draft-ietf-6tisch-tsch-05.txt   draft-ietf-6tisch-tsch-06.txt 
6TiSCH T. Watteyne, Ed. 6TiSCH T. Watteyne, Ed.
Internet-Draft Linear Technology Internet-Draft Linear Technology
Intended status: Informational MR. Palattella Intended status: Informational MR. Palattella
Expires: July 12, 2015 University of Luxembourg Expires: September 10, 2015 University of Luxembourg
LA. Grieco LA. Grieco
Politecnico di Bari Politecnico di Bari
January 8, 2015 March 9, 2015
Using IEEE802.15.4e TSCH in an IoT context: Using IEEE802.15.4e TSCH in an IoT context:
Overview, Problem Statement and Goals Overview, Problem Statement and Goals
draft-ietf-6tisch-tsch-05 draft-ietf-6tisch-tsch-06
Abstract Abstract
This document describes the environment, problem statement, and goals This document describes the environment, problem statement, and goals
for using the IEEE802.15.4e TSCH MAC protocol in the context of LLNs. for using the IEEE802.15.4e TSCH MAC protocol in the context of LLNs.
The set of goals enumerated in this document form an initial set The set of goals enumerated in this document form an initial set
only. only.
Status of This Memo Status of This Memo
skipping to change at page 1, line 37 skipping to change at page 1, line 37
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This Internet-Draft will expire on July 12, 2015. This Internet-Draft will expire on September 10, 2015.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. TSCH in the LLN Context . . . . . . . . . . . . . . . . . . . 4
3. TSCH in the LLN Context . . . . . . . . . . . . . . . . . . . 4 3. Problems and Goals . . . . . . . . . . . . . . . . . . . . . 6
4. Problems and Goals . . . . . . . . . . . . . . . . . . . . . 6 3.1. Network Formation . . . . . . . . . . . . . . . . . . . . 6
4.1. Network Formation . . . . . . . . . . . . . . . . . . . . 7 3.2. Network Maintenance . . . . . . . . . . . . . . . . . . . 7
4.2. Network Maintenance . . . . . . . . . . . . . . . . . . . 7 3.3. Multi-Hop Topology . . . . . . . . . . . . . . . . . . . 7
4.3. Multi-Hop Topology . . . . . . . . . . . . . . . . . . . 7 3.4. Routing and Timing Parents . . . . . . . . . . . . . . . 7
4.4. Routing and Timing Parents . . . . . . . . . . . . . . . 8 3.5. Resource Management . . . . . . . . . . . . . . . . . . . 8
4.5. Resource Management . . . . . . . . . . . . . . . . . . . 8 3.6. Dataflow Control . . . . . . . . . . . . . . . . . . . . 8
4.6. Dataflow Control . . . . . . . . . . . . . . . . . . . . 8 3.7. Deterministic Behavior . . . . . . . . . . . . . . . . . 8
4.7. Deterministic Behavior . . . . . . . . . . . . . . . . . 8 3.8. Scheduling Mechanisms . . . . . . . . . . . . . . . . . . 9
4.8. Scheduling Mechanisms . . . . . . . . . . . . . . . . . . 9 3.9. Secure Communication . . . . . . . . . . . . . . . . . . 9
4.9. Secure Communication . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 10
8.3. External Informative References . . . . . . . . . . . . . 12
Appendix A. TSCH Protocol Highlights . . . . . . . . . . . . . . 13 Appendix A. TSCH Protocol Highlights . . . . . . . . . . . . . . 13
A.1. Timeslots . . . . . . . . . . . . . . . . . . . . . . . . 13 A.1. Timeslots . . . . . . . . . . . . . . . . . . . . . . . . 13
A.2. Slotframes . . . . . . . . . . . . . . . . . . . . . . . 14 A.2. Slotframes . . . . . . . . . . . . . . . . . . . . . . . 14
A.3. Node TSCH Schedule . . . . . . . . . . . . . . . . . . . 14 A.3. Node TSCH Schedule . . . . . . . . . . . . . . . . . . . 14
A.4. Cells and Bundles . . . . . . . . . . . . . . . . . . . . 14 A.4. Cells and Bundles . . . . . . . . . . . . . . . . . . . . 14
A.5. Dedicated vs. Shared Cells . . . . . . . . . . . . . . . 15 A.5. Dedicated vs. Shared Cells . . . . . . . . . . . . . . . 15
A.6. Absolute Slot Number . . . . . . . . . . . . . . . . . . 15 A.6. Absolute Slot Number . . . . . . . . . . . . . . . . . . 15
A.7. Channel Hopping . . . . . . . . . . . . . . . . . . . . . 16 A.7. Channel Hopping . . . . . . . . . . . . . . . . . . . . . 16
A.8. Time Synchronization . . . . . . . . . . . . . . . . . . 16 A.8. Time Synchronization . . . . . . . . . . . . . . . . . . 16
A.9. Power Consumption . . . . . . . . . . . . . . . . . . . . 17 A.9. Power Consumption . . . . . . . . . . . . . . . . . . . . 17
A.10. Network TSCH Schedule . . . . . . . . . . . . . . . . . . 17 A.10. Network TSCH Schedule . . . . . . . . . . . . . . . . . . 17
A.11. Join Process . . . . . . . . . . . . . . . . . . . . . . 18 A.11. Join Process . . . . . . . . . . . . . . . . . . . . . . 18
A.12. Information Elements . . . . . . . . . . . . . . . . . . 18 A.12. Information Elements . . . . . . . . . . . . . . . . . . 18
A.13. Extensibility . . . . . . . . . . . . . . . . . . . . . . 18 A.13. Extensibility . . . . . . . . . . . . . . . . . . . . . . 18
