Internet DRAFT - draft-dujovne-6tisch-6top-sf0
draft-dujovne-6tisch-6top-sf0
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
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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
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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).
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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
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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.
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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:
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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
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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
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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,
<http://www.rfc-editor.org/info/rfc2119>.
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[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,
<http://www.rfc-editor.org/info/rfc7554>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
DOI 10.17487/RFC6982, July 2013,
<http://www.rfc-editor.org/info/rfc6982>.
[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
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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
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