One document matched: draft-ietf-6tisch-architecture-08.xml
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<front>
<title abbrev="6tisch-architecture">An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4</title>
<author initials="P" surname="Thubert" fullname="Pascal Thubert" role="editor">
<organization abbrev="Cisco">Cisco Systems, Inc</organization>
<address>
<postal>
<street>Building D</street>
<street>45 Allee des Ormes - BP1200 </street>
<city>MOUGINS - Sophia Antipolis</city>
<code>06254</code>
<country>FRANCE</country>
</postal>
<phone>+33 497 23 26 34</phone>
<email>pthubert@cisco.com</email>
</address>
</author>
<!--
<author initials="T" surname="Watteyne" fullname="Thomas Watteyne">
<organization abbrev="Linear Technology">Linear Technology, Dust Networks Product Group</organization>
<address>
<postal>
<street>30695 Huntwood Avenue</street>
<city>Hayward</city>
<region>CA</region>
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<country>USA</country>
</postal>
<phone>+1 (510) 400-2978</phone>
<email>twatteyne@linear.com</email>
</address>
</author>
<author fullname="Rene Struik" initials="R" surname="Struik">
<organization abbrev="Struik Security Consultancy">Struik Security Consultancy</organization>
<address>
<email>rstruik.ext@gmail.com</email>
</address>
</author>
<author initials="M." surname="Richardson" fullname="Michael C. Richardson">
<organization abbrev="SSW">Sandelman Software Works</organization>
<address>
<postal>
<street>470 Dawson Avenue</street>
<city>Ottawa</city>
<region>ON</region>
<code>K1Z 5V7</code>
<country>CA</country>
</postal>
<email>mcr+ietf@sandelman.ca</email>
<uri>http://www.sandelman.ca/</uri>
</address>
</author>
<author initials="X" surname="Vilajosana" fullname="Xavier Vilajosana" >
<organization>Universitat Oberta de Catalunya</organization>
<address>
<postal>
<street>156 Rambla Poblenou</street>
<city>Barcelona</city>
<region>Catalonia</region>
<code>08018</code>
<country>Spain</country>
</postal>
<phone>+34 (646) 633 681</phone>
<email>xvilajosana@uoc.edu</email>
</address>
</author-->
<!--author initials="Q" surname="Wang" fullname="Qin Wang" role="editor">
<organization>Univ. of Sci. and Tech. Beijing </organization>
<address>
<postal>
<street>30 Xueyuan Road</street>
<city>Beijing</city>
<region>Hebei</region>
<code>100083</code>
<country>China</country>
</postal>
<phone>+86 (10) 6233 4781</phone>
<email>wangqin@ies.ustb.edu.cn</email>
</address>
</author-->
<!--author initials="RA" surname="Assimiti" fullname="Robert Assimiti">
<organization abbrev="Centero">Centero</organization>
<address>
<postal>
<street>961 Indian Hills Parkway</street>
<city>Marietta</city>
<region>GA</region>
<code>30068</code>
<country>USA</country>
</postal>
<phone>+1 404 461 9614</phone>
<email>robert.assimiti@centerotech.com</email>
</address>
</author-->
<date/>
<area>Internet Area</area>
<workgroup>6TiSCH</workgroup>
<keyword>Draft</keyword>
<abstract>
<t>
This document is the first volume of the 6TiSCH architecture of an IPv6
Multi-Link subnet that is composed of a high speed powered backbone and
a number of IEEE802.15.4 TSCH low-power wireless networks attached and
synchronized by Backbone Routers. The architecture defines mechanisms
to establish and maintain routing and scheduling in a centralized,
distributed, or mixed fashion.
<!--
Backbone Routers perform proxy Neighbor Discovery operations over
the backbone on behalf of the wireless devices, so they can share a same
subnet and appear to be connected to the same backbone as classical devices.
-->
</t>
</abstract>
<!--note title="Requirements Language">
<t>
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 <xref target="RFC2119">RFC 2119</xref>.
</t>
</note-->
</front>
<middle>
<section title="Introduction">
<t>
The emergence of wireless technology has enabled a variety of new
devices to get interconnected, at a very low marginal cost per device,
at any distance ranging from Near Field to interplanetary, and in
circumstances where wiring may not be practical, for instance
on fast-moving or rotating devices.
</t>
<t>
At the same time, a new breed of Time Sensitive Networks is being
developed to enable traffic that is highly sensitive to jitter,
quite sensitive to latency, and with a high degree of operational
criticality so that loss should be minimized at all times.
Such traffic is not limited to professional Audio/ Video networks, but
is also found in command and control operations such as industrial
automation and vehicular sensors and actuators.
At IEEE802.1, the <xref target="IEEE802.1TSNTG">Audio/Video Task Group
</xref>
Time Sensitive Networking (TSN) to address Deterministic Ethernet.
The Medium access Control (MAC) of IEEE802.15.4
<xref target="IEEE802154"/> has evolved with the new
<xref target="I-D.ietf-6tisch-tsch">
IEEE802.15.4e TimeSlotted Channel Hopping (TSCH)</xref> mode
for deterministic industrial-type applications. TSCH was introduced
with the IEEE802.15.4e <xref target="IEEE802154e"/> amendment and will
be wrapped up in the next revision of the IEEE802.15.4 standard.
For all practical purpose, this document
is expected to be insensitive to the future versions of
the IEEE802.15.4 standard, which is thus referenced undated.
</t>
<t>
Though at a different time scale, both TSN and TSCH standards provide
Deterministic capabilities to the point that a packet that pertains
to a certain flow crosses the network from node to node following
a very precise schedule, as a train that leaves intermediate stations
at precise times along its path. With TSCH, time is formatted into
timeSlots, and an individual cell is allocated to unicast or
broadcast communication at the MAC level. The time-slotted operation
reduces collisions, saves energy, and enables to more closely engineer
the network for deterministic properties.
The channel hopping aspect is a simple and efficient technique to combat
multipath fading and external interference (for example by Wi-Fi emitters).
</t>
<t>
This document is the first volume of an architecture for an
IPv6 Multi-Link subnet
that is composed of a high speed powered backbone and a number of
IEEE802.15.4 TSCH wireless networks attached and synchronized by
backbone routers. Route Computation may be achieved in a centralized
fashion by a Path Computation Element (PCE) <xref target="PCE"/>, in a
distributed fashion using the <xref target="RFC6550">
Routing Protocol for Low Power and Lossy Networks (RPL)</xref>, or
in a mixed mode. The Backbone Routers may perform proxy
<xref target="RFC4861">IPv6 Neighbor Discovery (ND)</xref> operations
over the backbone on behalf of the wireless devices (also called motes),
so they can share a same IPv6 subnet and appear to be
connected to the same backbone as classical devices. The Backbone
Routers may alternatively redistribute the registration in a routing
protocol such as <xref target="RFC5340">OSPF</xref> or
<xref target="RFC2545">BGP</xref>, or inject them in a mobility
protocol such as <xref target="RFC6275">MIPv6</xref>,
<xref target="RFC3963">NEMO</xref>, or
<xref target="RFC6830">LISP</xref>.
</t>
<t>The 6TiSCH architecture defines four ways a schedule can be managed
and TimeSlots can be allocated: Static Scheduling, neighbor-to-neighbor
Scheduling, remote monitoring and scheduling management, and Hop-by-hop
scheduling. In the case of remote monitoring and scheduling management,
TimeSlots and other device resources are managed by an abstract Network
Management Entity (NME), which may cooperate with the PCE in order to
minimize the interaction with and the load on the constrained device.
</t>
<t>
The 6TiSCH architecture supports three different forwarding models,
G-MPLS Track Forwarding, which switches a frame received at a particular
TimeSlot into another TimeStot at Layer-2,
6LoWPAN Fragment Forwarding, which allows to forward individual 6loWPAN
fragments along the route set by the first fragment, and classical IPv6
Forwarding, where the node selects a feasible successor at Layer-3 on
a per packet basis, based on its routing table.
</t>
</section>
<section title="Terminology">
<t>
Readers are expected to be familiar with all the terms and concepts
that are discussed in <xref target="RFC4861">"Neighbor Discovery for
IP version 6"</xref>, <xref target="RFC4919">"IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions,
Problem Statement, and Goals"</xref>,
<xref target="RFC6775">Neighbor Discovery Optimization
for Low-power and Lossy Networks</xref> where the 6LoWPAN Router
(6LR) and the 6LoWPAN Border Router (6LBR) are introduced, and
<xref target="I-D.ietf-ipv6-multilink-subnets">
"Multi-link Subnet Support in IPv6"</xref>.
</t>
<t>
Readers may benefit from reading the <xref target="RFC6550"> "RPL:
IPv6 Routing Protocol for Low-Power and Lossy Networks" </xref> specification;
<xref target="RFC4903">"Multi-Link Subnet Issues"</xref>;
<xref target="RFC6275"> "Mobility Support in IPv6" </xref>;
<xref target="RFC4389"> "Neighbor Discovery Proxies (ND Proxy)" </xref>;
<xref target="RFC4862">"IPv6 Stateless Address Autoconfiguration"</xref>;
<xref target="RFC6620">"FCFS SAVI: First-Come, First-Served Source
Address Validation Improvement for Locally Assigned IPv6 Addresses"</xref>; and
<xref target="RFC4429">"Optimistic Duplicate Address Detection"</xref>
prior to this specification for a clear understanding of the art in ND-proxying and binding.
</t>
<t>
The draft uses terminology defined or referenced in
<xref target="I-D.ietf-6tisch-terminology"/>,
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>,
<xref target="I-D.ietf-roll-rpl-industrial-applicability"/>,
<xref target="RFC4080"/>, and <xref target="RFC5191"/>.
</t>
<t>
The draft also conforms to the terms and models described in
<xref target="RFC3444"/> and <xref target="RFC5889"/> and uses the vocabulary and the concepts
defined in <xref target="RFC4291"/> for the IPv6 Architecture.
</t>
</section>
<section title="Applications and Goals">
<t>
Some aspects of this architecture derive from existing industrial
standards for Process Control such as ISA100.11a
<xref target="ISA100.11a"/>and WirelessHART
<xref target="WirelessHART"/>,
by its focus on Deterministic Networking,
in particular with the use of the IEEE802.15.4
TSCH MAC and a centralized PCE.
This approach leverages the TSCH MAC benefits for high reliability
against interference, low-power consumption on deterministic traffic,
and its Traffic Engineering capabilities. In such applications,
Deterministic Networking applies mainly to control loops and
movement detection, but it can also be used for supervisory control
flows and management.
</t>
<t>
An incremental set of industrial requirements is addressed with the addition of an
autonomic and distributed routing operation based on RPL. These use-cases include
plant setup and decommissioning, as well as monitoring of lots of lesser
importance measurements such as corrosion and events.
RPL also enables mobile use cases such as mobile workers and cranes, as
discussed in
<xref target="I-D.ietf-roll-rpl-industrial-applicability"/>.