Appendix B. TSCH Gotchas . . . . . . . . . . . . . . . . . . . . 19 Appendix B. TSCH Features . . . . . . . . . . . . . . . . . . . 19
B.1. Collision Free Communication . . . . . . . . . . . . . . 19 B.1. Collision Free Communication . . . . . . . . . . . . . . 19
B.2. Multi-Channel vs. Channel Hopping . . . . . . . . . . . . 19 B.2. Multi-Channel vs. Channel Hopping . . . . . . . . . . . . 19
B.3. Cost of (continuous) Synchronization . . . . . . . . . . 19 B.3. Cost of (continuous) Synchronization . . . . . . . . . . 19
B.4. Topology Stability . . . . . . . . . . . . . . . . . . . 20 B.4. Topology Stability . . . . . . . . . . . . . . . . . . . 20
B.5. Multiple Concurrent Slotframes . . . . . . . . . . . . . 20 B.5. Multiple Concurrent Slotframes . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
IEEE802.15.4e [IEEE802154e] was published in 2012 as an amendment to IEEE802.15.4e [IEEE802154e] was published in 2012 as an amendment to
the Medium Access Control (MAC) protocol defined by the the Medium Access Control (MAC) protocol defined by the
IEEE802.15.4-2011 [IEEE802154] standard. IEEE802.15.4e will be IEEE802.15.4-2011 [IEEE802154] standard. IEEE802.15.4e will be
rolled into the next revision of IEEE802.15.4, scheduled to be rolled into the next revision of IEEE802.15.4, scheduled to be
published in 2015. The Timeslotted Channel Hopping (TSCH) mode of published in 2015. The Timeslotted Channel Hopping (TSCH) mode of
IEEE802.15.4e is the object of this document. IEEE802.15.4e is the object of this document.
This document describes the main issues arising from the adoption of This document describes the main issues arising from the adoption of
the IEEE802.15.4e TSCH in the LLN context, following the terminology the IEEE802.15.4e TSCH in the LLN context, following the terminology
defined in [I-D.ietf-6tisch-terminology]. defined in [I-D.ietf-6tisch-terminology]. Appendix A further gives
an overview of the key features of the IEEE802.15.4e Timeslotted
Channel Hopping (TSCH) amendment. Appendix B details features of
IEEE802.15.4e TSCH which might be interesting for the work of the
6TiSCH WG.
TSCH was designed to allow IEEE802.15.4 devices to support a wide TSCH was designed to allow IEEE802.15.4 devices to support a wide
range of applications including, but not limited to, industrial ones range of applications including, but not limited to, industrial ones
[IEEE802154e]. At its core is a medium access technique which uses [IEEE802154e]. At its core is a medium access technique which uses
time synchronization to achieve ultra low-power operation and channel time synchronization to achieve low power operation and channel
hopping to enable high reliability. Synchronization accuracy impacts hopping to enable high reliability. Synchronization accuracy impacts
power consumption, and can vary from micro-seconds to milli-seconds power consumption, and can vary from micro-seconds to milli-seconds
depending on the solution. This is very different from the "legacy" depending on the solution. This is very different from the "legacy"
IEEE802.15.4 MAC protocol, and is therefore better described as a IEEE802.15.4 MAC protocol, and is therefore better described as a
"redesign". TSCH does not amend the physical layer; i.e., it can "redesign". TSCH does not amend the physical layer; i.e., it can
operate on any IEEE802.15.4-compliant hardware. operate on any IEEE802.15.4-compliant hardware.
IEEE802.15.4e is the latest generation of ultra-lower power and IEEE802.15.4e is the latest generation of ultra-lower power and
reliable networking solutions for LLNs. [RFC5673] discusses reliable networking solutions for LLNs. [RFC5673] discusses
industrial applications, and highlights the harsh operating industrial applications, and highlights the harsh operating
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with end-to-end packet delivery ratios over 99.999% with end-to-end packet delivery ratios over 99.999%
[doherty07channel]. [doherty07channel].
IEEE802.15.4e has been designed for low-power constrained devices, IEEE802.15.4e has been designed for low-power constrained devices,
often called "motes". Several terms are used in the IETF to refer to often called "motes". Several terms are used in the IETF to refer to
those devices, including "LLN nodes" [RFC7102] and "constrained those devices, including "LLN nodes" [RFC7102] and "constrained
nodes" [RFC7228]. In this document, we use the generic (and shorter) nodes" [RFC7228]. In this document, we use the generic (and shorter)
term "node", used as a synonym for "LLN node", "constrained node" or term "node", used as a synonym for "LLN node", "constrained node" or
"mote". "mote".
