6TiSCH D. Dujovne, Ed. Internet-Draft Universidad Diego Portales Intended status: Informational LA. Grieco Expires: September 22, 2016 Politecnico di Bari MR. Palattella University of Luxembourg N. Accettura University of California Berkeley March 21, 2016 6TiSCH 6top Scheduling Function Zero (SF0) draft-dujovne-6tisch-6top-sf0-01 Abstract This document defines a 6top Scheduling Function called "Scheduling Function Zero" (SF0). SF0 dynamically adapts the number of reserved cells between neighbor nodes, based on the currently allocated bandwidth and the neighbour nodes' requirements. Neighbor nodes negotiate in a distributed neighbor-to-neighbor basis the cell(s) to be added/deleted. SF0 uses the 6P signaling messages to add/delete cells in the schedule. Some basic rules for deciding when to add/ delete cells and for selecting the cells to be added/deleted within the schedule are also provided. 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." Dujovne, et al. Expires September 22, 2016 [Page 1] Internet-Draft 6tisch-6top-sf0 March 2016 This Internet-Draft will expire on September 22, 2016. Copyright Notice Copyright (c) 2016 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. Scheduling Function Identifier . . . . . . . . . . . . . . . 3 3. Rules for Adding/Deleting Cells . . . . . . . . . . . . . . . 3 3.1. SF0 Triggering Events . . . . . . . . . . . . . . . . . . 3 3.2. SF0 Bandwidth Estimation Algorithm . . . . . . . . . . . 3 3.3. SF0 Allocation Policy . . . . . . . . . . . . . . . . . . 4 4. Rules for CellList . . . . . . . . . . . . . . . . . . . . . 5 5. 6P Timeout Value . . . . . . . . . . . . . . . . . . . . . . 6 6. Meaning of Metadata Information . . . . . . . . . . . . . . . 6 7. Node Behavior at Boot . . . . . . . . . . . . . . . . . . . . 6 8. Relocating Cells . . . . . . . . . . . . . . . . . . . . . . 6 9. Forced Cell Deletion Policy . . . . . . . . . . . . . . . . . 7 10. 6P Error Handling . . . . . . . . . . . . . . . . . . . . . . 7 11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. Implementation Status . . . . . . . . . . . . . . . . . . . . 7 13. Security Considerations . . . . . . . . . . . . . . . . . . . 8 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 16.1. Normative References . . . . . . . . . . . . . . . . . . 8 16.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction This document defines the Scheduling Function for the 6top sublayer [I-D.wang-6tisch-6top-sublayer] called "Scheduling Function Zero" (SF0). Dujovne, et al. Expires September 22, 2016 [Page 2] Internet-Draft 6tisch-6top-sf0 March 2016 This document addresses the requirements for a scheduling function listed in [I-D.wang-6tisch-6top-sublayer], Section 4.2, and follows the recommended outline from Section 4.3. 2. Scheduling Function Identifier The Scheduling Function Identifier (SFID) of SF0 is IANA_SFID_SF0. 3. Rules for Adding/Deleting Cells A node running SF0 determines when to add/delete cells in a three- step process: 1. It waits for a triggering event (Section 3.1). 2. It applies the Bandwidth Estimation Algorithm (BEA) for a particular neighbor to determine how much bandwidth is required to that neighbor (Section 3.2). 3. It applies the Allocation Policy to compare the number of required cells to the number of already scheduled cells, and determine the number of cells to add/delete (Section 3.3). 3.1. SF0 Triggering Events We RECOMMEND SF0 to be triggered at least by the following events: 1. If the Remaining Available Bandwidth (RAB) is less than the Minimum Remaining Bandwidth (MRB) 2. If there is any New Incoming Bandwidth Requirements from neighbour nodes (NIBR) This allows SF0 to be triggered by any change in local node bandwidth and/or incoming bandwidth. The exact mechanism of when SF0 is triggered is implementation-specific. 3.2. SF0 Bandwidth Estimation Algorithm The Bandwidth Estimation Algorithm takes into account the sum of the incoming bandwidth requirements from the neighbour nodes and the used outgoing bandwidth. This allows the node to estimate the total outgoing bandwidth requirement. As a consequence, the Bandwidth Estimation Algorithm for SF0 follows the steps described below: 1. Collect the New Incoming Bandwidth Requirements from neighbour nodes (NIBR) 2. Obtain the Current Outgoing Bandwidth Usage (COBU) 3. Obtain the number of Current Scheduled Bandwidth (CSB) 4. Calculate the New Outgoing Bandwidth (NOB) as: NOB=COBU+NIBR 5. Calculate the Remaining Available Bandwidth (RAB) as RAB=CSB-NOB Dujovne, et al. Expires September 22, 2016 [Page 3] Internet-Draft 6tisch-6top-sf0 March 2016 6. If the RAB is less than the Minimum Remaining Bandwidth (MRB), Add MRB to the NOB: NOB=NOB+MRB 7. Submit the request to the allocation policy 8. Return to step 1 and wait for a triggering event. 