format

   The 6P Cell is an element which is present in several messages.  It
   is a 4-byte field formatted as:

                          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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          slotOffset           |         channelOffset         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   slotOffset:  The slot offset of the cell.
   channelOffset:  The channel offset of the cell.

3.1.5.  6P ADD Request Format

                          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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Ver   |OpCode |    6OFID      | NumCells      | Container     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | CellList ...
     +-+-+-+-+-+-+-

   Ver:  Set to IANA_6P_VERSION.
   OpCode:  Set to IANA_ADD for a 6P ADD Request.




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   6OFID:  Identifier of the 6OF to be used by the receiver to handle
         the message.
   NumCells:  The number of additional TX cells the sender wants to
         schedule to the receiver.
   Container:  An indication of where in the schedule to take the cells
         from (which slotframe, which chunk, etc.).  This value is an
         indication to the 6OF.  The meaning of this field depends on
         the 6OF, and is hence out of scope of this document.
   CellList:  A list of 0, 1 of multiple 6P Cells.  The format of a 6P
         Cell is defined in Section 3.1.4

3.1.6.  6P DELETE Request Format

   The 6P DELETE Request has the exact same format as the 6P ADD
   Request, except for the OpCode which is set to IANA_DELETE.

3.1.7.  6P Response Format

                          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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Ver   |OpCode |    6OFID      | CellList ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Ver:  Set to IANA_6P_VERSION.
   6OFID:  Identifier of the 6OF to be used by the receiver to handle
      the message.
   OpCode:  One of the "return code" OpCodes listed in Section 3.1.3.
   CellList:  A list of 0, 1 of multiple 6P Cells.  The format of a 6P
      Cell is defined in Section 3.1.4.

3.2.  Protocol Behavior

   For illustration, we assume we use the topology in Figure 1, and that
   node A negotiates to add/delete cells to node B.

3.2.1.  Version Checking

   All messages contain a Version field.  If multiple Versions of the 6P
   protocol have been defined (in future specifications for Version
   values different than IANA_6P_VERSION), a node MAY implement multiple
   protocol versions at the same time.  When receiving a 6P message with
   a Version number it does not implement, a node MUST reply with a 6P
   Response and a return code of IANA_RC_ERR_VER.  The Version field in
   the 6P Response MUST be the same as the Version field in the
   corresponding 6P Request.





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3.2.2.  6OFID Checking

   All messages contain a 6OFID field.  If multiple 6OFs has been
   defined, a node MAY support multiple 6OFs at the same time.  When
   receiving a 6P message with an unsupported 6OFID, a node MUST reply
   with a 6P Response and a return code of IANA_RC_ERR_6OFID.  The
   Version field in the 6P Response MUST be the same as the Version
   field in the corresponding 6P Request.

3.2.3.  Concurrent Atomic Transactions

   Only a single 6P Atomic Transaction between two neighbors, in a given
   direction, can take place at the same time.  That is, a node MUST NOT
   issue a new 6P Request to a given neighbor before having received the
   6P Response for a previous request to that neighbor.  The only
   exception to this rule is when the previous Atomic Transaction has
   timed out.  If a node receives a 6P Request from a given neighbor
   before having sent the 6P Response to the previous 6P Request from
   that neighbor, it MUST send back a 6P Response with a return code of
   IANA_RC_ERR.

   A node MAY support concurrent Atomic Transactions from different
   neighbors.  In this case, in Figure 1, node C can have a different
   ongoing Atomic Transaction with nodes B and E.  In case a node does
   not have enough resources to handle concurrent Atomic Transactions
   from different neighbors, when it receives a 6P Request from a
   neighbor while already handling a different request from a different
   neighbor, it MUST reply to that second request with a 6P Response
   with return code IANA_RC_ERR_BUSY.

3.2.4.  Timeout

   A timeout happens when the node sending the 6P Request has not
   received the 6P Response.  The value of the timeout is coupled with
   how the cells between the nodes are scheduled.  The 6OF determines
   the value of the timeout.  The value of the timeout is out of scope
   of this document.

3.2.5.  Adding cells

   We assume the topology in Figure 1 where the 6OF on node C decides to
   add NumCell cells to node A.