</t>
<t>
A Backbone Router is included in order to scale the factory plant subnet to address
large deployments, with proxy ND and time synchronization over a high speed backbone.
</t>
<t>
The architecture also applies to building automation that leverage RPL's storing
mode to address multipath over a large number of hops, in-vehicle command and control
that can be as demanding as industrial applications, commercial automation and asset
Tracking with mobile scenarios, home automation and domotics which become more reliable
and thus provide a better user experience, and resource management (energy, water, etc.).
</t>
</section>
<section title="Overview">
<t>
The scope of the present work is a subnet that, in its basic
configuration, is made of a
<xref target="I-D.ietf-6tisch-tsch">TSCH</xref>
MAC Low Power Lossy Network (LLN).
</t>
<t>
<figure anchor="fig1" title="Basic Configuration of a 6TiSCH Network">
<artwork><![CDATA[
---+-------- ............ ------------
| External Network |
| +-----+
+-----+ | NME |
| | LLN Border | |
| | router +-----+
+-----+
o o o
o o o o
o o LLN o o o
o o o o
o
]]></artwork>
</figure>
</t>
<t>Security aspects of the join process by which a device obtains access
to the network are discussed in <xref target="sec"/>.
With TSCH, devices are time-synchronized at the MAC level. The use of
a particular RPL Instance for time synchronization is discussed in
<xref target="sync"/>. With this mechanism, the time synchronization
starts at the RPL root and follows the RPL DODAGs with no timing loop.
</t>
<t>
The LLN devices communicate over IPv6 <xref target="RFC2460"/>
using the <xref target="RFC6282">6LoWPAN Header Compression (
6LoWPAN HC)</xref>.
From the perspective of Layer-3, a single LLN interface
(typically an IEEE802.15.4-compliant radio) may be seen as a collection
of Links with different capabilities for unicast or multicast services.
An IPv6 subnet spans over multiple links, effectively forming a
Multi-Link subnet.
Within that subnet, neighbor devices are discovered with
<xref target="RFC6775"> 6LoWPAN Neighbor Discovery</xref> (6LoWPAN ND).
<xref target="RFC6550">RPL</xref> enables routing within the LLN,
in the so called Route Over fashion, either in storing (stateful) or
non-storing (stateless, with routing headers) mode.
</t>
<t>
RPL forms Destination Oriented
Directed Acyclic Graphs (DODAGs) within Instances of the protocol,
each Instance being associated with an Objective Function (OF) to
form a routing topology. A particular LLN device, the LLN Border Router
(LBR), acts as RPL root, 6LoWPAN HC terminator, and Border Router
for the LLN to the outside. The LBR is usually powered.
More on RPL Instances can be found in section 3.1 of
<xref target="RFC6550">RPL</xref>, in particular
"3.1.2. RPL Identifiers" and
"3.1.3. Instances, DODAGs, and DODAG Versions".
</t> <t>
This architecture expects that a 6LoWPAN node can connect as a
leaf to a RPL network, where the leaf support is the minimal
functionality to connect as a host to a RPL network without the need to
participate to the full routing protocol.
The architecture also expects that a 6LoWPAN node that is not aware
at all of the RPL protocol may also connect as a host. The derived
requirements are listed in
<xref target="I-D.thubert-6lo-rfc6775-update-reqs"/>.
</t>
<t>
An extended configuration of the subnet comprises multiple LLNs.
The LLNs are interconnected and synchronized over a backbone, that
can be wired or wireless. The backbone can be a classical IPv6
network, with Neighbor Discovery operating as defined in
<xref target="RFC4861"/> and <xref target="RFC4862"/>.
This architecture requires new work to standardize the
the registration of 6LoWPAN nodes to the Backbone Routers.
</t>
<t>
In the extended configuration, a Backbone Router (6BBR) acts
as an Energy Aware Default Router (NEAR) as defined in
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>.
The 6BBR performs ND proxy operations between the registered devices
and the classical ND devices that are located over the backbone.
6TiSCH 6BBRs synchronize with one another over the backbone, so as
to ensure that the multiple LLNs that form the IPv6 subnet stay
tightly synchronized.
</t>
<t>
<figure anchor="fig2" title="Extended Configuration of a 6TiSCH Network">
<artwork><![CDATA[
---+-------- ............ ------------
| External Network |
| +-----+
| +-----+ | NME |
+-----+ | +-----+ | |
| | Router | | PCE | +-----+
| | +--| |
+-----+ +-----+
| |
| Subnet Backbone |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o o
o o o o o o o o o o o
o o o LLN o o o o
o o o o o o o o o o o o
]]></artwork>
</figure>
</t>
<t>
In order to serve nodes that are multiple hops away, an integrated RPL
root and 6LBR may be collocated with the 6BBR, or attached to the 6BBR
in which case they would perform the registration on behalf of the
remote LLN nodes - they proxy the efficient ND registration over the LLN
in order for the 6BBR to perform proxy ND operations over the backbone.
</t>
<t>
If the Backbone is Deterministic (such as
defined by the Time Sensitive Networking WG at IEEE), then the
Backbone Router ensures that the end-to-end deterministic
behavior is maintained between the LLN and the backbone. The
<xref target="I-D.finn-detnet-architecture">DetNet Architecture</xref>
studies Layer-3 aspects of Deterministic Networks, and covers networks
that span multiple Layer-2 domains.
</t>
</section>
<section title="Scope">
<section title="Components">
<t>In order to control the complexity and the size of the 6TiSCH work,
the architecture and the associated IETF work are staged in volumes.
This document covers the first stage of the work, as specified by the
WG charter.
If the work continues as expected, further volumes will complete this
piece and provide the full coverage of IPv6 over TSCH.
</t>
<t>
The main architectural blocks are represented below to help detail what is
covered and what is not yet covered from the global 6TiSCH architecture
by this initial volume:
</t>
<t>
<figure anchor="fig4" title="Envisioned 6TiSCH protocol stack">
<artwork><![CDATA[
+-----+-----+
| PCEP|TEAS/|
| PCE |CCAMP|
+-----+-----+-----+-----+-------+-----+
| (COMI) |PANA |6LoWPAN| RPL |
| CoAP / DTLS | | ND | |
+-----+-----+-----+-----+-------+-----+
| UDP | ICMP |
+-----+-----+-----+-----+-------+-----+-----+
| IPv6 |
+-------------------------------------------+
| 6LoWPAN adaptation and compression (HC) |
+-------------------------------------------+
| 6top |
+-------------------------------------------+
| IEEE802.15.4 TSCH |
+-------------------------------------------+
]]></artwork>
</figure>
</t>
<t>
RPL is the routing protocol of choice for LLNs. So far, there was no
identified need to define a 6TiSCH specific Objective Function.
The <xref target="I-D.ietf-6tisch-minimal">Minimal 6TiSCH Configuration
</xref> describes the operation of RPL over a static schedule used in
a slotted aloha fashion, whereby all active slots may be used for
emission or reception of both unicast and multicast frames.
</t>
<t>
The architecture of the operation of RPL over a dynamic schedule is
deferred to a subsequent volume of the architecture.
</t>
<t>
<!--The COMAN list is working on network Management for LLN.
They are considering the Open Mobile Alliance (OMA) Lightweight M2M (LWM2M) Object system.
This standard includes DTLS, CoAP (core plus Block and Observe patterns),
SenML and CoAP Resource Directory.-->
6TiSCH has adopted the general direction of
<xref target="I-D.vanderstok-core-comi">
CoAP Management Interface (COMI)</xref> for the management of devices.
This is leveraged for instance for the implementation of the generic
data model for the 6top sublayer management interface
<xref target="I-D.ietf-6tisch-6top-interface"/>.
The proposed implementation is based on CoAP and CBOR,
and specified in <xref target="I-D.ietf-6tisch-coap">
6TiSCH Resource Management and Interaction using CoAP</xref>.
</t>
<t>
The work on centralized track computation is deferred to a subsequent volume
of the architecture. The Path Computation Element (PCE) is certainly
the core component of that architecture. Around the PCE, a protocol
such as an extension to a TEAS <xref target="TEAS"/> protocol
(maybe running over CoAP as illustrated) will be required to expose the
device capabilities and the network peers to the PCE, and a protocol
such as a lightweight PCEP or an adaptation of CCAMP <xref target="CCAMP"/>
G-MPLS formats and procedures will be used to publish the tracks,
computed by the PCE, to the devices (maybe in a fashion similar to RSVP-TE).
</t>
<t>
The selection of an authentication, an authorization and a Transport
layer security protocols are out of scope for this volume.
</t>
<t>
The <xref target="RFC6347">Datagram Transport Layer Security (DTLS)
</xref> is represented as an example of a protocol that could be used
to protect CoAP datagrams, and work at <xref target="DICE"/> may
optimize the protocol for constrained devices.
</t>
<t>
Similarly, the <xref target="RFC5191">
Protocol for Carrying Authentication for Network access (PANA)</xref>
is represented as an example of a protocol that could be leveraged to
secure the join process, as a Layer-3 alternate to IEEE802.1x/EAP.
Work resulting from <xref target="ACE"/> could be considered as well.
<!--There is also a debate whether
the node should be able to send any unprotected packet on the medium.-->
Regardless, the security model must ensure that, prior to a join process,
packets from a untrusted device are controlled in volume and in
reachability.
An overview of the security aspects of the join process can be found in
<xref target="sec"/>.
Related contributions are presented in <xref target="cont"/>.
</t>
<t>
The <xref target="I-D.wang-6tisch-6top-sublayer">6TiSCH Operation
sublayer (6top)</xref> is an Logical Link Control (LLC) or a portion
thereof that provides the abstraction of an IP link over a TSCH MAC.
The work on the operations of that layer, in particular related to
dynamic scheduling, is only introduced here, and should be detailed
further in a subsequent volume of the architecture.
</t>
</section>
<section title="Dependencies">
<t>
At the time of this writing, the components and protocols
that are required to implement this stage of architecture are not fully
available from the IETF. In particular, the requirements on an evolution
of 6LoWPAN Neighbor Discovery that are needed to implement the Backbone
Router as covered by this stage of the architecture are detailed in
<xref target="I-D.thubert-6lo-rfc6775-update-reqs"/>.
</t>
<t>
The 6TiSCH Architecture applies the concepts of Deterministic Networking
on a Layer-3 network. The 6TiSCH Architecture should inherit from
<xref target="I-D.finn-detnet-architecture">DetNet</xref> work and thus
depends on it. In turn, DetNet is expected
to integrate and maintain consistency with the work that has taken place
and is continuing at IEEE802.1TSN and AVnu.
</t>
<t>
The current charter positions 6TiSCH on IEEE802.15.4 only.
Though most of the design should be portable on other link types,
6TiSCH has a strong dependency on IEEE802.15.4 and its evolution.
A new version of the IEEE802.15.4 standard is expected in 2015.
That version should
integrate TSCH as well as other amendments and fixes into the main
specification. The impact on this Architecture should be minimal to
non-existent, but deeper work such as 6top and security may be impacted.