3.3. SF0 Allocation Policy The "Allocation Policy" is the set of rules used by SF0 to decide when to add/delete cells to a particular neighbor to satisfy the bandwidth requirements. SF0 uses the following parameters: SCHEDULEDCELLS: The number of cells scheduled from the current node to a particular neighbor. REQUIREDCELLS: The number of cells calculated by the Bandwidth Estimation Algorithm from the current node to that neighbor. SF0THRESH: Threshold parameter introducing cell over-provisioning in the allocation policy. It is a non-negative value expressed as number of cells. The definition of this value is implementation- specific; however, it is RECOMMENDED a SF0THRESH value of 3 cells. A setting of SF0THRESH>0 will cause the node to allocate at least SF0THRESH cells to each of its' neighbours. The SF0 allocation policy compares REQUIREDCELLS with SCHEDULEDCELLS and decides to add/delete cells taking into account SF0THRESH. This is illustrated in Figure 1. Dujovne, et al. Expires September 22, 2016 [Page 4] Internet-Draft 6tisch-6top-sf0 March 2016 SCHEDULEDCELLS <---------------------------------> +---+---+---+---+---+---+---+---+---+ | | | | | | | | | | +---+---+---+---+---+---+---+---+---+ |<----------------->| | SF0THRESH | | | REQUIREDCELLS | | +---+---+ | | DELETE | | | | | ONE/MORE +---+---+ | | CELLS | | REQUIREDCELLS | +---+---+---+---+---+---+ | DO | | | | | | | | NOTHING +---+---+---+---+---+---+ | | | REQUIREDCELLS | +---+---+---+---+---+---+---+---+---+---+ ADD | | | | | | | | | | | ONE/MORE +---+---+---+---+---+---+---+---+---+---+ CELLS Figure 1: The SF0 Allocation Policy 1. If REQUIREDCELLS<(SCHEDULEDCELLS-SF0THRESH), delete one or more cells. 2. If (SCHEDULEDCELLS-SF0THRESH)<=REQUIREDCELLS<=SCHEDULEDCELLS, do nothing. 3. If SCHEDULEDCELLS<=REQUIREDCELLS, add one or more cells. When SF0THRESH equals 0, any discrepancy between REQUIREDCELLS and SCHEDULEDCELLS triggers an action to add/delete cells. Positive values of SF0THRESH reduce the number of 6P Transactions. The Allocation Policy also translates the bandwidth requirement into cells according to their PDR. For example, if a cell with a 100% PDR is equivalent to 1Kbps, and the required bandwith is 8Kbps, then, the number of scheduled cells will be 8. However, if two of the allocated cells have a 70% PDR, there number of scheduled cells will be 9. 4. Rules for CellList When issuing a 6top ADD Request, SF0 executes the following sequence: Whitelist case: Dujovne, et al. Expires September 22, 2016 [Page 5] Internet-Draft 6tisch-6top-sf0 March 2016 The Transaction Source node: Prepares the CellList field by selecting randomly the required cells, verifying that the slot offset and channel offset are not occupied. The Transaction Destination node: Goes through the cells in the CellList in order, verifying whether there are no slotOffset conflicts. Blacklist case: The Transaction Source node: Prepares the CellList field by building a list of currently scheduled cells into the CellList. The Transaction Destination node: Selects randomly the required cells, verifying that the slot offset and channel offset are not occupied from the ones on the CellList. 5. 6P Timeout Value The 6P Timeout Value provided by SF0 allows the maximum number of TSCH link-layer retries. Given the TSCH parameters for the backoff mechanism, macMinBE and macMaxBE, and the length in seconds of the minimal Slotframe, SM, the timeout value is computed as: timeout = (2^(macMaxBE+1)-2^macMinBE) * SM TODO: Change general timeout to a timeout adapted to the schedule: SF to use the number of slots until the next scheduled cell. 6. Meaning of Metadata Information The Metadata 16-bit field is used as follows: BITS 0-7 [SLOTFRAME] are used to identify the slotframe number BITS 8-14 are RESERVED BIT 15 [WBLIST] is used to indicate that the CellList provided is a Whitelist (value=0) or a Blacklist (value=1). TODO: length of the SlotFrame SHOULD be an integer multiple of the length of the minimal SlotFrame. 7. Node Behavior at Boot In order to define a known state after the node is restarted, a CLEAR command is issued to each of the neighbour nodes to enable a new allocation process. TODO: Temporary cells from a pool for the join process. 