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. Wang & Vilajosana Expires April 11, 2016 [Page 1] Internet-Draft 6tisch-6top-sublayer October 2015 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 Wang & Vilajosana Expires April 11, 2016 [Page 2] Internet-Draft 6tisch-6top-sublayer October 2015 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 Wang & Vilajosana Expires April 11, 2016 [Page 3] Internet-Draft 6tisch-6top-sublayer October 2015 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: Wang & Vilajosana Expires April 11, 2016 [Page 4] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 5] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 6] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 7] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 8] Internet-Draft 6tisch-6top-sublayer October 2015 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 Wang & Vilajosana Expires April 11, 2016 [Page 9] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 10] Internet-Draft 6tisch-6top-sublayer October 2015 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. Wang & Vilajosana Expires April 11, 2016 [Page 11] Internet-Draft 6tisch-6top-sublayer October 2015 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, . [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. Wang & Vilajosana Expires April 11, 2016 [Page 12] Internet-Draft 6tisch-6top-sublayer October 2015 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, . [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. Wang & Vilajosana Expires April 11, 2016 [Page 13] 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 Wang & Vilajosana Expires April 11, 2016 [Page 14]