A 6TiSCH Interest Group was formed at IEEE to maintain the synchronization
and help foster work at the IEEE should 6TiSCH demand it.
</t>
<t>
ISA100 <xref target="ISA100"/> Common Network Management (CNM) is another
external work of interest for 6TiSCH. The group, referred to as ISA100.20,
defines a Common Network Management framework that should enable the
management of resources that are controlled by heterogeneous protocols
such as ISA100.11a <xref target="ISA100.11a"/>, WirelessHART
<xref target="WirelessHART"/>, and 6TiSCH. Interestingly, the
establishment of 6TiSCH Deterministic paths, called tracks,
are also in scope, and ISA100.20 is working on requirements for DetNet.
</t>
</section>
</section>
<section anchor='RPLvs6lo' title="6LoWPAN (and RPL)">
<t>
The architecture expects that a 6LoWPAN node that is not aware
at all of the RPL protocol may still connect as a host. It
suggests to extend 6LoWPAN ND <xref target="RFC6775"/> to carry the
sequence number that is needed by RPL to track the movements of the device,
and optionally some abstract information about the RPL instance
(topology) that the device will be reachable over.
</t><t>
In this design,
the root of the RPL network is integrated with the 6LoWPAN ND 6LBR,
but it is logically separated from the Backbone Router (6BBR) that
is used to connect the RPL topology to the backbone. This way,
the root has all information from 6LoWPAN ND and RPL about the LLN
devices attached to it.
</t><t>
This architecture also expects that the root of the RPL network
(proxy-)registers the LLN devices on their behalf to the 6BBR,
for whatever operation the 6BBR performs on the backbone, such
as ND proxy, or redistribution in a routing protocol.
It suggests to use an extension of the mixed mode of Efficient ND
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>
for the registration as described in
<xref target="I-D.thubert-6lowpan-backbone-router"/>.
</t><t>
It results
that, as illustrated in <xref target='figReg'/>, the periodic signaling
would start at the leaf node with 6LoWPAN ND, then would be carried
over RPL to the RPL root, and then with Efficient-ND to the 6BBR.
Efficient ND being an adaptation of 6LoWPAN ND, it makes sense to keep
those two homogeneous in the way they use the source and the target
addresses in the Neighbor Solicitation (NS) messages for registration,
as well as in the options that they use for that process.
<figure anchor='figReg' suppress-title='false'
title="(Re-)Registration Flow over Multi-Link Subnet">
<artwork><![CDATA[
6LoWPAN Node 6LR 6LBR 6BBR
(RPL leaf) (router) (root)
| | | |
| 6LoWPAN ND |6LoWPAN ND+RPL | Efficient ND | IPv6 ND
| LLN link |Route-Over mesh| IPv6 link | Backbone
| | | |
| NS(ARO) | | |
|-------------->| | |
| 6LoWPAN ND | DAR (then DAO)| |
| |-------------->| |
| | | NS(ARO) |
| | |-------------->|
| | | | DAD
| | | |------>
| | | |
| | | NA(ARO) |
| | |<--------------|
| | DAC | |
| |<--------------| |
| NA(ARO) | | |
|<--------------| | |
]]></artwork>
</figure>
</t><t>As the network builds up, a node should start as a
leaf to join the RPL network, and may later turn into both a RPL-capable
router and a 6LR, so as to accept leaf nodes
to recursively join the network.
</t>
<section anchor='leaf' title="RPL Leaf Support in 6LoWPAN ND">
<t>RPL needs a set of information in order to advertise
a leaf node through a DAO message and establish reachability.
</t><t>
At the bare minimum the leaf device must provide a sequence
number that matches the RPL specification in section 7.
Section 4.1 of
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>,
on the Address Registration Option (ARO),
already incorporates that addition with a new
field in the option called the Transaction ID.
</t><t>
If for some reason the node is aware of RPL topologies, then
providing the RPL InstanceID for the instances to which the
node wishes to participate would be a welcome addition.
In the absence of such information, the RPL router must
infer the proper instanceID from external rules and policies.
</t><t>
On the backbone, the InstanceID is expected to be mapped
onto a an overlay that matches the instanceID, for instance a VLANID.
<!--Neither WiFi nor Efficient ND do provide a mapping
to VLANIDs, and it is unclear, when a wireless node attaches to a
backbone where VLANs are defined, which VLAN the wireless device
attaches to. Considering that a VLAN is effectively the IP link on
the backbone, adding the InstanceID to both specifications could be
a welcome addition.-->
</t>
</section>
<section anchor='gone' title="registration Failures Due to Movement">
<t>Registration to the 6LBR through DAR/DAC messages <xref target="RFC6775"/>
may percolate slowly through an LLN mesh, and it might happen that in
the meantime, the 6LoWPAN node moves and registers somewhere else. Both RPL
and 6LoWPAN ND lack the capability to indicate that the same node is
registered elsewhere, so as to invalidate states down the deprecated path.
</t><t> In its current expression and functionality,
6LoWPAN ND considers that the registration is used for the purpose of DAD
only as opposed to that of achieving reachability, and as long as the same
node registers the IPv6 address, the protocol is functional. In order to
act as a RPL leaf registration protocol and achieve reachability, the
device must use the same TID for all its concurrent registrations, and
registrations with a past TID should be declined. The state for an obsolete
registration in the 6LR, as well as the RPL routers on the way, should be
invalidated. This can only be achieved with the addition of a new Status in
the DAC message, and a new error/clean-up flow in RPL.
</t>
</section>
<section anchor='prox' title="Proxy registration">
<t>The 6BBR provides the capability to defend an address that is owned by
a 6LoWPAN Node, and attract packets to that address, whether it is done by
proxying ND over a MultiLink Subnet, redistributing the address in a routing
protocol or advertising it through an alternate proxy registration such as
<xref target="RFC6830">the Locator/ID Separation Protocol</xref> (LISP) or
<xref target="RFC6275">Mobility Support in IPv6</xref> (MIPv6). In a LLN,
it makes sense to piggyback the request to proxy/defend an address with its
registration.
</t>
</section>
<section anchor='source' title="Target Registration">
<t>
In their current incarnations, both 6LoWPAN ND and Efficient ND expect
that the address being registered is the source of the NS(ARO) message and
thus impose that a Source Link-Layer Address (SLLA) option be present in the
message.
In a mesh scenario where the 6LBR is physically separated from the 6LoWPAN
Node, the 6LBR does not own the address being registered. This suggests that
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/> should evolve to
register the Target of the NS message as opposed to the Source Address.
From another perspective, it may happen, in the use case of a Star topology,
that the 6LR, 6LBR and 6BBR are effectively collapsed and should support
6LoWPAN ND clients. The convergence of efficient ND and 6LoWPAN ND into a
single protocol is thus highly desirable.
</t><t>
In any case, as long as the DAD process is not complete for the address
used as source of the packet, it is against the current practice to advertise
the SLLA, since this may corrupt the ND cache of the destination node, as
discussed in the <xref target="RFC4429">Optimistic DAD specification</xref>
with regards to the TENTATIVE state.
</t><t>
This may look like a chicken and an egg problem, but in fact 6LoWPAN ND
acknowledges that the Link-Local Address that is based on an EUI-64 address
of a LLN node may be autoconfigured without the need for DAD.
It results that a node could use that Address as source, with an SLLA
option in the message if required, to register any other addresses, either
Global or Unique-Local Addresses, which would be indicated in the Target.
</t>
<!--
If the some use cases, the client, the 6LR and the 6LBR and 6BBR are collapsed in a single box, be it
because the LLN client is one hop away from the Backbone. The burden of the
DAD operation falls on the 6BBR that needs to perform classical DAD over the
backbone
This configuration
is favored in some Industrial solutions because it reduces the chances of
loss as well as the latencies that are inherent to meshing.
-->
<t>
The suggested change is to register the target of the NS message, and use
Target Link-Layer Address (TLLA) in the NS as opposed to the SLLA in order to
install a Neighbor Cache Entry. This would apply to both Efficient ND
and 6LoWPAN ND in a very same manner, with the caveat that depending on the
nature of the link between the 6LBR and the 6BBR, the 6LBR may resort to
classical ND or DHCPv6 to obtain the address that it uses to source the NS
registration messages, whether for itself or on behalf of LLN nodes.
</t>
</section>
<section anchor='Rroot' title="RPL root vs. 6LBR">
<t>6LoWPAN ND is unclear on how the 6LBR is discovered, and how the liveliness
of the 6LBR is asserted over time. On the other hand, the discovery
and liveliness of the RPL root are obtained through the RPL protocol.
</t><t>
When 6LoWPAN ND is coupled with RPL, the 6LBR and RPL root functionalities
are co-located in order that the address of the 6LBR be indicated by RPL
DIO messages and to associate the unique ID from the DAR/DAC exchange with
the state that is maintained by RPL. The DAR/DAC exchange becomes a
preamble to the DAO messages that are used from then on to reconfirm the
registration, thus eliminating a duplication of functionality between DAO
and DAR messages.
</t>
</section>
<section anchor='Sec' title="Securing the Registration">
<t>
A typical attack against IPv6 ND is address spoofing, whereby a rogue node
claims the IPv6 Address of another node in and hijacks its traffic. The
threats against IPv6 ND as described in
<xref target="RFC3971">SEcure Neighbor Discovery (SEND)</xref>
are applicable to 6LoPWAN ND as well, but the solution can not work as the
route over network does not permit direct peer to peer communication.
</t><t>
Additionally SEND requires considerably enlarged ND messages to carry
cryptographic material, and requires that each protected address is generated
cryptographically, which implies the computation of a different key for
each Cryptographically Generated Address (CGA). SEND as defined in
<xref target="RFC3971"/> is thus largely unsuitable for application in a LLN.
</t><t>
With 6LoWPAN ND, as illustrated in <xref target='figReg'/>, it is
possible to leverage the registration state in the 6LBR, which may store
additional security information for later proof of ownership. If this
information proves the ownership independently of the address itself,
then a single proof may be used to protect multiple addresses.
</t><t>
Once an Address is registered,
the 6LBR maintains a state for that Address and is in position to bind
securely the first registration with the Node that placed it, whether the
Address is CGA or not. It should thus be possible to protect the ownership of
all the addresses of a 6LoWPAN Node with a single key, and there should not
be a need to carry the cryptographic material more than once to the 6LBR.
</t><t>
The energy constraint is usually a foremost factor, and attention should be
paid to minimize the burden on the CPU. Hardware-assisted support of variants
of the <xref target="RFC3610">Counter with CBC-MAC</xref> (CCM) authenticated
encryption block cipher mode such as CCM* are common in LowPower ship-set
implementations, and 6LoWPAN ND security mechanism should be capable to
reuse them when applicable.
</t><t>
Finally, the code footprint in the device being also an issue, the capability
to reuse not only hardware-assist mechanisms but also software across layers
has to be considered. For instance, if code has to be present for upper-layer
operations, e.g <xref target="RFC6655">AES-CCM Cipher Suites for Transport
Layer Security (TLS)</xref>, then the capability to reuse that code should be
considered.