8. Relocating Cells SF0 uses Packet Delivery Rate (PDR) statistics to monitor the currently allocated cells for cell re-allocation (by changing their Dujovne, et al. Expires September 22, 2016 [Page 6] Internet-Draft 6tisch-6top-sf0 March 2016 slotOffset and/or channelOffset) when it finds out that the PDR of one or more softcells below 20% of the average PDR. 9. Forced Cell Deletion Policy TODO: When all the cells are scheduled, we need a policy to free cells, for example, under alarm conditions or if a node dissappears from the neighbour list. 10. 6P Error Handling A node implementing SF0 handles a 6P Response depending on the Return Code it contains: RC_SUCCESS: If the number of elements in the CellList is the number of cells specified in the NumCells field of the 6P ALL Request, the operation is complete. The node does not take further action. If the number of elements in the CellList is smaller (possibly 0) than the number of cells specified in the NumCells field of the 6P ALL Request, the neighbor has received the request, but less than NumCells of the cells in the CellList were. In that case, the node MAY retry immediately with a different CellList if the amount of storage space permits, or build a new (random) CellList. RC_ERR_VER: The node MUST NOT retry immediately. The node MAY add the neighbor node on a blacklist. The node MAY retry to contact this neighbor later. RC_ERR_6OFID: The node MUST NOT retry immediately. The node MAY add the neighbor node on a blacklist. The node MAY retry to contact this neighbor later. RC_ERR_NORESOURCES: Wait for a timeout and restart the scheduling process. RC_ERR_BUSY: Issue a RESET command. 11. Examples TODO 12. Implementation Status This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC6982]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was Dujovne, et al. Expires September 22, 2016 [Page 7] Internet-Draft 6tisch-6top-sf0 March 2016 supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to [RFC6982], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". OpenWSN: This specification is implemented in the OpenWSN project [OpenWSN]. The authors of this document are collaborating with the OpenWSN community to gather feedback about the status and performance of the protocols described in this document. Results from that discussion will appear in this section in future revision of this specification. 13. Security Considerations TODO 14. IANA Considerations o IANA_SFID_SF0 15. Acknowledgments Thanks to Kris Pister for his contribution in designing the default Bandwidth Estimation Algorithm. Thanks to Qin Wang and Thomas Watteyne for their support in defining the interaction between SF0 and the 6top sublayer. This work is partially supported by the Fondecyt 1121475 Project, the Inria-Chile "Network Design" group, and the IoT6 European Project (STREP) of the 7th Framework Program (Grant 288445). 16. References 16.1. 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, . Dujovne, et al. Expires September 22, 2016 [Page 8] Internet-Draft 6tisch-6top-sf0 March 2016 [IEEE802154e] 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 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. 16.2. 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, . [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013, . [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-07 (work in progress), March 2016. [I-D.wang-6tisch-6top-sublayer] Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer (6top)", draft-wang-6tisch-6top-sublayer-04 (work in progress), November 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. Authors' Addresses Dujovne, et al. Expires September 22, 2016 [Page 9] Internet-Draft 6tisch-6top-sf0 March 2016 Diego Dujovne (editor) Universidad Diego Portales Escuela de Informatica y Telecomunicaciones Av. Ejercito 441 Santiago, Region Metropolitana Chile Phone: +56 (2) 676-8121 Email: diego.dujovne@mail.udp.cl Luigi Alfredo Grieco Politecnico di Bari Department of Electrical and Information Engineering Via Orabona 4 Bari 70125 Italy Phone: 00390805963911 Email: a.grieco@poliba.it Maria Rita Palattella University of Luxembourg Interdisciplinary Centre for Security, Reliability and Trust 4, rue Alphonse Weicker Luxembourg L-2721 LUXEMBOURG Phone: (+352) 46 66 44 5841 Email: maria-rita.palattella@uni.lu Nicola Accettura University of California Berkeley Berkeley Sensor & Actuator Center 490 Cory Hall Berkeley, California 94720 USA Email: nicola.accettura@eecs.berkeley.edu Dujovne, et al. Expires September 22, 2016 [Page 10]