   Node C's 6OF selects NumCandidate>=NumCell cells from its schedule as
   candidate transmit cells to node A.  NumCandidate MUST be larger or
   equal to NumCell.  How many cells it selects (NumCandidate) and how
   that selection is done is specified in the 6OF and out of scope of
   this document.  Node C sends a 6P ADD Request to node A which



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   contains the value of NumCells and the NumCandidate cells in the
   CellList.

   Upon receiving the request, node A's 6OF verifies which of the cells
   in the CellList it can add as receive cells from node C in its own
   schedule.  How that selection is done is specified in the 6OF and out
   of scope of this document.  That verification can succeed (NumCell
   cells from the CellList can be used), fail (none of the cells from
   the CellList can be used) or partially succeed (less than NumCell
   cells from the CellList can be used).  In all cases, node A MUST send
   a 6P Response with return code set to IANA_RC_SUCCESS, and which
   specifies the list of cells that were scheduled as receive cells from
   C.  That can contain 0 elements (when the verification failed),
   NumCell elements (succeeded) or between 0 and NumCell elements
   (partially succeeded).

   Upon receiving the response, node C adds the cells specified in the
   CellList as transmit cells to node A.

3.2.6.  Deleting cells

   The behavior for deleting cells is equivalent to that of adding cells
   except that:

   o  The nodes delete the cells they agree upon rather than adding
      them.
   o  All cells in the CellList MUST be already scheduled between the
      two nodes.
   o  If the CellList in the 6P Request is empty, the 6OF on the
      receiving node is free to delete any cell from the sender.
   o  The CellList MUST either be equal, contain exactly NumCell cells,
      or more than NumCell cells.  The case where the CellList is not
      empty but contains less than NumCell cells is not supported.

3.2.7.  Handling error responses

   A return code with a name starts with "RC_ERR" in Figure 4 indicates
   an error.  When a node receives a 6P Response with such an error, it
   MUST consider the Atomic Transaction has failed.  In particular, if
   this was a response to a 6P ADD/DELETE Request, the node MUST NOT
   add/delete any of the cells involved in this Atomic Transaction.
   Similarly, a node sending a 6P Response with an "RC_ERR" return code
   MUST NOT add/delete any cells as part of that Atomic Transaction.
   The 6OF defines what to do after an error has occurred.  Defining
   what to do after an error has occurred is out of scope of this
   document.





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3.3.  Security

   6P messages are secured through link-layer security.  When link-layer
   security is enabled, the 6P messages MUST be secured.  This is
   possible because 6P messages are carried as Payload IE.

4.  Guidelines for 6top Objective Functions (6OF)

4.1.  6OF Identifier (6OFID)

   Each 6OF has an identifier.  The identifier is encoded as a 1-byte
   field.  The identifier space is divided in the following ranges.

                          Range      Meaning
                        +-----------+-------------+
                        | 0x00      | reserved    |
                        +-----------+--------------
                        | 0x01-0x7f | managed     |
                        +-----------+--------------
                        | 0x80-0xfe | unmanaged   |
                        +-----------+-------------+
                        | 0xff      | reserved    |
                        +-----------+-------------+

                          Figure 5: 6OFID range.

   6OF identifiers in the managed space MUST be managed by IANA.

4.2.  Requirements for a 6OF

   The specification for a 6OF

   o  MUST specify an identifier for that 6OF.
   o  MUST specify a set of rules for a node to decide when to add one
      or more cells to a neighbor.
   o  MUST specify a set of rules for a node to decide when to delete
      one or more cells to a neighbor.
   o  MUST specify a value for the timeout, or a rule to calculate it.
   o  MUST specify a meaning for the "Container" field in the 6P ADD
      Request.
   o  MUST specify the rule for selecting the cells (including their
      number) to add to the CellList field in the 6P ADD Request.
   o  MUST specify the rule for verifying which cells from the CellList
      it can add to it schedule.
   o  MUST specify what to do after an error has occurred (either the
      node sent a 6P Response with an error code, or received one).
   o  SHOULD clearly state the application domain the 6OF is created
      for.



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   o  SHOULD contain examples which highlight normal and error
      scenarios.
   o  SHOULD contain a performance evaluation of the scheme, possibly
      through references to external documents.

5.  Security Considerations

   TODO: analyze risks

   6P messages are carried inside IEEE802.15.4 Payload Information
   Elements (IEs).  Those Payload IEs are encrypted and authenticated at
   the link layer through CCM*.  6P benefits from the same level of
   security as any other Payload IE.  The 6P protocol does not define
   its own security mechanisms.  A key management solution is out of
   scope for this document.  The 6P protocol will benefit for the key
   management solution used in the network.