</t>
</section>
</section>
<section title="TSCH and 6top">
<section title="6top">
<t>
6top is a logical link control sitting between the IP layer and the
TSCH MAC layer, which provides the link abstraction that is required
for IP operations. The 6top operations are specified in
<xref target="I-D.wang-6tisch-6top-sublayer"/>. In particular, 6top
provides a management interface that enables an external
management entity to schedule cells and slotFrames, and allows the
addition of complementary functionality, for instance to support a
dynamic schedule management based on observed resource usage as
discussed in <xref target="dynsched"/>.
</t>
<t>
The 6top data model and management interfaces are further discussed
in <xref target='topint'/>.
</t>
<section title="Hard Cells">
<t>
The architecture defines "soft" cells and "hard" cells. "Hard" cells
are owned and managed by an separate scheduling entity (e.g. a PCE)
that specifies the slotOffset/channelOffset of the cells to be
added/moved/deleted, in which case 6top can only act as instructed,
and may not move hard cells in the TSCH schedule on its own.
</t>
</section>
<section title="Soft Cells">
<t>
6top contains a monitoring process which monitors the performance of
cells, and can move a cell in the TSCH schedule when it performs
poorly.
This is only applicable to cells which are marked as "soft".
To reserve a soft cell, the higher layer does not indicate the exact
slotOffset/channelOffset of the cell to add, but rather the resulting
bandwidth and QoS requirements. When the monitoring process triggers
a cell reallocation, the two neighbor devices communicating over this
cell negotiate its new position in the TSCH schedule.
</t>
</section>
</section>
<section title="6top and RPL Objective Function operations">
<!-- 8.1.1. Support to RPL Neighbor Discovery and Parent Selection -->
<t>
An implementation of a <xref target="RFC6550">RPL</xref> Objective Function
(OF), such as the <xref target="RFC6552"> RPL Objective Function Zero (OF0)
</xref> that is used in the <xref target="I-D.ietf-6tisch-minimal"> Minimal
6TiSCH Configuration </xref> to support RPL over a static schedule, may
leverage, for its internal computation, the information maintained by 6top.
</t>
<t>Most OFs require metrics about reachability, such as the ETX.
6top creates and maintains an abstract neighbor table,
and this state may be leveraged to feed an OF and/or store OF information
as well.
In particular, 6top creates and maintains an abstract neighbor table. A neighbor
table entry contains a set of statistics with
respect to that specific neighbor including the time when the last packet has
been received from that neighbor, a set of cell quality metrics (e.g. RSSI or LQI),
the number of packets sent to the neighbor or the number of packets received
from it. This information can be obtained through 6top management APIs as
detailed in the <xref target="I-D.wang-6tisch-6top-sublayer">6top sublayer
specification </xref> and used for instance to compute a Rank Increment that will
determine the selection of the preferred parent.
</t>
<t>
6top provides statistics about the underlying layer so the OF can be tuned
to the nature of the TSCH MAC layer. 6top also enables the RPL OF to
influence the MAC behaviour, for instance by configuring the periodicity of
IEEE802.15.4 Extended Beacons (EB's). By augmenting the EB periodicity, it is
possible to change the network dynamics so as to improve the support of
devices that may change their point of attachment in the 6TiSCH network.
</t>
<!-- PT: I took of the text about time source; the way we do it is a bit reverse:
we have an Instance that is used for time sourcing, and the preferred parent
becomes the time source. If we change preferred parent we use the new one as
time source -->
<t>
Some RPL control messages, such as the DODAG Information Object (DIO) are
ICMPv6 messages that are broadcast to all neighbor nodes.
With 6TiSCH, the broadcast channel requirement is addressed by 6top
by configuring TSCH to provide a broadcast channel,
as opposed to, for instance, piggybacking the DIO messages in
Enhance Beacons. Consideration was given towards finding a way to
embed the Route Advertisements and the RPL DIO messages
(both of which are multicast) into the IEEE802.15.4 Enhanced Beacons.
It was determined that this produced undue timer coupling among
layers, that the resulting packet size was potentially too large,
and required it is not yet clear that there is any need for Enhanced
Beacons in a production network.
</t>
<!--t>
In the TSCH schedule, each cell has the IEEE802.15.4e LinkType attribute.
Setting the LinkType to ADVERTISING indicates that the cell MAY be used to send an
Enhanced Beacon. When a node forms its Enhanced Beacon, the cell,
with LinkType=ADVERTISING, SHOULD be included in the FrameAndLinkIE,
and its LinkOption field SHOULD be set to the combination of
"Receive" and "Timekeeping". The receiver of the Enhanced Beacon MAY
be listening at the cell to get the Enhanced Beacon ([IEEE802154e]).
6top takes this way to establish broadcast channel, which not only
allows TSCH to broadcast Enhanced Beacons, but also allows protocol
exchanges by an upper layer such as RPL.
</t>
<t>
To broadcast ICMPv6 control messages used by RPL such as DIO or DAO,
6top uses the payload of a Data frames. The message is inserted into the
queue associated with the cells which LinkType is set to ADVERTISING.
Then, taking advantage of the broadcast cell feature established with
FrameAndLinkIE (as described above), the RPL control message can be
received by neighbors, which enables the maintenance of RPL DODAGs.
</t>
<t>
A LinkOption combining "Receive" and "Timekeeping" bits indicates to
the receivers of the Enhanced Beacon that the cell MUST be used as a
broadcast cell. The frequency of sending Enhanced Beacons or other
broadcast messages by the upper layer is determined by the timers
associated with the messages. For example, the transmission of
Enhance Beacons is triggered by a timer in 6top; transmission of a
DIO message is triggered by the trickle timer of RPL.
</t-->
</section>
<section anchor="sync" title="Network Synchronization">
<t>
Nodes in a TSCH network must be time synchronized.
A node keeps synchronized to its time source neighbor
through a combination of frame-based and acknowledgment-based synchronization.
In order to maximize battery life and network throughput, it is advisable that RPL ICMP discovery
and maintenance traffic (governed by the trickle timer) be somehow coordinated with the
transmission of time synchronization packets (especially with enhanced beacons).
This could be achieved through an interaction of the 6top sublayer and the RPL objective Function,
or could be controlled by a management entity.
</t>
<!-- TW: Concept of TSGI developed in separate standards-track draft? -->
<t>
Time distribution requires a loop-less structure. Nodes taken in a synchronization loop will rapidly
desynchronize from the network and become isolated. It is expected that a RPL DAG with
a dedicated global Instance is deployed for the purpose of time synchronization.
That Instance is referred to as the Time Synchronization Global Instance (TSGI).
The TSGI can be operated in either of the 3 modes that are detailed
in section 3.1.3 of <xref target="RFC6550">RPL</xref>,
"Instances, DODAGs, and DODAG Versions".
Multiple uncoordinated DODAGs with independent roots may be used if all the roots
share a common time source such as the Global Positioning System (GPS). In the absence
of a common time source, the TSGI should form a single DODAG with a virtual root.
A backbone network is then used to synchronize and coordinate RPL operations between
the backbone routers that act as sinks for the LLN.
Optionally, RPL's periodic operations may be used to
transport the network synchronization. This may
mean that 6top would need to trigger (override) the trickle timer if
no other traffic has occurred for such a time that nodes may get out
of synchronization.
</t>
<t>
A node that has not joined the TSGI advertises a MAC level Join Priority
of 0xFF to notify its neighbors that is not capable of serving as time parent.
A node that has joined the TSGI advertises a MAC level Join Priority set to
its DAGRank() in that Instance, where DAGRank() is the operation specified in
section 3.5.1 of <xref target="RFC6550"/>, "Rank Comparison".
</t>
<!-- TW: Official request made to move alter IEEE802.15.4e text. Maybe remove last sentence? -->
<t>
A root is configured or obtains by some external means the knowledge of the RPLInstanceID
for the TSGI. The root advertises its DagRank in the TSGI, that must be less than 0xFF,
as its Join Priority (JP) in its IEEE802.15.4 Extended Beacons (EB). We'll note that the
JP is now specified between 0 and 0x3F leaving 2 bits in the octet unused in the IEEE802.15.4e
specification. After consultation with IEEE authors, it was asserted that 6TiSCH can make
a full use of the octet to carry an integer value up to 0xFF.
</t>
<t>
A node that reads a Join Priority of less than 0xFF should join the neighbor with
the lesser Join Priority and use it as time parent. If the node is configured to
serve as time parent, then the node should join the TSGI, obtain a Rank in that Instance
and start advertising its own DagRank in the TSGI as its Join Priority in its EBs.
</t>
</section>
<section anchor="slotFrames" title="SlotFrames and Priorities">
<t>
6TiSCH enables in essence the capability to use IPv6 over a MAC
layer that enables to schedule some of the transmissions. In order
to ensure that the medium is free of contending packets when time
arrives for a scheduled transmission, a window of time is defined
around the scheduled transmission time where the medium must be free of
contending energy.
</t>
<t>
One simple way to obtain such a window is to format time and
frequencies in cells of transmission of equal duration. This is the
method that is adopted in IEEE802.15.4 TSCH as well as the Long Term
Evolution (LTE) of cellular networks.
</t>
<t>
In order to describe that formatting of time and frequencies, the
6TiSCH architecture defines a global concept that is called a Channel
Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of
cells with an height equal to the number of available channels
(indexed by ChannelOffsets) and a width (in timeSlots) that is the
period of the network scheduling operation (indexed by slotOffsets) for
that CDU matrix. The size of a cell is a timeSlot duration, and
values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to
accommodate for the transmission of a frame and an ack, including the
security validation on the receive side which may take up to a few
milliseconds on some device architecture.
</t>
<t>
A CDU matrix iterates over and over with a pseudo-random rotation from
an epoch time.
In a given network, there might be multiple CDU matrices that operate
with different width, so they have different durations and represent
different periodic operations.
It is recommended that all CDU matrices in a 6TiSCH domain operate with
the same cell duration and are aligned, so as to reduce the
chances of interferences from slotted-aloha operations.
The knowledge of the CDU matrices is shared
between all the nodes and used in particular to define slotFrames.
</t>
<t>
A slotFrame is a MAC-level abstraction that is common to all nodes and
contains a series of timeSlots of equal length and precedence.
It is characterized by a slotFrame_ID, and a slotFrame_size.
A slotFrame aligns to a CDU matrix for its parameters, such as number
and duration of timeSlots.
</t>
<t>
Multiple slotFrames can coexist in a node schedule, i.e., a node can
have multiple activities scheduled in different slotFrames, based on
the precedence of the 6TiSCH topologies. The slotFrames may be
aligned to different CDU matrices and thus have different width.
There is typically one slotFrame for scheduled traffic that has the
highest precedence and one or more slotFrame(s) for RPL traffic.
The timeSlots in the slotFrame are indexed by the SlotOffset;
the first cell is at SlotOffset 0.