Bringing industrial-like performance into the LLN stack developed by Enabling the LLN protocol stack to operate in industrial environments
Internet of Things (IoT) related IETF working groups such as 6Lo, opens up new application domains for these networks. Sensors
ROLL and CoRE opens up new application domains for these networks. deployed in smart cities [RFC5548] will be able to be installed for
years without needing battery replacement. "Umbrella" networks will
Sensors deployed in smart cities [RFC5548] will be able to be interconnect smart elements from different entities in smart
installed for years without needing battery replacement. "Umbrella" buildings [RFC5867]. Peel-and-stick switches will obsolete the need
networks will interconnect smart elements from different entities in for costly conduits for lighting solutions in smart homes [RFC5826].
smart buildings [RFC5867]. Peel-and-stick switches will obsolete the
need for costly conduits for lighting solutions in smart homes
[RFC5826].
IEEE802.15.4e TSCH focuses on the MAC layer only. This clean IEEE802.15.4e TSCH focuses on the MAC layer only. This clean
layering allows for TSCH to fit under an IPv6 enabled protocol stack layering allows for TSCH to fit under an IPv6 enabled protocol stack
for LLNs, running 6LoWPAN [RFC6282], IPv6 Routing Protocol for Low for LLNs, running 6LoWPAN [RFC6282], IPv6 Routing Protocol for Low
power and Lossy Networks (RPL) [RFC6550] and the Constrained power and Lossy Networks (RPL) [RFC6550] and the Constrained
Application Protocol (CoAP) [RFC7252]. What is missing is a Logical Application Protocol (CoAP) [RFC7252]. What is missing is a
Link Control (LLC) layer between the IP abstraction of a link and the functional entity which is in charge of scheduling TSCH timeslots for
TSCH MAC, which is in charge of scheduling a timeslot for a given frames to be sent on. In this document, we refer to this entity as
packet coming down the stack from the upper layer. the "Logical Link Control" (LLC), bearing in mind that realizations
of this entity can be of different types, including a distributed
protocol or a centralized server in charge of scheduling.
While [IEEE802154e] defines the mechanisms for a TSCH node to While [IEEE802154e] defines the mechanisms for a TSCH node to
communicate, it does not define the policies to build and maintain communicate, it does not define the policies to build and maintain
the communication schedule, match that schedule to the multi-hop the communication schedule, match that schedule to the multi-hop
paths maintained by RPL, adapt the resources allocated between paths maintained by RPL, adapt the resources allocated between
neighbor nodes to the data traffic flows, enforce a differentiated neighbor nodes to the data traffic flows, enforce a differentiated
treatment for data generated at the application layer and signaling treatment for data generated at the application layer and signaling
messages needed by 6LoWPAN and RPL to discover neighbors, react to messages needed by 6LoWPAN and RPL to discover neighbors, react to
topology changes, self-configure IP addresses, or manage keying topology changes, self-configure IP addresses, or manage keying
material. material.
In other words, IEEE802.15.4e TSCH is designed to allow optimizations In other words, IEEE802.15.4e TSCH is designed to allow optimizations
and strong customizations, simplifying the merging of TSCH with a and strong customizations, simplifying the merging of TSCH with a
protocol stack based on IPv6, 6LoWPAN, and RPL. protocol stack based on IPv6, 6LoWPAN, and RPL.
2. Requirements Language 2. TSCH in the LLN Context
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. TSCH in the LLN Context
To map the services required by the IP layer to the services provided To map the services required by the IP layer to the services provided
by the link layer, an adaptation layer is used by the link layer, an adaptation layer is used
[palattella12standardized]. The 6LoWPAN working group started [palattella12standardized]. The 6LoWPAN working group started
working in 2007 on specifications for transmitting IPv6 packets over working in 2007 on specifications for transmitting IPv6 packets over
IEEE802.15.4 networks [RFC4919]. Low-power WPANs are characterized IEEE802.15.4 networks [RFC4919]. Low-power Wireless Personal Area
by small packet sizes, support for addresses with different lengths, Networks (WPANs) typically feature small frame sizes, support for
low bandwidth, star and mesh topologies, battery powered devices, low addresses with different lengths, low bandwidth, star and mesh
cost, large number of devices, unknown node positions, high topologies, battery powered devices, low cost, large number of
unreliability, and periods during which communication interfaces are devices, unknown node positions, high unreliability, and periods
turned off to save energy. Given these features, it is clear that during which communication interfaces are turned off to save energy.
the adoption of IPv6 on top of a Low-Power WPAN is not Given these features, it is clear that the adoption of IPv6 on top of
straightforward, but poses strong requirements for the optimization a Low-Power WPAN is not straightforward, but poses strong
of this adaptation layer. requirements for the optimization of this adaptation layer.
For instance, due to the IPv6 default minimum MTU size (1280 bytes), For instance, due to the IPv6 default minimum MTU size (1280 bytes),
an un-fragmented IPv6 packet is too large to fit in an IEEE802.15.4 an un-fragmented IPv6 packet is too large to fit in an IEEE802.15.4
frame. Moreover, the overhead due to the 40-byte long IPv6 header frame. Moreover, the overhead due to the 40-byte long IPv6 header
wastes the scarce bandwidth available at the PHY layer [RFC4944]. wastes the scarce bandwidth available at the PHY layer [RFC4944].