6.  IANA Consideration

   o  TODO: IANA_6TOP_IE_GROUP_ID
   o  TODO: IANA_6P_VERSION
   o  TODO: IANA_ADD
   o  TODO: IANA_DELETE
   o  TODO: IANA_RC_SUCCESS
   o  TODO: IANA_RC_ERR_VER
   o  TODO: IANA_RC_ERR_BUSY
   o  TODO: IANA_RC_ERR

7.  References

7.1.  Normative References

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

   [IEEE802154e]
              IEEE standard for Information Technology, "IEEE std.
              802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
              Networks (LR-WPANs) Amendment 1: MAC sublayer", April
              2012.

   [IEEE802154]
              IEEE standard for Information Technology, "IEEE std.
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks", June 2011.



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7.2.  Informative References

   [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
              IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
              Internet of Things (IoT): Problem Statement", RFC 7554,
              DOI 10.17487/RFC7554, May 2015,
              <http://www.rfc-editor.org/info/rfc7554>.

   [I-D.ietf-6tisch-minimal]
              Vilajosana, X. and K. Pister, "Minimal 6TiSCH
              Configuration", draft-ietf-6tisch-minimal-12 (work in
              progress), September 2015.

   [I-D.ietf-6tisch-terminology]
              Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
              "Terminology in IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-ietf-6tisch-terminology-05 (work in
              progress), July 2015.

   [OpenWSN]  Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F.,
              Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN:
              a Standards-Based Low-Power Wireless Development
              Environment", Transactions on Emerging Telecommunications
              Technologies , August 2012.

Appendix A.  [TEMPORARY] IEEE Liaison Considerations

   The 6P messages are carried into a single IEEE802.15.4 Payload
   Information Element.  We need a mechanism to discriminate 6P messages
   from other IEs.  In the text, we assume a Payload IE Group ID
   (IANA_6TOP_IE_GROUP_ID) assigned.  Another option would be for the
   IEEE to assign a Payload IE Group ID to the IETF, and for 6TiSCH to
   coordinate the creation of a IANA entry for subIEs.

Appendix B.  [TEMPORARY] Terms for the Terminology Draft

   Terms introduced by this document, and which needs to be added to
   [I-D.ietf-6tisch-terminology]:

   6top:       The "6TiSCH Operation Sublayer", which the next highest
               layer of the IEEE802.15.4e TSCH medium access control
               layer.  It implements and terminates the "6top Protocol"
               (6P), and contains a "6top Objective Function" (6OF).  It
               is defined in LINK_draft-wang-6tisch-6top-sublayer.
   6OF:        The "6top Objective Function", the policy inside the
               "6TiSCH Operation Sublayer" (6top) which decides when to
               add/remove cells.  It is defined in LINK_draft-wang-
               6tisch-6top-sublayer.



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Internet-Draft            6tisch-6top-sublayer              October 2015


   6OFID:      The "6top Objective Function Identifier", a 4-bit field
               identifying a 6OF.  It is defined in LINK_draft-wang-
               6tisch-6top-sublayer.
   6P:         The "6top Protocol", which allows neighbor nodes to
               communicate to add/delete cells to one another in their
               TSCH schedule.  It is defined in LINK_draft-wang-6tisch-
               6top-sublayer.
   6top Atomic Transaction:  Part of the "6top Protocol" (6P), the
               action of two neighbors exchanging a 6P request message
               and the corresponding 6P response message.  It is defined
               in LINK_draft-wang-6tisch-6top-sublayer.

Appendix C.  [TEMPORARY] Changelog

   o  -02

      *  introduces the 6P protocol and the notion of 6top Atomic
         Transaction.
      *  introduces the concept of 6OF and its 6OFID.

Authors' Addresses

   Qin Wang (editor)
   Univ. of Sci. and Tech. Beijing
   30 Xueyuan Road
   Beijing, Hebei  100083
   China

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


   Xavier Vilajosana
   Universitat Oberta de Catalunya
   156 Rambla Poblenou
   Barcelona, Catalonia  08018
   Spain

   Phone: +34 (646) 633 681
   Email: xvilajosana@uoc.edu











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