</t>
<t>
When a packet is received from a higher layer for transmission,
6top inserts that packet in the outgoing queue
which matches the packet best (Differentiated Services
<xref target="RFC2474"/> can therefore be used).
At each scheduled transmit slot, 6top looks for the frame
in all the outgoing queues that best matches the cells.
If a frame is found, it is given to the TSCH MAC for transmission.
</t>
</section>
<section anchor="DistRsvTS" title="Distributing the reservation of cells">
<t>
6TiSCH expects a high degree of scalability together with a distributed
routing functionality based on RPL. To achieve
this goal, the spectrum must be allocated in a way that allows for
spatial reuse between zones that will not interfere with one another.
In a large and spatially distributed network, a 6TiSCH node is often in a
good position to determine usage of spectrum in its vicinity.
</t>
<t>
Use cases for distributed routing are often associated with a
statistical distribution of best-effort traffic with variable needs for
bandwidth on each individual link. With 6TiSCH, the link abstraction
is implemented as a bundle of cells; the size of a bundle is
optimal when both the energy wasted idle listening and the packet
drops due to congestion loss are minimized. This can be maintained if
the number of cells in a bundle is adapted dynamically, and with enough
reactivity, to match the variations of best-effort traffic. In turn,
the agility to fulfill the needs for additional cells improves when the
number of interactions with other devices and the protocol latencies
are minimized.
</t>
<t>
6TiSCH limits that interaction to RPL parents that will only
negotiate with other RPL parents, and performs that negotiation by
groups of cells as opposed to individual cells. The 6TiSCH architecture
allows RPL parents to adjust dynamically, and independently from
the PCE, the amount of bandwidth that is used to communicate between
themselves and their children, in both directions; to that effect,
an allocation mechanism enables a RPL parent to obtain the exclusive
use of a portion of a CDU matrix within its interference domain.
Note that a PCE is expected to have precedence in the allocation,
so that a RPL parent would only be able to obtain portions that are
not in-use by the PCE.
</t>
<t>
The 6TiSCH architecture introduces the concept of chunks
<xref target="I-D.ietf-6tisch-terminology"/>) to operate
such spectrum distribution for a whole group of cells at a time.
The CDU matrix is formatted into a set of chunks, each of them
identified uniquely by a chunk-ID. The knowledge of this
formatting is shared between all the nodes in a 6TiSCH network. 6TiSCH
also defines the process of chunk ownership appropriation whereby a
RPL parent discovers a chunk that is not used in its interference
domain (e.g lack of energy detected in reference cells in that chunk);
then claims the chunk, and then defends it in case another RPL parent
would attempt to appropriate it while it is in use.
The chunk is the basic unit of ownership that is used in that process.
</t>
<t>
<figure anchor="fig10" title="CDU matrix Partitioning in Chunks">
<artwork>
<![CDATA[
+-----+-----+-----+-----+-----+-----+-----+ +-----+
chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ|
+-----+-----+-----+-----+-----+-----+-----+ +-----+
chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1|
+-----+-----+-----+-----+-----+-----+-----+ +-----+
...
+-----+-----+-----+-----+-----+-----+-----+ +-----+
chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG|
+-----+-----+-----+-----+-----+-----+-----+ +-----+
0 1 2 3 4 5 6 M
]]>
</artwork>
</figure>
</t>
<t>
As a result of the process of chunk ownership appropriation, the RPL
parent has exclusive authority to decide which cell in the appropriated
chunk can be used by which node in its interference domain. In other words, it is
implicitly delegated the right to manage the portion of the CDU matrix
that is represented by the chunk. The RPL parent may thus orchestrate
which transmissions occur in any of the cells in the chunk, by
allocating cells from the chunk to any form of communication (unicast,
multicast) in any direction between itself and its children.
Initially, those cells are added to the heap of free cells, then
dynamically placed into existing bundles, in new bundles, or allocated
opportunistically for one transmission.
</t>
<t>
The appropriation of a chunk can also be requested explicitly by the
PCE to any node. In that case, the node still may need to perform the
appropriation process to validate that no other node has claimed that
chunk already. After a successful appropriation, the PCE owns the cells
in that chunk, and may use them as hard cells to set up tracks.
</t>
</section>
</section>
<!--
<section title="Functional Flows">
<t>
<list hangIndent="6" style="hanging">
<t hangText="Join:"></t>
<t hangText="Time Synchronization:"></t>
<t hangText="Setup for routing:"></t>
<t hangText="PCE reservation:"></t>
<t hangText="Distributed reservation:"></t>
<t hangText="Dynamic slot (de)allocation:"></t>
<t hangText="DSCP mapping:"></t>
</list>
</t>
</section>
-->
<section title="Communication Paradigms and Interaction Models">
<t>
<xref target="I-D.ietf-6tisch-terminology"/> defines the terms
of Communication Paradigms and Interaction Models, which can be placed
in parallel to the Information Models and Data Models that are defined in
<xref target="RFC3444"/>.
</t>
<t>
A Communication Paradigms would be an abstract view of a protocol exchange,
and would come with an Information Model for the information that is being exchanged.
In contrast, an Interaction Models would be more refined and could point on standard operation
such as a Representational state transfer (REST) "GET" operation and would match
a Data Model for the data that is provided over the protocol exchange.
</t>
<t>
section 2.1.3 of
<xref target="I-D.ietf-roll-rpl-industrial-applicability"/> and next
sections discuss application-layer paradigms, such as Source-sink (SS)
that is a Multipeer to Multipeer (MP2MP) model primarily used for
alarms and alerts, Publish-subscribe (PS, or pub/sub) that is typically
used for sensor data, as well as Peer-to-peer (P2P) and
Peer-to-multipeer (P2MP) communications.
Additional considerations on Duocast and its N-cast generalization are
also provided.
Those paradigms are frequently used in industrial automation, which is
a major use case for IEEE802.15.4 TSCH wireless networks with
<xref target="ISA100.11a"/> and <xref target="WirelessHART"/>, that
provides a wireless access to <xref target="HART"/> applications and
devices.
</t>
<t>
This specification focuses on Communication Paradigms and Interaction
Models for packet forwarding and TSCH resources (cells) management.
Management mechanisms for the TSCH schedule at Link-layer (one-hop),
Network-layer (multithop along a track), and Application-layer
(remote control) are discussed in <xref target="schd"/>.
Link-layer frame forwarding interactions are discussed in <xref target="fwd"/>, and
Network-layer Packet routing is addressed in <xref target="rtg"/>.
</t>
<section anchor="schd" title="Schedule Management Mechanisms">
<t>
6TiSCH uses 4 paradigms to manage the TSCH schedule of the LLN nodes: Static Scheduling,
neighbor-to-neighbor Scheduling, remote monitoring and scheduling management, and Hop-by-hop scheduling.
Multiple mechanisms are defined that implement the associated Interaction Models,
and can be combined and used in the same LLN.
Which mechanism(s) to use depends on application requirements.
</t>
<section anchor="mini" title="Static Scheduling">
<t>
In the simplest instantiation of a 6TiSCH network, a common fixed
schedule may be shared by all nodes in the network. Cells are shared,
and nodes contend for slot access in a slotted aloha manner.
</t>
<t>
A static TSCH schedule can be used to bootstrap a network, as an
initial phase during implementation, or as a fall-back mechanism in
case of network malfunction. This schedule can be preconfigured or
learnt by a node when joining the network. Regardless, the schedule remains unchanged
after the node has joined a network. The Routing Protocol for LLNs
(RPL) is used on the resulting network. This "minimal" scheduling
mechanism that implements this paradigm is detailed in
<xref target="I-D.ietf-6tisch-minimal"/>.
</t>
</section>
<section anchor="dynsched" title="Neighbor-to-neighbor Scheduling">
<t>
In the simplest instantiation of a 6TiSCH network described in
<xref target="mini"/>, nodes may expect a packet at any cell in
the schedule and will waste energy idle listening. In a more
complex instantiation of a 6TiSCH network, a matching portion of the
schedule is established between peers to reflect the observed amount
of transmissions between those nodes. The aggregation of the cells
between a node and a peer forms a bundle that the 6top layer uses to
implement the abstraction of a link for IP. The bandwidth on that
link is proportional to the number of cells in the bundle.
</t>
<t>
If the size of a bundle is configured to fit an average amount of
bandwidth, peak traffic is dropped. If the size is
configured to allow for peak emissions, energy is be wasted
idle listening.
</t>
<t>
In the most efficient instantiation of a 6TiSCH network, the size of
the bundles that implement the links may be changed dynamically
in order to adapt to the need of end-to-end flows routed by RPL.
An optional On-The-Fly (OTF) component may be used to monitor
bandwidth usage and perform requests for dynamic allocation by
the 6top sublayer.
The OTF component is not part of the 6top sublayer. It may be
collocated on the same device or may be partially or fully offloaded
to an external system.
</t>
<t>
The <xref target="I-D.wang-6tisch-6top-sublayer">6top sublayer </xref>
defines a protocol for neighbor nodes to reserve soft cells to one another.
Because this reservation is done without global knowledge of the schedule of
nodes in the LLN, scheduling collisions are possible. 6top defines a monitoring
process which continuously tracks the packet delivery ratio of soft cells.
It uses these statistics to trigger the reallocation of a soft cell in the
schedule, using a negotiation protocol between the neighbors nodes communicating
over that cell.
</t>
<t>
Monitoring and relocation is done in the 6top layer. For the upper layer,
the connection between two neighbor nodes appears as an number of cells.
Depending on traffic requirements, the upper layer can request 6top to add
or delete a number of cells scheduled to a particular neighbor, without
being responsible for choosing the exact slotOffset/channelOffset of those cells.
</t>
</section>
<section anchor="topint" title="remote Monitoring and Schedule Management">
<t>
The 6top interface document
<xref target="I-D.ietf-6tisch-6top-interface"/>
specifies the generic data model that can be used to monitor and manage
resources of the 6top sublayer. Abstract methods are suggested for use
by a management entity in the device. The data model also enables
remote control operations on the 6top sublayer.
</t>
<t>
The capability to interact with the node 6top sublayer from multiple hops away
can be leveraged for monitoring, scheduling, or a combination of thereof.
The architecture supports variations on the deployment model, and
focuses on the flows rather than
whether there is a proxy or a translation operation en-route.
</t>
<t>
<xref target="I-D.ietf-6tisch-coap"/> defines an mapping of
the 6top set of commands, which is described in
<xref target="I-D.ietf-6tisch-6top-interface"/>, to CoAP resources.
This allows an entity to interact with the 6top layer of a node that
is multiple hops away in a RESTful fashion.
</t>
<t>
<xref target="I-D.ietf-6tisch-coap"/> defines a basic set CoAP
resources and associated RESTful access methods
(GET/PUT/POST/DELETE). The payload (body) of the CoAP messages
is encoded using the CBOR format.
The draft also defines the concept of "profiles" to allow for future
or specific extensions, as well as a mechanism for a CoAP client to
discover the profiles installed on a node.