For these reasons, the 6LoWPAN working group has defined an effective For these reasons, the 6LoWPAN working group has defined an effective
adaptation layer [RFC6282]. Further issues encompass the auto- adaptation layer [RFC6282]. Further issues encompass the auto-
configuration of IPv6 addresses [RFC2460][RFC4862], the compliance configuration of IPv6 addresses [RFC2460][RFC4862], the compliance
with the recommendation on supporting link-layer subnet broadcast in with the recommendation on supporting link-layer subnet broadcast in
shared networks [RFC3819], the reduction of routing and management shared networks [RFC3819], the reduction of routing and management
overhead [RFC6606], the adoption of lightweight application protocols overhead [RFC6606], the adoption of lightweight application protocols
(or novel data encoding techniques), and the support for security (or novel data encoding techniques), and the support for security
mechanisms (confidentiality and integrity protection, device mechanisms (confidentiality and integrity protection, device
bootstrapping, key establishment, and management). bootstrapping, key establishment, and management).
These features can run on top of TSCH. There are, however, important These features can run on top of TSCH. There are, however, important
issues to solve, as highlighted in Section 4. issues to solve, as highlighted in Section 3.
Routing issues are challenging for 6LoWPAN, given the low-power and Routing issues are challenging for 6LoWPAN, given the low-power and
lossy radio links, the battery-powered nodes, the multi-hop mesh lossy radio links, the battery-powered nodes, the multi-hop mesh
topologies, and the frequent topology changes due to mobility. topologies, and the frequent topology changes due to mobility.
Successful solutions take into account the specific application Successful solutions take into account the specific application
requirements, along with IPv6 behavior and 6LoWPAN mechanisms requirements, along with IPv6 behavior and 6LoWPAN mechanisms
[palattella12standardized]. The ROLL working group has defined RPL [palattella12standardized]. The ROLL working group has defined RPL
in [RFC6550]. RPL can support a wide variety of link layers, in [RFC6550]. RPL can support a wide variety of link layers,
including ones that are constrained, potentially lossy, or typically including ones that are constrained, potentially lossy, or typically
utilized in conjunction with host or router devices with very limited utilized in conjunction with host or router devices with very limited
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(P2MP) data streams are used for actuation purposes, where messages (P2MP) data streams are used for actuation purposes, where messages
are sent from DODAG roots to destination nodes. Point-to-Point (P2P) are sent from DODAG roots to destination nodes. Point-to-Point (P2P)
traffic allows communication between two devices belonging to the traffic allows communication between two devices belonging to the
same LLN, such as a sensor and an actuator. A packet flows from the same LLN, such as a sensor and an actuator. A packet flows from the
source to the common ancestor of those two communicating devices, source to the common ancestor of those two communicating devices,
then downward towards the destination. RPL therefore has to discover then downward towards the destination. RPL therefore has to discover
both upward routes (i.e. from nodes to DODAG roots) in order to both upward routes (i.e. from nodes to DODAG roots) in order to
enable MP2P and P2P flows, and downward routes (i.e. from DODAG roots enable MP2P and P2P flows, and downward routes (i.e. from DODAG roots
to nodes) to support P2MP and P2P traffic. to nodes) to support P2MP and P2P traffic.
Section 4 highlights the challenges that need to be addressed to use Section 3 highlights the challenges that need to be addressed to use
RPL on top of TSCH. RPL on top of TSCH.
Several open-source initiatives have emerged around TSCH. The Open-source initiatives have emerged around TSCH, with the OpenWSN
OpenWSN project [OpenWSN][OpenWSNETT] is an open-source project [OpenWSN][OpenWSNETT] being the first open-source
implementation of a standards-based protocol stack, which aims at implementation of a standards-based protocol stack. This
evaluating the applicability of TSCH to different applications. This
implementation was used as the foundation for an IP for Smart Objects implementation was used as the foundation for an IP for Smart Objects
Alliance (IPSO) [IPSO] interoperability event in 2011. In the Alliance (IPSO) [IPSO] interoperability event in 2011. In the
absence of a standardized scheduling mechanism for TSCH, a "slotted absence of a standardized scheduling mechanism for TSCH, a "slotted
Aloha" schedule was used. Aloha" schedule was used.
4. Problems and Goals 3. Problems and Goals
As highlighted in Appendix A, TSCH differs from traditional low-power As highlighted in Appendix A, TSCH differs from other low-power MAC
MAC protocols because of its scheduled nature. TSCH defines the protocols because of its scheduled nature. TSCH defines the
mechanisms to execute a communication schedule, yet it is the entity mechanisms to execute a communication schedule, yet it is the entity
that sets up that schedule which controls the topology of the that sets up that schedule which controls the topology of the
network. This scheduling entity also controls the resources network. This scheduling entity also controls the resources
allocated to each link in that topology. allocated to each link in that topology.