</t>
<t>
The entity issuing the CoAP requests can be a central scheduling entity
(e.g. a PCE), a node multiple hops away with the authority to modify the TSCH
schedule (e.g. the head of a local cluster), or a external device monitoring the
overall state of the network (e.g. NME). It is also possible that a
mapping entity on the backbone transforms a non-CoAP protocol such
as PCEP into the RESTful interfaces that the 6TiSCH devices support.
</t>
<!--t>
<list hangIndent="6" style="hanging">
<t hangText="Query">
The CoAP client may retrieve information from a specific node in the
network. This is typically a CoAP GET request issued on the appropriate
resource on the node.
</t>
<t hangText="Report">
The CoAP client may register for periodic updates from a resource, for example
to monitor the state of some statistics maintained by the node. This is typically
done through CoAP Observe.
</t>
<t hangText="Action">
The CoAP client may request the node to take some action, for example add a cell
to its TSCH schedule. This is typically a CoAP PUT/POST/DELETE request issued
on the appropriate resource on the node.
</t>
<t hangText="Request">
The node may issue a request to the client to trigger some action, for example
the calculation of a multi-hop route. This is typically a CoAP POST request issued
by the node on the appropriate resource on the CoAP client.
</t>
<t hangText="Event">
The node may indicate the occurrence of a specific event to the CoAP client,
for example the discovery of a new neighbor. This is typically a CoAP PUT request
issued by the node on the appropriate resource on the CoAP client.
</t>
</list>
</t>
<t>
This architecture will be refined to comply with
<xref target="I-D.finn-detnet-architecture">DetNet</xref>
when/if the work is formalized.
</t -->
</section>
<section title="Hop-by-hop Scheduling">
<t>
A node can reserve a track to a destination node multiple hops away by installing soft
cells at each intermediate node. This forms a track of soft cells. It is the
responsibility of the 6top sublayer of each node on the track to monitor these soft
cells and trigger relocation when needed.
</t>
<t>
This hop-by-hop reservation mechanism is expected to be similar
in essence to
<xref target="RFC3209"/> and/or <xref target="RFC4080"/>/<xref target="RFC5974"/>.
The protocol for a node to trigger hop-by-hop
scheduling is not yet defined.
</t>
</section>
</section> <section anchor="fwd" title="Forwarding Models">
<!-- TW: Forwarding models should be formalized in a standards-track draft? One should be MUST (IPv6?), the others SHOULD? -->
<t>
By forwarding, this specification means the per-packet operation that
allows to deliver a packet to a next hop or an upper layer in this node.
Forwarding is based on pre-existing state that was installed as a
result of a routing computation <xref target="rtg"/>.
6TiSCH supports three different forwarding model, G-MPLS Track Forwarding (TF),
6LoWPAN Fragment Forwarding (FF) and IPv6 Forwarding (6F).
</t>
<section title="Track Forwarding">
<t>
A Track is a unidirectional path between a source and a destination.
In a Track cell, the normal operation of IEEE802.15.4
Automatic Repeat-reQuest (ARQ) usually happens, though the
acknowledgment may be omitted in some cases, for instance if there
is no scheduled cell for a retry.
</t>
<t>
Track Forwarding is the simplest and fastest. A bundle of cells set
to receive (RX-cells) is uniquely paired to a bundle of cells that
are set to transmit (TX-cells), representing a layer-2 forwarding
state that can be used regardless of the network layer protocol.
This model can effectively be seen as a Generalized Multi-protocol
Label Switching (G-MPLS) operation in that the information used to
switch a frame is not an explicit label, but rather related to other
properties of the way the packet was received, a particular cell in
the case of 6TiSCH.
As a result, as long as the TSCH MAC (and Layer-2 security) accepts
a frame, that frame can be switched regardless of the protocol,
whether this is an IPv6 packet, a 6LoWPAN fragment, or a frame from
an alternate protocol such as WirelessHART or ISA100.11a.
</t>
<t>
A data frame that is forwarded along a Track normally has
a destination MAC address that is set to broadcast -
or a multicast address depending on MAC support.
This way, the MAC layer in the intermediate nodes accepts the
incoming frame and 6top switches it without incurring a change in
the MAC header. In the case of IEEE802.15.4, this means effectively
broadcast, so that along the Track the short address for the
destination of the frame is set to 0xFFFF.
</t>
<t>
A Track is thus formed end-to-end as a succession of paired bundles,
a receive bundle from the previous hop and a transmit bundle to
the next hop along the Track, and a cell in such a bundle belongs to
at most one Track.
For a given iteration of the device schedule, the effective channel
of the cell is obtained by adding a pseudo-random number to the
channelOffset of the cell, which results in a rotation of the
frequency that used for transmission.
The bundles may be computed so as to accommodate both variable rates
and retransmissions, so they might not be fully used at a given
iteration of the schedule.
The 6TiSCH architecture provides additional means to avoid waste of
cells as well as overflows in the transmit bundle, as follows:
</t>
<t>
In one hand, a TX-cell that is not needed for the current iteration
may be reused opportunistically on a per-hop basis for routed
packets.
When all of the frame that were received for a given Track are
effectively transmitted, any available TX-cell for that Track
can be reused for upper layer traffic for which the next-hop router
matches the next hop along the Track. In that case, the cell
that is being used is effectively a TX-cell from the Track, but the
short address for the destination is that of the next-hop router.
It results that a frame that is received in a RX-cell of a Track
with a destination MAC address set to this node as opposed to
broadcast must be extracted from the Track and delivered to the
upper layer (a frame with an unrecognized MAC address is dropped at
the lower MAC layer and thus is not received at the 6top sublayer).
</t>
<t>On the other hand, it might happen that there are not enough
TX-cells in the transmit bundle to accommodate the Track traffic,
for instance if more retransmissions are needed than provisioned.
In that case, the frame can be placed for transmission in the
bundle that is used for layer-3 traffic towards the next hop along
the track as long as it can be routed by the upper layer, that is,
typically, if the frame transports an IPv6 packet. The MAC address
should be set to the next-hop MAC address to avoid confusion.
It results that a frame that is received over a layer-3 bundle may
be in fact associated to a Track. In a classical IP link such as an
Ethernet, off-track traffic is typically in excess over reservation
to be routed along the non-reserved path based on its QoS setting.
But with 6TiSCH, since the use of the layer-3 bundle may be due to
transmission failures, it makes sense for the receiver to recognize
a frame that should be re-tracked, and to place it back on the
appropriate bundle if possible.
A frame should be re-tracked if the Per-Hop-Behavior
group indicated in the Differentiated Services Field in the
IPv6 header is set to Deterministic Forwarding, as discussed in
<xref target="pmh"/>.
A frame is re-tracked by scheduling it for transmission over the
transmit bundle associated to the Track,
with the destination MAC address set to broadcast.
</t>
<t>
There are 2 modes for a Track, transport mode and tunnel mode.
</t>
<section title="Transport Mode">
<t>
In transport mode, the Protocol Data Unit (PDU) is associated
with flow-dependant meta-data that refers uniquely to the Track,
so the 6top sublayer can place the frame in the appropriate cell
without ambiguity. In the case of IPv6 traffic, this flow
identification is transported in the Flow Label of the IPv6
header.
Associated with the source IPv6 address, the Flow Label forms a
globally unique identifier for that particular Track that is
validated at egress before restoring
the destination MAC address (DMAC) and punting to the upper layer.
</t>
<t>
<figure title="Track Forwarding, Transport Mode">
<artwork><![CDATA[
| ^
+--------------+ | |
| IPv6 | | |
+--------------+ | |
| 6LoWPAN HC | | |
+--------------+ ingress egress
| 6top | sets +----+ +----+ restores
+--------------+ dmac to | | | | dmac to
| TSCH MAC | brdcst | | | | self
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
]]></artwork>
</figure>
</t>
</section>
<section title="Tunnel Mode">
<t>
In tunnel mode, the frames originate from an arbitrary protocol over a compatible MAC
that may or may not be synchronized with the 6TiSCH network. An example of
this would be a router with a dual radio that is capable of receiving and sending WirelessHART
or ISA100.11a frames with the second radio, by presenting itself as an access
Point or a Backbone Router, respectively.
</t>
<t>
In that mode, some entity (e.g. PCE) can coordinate with a
WirelessHART Network Manager or an ISA100.11a System Manager to
specify the flows that are to be transported transparently
over the Track.
</t>
<t>
<figure anchor="fig6" title="Track Forwarding, Tunnel Mode">
<artwork><![CDATA[
+--------------+
| IPv6 |
+--------------+
| 6LoWPAN HC |
+--------------+ set restore
| 6top | +dmac+ +dmac+
+--------------+ to|brdcst to|nexthop
| TSCH MAC | | | | |
+--------------+ | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+ | ingress egress |
| |
+--------------+ | |
| LLN PHY | | |
+--------------+ | |
| TSCH MAC | | |
+--------------+ | dmac = | dmac =
|ISA100/WiHART | | nexthop v nexthop
+--------------+
]]></artwork>
</figure>
</t>
<t>
In that case, the flow information that identifies the Track at
the ingress 6TiSCH router is derived from the RX-cell. The dmac
is set to this node but the flow information indicates that the
frame must be tunneled over a particular Track so the frame is
not passed to the upper layer. Instead, the dmac is forced to
broadcast and the frame is passed to the 6top sublayer for switching.
</t>
<t>
At the egress 6TiSCH router, the reverse operation occurs. Based
on metadata associated to the Track, the frame is passed to the
appropriate link layer with the destination MAC restored.
</t>
</section>
<section title="Tunnel Metadata">
<t>
Metadata coming with the Track configuration is expected to provide the destination MAC address
of the egress endpoint as well as the tunnel mode and specific data depending on the mode,
for instance a service access point for frame delivery at egress.
If the tunnel egress point does not have a MAC address that matches the configuration,
the Track installation fails.
</t>
<t>
In transport mode, if the final layer-3 destination is the tunnel termination, then it is possible
that the IPv6 address of the destination is compressed at the 6LoWPAN sublayer based on the MAC address.
It is thus mandatory at the ingress point to validate that the MAC address that was used at the 6LoWPAN
sublayer for compression matches that of the tunnel egress point. For that reason, the node that injects
a packet on a Track checks that the destination is effectively that of the tunnel egress point
before it overwrites it to broadcast.
The 6top sublayer at the tunnel egress point reverts that operation to the MAC address obtained
from the tunnel metadata.
</t>
</section>
</section>
<section title="Fragment Forwarding">
<t>
Considering that 6LoWPAN packets can be as large as 1280 bytes (the IPv6 MTU),
and that the non-storing mode of RPL implies Source Routing that requires space for routing
headers, and that a IEEE802.15.4 frame with security may carry in the order of 80 bytes of
effective payload, an IPv6 packet might be fragmented into more than 16 fragments at the
6LoWPAN sublayer.
</t>
<t>
This level of fragmentation is much higher than that traditionally experienced over the Internet
with IPv4 fragments, where fragmentation is already known as harmful.
</t>
<t>
In the case to a multihop route within a 6TiSCH network, Hop-by-Hop recomposition occurs at each
hop in order to reform the packet and route it. This creates additional latency and forces intermediate
nodes to store a portion of a packet for an undetermined time, thus impacting critical resources such
as memory and battery.
</t>
<t>
<xref target="I-D.thubert-roll-forwarding-frags"/> describes a mechanism whereby the datagram tag in the
6LoWPAN Fragment is used as a label for switching at the 6LoWPAN sublayer. The draft allows for a degree of
flow control based on an Explicit Congestion Notification, as well as end-to-end individual fragment recovery.
</t>
<t>
<figure anchor="fig7" title="Forwarding First Fragment">
<artwork><![CDATA[
| ^
+--------------+ | |
| IPv6 | | +----+ +----+ |
+--------------+ | | | | | |
| 6LoWPAN HC | | learn learn |
+--------------+ | | | | | |
| 6top | | | | | | |
+--------------+ | | | | | |
| TSCH MAC | | | | | | |
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
]]></artwork>
</figure>
</t>
<t>
In that model, the first fragment is routed based on the IPv6 header that is present in that fragment.
The 6LoWPAN sublayer learns the next hop selection, generates a new datagram tag for transmission to
the next hop, and stores that information indexed by the incoming MAC address and datagram tag. The next
fragments are then switched based on that stored state.
</t>
<t>
<figure anchor="fig8" title="Forwarding Next Fragment">
<artwork><![CDATA[
| ^
+--------------+ | |
| IPv6 | | |
+--------------+ | |
| 6LoWPAN HC | | replay replay |
+--------------+ | | | | | |
| 6top | | | | | | |
+--------------+ | | | | | |
| TSCH MAC | | | | | | |
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
]]></artwork>
</figure>
</t>
<t>
A bitmap and an ECN echo in the end-to-end acknowledgment enable the source to resend the missing
fragments selectively. The first fragment may be resent to carve a new path in case of a path failure.
The ECN echo set indicates that the number of outstanding fragments should be reduced.
</t>
</section>
<section title="IPv6 Forwarding">
<t>
As the packets are routed at Layer-3, traditional QoS and RED operations are expected to prioritize
flows; the application of Differentiated Services is further discussed in
<xref target="I-D.svshah-tsvwg-lln-diffserv-recommendations"/>.
</t>
<t>
<figure anchor="fig9" title="IP Forwarding">
<artwork><![CDATA[
| ^
+--------------+ | |
| IPv6 | | +-QoS+ +-QoS+ |
+--------------+ | | | | | |
| 6LoWPAN HC | | | | | | |
+--------------+ | | | | | |
| 6top | | | | | | |
+--------------+ | | | | | |
| TSCH MAC | | | | | | |
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
]]></artwork>
</figure>
</t>
</section>
</section>
<section anchor="rtg" title="Centralized vs. Distributed Routing">
<t>
6TiSCH supports a mixed model of centralized routes and distributed routes.
Centralized routes can for example be computed by a entity such as a PCE.
Distributed routes are computed by RPL.
</t>
<t>
Both methods may inject routes in the Routing Tables of the 6TiSCH routers.
In either case, each route is associated with a 6TiSCH topology that can
be a RPL Instance topology or a track. The 6TiSCH topology is
indexed by a Instance ID, in a format that reuses the RPLInstanceID as
defined in <xref target="RFC6550">RPL</xref>.
</t>
<t>
Both RPL and PCE rely on shared sources such as policies to define Global
and Local RPLInstanceIDs that can be used by either method. It is possible
for centralized and distributed routing to share a same topology.
Generally they will operate in different slotFrames, and centralized
routes will be used for scheduled traffic and will have precedence over
distributed routes in case of conflict between the slotFrames.
</t>
<section anchor="pmh" title="Packet Marking and Handling">
<t>
All packets inside a 6TiSCH domain must carry the Instance ID that
identifies the 6TiSCH topology that is to be used for
routing and forwarding that packet. The location of that information
must be the same for all packets forwarded inside the domain.
</t>
<t>
For packets that are routed by a PCE along a Track, the tuple formed by the
IPv6 source address and a local RPLInstanceID in the packet identify
uniquely the Track and associated transmit bundle.
Additionally, an IP packet that is sent along a Track uses the
Differentiated Services Per-Hop-Behavior Group called
Deterministic Forwarding, as described in
<xref target="I-D.svshah-tsvwg-deterministic-forwarding"/>.
</t>
<t>
For packets that are routed by RPL, that information is the RPLInstanceID
which is carried in the RPL Packet Information, as discussed in section 11.2
of <xref target="RFC6550"/>, "Loop Avoidance and Detection".
</t>
<t>The RPL Packet Information (RPI) is carried in IPv6 packets as a RPL
option in the IPv6 Hop-By-Hop Header <xref target="RFC6553"/>.
</t><t>
6Lo is currently considering a Next Header Compression (NHC) for the RPI
(RPI-NHC).
The RPI-NHC is specified in <xref target="I-D.thubert-6lo-rpl-nhc"/>, and
is the compressed equivalent to the whole HbH header with the RPL option.
</t>
<t>An alternative form of compression that integrates the compression on
IP-in-IP encapsulation and the Routing Header type 3 <xref target="RFC6554"/>
with that of the RPI in a new 6LoWPAN dispatch/header type is concurrently
being evaluated as <xref target="I-D.thubert-6lo-routing-dispatch"/>.</t>
<t>
<!--In a 6TiSCH network, the routing dispatch is the recommended encoding the
RPL Packet Information.-->
</t>
<t>
Either way, the method and format used for encoding the RPLInstanceID
is generalized to all 6TiSCH topological Instances, which include
both RPL Instances and Tracks.
</t>
</section>
</section>
</section>
<section title="IANA Considerations">
<t>
This specification does not require IANA action.
</t>
</section>
<section anchor='sec' title="Security Considerations">
<t>
This architecture operates on IEEE802.15.4 and expects link-layer security to
be enabled at all times between connected devices, except for the very first
step of the device join process, where a joining device may need some initial,
unsecured exchanges so as to obtain its initial key material.
Work has already started at the 6TiSCH Security Design Team and an
overview of the current state of that work is presented in
<xref target="join"/>.
</t> <t>
Future work on 6TiSCH security and will examine in deeper detail how
to secure transactions end-to-end, and to maintain the
security posture of a device over its lifetime.
The result of that work will be described in a subsequent volume of this
architecture.
</t>
<section anchor='join' title="Join Process Highlights">
<t>The architecture specifies three logical elements to describe the join
process:
<list hangIndent="6" style="hanging">
<t hangText="Joining Node (JN):">
Node that wishes to become part of the network; </t>
<t hangText="Join Coordination Entity (JCE)">:
A Join Coordination Entity (JCE) that arbitrates network access and hands
out network parameters (such as keying material);</t>
<t hangText="Join Assistant (JA),">
a one-hop (radio) neighbor of the joining node
that acts as proxy network node and may provide connectivity
with the JCE.</t>
</list>
</t>
<t>The join protocol consists of three major activities:
<list hangIndent="6" style="hanging">
<t hangText="Device Authentication:">
The JN and the JA mutually authenticate each other
and establish a shared key, so as to ensure on-going authenticated
communications. This may involve a server as a third party.</t>
<t hangText="Authorization:">
The JA decides on whether/how to authorize a JN
(if denied, this may result in loss of bandwidth).
Conversely, the JN decides on whether/how to authorize the network
(if denied, it will not join the network).
Authorization decisions may involve other nodes in the network.</t>
<t hangText="Configuration/Parameterization:">
The JA distributes configuration information to the JN, such as scheduling
information, IP address assignment information, and network policies.
This may originate from other network devices, for which the JA may act as
proxy. This step may also include distribution of information
from the JN to the JA and other nodes in the network and, more generally,
synchronization of information between these entities.</t>
</list>
</t>
<t>The device joining process is depicted in <xref target='fig-first-example'/>,
where it is assumed that devices have access to certificates and where
entities have access to the root CA keys of their communicating parties
(initial set-up requirement).
Under these assumptions, the authentication step of the device joining
process does not require online involvement of a third party.
Mutual authentication is performed between the JN and the JA using their
certificates, which also results in a shared key between these two entities.
</t><t>
The JA assists the JN in mutual authentication with a remote server node
(primarily via provision of a communication path with the server), which
also results in a shared (end-to-end) key between those two entities.
The server node may be a JCE that arbitrages the network authorization of the
JN (where the JA will deny bandwidth if authorization is not successful);
it may distribute network-specific configuration parameters
(including network-wide keys) to the JN.
In its turn, the JN may distribute and synchronize information (including,
e.g., network statistics) to the server node and, if so desired, also to the
JA. The actual decision of the JN to become part of the network may
depend on authorization of the network itself.</t>
<t>The server functionality is a role which may be implemented with one
(centralized) or multiple devices (distributed).
In either case, mutual authentication is established
with each physical server entity with which a role is implemented. </t>
<t>
Note that in the above description, the JA does not solely act as a relay
node, thereby allowing it to first filter traffic to be relayed based on
cryptographic authentication criteria - this provides first-level access
control and mitigates certain types of denial-of-service attacks
on the network at large. </t>
<t>Depending on more detailed insight in cost/benefit trade-offs, this
process might be complemented by a more "relaxed" mechanism, where the
JA acts as a relay node only.
The final architecture will provide mechanisms to also cover cases where
the initial set-up requirements are not met or where some other
out-of-sync behavior occurs; it will also suggest some optimizations in
case JCE-related information is already available with the JA
(via caching of information).</t>
<t> When a device rejoins the network in the same authorization domain,
the authorization step could be omitted if the server distributes the
authorization state for the device to the JA when the device
initially joined the network. However, this generally still requires
the exchange of updated configuration information, e.g., related to time
schedules and bandwidth allocation.</t>
<figure title='Network joining, with only authorization by third party'
anchor='fig-first-example'>
<artwork><![CDATA[
{joining node} {neighbor} {server, etc.} Example:
+---------+ +---------+ +---------+
| Joining | | Join | +--| CA |certificate
| Node | |Assistant| | +---------+ issuance
+---------+ +---------+ | +---------+
| | +--|Authoriz.| membership
|<----Beaconing------| | +---------+ test (JCE)
| | | +---------+
|<--Authentication-->| +--| Routing | IP address
| |<--Authorization-->| +--------- assignment
|<-------------------| | +---------+
| | +--| Gateway | backbone,
|------------------->| | +---------+ cloud
| |<--Configuration-->| +---------+
|<-------------------| +--|Bandwidth| PCE
+---------+ schedule
. . .
. . .
]]></artwork>
</figure>
</section>
</section>
<section title="Acknowledgments">
<section title="Contributors">
<t>The co-authors of this document are listed below:
<list hangIndent="6" style="hanging">
<t hangText="Robert Assimiti">
for his breakthrough work on RPL over TSCH and initial text and
guidance.