How this entity should operate is out of scope of TSCH. The How this entity should operate is out of scope of TSCH. The
remainder of this section highlights the problems this entity needs remainder of this section highlights the problems this entity needs
to address. For simplicity, we refer to this entity by the generic to address. For simplicity, we refer to this entity by the generic
name "LLC". Note that the 6top sublayer, currently being defined in name "LLC". Note that the 6top sublayer, currently being defined in
[I-D.wang-6tisch-6top-sublayer], can be seen as an embodiment of this [I-D.wang-6tisch-6top-sublayer], can be seen as an embodiment of this
generic "LLC". generic "LLC".
Some of the issues the LLC needs to target might overlap with the Some of the issues the LLC needs to target might overlap with the
scope of other protocols (e.g., 6LoWPAN, RPL, and RSVP). In this scope of other protocols (e.g., 6LoWPAN, RPL, and RSVP). In this
case, it is entailed that the LLC will profit from the services case, it is entailed that the LLC will profit from the services
provided by other protocols to pursue these objectives. provided by other protocols to pursue these objectives.
4.1. Network Formation 3.1. Network Formation
The LLC needs to control the way the network is formed, including how The LLC needs to control the way the network is formed, including how
new nodes join, and how already joined nodes advertise the presence new nodes join, and how already joined nodes advertise the presence
of the network. The LLC needs to: of the network. The LLC needs to:
1. Define the Information Elements included in the Enhanced Beacons 1. Define the Information Elements included in the Enhanced Beacons
advertising the presence of the network. [IEEE802154e] advertising the presence of the network.
2. For a new node, define rules to process and filter received 2. For a new node, define rules to process and filter received
Enhanced Beacons. Enhanced Beacons.
3. Define the joining procedure. This might include a mechanism to 3. Define the joining procedure. This might include a mechanism to
assign a unique 16-bit address to a node, and the management of assign a unique 16-bit address to a node, and the management of
initial keying material. initial keying material.
4. Define a mechanism to secure the joining process and the 4. Define a mechanism to secure the joining process and the
subsequent optional process of scheduling more communication subsequent optional process of scheduling more communication
cells. cells.
4.2. Network Maintenance 3.2. Network Maintenance
Once a network is formed, the LLC needs to maintain the network's Once a network is formed, the LLC needs to maintain the network's
health, allowing for nodes to stay synchronized. The LLC needs to: health, allowing for nodes to stay synchronized. The LLC needs to:
1. Manage each node's time source neighbor. 1. Manage each node's time source neighbor.
2. Define a mechanism for a node to update the join priority it 2. Define a mechanism for a node to update the join priority it
announces in its Enhanced Beacon. announces in its Enhanced Beacon.
3. Schedule transmissions of Enhanced Beacons to advertise the 3. Schedule transmissions of Enhanced Beacons to advertise the
presence of the network. presence of the network.
4.3. Multi-Hop Topology 3.3. Multi-Hop Topology
RPL, given a weighted connectivity graph, determines multi-hop RPL, given a weighted connectivity graph, determines multi-hop
routes. The LLC needs to: routes. The LLC needs to:
1. Define a mechanism to gather topological information, node and 1. Define a mechanism to gather topological information, node and
link state, which it can then feed to RPL. link state, which it can then feed to RPL.
2. Ensure that the TSCH schedule contains cells along the multi-hop 2. Ensure that the TSCH schedule contains cells along the multi-hop
routes identified by RPL. routes identified by RPL (a cell in a TSCH schedule is an atomic
"unit" of resource, see Section 3.5).
3. Where applicable, maintain independent sets of cells to transport 3. Where applicable, maintain independent sets of cells to transport
independent flows of data. independent flows of data.
4.4. Routing and Timing Parents 3.4. Routing and Timing Parents
At all times, a TSCH node needs to have a time source neighbor it can At all times, a TSCH node needs to have a time source neighbor it can
synchronize to. The LLC therefore needs to assign a time source synchronize to. The LLC therefore needs to assign a time source
neighbor to allow for correct operation of the TSCH network. A time neighbor to allow for correct operation of the TSCH network. A time
source neighbors could, or not, be taken from the RPL routing parent source neighbors could, or not, be taken from the RPL routing parent
set. set.
4.5. Resource Management 3.5. Resource Management
A cell in a TSCH schedule is an atomic "unit" of resource. The A cell in a TSCH schedule is an atomic "unit" of resource. The
number of cells to assign between neighbor nodes needs to be number of cells to assign between neighbor nodes needs to be
appropriate for the size of the traffic flow. The LLC needs to: appropriate for the size of the traffic flow. The LLC needs to:
1. Define a mechanism for neighbor nodes to exchange information 1. Define a mechanism for neighbor nodes to exchange information
about their schedule and, if applicable, negotiate the addition/ about their schedule and, if applicable, negotiate the addition/
deletion of cells. deletion of cells.
2. Allow for an entity (e.g., a set of devices, a distributed 2. Allow for an entity (e.g., a set of devices, a distributed
protocol, a PCE, etc.) to take control of the schedule. protocol, a Path Computation Element (PCE), etc.) to take control
of the schedule.