</t>
<t hangText="Kris Pister">
for creating it all and his continuing guidance through the elaboration
of this design.
</t>
<t hangText="Michael Richardson">
for his leadership role in the Security Design Team and his
contribution throughout this document.
</t>
<t hangText="Rene Struik">
for the security section and his contribution to the Security Design
Team.
</t>
<t hangText="Xavier Vilajosana">
who lead the design of the minimal support with RPL and contributed
deeply to the 6top design and the G-MPLS operation of track switching.
</t>
<t hangText="Qin Wang">
who lead the design of the 6top sublayer and contributed related text
that was moved and/or adapted in this document.
</t>
<t hangText="Thomas Watteyne">
for his contribution to the whole design, in
particular on TSCH and security.
</t>
</list>
</t>
</section>
<section title="Special Thanks"><t>
Special thanks to Tero Kivinen, Jonathan Simon, Giuseppe Piro, Subir Das
and Yoshihiro Ohba for their deep contribution to the initial security
work, and to Diego Dujovne for starting and leading the On-the-Fly effort.
</t><t>
Special thanks also to Pat Kinney for his support in maintaining the
connection active and the design in line with work happening at
IEEE802.15.4.
</t> <t>
Also special thanks to Ted Lemon who was the INT Area A-D while this
specification was developed for his great support and help throughout.
</t>
</section>
<section title="And Do not Forget">
<t>This specification is the result of multiple interactions, in
particular during the 6TiSCH (bi)Weekly Interim call, relayed through
the 6TiSCH mailing list at the IETF.
</t><t>
The authors wish to thank:
Alaeddine Weslati, Chonggang Wang, Georgios Exarchakos, Zhuo Chen,
Alfredo Grieco, Bert Greevenbosch, Cedric Adjih, Deji Chen, Martin Turon,
Dominique Barthel, Elvis Vogli, Geraldine Texier, Malisa Vucinic,
Guillaume Gaillard, Herman Storey, Kazushi Muraoka, Ken Bannister,
Kuor Hsin Chang, Laurent Toutain, Maik Seewald, Maria Rita Palattella,
Michael Behringer, Nancy Cam Winget, Nicola Accettura, Nicolas Montavont,
Oleg Hahm, Patrick Wetterwald, Paul Duffy, Peter van der Stock, Rahul Sen,
Pieter de Mil, Pouria Zand, Rouhollah Nabati, Rafa Marin-Lopez,
Raghuram Sudhaakar, Sedat Gormus, Shitanshu Shah, Steve Simlo,
Tengfei Chang, Tina Tsou, Tom Phinney, Xavier Lagrange, Ines Robles and
Samita Chakrabarti for their participation and various contributions.
</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
<!-- 6TiSCH -->
<?rfc include='reference.I-D.ietf-6tisch-terminology'?>
<?rfc include='reference.I-D.ietf-6tisch-tsch'?>
<!-- others -->
<?rfc include="reference.RFC.2460"?> <!-- Internet Protocol, Version 6 (IPv6) Specification -->
<?rfc include="reference.RFC.4861"?> <!-- neighbor Discovery for IP version 6 (IPv6) -->
<?rfc include="reference.RFC.4862"?> <!-- IPv6 Stateless Address Autoconfiguration -->
<?rfc include="reference.RFC.6282"?> <!-- Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks -->
<?rfc include="reference.RFC.6550"?> <!-- RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks -->
<?rfc include="reference.RFC.6552"?> <!-- RPL OF0: Objective Function Zero for RPL-->
<?rfc include="reference.RFC.6553"?> <!-- RPL Option for Carrying RPL Information in Data-Plane Datagrams -->
<?rfc include="reference.RFC.6554"?> <!-- An IPv6 Routing Header for Source Routes with RPL -->
<?rfc include="reference.RFC.6775"?> <!-- neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) -->
</references>
<references title="Informative References">
<?rfc include="reference.RFC.6620"?> <!-- FCFS SAVI: First-Come, First-Served Source Address Validation -->
<?rfc include="reference.RFC.6655"?> <!-- AES-CCM Cipher Suites for Transport Layer Security (TLS) -->
<?rfc include="reference.RFC.5191"?> <!-- Protocol for Carrying Authentication for Network Access (PANA) -->
<?rfc include="reference.RFC.5340"?> <!-- OSPF for IPv6 -->
<?rfc include="reference.RFC.6275"?> <!-- Mobility Support in IPv6 -->
<?rfc include="reference.RFC.2474"?> <!-- Differentiated Services Field -->
<?rfc include="reference.RFC.2545"?> <!-- BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing -->
<?rfc include="reference.RFC.3963"?> <!-- Network Mobility (NEMO) -->
<?rfc include="reference.RFC.3209"?> <!-- RSVP TE -->
<?rfc include="reference.RFC.3971"?> <!-- SEcure Neighbor Discovery (SEND) -->
<?rfc include="reference.RFC.4291"?> <!-- IP Version 6 Addressing Architecture -->
<?rfc include="reference.RFC.4429"?> <!-- IP Version 6 Optimistic DAD -->
<?rfc include="reference.RFC.3444"?> <!-- On the Difference between Information Models and Data Models -->
<?rfc include="reference.RFC.3610"?> <!-- Counter with CBC-MAC (CCM) -->
<!-- 6TiSCH -->
<?rfc include="reference.RFC.4080"?> <!-- Next Steps in Signaling (NSIS): Framework -->
<?rfc include="reference.RFC.4389"?> <!-- IP Version 6 ND Proxy -->
<?rfc include="reference.RFC.4919"?> <!-- IPv6 over Low-Power Wireless Personal Area Networks -->
<?rfc include="reference.RFC.4903"?> <!-- IPv6 Multi-Link Subnet Issues -->
<?rfc include="reference.RFC.5889"?> <!-- IP Addressing Model in Ad Hoc Networks -->
<?rfc include="reference.RFC.5974"?> <!-- NSIS Signaling Layer Protocol (NSLP) for Quality-of-Service Signaling -->
<?rfc include="reference.RFC.6347"?> <!-- Datagram Transport Layer Security Version 1.2 -->
<?rfc include="reference.RFC.6830"?> <!-- The Locator/ID Separation Protocol (LISP) -->
<?rfc include='reference.I-D.ietf-6tisch-minimal'?>
<?rfc include='reference.I-D.ietf-6tisch-6top-interface'?>
<?rfc include='reference.I-D.ietf-6tisch-coap'?>
<!-- others -->
<?rfc include='reference.I-D.finn-detnet-architecture'?>
<?rfc include='reference.I-D.ietf-ipv6-multilink-subnets'?>
<?rfc include='reference.I-D.ietf-roll-rpl-industrial-applicability'?>
<?rfc include='reference.I-D.chakrabarti-nordmark-6man-efficient-nd'?>
<?rfc include='reference.I-D.thubert-6lowpan-backbone-router'?>
<?rfc include='reference.I-D.thubert-roll-forwarding-frags'?>
<?rfc include='reference.I-D.svshah-tsvwg-lln-diffserv-recommendations'?>
<?rfc include='reference.I-D.svshah-tsvwg-deterministic-forwarding'?>
<?rfc include='reference.I-D.thubert-6lo-rpl-nhc.xml'?>
<?rfc include='reference.I-D.thubert-6lo-routing-dispatch'?>
<?rfc include='reference.I-D.thubert-6lo-rfc6775-update-reqs'?>
<?rfc include='reference.I-D.vanderstok-core-comi'?>
<?rfc include='reference.I-D.dujovne-6tisch-on-the-fly'?>
<?rfc include='reference.I-D.wang-6tisch-6top-sublayer'?>
<?rfc include='reference.I-D.richardson-6tisch-security-architecture'?>
<?rfc include='reference.I-D.struik-6tisch-security-architecture-elements'?>
</references>
<references title="Other Informative References">
<reference anchor="IEEE802154">
<front>
<title>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
</title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="IEEE802154e">
<front>
<title>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 as amended by IEEE std.
802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
Networks (LR-WPANs) Amendment 1: MAC sublayer
</title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date month="April" year="2012"/>
</front>
</reference>
<reference anchor="IEEE802.1TSNTG" target="http://www.ieee802.org/1/pages/avbridges.html">
<front>
<title>IEEE 802.1 Time-Sensitive Networks Task Group</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date day="08" month="March" year="2013" />
</front>
</reference>
<reference anchor="WirelessHART">
<front>
<title>Industrial Communication Networks - Wireless Communication Network and Communication Profiles - WirelessHART - IEC 62591</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date year="2010" />
</front>
</reference>
<reference anchor="HART">
<front>
<title>Highway Addressable remote Transducer, a group of specifications for industrial process and control devices administered by the HART Foundation</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="ISA100.11a" target="http://www.isa.org/Community/SP100WirelessSystemsforAutomation">
<front>
<title>Wireless Systems for Industrial Automation: Process Control and Related Applications - ISA100.11a-2011 - IEC 62734</title>
<author>
<organization>ISA/ANSI</organization>
</author>
<date year="2011" />
</front>
</reference>
<reference anchor="ISA100" target="https://www.isa.org/isa100/">
<front>
<title>ISA100, Wireless Systems for Automation</title>
<author>
<organization>ISA/ANSI</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="TEAS" target="https://datatracker.ietf.org/doc/charter-ietf-teas/">
<front>
<title>Traffic Engineering Architecture and Signaling</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="PCE" target="https://datatracker.ietf.org/doc/charter-ietf-pce/">
<front>
<title>Path Computation Element</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="CCAMP" target="https://datatracker.ietf.org/doc/charter-ietf-ccamp/">
<front>
<title>Common Control and Measurement Plane</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="DICE" target="https://datatracker.ietf.org/doc/charter-ietf-dice/">
<front>
<title>DTLS In Constrained Environments</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="ACE" target="https://datatracker.ietf.org/doc/charter-ietf-ace/">
<front>
<title>Authentication and Authorization for Constrained Environments</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
</references>
<section anchor="cont" title="Personal submissions relevant to the next volumes">
<t>This volume only covers a portion of the total work that is needed to
cover the full 6TiSCH architecture. Missing portions include Deterministic
Networking with Track Forwarding, Dynamic Scheduling, and Security.
</t>
<t>
<xref target="I-D.richardson-6tisch-security-architecture"/> elaborates on
the potential use of 802.1AR certificates, and some options for
the join process are presented in more details.
</t>
<t>
<xref target="I-D.struik-6tisch-security-architecture-elements"/>
describes 6TiSCH security architectural elements with
high level requirements and the security framework that are relevant
for the design of the 6TiSCH security solution.
</t> <t>
<xref target="I-D.dujovne-6tisch-on-the-fly"/> discusses the use of
the 6top sublayer <xref target="I-D.wang-6tisch-6top-sublayer"/> to adapt
dynamically the number of cells between a RPL parent and a child to the
needs of the actual traffic.
</t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-21 10:17:40 |