4.6. Dataflow Control 3.6. Dataflow Control
TSCH defines mechanisms for a node to signal it cannot accept an TSCH defines mechanisms for a node to signal it cannot accept an
incoming packet. It does not, however, define the policy which incoming packet. It does not, however, define the policy which
determines when to stop accepting packets. The LLC needs to: determines when to stop accepting packets. The LLC needs to:
1. Define a queuing policy for incoming and outgoing packets. 1. Allow for the implementation and configuration of policy to queue
incoming and outgoing packets.
2. Manage the buffer space, and indicate to TSCH when to stop 2. Manage the buffer space, and indicate to TSCH when to stop
accepting incoming packets. accepting incoming packets.
3. Handle transmissions that have failed. A transmission is 3. Handle transmissions that have failed. A transmission is
declared failed when TSCH has retransmitted the packet multiple declared failed when TSCH has retransmitted the packet multiple
times, without receiving an acknowledgment. This covers both times, without receiving an acknowledgment. This covers both
dedicated and shared cells. dedicated and shared cells.
4.7. Deterministic Behavior 3.7. Deterministic Behavior
As highlighted in [RFC5673], in some applications, data is generated As highlighted in [RFC5673], in some applications, data is generated
periodically and has a well understood data bandwidth requirement, periodically and has a well understood data bandwidth requirement,
which is deterministic and predictable. The LLC needs to: which is deterministic and predictable. The LLC needs to:
1. Ensure timely delivery of such data. 1. Ensure that the data is delivered to its final destination before
a deadline possibly determined by the application.
2. Provide a mechanism for such deterministic flows to coexist with 2. Provide a mechanism for such deterministic flows to coexist with
bursty or infrequent traffic flows of different priorities. bursty or infrequent traffic flows of different priorities.
4.8. Scheduling Mechanisms 3.8. Scheduling Mechanisms
Several scheduling mechanisms can be envisioned, and possibly coexist Several scheduling mechanisms can be envisioned, and possibly coexist
in the same network. For example, in the same network. For example,
[I-D.phinney-roll-rpl-industrial-applicability] describes how the [I-D.phinney-roll-rpl-industrial-applicability] describes how the
allocation of bandwidth can be optimized by an external Path allocation of bandwidth can be optimized by an external Path
Computation Element (PCE). Another centralized (PCE-based) traffic- Computation Element (PCE) [RFC4655]. Another centralized (PCE-based)
aware scheduling algorithm is defined in [TASA-PIMRC]. traffic-aware scheduling algorithm is defined in [TASA-PIMRC].
Alternatively, two neighbor nodes can adapt the number of cells Alternatively, two neighbor nodes can adapt the number of cells
autonomously by monitoring the amount of traffic, and negotiating the autonomously by monitoring the amount of traffic, and negotiating the
allocation to extra cell when needed. An example of decentralized allocation to extra cell when needed. An example of decentralized
algorithm is provided in [tinka10decentralized]. This mechanism can algorithm (i.e. no PCE is needed) is provided in
be used to establish multi-hop paths in a fashion similar to RSVP. [tinka10decentralized]. This mechanism can be used to establish
The LLC needs to: multi-hop paths in a fashion similar to RSVP [RFC2205]. The LLC
needs to:
1. Provide a mechanism for two 6TiSCH devices to negotiate the 1. Provide a mechanism for two devices to negotiate the allocation
allocation and deallocation of cells between them. and deallocation of cells between them.
2. Provide a mechanism for device to monitor and manage the 6TiSCH 2. Provide a mechanism for device to monitor and manage the
capabilities of a node several hops away. capabilities of a node several hops away.
3. Define an mechanism for these different scheduling mechanisms to 3. Define an mechanism for these different scheduling mechanisms to
coexist in the same network. coexist in the same network.
4.9. Secure Communication 3.9. Secure Communication
Given some keying material, TSCH defines mechanisms to encrypt and Given some keying material, TSCH defines mechanisms to encrypt and
authenticate MAC frames. It does not define how this keying material authenticate MAC frames. It does not define how this keying material
is generated. The LLC needs to: is generated. The LLC needs to:
1. Define the keying material and authentication mechanism needed by 1. Define the keying material and authentication mechanism needed by
a new node to join an existing network. a new node to join an existing network.
2. Define a mechanism to allow for the secure transfer of 2. Define a mechanism to allow for the secure transfer of
application data between neighbor nodes. application data between neighbor nodes.
3. Define a mechanism to allow for the secure transfer of signaling 3. Define a mechanism to allow for the secure transfer of signaling
data between nodes and the LLC. data between nodes and the LLC.
5. IANA Considerations 4. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
6. Security Considerations 5. Security Considerations
This memo is an informational overview of existing standards, and This memo is an informational overview of existing standards, and
does define any new mechanisms or protocols. does not define any new mechanisms or protocols.
It does describe the need for the 6TiSCH WG to define a secure It does describe the need for the 6TiSCH WG to define a secure
solution. In particular, Section 4.1 describes security in the join solution. In particular, Section 3.1 describes security in the join
process. Section 4.9 discusses data frame protection. process. Section 3.9 discusses data frame protection.
7. Acknowledgments 6. Acknowledgments
Special thanks to Dominique Barthel, Patricia Brett, Guillaume Special thanks to Dominique Barthel, Patricia Brett, Guillaume
Gaillard, Pat Kinney, Ines Robles, Timothy J. Salo, Jonathan Simon, Gaillard, Pat Kinney, Ines Robles, Timothy J. Salo, Jonathan Simon,
Rene Struik, Xavi Vilajosana for reviewing the document and providing Rene Struik, Xavi Vilajosana for reviewing the document and providing
valuable feedback. Thanks to the IoT6 European Project (STREP) of valuable feedback. Thanks to the IoT6 European Project (STREP) of
the 7th Framework Program (Grant 288445). the 7th Framework Program (Grant 288445).
8. References 7. References
8.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [IEEE802154e]
Requirement Levels", BCP 14, RFC 2119, March 1997. 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.
8.2. Informative References [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.
7.2. Informative References
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014. Application Protocol (CoAP)", RFC 7252, June 2014.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, May 2014. Constrained-Node Networks", RFC 7228, May 2014.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, January 2014. Lossy Networks", RFC 7102, January 2014.
skipping to change at page 11, line 29 skipping to change at page 11, line 42
Networks", RFC 4944, September 2007. Networks", RFC 4944, September 2007.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs): over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals", RFC Overview, Assumptions, Problem Statement, and Goals", RFC
4919, August 2007. 4919, August 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. Address Autoconfiguration", RFC 4862, September 2007.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89, Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004. RFC 3819, July 2004.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[I-D.ietf-6tisch-terminology] [I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE "Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-02 (work in 802.15.4e", draft-ietf-6tisch-terminology-03 (work in
progress), July 2014. progress), January 2015.
[I-D.wang-6tisch-6top-sublayer] [I-D.wang-6tisch-6top-sublayer]
Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH
Operation Sublayer (6top)", draft-wang-6tisch-6top- Operation Sublayer (6top)", draft-wang-6tisch-6top-
sublayer-01 (work in progress), July 2014. sublayer-01 (work in progress), July 2014.
[I-D.phinney-roll-rpl-industrial-applicability] [I-D.phinney-roll-rpl-industrial-applicability]
Phinney, T., Thubert, P., and R. Assimiti, "RPL Phinney, T., Thubert, P., and R. Assimiti, "RPL
applicability in industrial networks", draft-phinney-roll- applicability in industrial networks", draft-phinney-roll-
rpl-industrial-applicability-02 (work in progress), rpl-industrial-applicability-02 (work in progress),
February 2013. February 2013.
8.3. External Informative References
[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.
[OpenWSN] "Berkeley's OpenWSN Project Homepage", [OpenWSN] "Berkeley's OpenWSN Project Homepage",
<http://www.openwsn.org/>. <http://www.openwsn.org/>.
[OpenWSNETT] [OpenWSNETT]
Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F., Watteyne, T., Vilajosana, X., Kerkez, B., Chraim, F.,
Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN: Weekly, K., Wang, Q., Glaser, S., and K. Pister, "OpenWSN:
a Standards-Based Low-Power Wireless Development a Standards-Based Low-Power Wireless Development
Environment", Transactions on Emerging Telecommunications Environment", Transactions on Emerging Telecommunications
Technologies , August 2012. Technologies , August 2012.
[IPSO] "IP for Smart Objects Alliance Homepage", [IPSO] "IP for Smart Objects Alliance Homepage",
<http://www.ipso-alliance.org/>. <http://www.ipso-alliance.org/>.
[CurrentCalculator] [CurrentCalculator]
Linear Technology, "Application Note: Using the Current Linear Technology, "Application Note: Using the Current
Calculator to Estimate Mote Power", August 2012, Calculator to Estimate Mote Power", August 2012,
<http://cds.linear.com/docs/en/application-note/ <http://www.linear.com/docs/42452>.
Application_Note_-
_Using_the_Current_Calculator_to_Estimate_Mote_Power.pdf>.
[doherty07channel] [doherty07channel]
Doherty, L., Lindsay, W., and J. Simon, "Channel-Specific Doherty, L., Lindsay, W., and J. Simon, "Channel-Specific
Wireless Sensor Network Path Data", IEEE International Wireless Sensor Network Path Data", IEEE International
Conference on Computer Communications and Networks (ICCCN) Conference on Computer Communications and Networks (ICCCN)
2008, 2007. 2008, 2007.
[tinka10decentralized] [tinka10decentralized]
Tinka, A., Watteyne, T., and K. Pister, "A Decentralized Tinka, A., Watteyne, T., and K. Pister, "A Decentralized
Scheduling Algorithm for Time Synchronized Channel Scheduling Algorithm for Time Synchronized Channel
Hopping", Ad Hoc Networks 2010, 2010, < Hopping", Ad Hoc Networks 2010, 2010.
http://robotics.eecs.berkeley.edu/~pister/
publications/2008/TSMP%20DSN08.pdf>.
[watteyne09reliability] [watteyne09reliability]
Watteyne, T., Mehta, A., and K. Pister, "Reliability Watteyne, T., Mehta, A., and K. Pister, "Reliability
Through Frequency Diversity: Why Channel Hopping Makes Through Frequency Diversity: Why Channel Hopping Makes
Sense", International Conference on Performance Evaluation Sense", International Conference on Performance Evaluation
of Wireless Ad Hoc, Sensor, and Ubiquitous Networks (PE- of Wireless Ad Hoc, Sensor, and Ubiquitous Networks (PE-
WASUN) 2009, Oct. 2009, <http://www.ietf.org/mail- WASUN) 2009, Oct. 2009.
archive/web/roll/current/pdfa_EzmuDIv3.pdf>.
[TASA-PIMRC] [TASA-PIMRC]
Palattella, MR., Accettura, N., Dohler, M., Grieco, LA., Palattella, MR., Accettura, N., Dohler, M., Grieco, LA.,
and G. Boggia, "Traffic Aware Scheduling Algorithm for and G. Boggia, "Traffic Aware Scheduling Algorithm for
Multi-Hop IEEE 802.15.4e Networks", IEEE PIMRC 2012, Sept. Multi-Hop IEEE 802.15.4e Networks", IEEE PIMRC 2012, Sept.
2012, < http://www.cttc.es/resources/ 2012.
doc/120531-submitted-tasa-25511.pdf>.
[palattella12standardized] [palattella12standardized]
Palattella, MR., Accettura, N., Vilajosana, X., Watteyne, Palattella, MR., Accettura, N., Vilajosana, X., Watteyne,
T., Grieco, LA., Boggia, G., and M. Dohler, "Standardized T., Grieco, LA., Boggia, G., and M. Dohler, "Standardized
Protocol Stack For The Internet Of (Important) Things", Protocol Stack For The Internet Of (Important) Things",
IEEE Communications Surveys and Tutorials 2012, Dec. 2012, IEEE Communications Surveys and Tutorials 2012, Dec. 2012.
< http://www.cttc.es/resources/doc/121025-
completestackforiot-clean-4818610916636121981.pdf>.
Appendix A. TSCH Protocol Highlights Appendix A. TSCH Protocol Highlights
This appendix gives an overview of the key features of the This appendix gives an overview of the key features of the
IEEE802.15.4e Timeslotted Channel Hopping (TSCH) amendment. It makes IEEE802.15.4e Timeslotted Channel Hopping (TSCH) amendment. It makes
no attempt at repeating the standard, but rather focuses on the no attempt at repeating the standard, but rather focuses on the
following: following:
o Concepts which are sufficiently different from traditional o Concepts which are sufficiently different from other IEEE802.15.4
IEEE802.15.4 networking that they may need to be defined and networking that they may need to be defined and presented
presented precisely. precisely.
o Techniques and ideas which are part of IEEE802.15.4e and which o Techniques and ideas which are part of IEEE802.15.4e and which
might be useful for the work of the 6TiSCH WG. might be useful for the work of the 6TiSCH WG.
A.1. Timeslots A.1. Timeslots
All nodes in a TSCH network are synchronized. Time is sliced up into All nodes in a TSCH network are synchronized. Time is sliced up into
timeslots. A timeslot is long enough for a MAC frame of maximum size timeslots. A timeslot is long enough for a MAC frame of maximum size
to be sent from node A to node B, and for node B to reply with an to be sent from node A to node B, and for node B to reply with an
acknowledgment (ACK) frame indicating successful reception. acknowledgment (ACK) frame indicating successful reception.
skipping to change at page 19, line 8 skipping to change at page 19, line 8
A.13. Extensibility A.13. Extensibility
The TSCH standard is designed to be extensible. It introduces the The TSCH standard is designed to be extensible. It introduces the
mechanisms as "building block" (e.g., cells, bundles, slotframes, mechanisms as "building block" (e.g., cells, bundles, slotframes,
etc.), but leaves entire freedom to the upper layer to assemble etc.), but leaves entire freedom to the upper layer to assemble
those. The MAC protocol can be extended by defining new Header IEs. those. The MAC protocol can be extended by defining new Header IEs.
An intermediate layer can be defined to manage the MAC layer by An intermediate layer can be defined to manage the MAC layer by
defining new Payload IEs. defining new Payload IEs.
Appendix B. TSCH Gotchas Appendix B. TSCH Features
This section lists features of TSCH which we believe are important This section details features of IEEE802.15.4e TSCH which might be
and beneficial to the work of 6TiSCH. interesting for the work of the 6TiSCH WG. It does not define any
requirements.
B.1. Collision Free Communication B.1. Collision Free Communication
TSCH allows one to design a schedule which yields collision-free TSCH allows one to design a schedule which yields collision-free
communication. This is done by building the schedule with dedicated communication. This is done by building the schedule with dedicated
cells in such a way that at most one node communicates with a cells in such a way that at most one node communicates with a
specific neighbor in each slotOffset/channelOffset cell. Multiple specific neighbor in each slotOffset/channelOffset cell. Multiple
pairs of neighbor nodes can exchange data at the same time, but on pairs of neighbor nodes can exchange data at the same time, but on
different frequencies. different frequencies.
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